diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
index 2499ccd..8e82c01 100644
--- a/.cargo_vcs_info.json
+++ b/.cargo_vcs_info.json
@@ -1,5 +1,5 @@
 {
   "git": {
-    "sha1": "30668016aca6bd3b02c766e8347e0b4080d4c296"
+    "sha1": "ed185cfb1c447c1b4bd6ac021c9ec3bb02c9e2f2"
   }
 }
diff --git a/.github/workflows/rust.yml b/.github/workflows/rust.yml
new file mode 100644
index 0000000..ffe0eda
--- /dev/null
+++ b/.github/workflows/rust.yml
@@ -0,0 +1,56 @@
+name: Rust
+
+on: [push, pull_request]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  check:
+    name: Test
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: true
+      matrix:
+        rust:
+          - stable
+          - beta
+          - nightly
+          - 1.46.0
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+
+      - name: Install Rust toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.rust }}
+          override: true
+
+      - name: Default features
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --features example_generated
+
+  embedded:
+    name: Build (embedded)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+
+      - name: Install Rust toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          target: thumbv6m-none-eabi
+          override: true
+
+      - name: Default features
+        uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: -Z avoid-dev-deps --features example_generated --target thumbv6m-none-eabi
diff --git a/.gitignore b/.gitignore
index fbd9642..61c3331 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+wip
 target
 Cargo.lock
 
diff --git a/Android.bp b/Android.bp
index 2ca1e2f..f10ca4d 100644
--- a/Android.bp
+++ b/Android.bp
@@ -38,20 +38,30 @@
 }
 
 rust_defaults {
-    name: "bitflags_defaults",
+    name: "bitflags_test_defaults",
     crate_name: "bitflags",
     // has rustc warnings
     srcs: ["src/lib.rs"],
+    cargo_env_compat: true,
+    cargo_pkg_version: "1.3.2",
     test_suites: ["general-tests"],
     auto_gen_config: true,
-    edition: "2015",
+    edition: "2018",
     features: ["default"],
-    cfgs: ["bitflags_const_fn"],
+    rustlibs: [
+        "libserde",
+        "libserde_json",
+        "libwalkdir",
+    ],
+    proc_macros: [
+        "librustversion",
+        "libserde_derive",
+    ],
 }
 
 rust_test_host {
     name: "bitflags_host_test_src_lib",
-    defaults: ["bitflags_defaults"],
+    defaults: ["bitflags_test_defaults"],
     test_options: {
         unit_test: true,
     },
@@ -59,7 +69,43 @@
 
 rust_test {
     name: "bitflags_device_test_src_lib",
-    defaults: ["bitflags_defaults"],
+    defaults: ["bitflags_test_defaults"],
+}
+
+rust_defaults {
+    name: "bitflags_test_defaults_bitflags",
+    crate_name: "bitflags",
+    // has rustc warnings
+    srcs: ["tests/basic.rs"],
+    cargo_env_compat: true,
+    cargo_pkg_version: "1.3.2",
+    test_suites: ["general-tests"],
+    auto_gen_config: true,
+    edition: "2018",
+    features: ["default"],
+    rustlibs: [
+        "libbitflags",
+        "libserde",
+        "libserde_json",
+        "libwalkdir",
+    ],
+    proc_macros: [
+        "librustversion",
+        "libserde_derive",
+    ],
+}
+
+rust_test_host {
+    name: "bitflags_host_test_tests_basic",
+    defaults: ["bitflags_test_defaults_bitflags"],
+    test_options: {
+        unit_test: true,
+    },
+}
+
+rust_test {
+    name: "bitflags_device_test_tests_basic",
+    defaults: ["bitflags_test_defaults_bitflags"],
 }
 
 rust_library {
@@ -67,10 +113,11 @@
     // has rustc warnings
     host_supported: true,
     crate_name: "bitflags",
+    cargo_env_compat: true,
+    cargo_pkg_version: "1.3.2",
     srcs: ["src/lib.rs"],
-    edition: "2015",
+    edition: "2018",
     features: ["default"],
-    cfgs: ["bitflags_const_fn"],
     apex_available: [
         "//apex_available:platform",
         "com.android.compos",
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0d49101..12fea16 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,60 @@
+# 1.3.2
+
+- Allow `non_snake_case` in generated flags types ([#256])
+
+[#252]: https://github.com/bitflags/bitflags/pull/256
+
+# 1.3.1
+
+- Revert unconditional `#[repr(transparent)]` ([#252])
+
+[#252]: https://github.com/bitflags/bitflags/pull/252
+
+# 1.3.0 (yanked)
+
+- Add `#[repr(transparent)]` ([#187])
+
+- End `empty` doc comment with full stop ([#202])
+
+- Fix typo in crate root docs ([#206])
+
+- Document from_bits_unchecked unsafety ([#207])
+
+- Let `is_all` ignore extra bits ([#211])
+
+- Allows empty flag definition ([#225])
+
+- Making crate accessible from std ([#227])
+
+- Make `from_bits` a const fn ([#229])
+
+- Allow multiple bitflags structs in one macro invocation ([#235])
+
+- Add named functions to perform set operations ([#244])
+
+- Fix typos in method docs ([#245])
+
+- Modernization of the `bitflags` macro to take advantage of newer features and 2018 idioms ([#246])
+
+- Fix regression (in an unreleased feature) and simplify tests ([#247])
+
+- Use `Self` and fix bug when overriding `stringify!` ([#249])
+
+[#187]: https://github.com/bitflags/bitflags/pull/187
+[#202]: https://github.com/bitflags/bitflags/pull/202
+[#206]: https://github.com/bitflags/bitflags/pull/206
+[#207]: https://github.com/bitflags/bitflags/pull/207
+[#211]: https://github.com/bitflags/bitflags/pull/211
+[#225]: https://github.com/bitflags/bitflags/pull/225
+[#227]: https://github.com/bitflags/bitflags/pull/227
+[#229]: https://github.com/bitflags/bitflags/pull/229
+[#235]: https://github.com/bitflags/bitflags/pull/235
+[#244]: https://github.com/bitflags/bitflags/pull/244
+[#245]: https://github.com/bitflags/bitflags/pull/245
+[#246]: https://github.com/bitflags/bitflags/pull/246
+[#247]: https://github.com/bitflags/bitflags/pull/247
+[#249]: https://github.com/bitflags/bitflags/pull/249
+
 # 1.2.1
 
 - Remove extraneous `#[inline]` attributes ([#194])
diff --git a/Cargo.toml b/Cargo.toml
index b803644..9d54c72 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,11 +11,11 @@
 # will likely look very different (and much more reasonable)
 
 [package]
+edition = "2018"
 name = "bitflags"
-version = "1.2.1"
+version = "1.3.2"
 authors = ["The Rust Project Developers"]
-build = "build.rs"
-exclude = [".travis.yml", "appveyor.yml", "bors.toml"]
+exclude = ["bors.toml"]
 description = "A macro to generate structures which behave like bitflags.\n"
 homepage = "https://github.com/bitflags/bitflags"
 documentation = "https://docs.rs/bitflags"
@@ -26,9 +26,33 @@
 repository = "https://github.com/bitflags/bitflags"
 [package.metadata.docs.rs]
 features = ["example_generated"]
+[dependencies.compiler_builtins]
+version = "0.1.2"
+optional = true
+
+[dependencies.core]
+version = "1.0.0"
+optional = true
+package = "rustc-std-workspace-core"
+[dev-dependencies.rustversion]
+version = "1.0"
+
+[dev-dependencies.serde]
+version = "1.0"
+
+[dev-dependencies.serde_derive]
+version = "1.0"
+
+[dev-dependencies.serde_json]
+version = "1.0"
+
+[dev-dependencies.trybuild]
+version = "1.0"
+
+[dev-dependencies.walkdir]
+version = "2.3"
 
 [features]
 default = []
 example_generated = []
-[badges.travis-ci]
-repository = "bitflags/bitflags"
+rustc-dep-of-std = ["core", "compiler_builtins"]
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
index afbe066..be9e05a 100644
--- a/Cargo.toml.orig
+++ b/Cargo.toml.orig
@@ -1,10 +1,10 @@
 [package]
-
 name = "bitflags"
 # NB: When modifying, also modify:
 #   1. html_root_url in lib.rs
 #   2. number in readme (for breaking changes)
-version = "1.2.1"
+version = "1.3.2"
+edition = "2018"
 authors = ["The Rust Project Developers"]
 license = "MIT/Apache-2.0"
 keywords = ["bit", "bitmask", "bitflags", "flags"]
@@ -16,22 +16,24 @@
 description = """
 A macro to generate structures which behave like bitflags.
 """
-exclude = [
-    ".travis.yml",
-    "appveyor.yml",
-    "bors.toml"
-]
-build = "build.rs"
+exclude = ["bors.toml"]
 
-[badges]
-travis-ci = { repository = "bitflags/bitflags" }
+[dependencies]
+core = { version = '1.0.0', optional = true, package = 'rustc-std-workspace-core' }
+compiler_builtins = { version = '0.1.2', optional = true }
+
+[dev-dependencies]
+trybuild = "1.0"
+rustversion = "1.0"
+walkdir = "2.3"
+serde = "1.0"
+serde_derive = "1.0"
+serde_json = "1.0"
 
 [features]
 default = []
 example_generated = []
+rustc-dep-of-std = ["core", "compiler_builtins"]
 
 [package.metadata.docs.rs]
-features = [ "example_generated" ]
-
-[workspace]
-members = ["test_suite"]
+features = ["example_generated"]
diff --git a/METADATA b/METADATA
index 2f3c213..0e660ff 100644
--- a/METADATA
+++ b/METADATA
@@ -7,13 +7,13 @@
   }
   url {
     type: ARCHIVE
-    value: "https://static.crates.io/crates/bitflags/bitflags-1.2.1.crate"
+    value: "https://static.crates.io/crates/bitflags/bitflags-1.3.2.crate"
   }
-  version: "1.2.1"
+  version: "1.3.2"
   license_type: NOTICE
   last_upgrade_date {
-    year: 2019
-    month: 12
-    day: 12
+    year: 2021
+    month: 9
+    day: 22
   }
 }
diff --git a/README.md b/README.md
index df12934..0da0f85 100644
--- a/README.md
+++ b/README.md
@@ -1,11 +1,10 @@
 bitflags
 ========
 
-[![Build Status](https://travis-ci.com/bitflags/bitflags.svg?branch=master)](https://travis-ci.com/bitflags/bitflags)
+[![Rust](https://github.com/bitflags/bitflags/workflows/Rust/badge.svg)](https://github.com/bitflags/bitflags/actions)
 [![Join the chat at https://gitter.im/bitflags/Lobby](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/bitflags/Lobby?utm_source=badge&utm_medium=badge&utm_content=badge)
 [![Latest version](https://img.shields.io/crates/v/bitflags.svg)](https://crates.io/crates/bitflags)
 [![Documentation](https://docs.rs/bitflags/badge.svg)](https://docs.rs/bitflags)
-![Minimum rustc version](https://img.shields.io/badge/rustc-1.20+-yellow.svg)
 ![License](https://img.shields.io/crates/l/bitflags.svg)
 
 A Rust macro to generate structures which behave like a set of bitflags
@@ -19,16 +18,15 @@
 
 ```toml
 [dependencies]
-bitflags = "1.0"
+bitflags = "1.3"
 ```
 
-and this to your crate root:
+and this to your source code:
 
 ```rust
-#[macro_use]
-extern crate bitflags;
+use bitflags::bitflags;
 ```
 
 ## Rust Version Support
 
-The minimum supported Rust version is 1.20 due to use of associated constants.
+The minimum supported Rust version is 1.46 due to use of associated constants and const functions.
diff --git a/build.rs b/build.rs
deleted file mode 100644
index 985757a..0000000
--- a/build.rs
+++ /dev/null
@@ -1,44 +0,0 @@
-use std::env;
-use std::process::Command;
-use std::str::{self, FromStr};
-
-fn main(){
-    let minor = match rustc_minor_version() {
-        Some(minor) => minor,
-        None => return,
-    };
-
-    // const fn stabilized in Rust 1.31:
-    if minor >= 31 {
-        println!("cargo:rustc-cfg=bitflags_const_fn");
-    }
-}
-
-fn rustc_minor_version() -> Option<u32> {
-    let rustc = match env::var_os("RUSTC") {
-        Some(rustc) => rustc,
-        None => return None,
-    };
-
-    let output = match Command::new(rustc).arg("--version").output() {
-        Ok(output) => output,
-        Err(_) => return None,
-    };
-
-    let version = match str::from_utf8(&output.stdout) {
-        Ok(version) => version,
-        Err(_) => return None,
-    };
-
-    let mut pieces = version.split('.');
-    if pieces.next() != Some("rustc 1") {
-        return None;
-    }
-
-    let next = match pieces.next() {
-        Some(next) => next,
-        None => return None,
-    };
-
-    u32::from_str(next).ok()
-}
\ No newline at end of file
diff --git a/cargo2android.json b/cargo2android.json
index a4a2e17..ac356cf 100644
--- a/cargo2android.json
+++ b/cargo2android.json
@@ -4,8 +4,13 @@
     "com.android.compos",
     "com.android.virt"
   ],
-  "dependencies": true,
+  "dependency-blocklist": [
+    "trybuild"
+  ],
   "device": true,
   "run": true,
-  "tests": true
+  "tests": true,
+  "test-blocklist": [
+    "tests/compile.rs"
+  ]
 }
\ No newline at end of file
diff --git a/patches/std.diff b/patches/std.diff
new file mode 100644
index 0000000..c2ccaee
--- /dev/null
+++ b/patches/std.diff
@@ -0,0 +1,15 @@
+diff --git a/src/lib.rs b/src/lib.rs
+index 935e432..36c0699 100644
+--- a/src/lib.rs
++++ b/src/lib.rs
+@@ -278,6 +278,10 @@
+ #![cfg_attr(not(test), no_std)]
+ #![doc(html_root_url = "https://docs.rs/bitflags/1.3.2")]
+ 
++// ANDROID: Unconditionally use std to allow building as a dylib
++#[macro_use]
++extern crate std;
++
+ #[doc(hidden)]
+ pub extern crate core as _core;
+ 
diff --git a/src/lib.rs b/src/lib.rs
index 7b01db0..36c0699 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -11,15 +11,14 @@
 //! A typesafe bitmask flag generator useful for sets of C-style bitmask flags.
 //! It can be used for creating typesafe wrappers around C APIs.
 //!
-//! The `bitflags!` macro generates a `struct` that manages a set of flags. The
+//! The `bitflags!` macro generates `struct`s that manage a set of flags. The
 //! flags should only be defined for integer types, otherwise unexpected type
 //! errors may occur at compile time.
 //!
 //! # Example
 //!
 //! ```
-//! #[macro_use]
-//! extern crate bitflags;
+//! use bitflags::bitflags;
 //!
 //! bitflags! {
 //!     struct Flags: u32 {
@@ -47,11 +46,10 @@
 //! implementations:
 //!
 //! ```
-//! #[macro_use]
-//! extern crate bitflags;
-//!
 //! use std::fmt;
 //!
+//! use bitflags::bitflags;
+//!
 //! bitflags! {
 //!     struct Flags: u32 {
 //!         const A = 0b00000001;
@@ -84,21 +82,19 @@
 //!
 //! # Visibility
 //!
-//! The generated struct and its associated flag constants are not exported
+//! The generated structs and their associated flag constants are not exported
 //! out of the current module by default. A definition can be exported out of
-//! the current module by adding `pub` before `flags`:
+//! the current module by adding `pub` before `struct`:
 //!
 //! ```
-//! #[macro_use]
-//! extern crate bitflags;
-//!
 //! mod example {
+//!     use bitflags::bitflags;
+//!
 //!     bitflags! {
 //!         pub struct Flags1: u32 {
 //!             const A = 0b00000001;
 //!         }
-//!     }
-//!     bitflags! {
+//!
 //! #       pub
 //!         struct Flags2: u32 {
 //!             const B = 0b00000010;
@@ -114,26 +110,44 @@
 //!
 //! # Attributes
 //!
-//! Attributes can be attached to the generated `struct` by placing them
-//! before the `flags` keyword.
+//! Attributes can be attached to the generated `struct`s by placing them
+//! before the `struct` keyword.
+//!
+//! ## Representations
+//!
+//! It's valid to add a `#[repr(C)]` or `#[repr(transparent)]` attribute to a type
+//! generated by `bitflags!`. In these cases, the type is guaranteed to be a newtype.
+//!
+//! ```
+//! use bitflags::bitflags;
+//!
+//! bitflags! {
+//!     #[repr(transparent)]
+//!     struct Flags: u32 {
+//!         const A = 0b00000001;
+//!         const B = 0b00000010;
+//!         const C = 0b00000100;
+//!     }
+//! }
+//! ```
 //!
 //! # Trait implementations
 //!
 //! The `Copy`, `Clone`, `PartialEq`, `Eq`, `PartialOrd`, `Ord` and `Hash`
-//! traits automatically derived for the `struct` using the `derive` attribute.
+//! traits are automatically derived for the `struct`s using the `derive` attribute.
 //! Additional traits can be derived by providing an explicit `derive`
-//! attribute on `flags`.
+//! attribute on `struct`.
 //!
-//! The `Extend` and `FromIterator` traits are implemented for the `struct`,
+//! The `Extend` and `FromIterator` traits are implemented for the `struct`s,
 //! too: `Extend` adds the union of the instances of the `struct` iterated over,
 //! while `FromIterator` calculates the union.
 //!
-//! The `Binary`, `Debug`, `LowerHex`, `Octal` and `UpperHex` trait is also
+//! The `Binary`, `Debug`, `LowerHex`, `Octal` and `UpperHex` traits are also
 //! implemented by displaying the bits value of the internal struct.
 //!
 //! ## Operators
 //!
-//! The following operator traits are implemented for the generated `struct`:
+//! The following operator traits are implemented for the generated `struct`s:
 //!
 //! - `BitOr` and `BitOrAssign`: union
 //! - `BitAnd` and `BitAndAssign`: intersection
@@ -143,7 +157,7 @@
 //!
 //! # Methods
 //!
-//! The following methods are defined for the generated `struct`:
+//! The following methods are defined for the generated `struct`s:
 //!
 //! - `empty`: an empty set of flags
 //! - `all`: the set of all defined flags
@@ -159,23 +173,34 @@
 //! - `is_empty`: `true` if no flags are currently stored
 //! - `is_all`: `true` if currently set flags exactly equal all defined flags
 //! - `intersects`: `true` if there are flags common to both `self` and `other`
-//! - `contains`: `true` all of the flags in `other` are contained within `self`
+//! - `contains`: `true` if all of the flags in `other` are contained within `self`
 //! - `insert`: inserts the specified flags in-place
 //! - `remove`: removes the specified flags in-place
 //! - `toggle`: the specified flags will be inserted if not present, and removed
 //!             if they are.
 //! - `set`: inserts or removes the specified flags depending on the passed value
+//! - `intersection`: returns a new set of flags, containing only the flags present
+//!                   in both `self` and `other` (the argument to the function).
+//! - `union`: returns a new set of flags, containing any flags present in
+//!            either `self` or `other` (the argument to the function).
+//! - `difference`: returns a new set of flags, containing all flags present in
+//!                 `self` without any of the flags present in `other` (the
+//!                 argument to the function).
+//! - `symmetric_difference`: returns a new set of flags, containing all flags
+//!                           present in either `self` or `other` (the argument
+//!                           to the function), but not both.
+//! - `complement`: returns a new set of flags, containing all flags which are
+//!                 not set in `self`, but which are allowed for this type.
 //!
 //! ## Default
 //!
-//! The `Default` trait is not automatically implemented for the generated struct.
+//! The `Default` trait is not automatically implemented for the generated structs.
 //!
 //! If your default value is equal to `0` (which is the same value as calling `empty()`
 //! on the generated struct), you can simply derive `Default`:
 //!
 //! ```
-//! #[macro_use]
-//! extern crate bitflags;
+//! use bitflags::bitflags;
 //!
 //! bitflags! {
 //!     // Results in default value with bits: 0
@@ -196,8 +221,7 @@
 //! If your default value is not equal to `0` you need to implement `Default` yourself:
 //!
 //! ```
-//! #[macro_use]
-//! extern crate bitflags;
+//! use bitflags::bitflags;
 //!
 //! bitflags! {
 //!     struct Flags: u32 {
@@ -225,8 +249,7 @@
 //! Flags with a value equal to zero will have some strange behavior that one should be aware of.
 //!
 //! ```
-//! #[macro_use]
-//! extern crate bitflags;
+//! use bitflags::bitflags;
 //!
 //! bitflags! {
 //!     struct Flags: u32 {
@@ -249,28 +272,27 @@
 //!     assert!(none.is_empty());
 //! }
 //! ```
+//!
+//! Users should generally avoid defining a flag with a value of zero.
 
-#![no_std]
-#![doc(html_root_url = "https://docs.rs/bitflags/1.2.1")]
+#![cfg_attr(not(test), no_std)]
+#![doc(html_root_url = "https://docs.rs/bitflags/1.3.2")]
 
 // ANDROID: Unconditionally use std to allow building as a dylib
 #[macro_use]
 extern crate std;
 
-// Re-export libcore using an alias so that the macros can work without
-// requiring `extern crate core` downstream.
 #[doc(hidden)]
 pub extern crate core as _core;
 
-/// The macro used to generate the flag structure.
+/// The macro used to generate the flag structures.
 ///
 /// See the [crate level docs](../bitflags/index.html) for complete documentation.
 ///
 /// # Example
 ///
 /// ```
-/// #[macro_use]
-/// extern crate bitflags;
+/// use bitflags::bitflags;
 ///
 /// bitflags! {
 ///     struct Flags: u32 {
@@ -295,11 +317,10 @@
 /// implementations:
 ///
 /// ```
-/// #[macro_use]
-/// extern crate bitflags;
-///
 /// use std::fmt;
 ///
+/// use bitflags::bitflags;
+///
 /// bitflags! {
 ///     struct Flags: u32 {
 ///         const A = 0b00000001;
@@ -333,78 +354,18 @@
 macro_rules! bitflags {
     (
         $(#[$outer:meta])*
-        pub struct $BitFlags:ident: $T:ty {
+        $vis:vis struct $BitFlags:ident: $T:ty {
             $(
                 $(#[$inner:ident $($args:tt)*])*
                 const $Flag:ident = $value:expr;
-            )+
+            )*
         }
-    ) => {
-        __bitflags! {
-            $(#[$outer])*
-            (pub) $BitFlags: $T {
-                $(
-                    $(#[$inner $($args)*])*
-                    $Flag = $value;
-                )+
-            }
-        }
-    };
-    (
-        $(#[$outer:meta])*
-        struct $BitFlags:ident: $T:ty {
-            $(
-                $(#[$inner:ident $($args:tt)*])*
-                const $Flag:ident = $value:expr;
-            )+
-        }
-    ) => {
-        __bitflags! {
-            $(#[$outer])*
-            () $BitFlags: $T {
-                $(
-                    $(#[$inner $($args)*])*
-                    $Flag = $value;
-                )+
-            }
-        }
-    };
-    (
-        $(#[$outer:meta])*
-        pub ($($vis:tt)+) struct $BitFlags:ident: $T:ty {
-            $(
-                $(#[$inner:ident $($args:tt)*])*
-                const $Flag:ident = $value:expr;
-            )+
-        }
-    ) => {
-        __bitflags! {
-            $(#[$outer])*
-            (pub ($($vis)+)) $BitFlags: $T {
-                $(
-                    $(#[$inner $($args)*])*
-                    $Flag = $value;
-                )+
-            }
-        }
-    };
-}
 
-#[macro_export(local_inner_macros)]
-#[doc(hidden)]
-macro_rules! __bitflags {
-    (
-        $(#[$outer:meta])*
-        ($($vis:tt)*) $BitFlags:ident: $T:ty {
-            $(
-                $(#[$inner:ident $($args:tt)*])*
-                $Flag:ident = $value:expr;
-            )+
-        }
+        $($t:tt)*
     ) => {
         $(#[$outer])*
         #[derive(Copy, PartialEq, Eq, Clone, PartialOrd, Ord, Hash)]
-        $($vis)* struct $BitFlags {
+        $vis struct $BitFlags {
             bits: $T,
         }
 
@@ -413,63 +374,52 @@
                 $(
                     $(#[$inner $($args)*])*
                     $Flag = $value;
-                )+
+                )*
             }
         }
+
+        bitflags! {
+            $($t)*
+        }
     };
+    () => {};
 }
 
+// A helper macro to implement the `all` function.
 #[macro_export(local_inner_macros)]
 #[doc(hidden)]
-#[cfg(bitflags_const_fn)]
-macro_rules! __fn_bitflags {
+macro_rules! __impl_all_bitflags {
     (
-        $(# $attr_args:tt)*
-        const fn $($item:tt)*
+        $BitFlags:ident: $T:ty {
+            $(
+                $(#[$attr:ident $($args:tt)*])*
+                $Flag:ident = $value:expr;
+            )+
+        }
     ) => {
-        $(# $attr_args)*
-        const fn $($item)*
+        // See `Debug::fmt` for why this approach is taken.
+        #[allow(non_snake_case)]
+        trait __BitFlags {
+            $(
+                const $Flag: $T = 0;
+            )+
+        }
+        #[allow(non_snake_case)]
+        impl __BitFlags for $BitFlags {
+            $(
+                __impl_bitflags! {
+                    #[allow(deprecated)]
+                    $(? #[$attr $($args)*])*
+                    const $Flag: $T = Self::$Flag.bits;
+                }
+            )+
+        }
+        Self { bits: $(<Self as __BitFlags>::$Flag)|+ }
     };
     (
-        $(# $attr_args:tt)*
-        pub const fn $($item:tt)*
+        $BitFlags:ident: $T:ty { }
     ) => {
-        $(# $attr_args)*
-        pub const fn $($item)*
-    };
-    (
-        $(# $attr_args:tt)*
-        pub const unsafe fn $($item:tt)*
-    ) => {
-        $(# $attr_args)*
-        pub const unsafe fn $($item)*
-    };
-}
-
-#[macro_export(local_inner_macros)]
-#[doc(hidden)]
-#[cfg(not(bitflags_const_fn))]
-macro_rules! __fn_bitflags {
-    (
-        $(# $attr_args:tt)*
-        const fn $($item:tt)*
-    ) => {
-        $(# $attr_args)*
-        fn $($item)*
-    };
-    (
-        $(# $attr_args:tt)*
-        pub const fn $($item:tt)*
-    ) => {
-        $(# $attr_args)*
-        pub fn $($item)*
-    };
-    (
-        $(# $attr_args:tt)*
-        pub const unsafe fn $($item:tt)*
-    ) => {
-        $(# $attr_args)*
-        pub unsafe fn $($item)*
+        Self { bits: 0 }
     };
 }
 
@@ -481,7 +431,7 @@
             $(
                 $(#[$attr:ident $($args:tt)*])*
                 $Flag:ident = $value:expr;
-            )+
+            )*
         }
     ) => {
         impl $crate::_core::fmt::Debug for $BitFlags {
@@ -499,11 +449,12 @@
                     $(
                         #[inline]
                         fn $Flag(&self) -> bool { false }
-                    )+
+                    )*
                 }
 
                 // Conditionally override the check for just those flags that
                 // are not #[cfg]ed away.
+                #[allow(non_snake_case)]
                 impl __BitFlags for $BitFlags {
                     $(
                         __impl_bitflags! {
@@ -518,20 +469,20 @@
                                 }
                             }
                         }
-                    )+
+                    )*
                 }
 
                 let mut first = true;
                 $(
-                    if <$BitFlags as __BitFlags>::$Flag(self) {
+                    if <Self as __BitFlags>::$Flag(self) {
                         if !first {
                             f.write_str(" | ")?;
                         }
                         first = false;
-                        f.write_str(__bitflags_stringify!($Flag))?;
+                        f.write_str($crate::_core::stringify!($Flag))?;
                     }
-                )+
-                let extra_bits = self.bits & !$BitFlags::all().bits();
+                )*
+                let extra_bits = self.bits & !Self::all().bits();
                 if extra_bits != 0 {
                     if !first {
                         f.write_str(" | ")?;
@@ -571,227 +522,295 @@
         impl $BitFlags {
             $(
                 $(#[$attr $($args)*])*
-                pub const $Flag: $BitFlags = $BitFlags { bits: $value };
-            )+
+                pub const $Flag: Self = Self { bits: $value };
+            )*
 
-            __fn_bitflags! {
-                /// Returns an empty set of flags
-                #[inline]
-                pub const fn empty() -> $BitFlags {
-                    $BitFlags { bits: 0 }
+            /// Returns an empty set of flags.
+            #[inline]
+            pub const fn empty() -> Self {
+                Self { bits: 0 }
+            }
+
+            /// Returns the set containing all flags.
+            #[inline]
+            pub const fn all() -> Self {
+                __impl_all_bitflags! {
+                    $BitFlags: $T {
+                        $(
+                            $(#[$attr $($args)*])*
+                            $Flag = $value;
+                        )*
+                    }
                 }
             }
 
-            __fn_bitflags! {
-                /// Returns the set containing all flags.
-                #[inline]
-                pub const fn all() -> $BitFlags {
-                    // See `Debug::fmt` for why this approach is taken.
-                    #[allow(non_snake_case)]
-                    trait __BitFlags {
-                        $(
-                            const $Flag: $T = 0;
-                        )+
-                    }
-                    impl __BitFlags for $BitFlags {
-                        $(
-                            __impl_bitflags! {
-                                #[allow(deprecated)]
-                                $(? #[$attr $($args)*])*
-                                const $Flag: $T = Self::$Flag.bits;
-                            }
-                        )+
-                    }
-                    $BitFlags { bits: $(<$BitFlags as __BitFlags>::$Flag)|+ }
-                }
-            }
-
-            __fn_bitflags! {
-                /// Returns the raw value of the flags currently stored.
-                #[inline]
-                pub const fn bits(&self) -> $T {
-                    self.bits
-                }
+            /// Returns the raw value of the flags currently stored.
+            #[inline]
+            pub const fn bits(&self) -> $T {
+                self.bits
             }
 
             /// Convert from underlying bit representation, unless that
             /// representation contains bits that do not correspond to a flag.
             #[inline]
-            pub fn from_bits(bits: $T) -> $crate::_core::option::Option<$BitFlags> {
-                if (bits & !$BitFlags::all().bits()) == 0 {
-                    $crate::_core::option::Option::Some($BitFlags { bits })
+            pub const fn from_bits(bits: $T) -> $crate::_core::option::Option<Self> {
+                if (bits & !Self::all().bits()) == 0 {
+                    $crate::_core::option::Option::Some(Self { bits })
                 } else {
                     $crate::_core::option::Option::None
                 }
             }
 
-            __fn_bitflags! {
-                /// Convert from underlying bit representation, dropping any bits
-                /// that do not correspond to flags.
-                #[inline]
-                pub const fn from_bits_truncate(bits: $T) -> $BitFlags {
-                    $BitFlags { bits: bits & $BitFlags::all().bits }
-                }
+            /// Convert from underlying bit representation, dropping any bits
+            /// that do not correspond to flags.
+            #[inline]
+            pub const fn from_bits_truncate(bits: $T) -> Self {
+                Self { bits: bits & Self::all().bits }
             }
 
-            __fn_bitflags! {
-                /// Convert from underlying bit representation, preserving all
-                /// bits (even those not corresponding to a defined flag).
-                #[inline]
-                pub const unsafe fn from_bits_unchecked(bits: $T) -> $BitFlags {
-                    $BitFlags { bits }
-                }
+            /// Convert from underlying bit representation, preserving all
+            /// bits (even those not corresponding to a defined flag).
+            ///
+            /// # Safety
+            ///
+            /// The caller of the `bitflags!` macro can chose to allow or
+            /// disallow extra bits for their bitflags type.
+            ///
+            /// The caller of `from_bits_unchecked()` has to ensure that
+            /// all bits correspond to a defined flag or that extra bits
+            /// are valid for this bitflags type.
+            #[inline]
+            pub const unsafe fn from_bits_unchecked(bits: $T) -> Self {
+                Self { bits }
             }
 
-            __fn_bitflags! {
-                /// Returns `true` if no flags are currently stored.
-                #[inline]
-                pub const fn is_empty(&self) -> bool {
-                    self.bits() == $BitFlags::empty().bits()
-                }
+            /// Returns `true` if no flags are currently stored.
+            #[inline]
+            pub const fn is_empty(&self) -> bool {
+                self.bits() == Self::empty().bits()
             }
 
-            __fn_bitflags! {
-                /// Returns `true` if all flags are currently set.
-                #[inline]
-                pub const fn is_all(&self) -> bool {
-                    self.bits == $BitFlags::all().bits
-                }
+            /// Returns `true` if all flags are currently set.
+            #[inline]
+            pub const fn is_all(&self) -> bool {
+                Self::all().bits | self.bits == self.bits
             }
 
-            __fn_bitflags! {
-                /// Returns `true` if there are flags common to both `self` and `other`.
-                #[inline]
-                pub const fn intersects(&self, other: $BitFlags) -> bool {
-                    !$BitFlags{ bits: self.bits & other.bits}.is_empty()
-                }
+            /// Returns `true` if there are flags common to both `self` and `other`.
+            #[inline]
+            pub const fn intersects(&self, other: Self) -> bool {
+                !(Self { bits: self.bits & other.bits}).is_empty()
             }
 
-            __fn_bitflags! {
-                /// Returns `true` all of the flags in `other` are contained within `self`.
-                #[inline]
-                pub const fn contains(&self, other: $BitFlags) -> bool {
-                    (self.bits & other.bits) == other.bits
-                }
+            /// Returns `true` if all of the flags in `other` are contained within `self`.
+            #[inline]
+            pub const fn contains(&self, other: Self) -> bool {
+                (self.bits & other.bits) == other.bits
             }
 
             /// Inserts the specified flags in-place.
             #[inline]
-            pub fn insert(&mut self, other: $BitFlags) {
+            pub fn insert(&mut self, other: Self) {
                 self.bits |= other.bits;
             }
 
             /// Removes the specified flags in-place.
             #[inline]
-            pub fn remove(&mut self, other: $BitFlags) {
+            pub fn remove(&mut self, other: Self) {
                 self.bits &= !other.bits;
             }
 
             /// Toggles the specified flags in-place.
             #[inline]
-            pub fn toggle(&mut self, other: $BitFlags) {
+            pub fn toggle(&mut self, other: Self) {
                 self.bits ^= other.bits;
             }
 
             /// Inserts or removes the specified flags depending on the passed value.
             #[inline]
-            pub fn set(&mut self, other: $BitFlags, value: bool) {
+            pub fn set(&mut self, other: Self, value: bool) {
                 if value {
                     self.insert(other);
                 } else {
                     self.remove(other);
                 }
             }
+
+            /// Returns the intersection between the flags in `self` and
+            /// `other`.
+            ///
+            /// Specifically, the returned set contains only the flags which are
+            /// present in *both* `self` *and* `other`.
+            ///
+            /// This is equivalent to using the `&` operator (e.g.
+            /// [`ops::BitAnd`]), as in `flags & other`.
+            ///
+            /// [`ops::BitAnd`]: https://doc.rust-lang.org/std/ops/trait.BitAnd.html
+            #[inline]
+            #[must_use]
+            pub const fn intersection(self, other: Self) -> Self {
+                Self { bits: self.bits & other.bits }
+            }
+
+            /// Returns the union of between the flags in `self` and `other`.
+            ///
+            /// Specifically, the returned set contains all flags which are
+            /// present in *either* `self` *or* `other`, including any which are
+            /// present in both (see [`Self::symmetric_difference`] if that
+            /// is undesirable).
+            ///
+            /// This is equivalent to using the `|` operator (e.g.
+            /// [`ops::BitOr`]), as in `flags | other`.
+            ///
+            /// [`ops::BitOr`]: https://doc.rust-lang.org/std/ops/trait.BitOr.html
+            #[inline]
+            #[must_use]
+            pub const fn union(self, other: Self) -> Self {
+                Self { bits: self.bits | other.bits }
+            }
+
+            /// Returns the difference between the flags in `self` and `other`.
+            ///
+            /// Specifically, the returned set contains all flags present in
+            /// `self`, except for the ones present in `other`.
+            ///
+            /// It is also conceptually equivalent to the "bit-clear" operation:
+            /// `flags & !other` (and this syntax is also supported).
+            ///
+            /// This is equivalent to using the `-` operator (e.g.
+            /// [`ops::Sub`]), as in `flags - other`.
+            ///
+            /// [`ops::Sub`]: https://doc.rust-lang.org/std/ops/trait.Sub.html
+            #[inline]
+            #[must_use]
+            pub const fn difference(self, other: Self) -> Self {
+                Self { bits: self.bits & !other.bits }
+            }
+
+            /// Returns the [symmetric difference][sym-diff] between the flags
+            /// in `self` and `other`.
+            ///
+            /// Specifically, the returned set contains the flags present which
+            /// are present in `self` or `other`, but that are not present in
+            /// both. Equivalently, it contains the flags present in *exactly
+            /// one* of the sets `self` and `other`.
+            ///
+            /// This is equivalent to using the `^` operator (e.g.
+            /// [`ops::BitXor`]), as in `flags ^ other`.
+            ///
+            /// [sym-diff]: https://en.wikipedia.org/wiki/Symmetric_difference
+            /// [`ops::BitXor`]: https://doc.rust-lang.org/std/ops/trait.BitXor.html
+            #[inline]
+            #[must_use]
+            pub const fn symmetric_difference(self, other: Self) -> Self {
+                Self { bits: self.bits ^ other.bits }
+            }
+
+            /// Returns the complement of this set of flags.
+            ///
+            /// Specifically, the returned set contains all the flags which are
+            /// not set in `self`, but which are allowed for this type.
+            ///
+            /// Alternatively, it can be thought of as the set difference
+            /// between [`Self::all()`] and `self` (e.g. `Self::all() - self`)
+            ///
+            /// This is equivalent to using the `!` operator (e.g.
+            /// [`ops::Not`]), as in `!flags`.
+            ///
+            /// [`Self::all()`]: Self::all
+            /// [`ops::Not`]: https://doc.rust-lang.org/std/ops/trait.Not.html
+            #[inline]
+            #[must_use]
+            pub const fn complement(self) -> Self {
+                Self::from_bits_truncate(!self.bits)
+            }
+
         }
 
         impl $crate::_core::ops::BitOr for $BitFlags {
-            type Output = $BitFlags;
+            type Output = Self;
 
             /// Returns the union of the two sets of flags.
             #[inline]
-            fn bitor(self, other: $BitFlags) -> $BitFlags {
-                $BitFlags { bits: self.bits | other.bits }
+            fn bitor(self, other: $BitFlags) -> Self {
+                Self { bits: self.bits | other.bits }
             }
         }
 
         impl $crate::_core::ops::BitOrAssign for $BitFlags {
-
             /// Adds the set of flags.
             #[inline]
-            fn bitor_assign(&mut self, other: $BitFlags) {
+            fn bitor_assign(&mut self, other: Self) {
                 self.bits |= other.bits;
             }
         }
 
         impl $crate::_core::ops::BitXor for $BitFlags {
-            type Output = $BitFlags;
+            type Output = Self;
 
             /// Returns the left flags, but with all the right flags toggled.
             #[inline]
-            fn bitxor(self, other: $BitFlags) -> $BitFlags {
-                $BitFlags { bits: self.bits ^ other.bits }
+            fn bitxor(self, other: Self) -> Self {
+                Self { bits: self.bits ^ other.bits }
             }
         }
 
         impl $crate::_core::ops::BitXorAssign for $BitFlags {
-
             /// Toggles the set of flags.
             #[inline]
-            fn bitxor_assign(&mut self, other: $BitFlags) {
+            fn bitxor_assign(&mut self, other: Self) {
                 self.bits ^= other.bits;
             }
         }
 
         impl $crate::_core::ops::BitAnd for $BitFlags {
-            type Output = $BitFlags;
+            type Output = Self;
 
             /// Returns the intersection between the two sets of flags.
             #[inline]
-            fn bitand(self, other: $BitFlags) -> $BitFlags {
-                $BitFlags { bits: self.bits & other.bits }
+            fn bitand(self, other: Self) -> Self {
+                Self { bits: self.bits & other.bits }
             }
         }
 
         impl $crate::_core::ops::BitAndAssign for $BitFlags {
-
             /// Disables all flags disabled in the set.
             #[inline]
-            fn bitand_assign(&mut self, other: $BitFlags) {
+            fn bitand_assign(&mut self, other: Self) {
                 self.bits &= other.bits;
             }
         }
 
         impl $crate::_core::ops::Sub for $BitFlags {
-            type Output = $BitFlags;
+            type Output = Self;
 
             /// Returns the set difference of the two sets of flags.
             #[inline]
-            fn sub(self, other: $BitFlags) -> $BitFlags {
-                $BitFlags { bits: self.bits & !other.bits }
+            fn sub(self, other: Self) -> Self {
+                Self { bits: self.bits & !other.bits }
             }
         }
 
         impl $crate::_core::ops::SubAssign for $BitFlags {
-
             /// Disables all flags enabled in the set.
             #[inline]
-            fn sub_assign(&mut self, other: $BitFlags) {
+            fn sub_assign(&mut self, other: Self) {
                 self.bits &= !other.bits;
             }
         }
 
         impl $crate::_core::ops::Not for $BitFlags {
-            type Output = $BitFlags;
+            type Output = Self;
 
             /// Returns the complement of this set of flags.
             #[inline]
-            fn not(self) -> $BitFlags {
-                $BitFlags { bits: !self.bits } & $BitFlags::all()
+            fn not(self) -> Self {
+                Self { bits: !self.bits } & Self::all()
             }
         }
 
         impl $crate::_core::iter::Extend<$BitFlags> for $BitFlags {
-            fn extend<T: $crate::_core::iter::IntoIterator<Item=$BitFlags>>(&mut self, iterator: T) {
+            fn extend<T: $crate::_core::iter::IntoIterator<Item=Self>>(&mut self, iterator: T) {
                 for item in iterator {
                     self.insert(item)
                 }
@@ -799,7 +818,7 @@
         }
 
         impl $crate::_core::iter::FromIterator<$BitFlags> for $BitFlags {
-            fn from_iter<T: $crate::_core::iter::IntoIterator<Item=$BitFlags>>(iterator: T) -> $BitFlags {
+            fn from_iter<T: $crate::_core::iter::IntoIterator<Item=Self>>(iterator: T) -> Self {
                 let mut result = Self::empty();
                 result.extend(iterator);
                 result
@@ -817,7 +836,7 @@
     // Input:
     //
     //     ? #[cfg(feature = "advanced")]
-    //     ? #[deprecated(note = "Use somthing else.")]
+    //     ? #[deprecated(note = "Use something else.")]
     //     ? #[doc = r"High quality documentation."]
     //     fn f() -> i32 { /* ... */ }
     //
@@ -872,7 +891,7 @@
     // Input:
     //
     //     ? #[cfg(feature = "advanced")]
-    //     ? #[deprecated(note = "Use somthing else.")]
+    //     ? #[deprecated(note = "Use something else.")]
     //     ? #[doc = r"High quality documentation."]
     //     const f: i32 { /* ... */ }
     //
@@ -916,16 +935,6 @@
     };
 }
 
-// Same as std::stringify but callable from __impl_bitflags, which needs to use
-// local_inner_macros so can only directly call macros from this crate.
-#[macro_export]
-#[doc(hidden)]
-macro_rules! __bitflags_stringify {
-    ($s:ident) => {
-        stringify!($s)
-    };
-}
-
 #[cfg(feature = "example_generated")]
 pub mod example_generated;
 
@@ -939,6 +948,7 @@
         #[doc = "> you are the easiest person to fool."]
         #[doc = "> "]
         #[doc = "> - Richard Feynman"]
+        #[derive(Default)]
         struct Flags: u32 {
             const A = 0b00000001;
             #[doc = "<pcwalton> macros are way better at generating code than trans is"]
@@ -949,9 +959,7 @@
             #[doc = "<strcat> wait what?"]
             const ABC = Self::A.bits | Self::B.bits | Self::C.bits;
         }
-    }
 
-    bitflags! {
         struct _CfgFlags: u32 {
             #[cfg(unix)]
             const _CFG_A = 0b01;
@@ -960,17 +968,18 @@
             #[cfg(unix)]
             const _CFG_C = Self::_CFG_A.bits | 0b10;
         }
-    }
 
-    bitflags! {
         struct AnotherSetOfFlags: i8 {
             const ANOTHER_FLAG = -1_i8;
         }
+
+        struct LongFlags: u32 {
+            const LONG_A = 0b1111111111111111;
+        }
     }
 
     bitflags! {
-        struct LongFlags: u32 {
-            const LONG_A = 0b1111111111111111;
+        struct EmptyFlags: u32 {
         }
     }
 
@@ -982,6 +991,8 @@
 
         assert_eq!(AnotherSetOfFlags::empty().bits(), 0b00);
         assert_eq!(AnotherSetOfFlags::ANOTHER_FLAG.bits(), !0_i8);
+
+        assert_eq!(EmptyFlags::empty().bits(), 0b00000000);
     }
 
     #[test]
@@ -996,6 +1007,9 @@
             AnotherSetOfFlags::from_bits(!0_i8),
             Some(AnotherSetOfFlags::ANOTHER_FLAG)
         );
+
+        assert_eq!(EmptyFlags::from_bits(0), Some(EmptyFlags::empty()));
+        assert_eq!(EmptyFlags::from_bits(0b1), None);
     }
 
     #[test]
@@ -1011,6 +1025,9 @@
             AnotherSetOfFlags::from_bits_truncate(0_i8),
             AnotherSetOfFlags::empty()
         );
+
+        assert_eq!(EmptyFlags::from_bits_truncate(0), EmptyFlags::empty());
+        assert_eq!(EmptyFlags::from_bits_truncate(0b1), EmptyFlags::empty());
     }
 
     #[test]
@@ -1019,9 +1036,25 @@
         assert_eq!(unsafe { Flags::from_bits_unchecked(0) }, Flags::empty());
         assert_eq!(unsafe { Flags::from_bits_unchecked(0b1) }, Flags::A);
         assert_eq!(unsafe { Flags::from_bits_unchecked(0b10) }, Flags::B);
-        assert_eq!(unsafe { Flags::from_bits_unchecked(0b11) }, (Flags::A | Flags::B));
-        assert_eq!(unsafe { Flags::from_bits_unchecked(0b1000) }, (extra | Flags::empty()));
-        assert_eq!(unsafe { Flags::from_bits_unchecked(0b1001) }, (extra | Flags::A));
+
+        assert_eq!(
+            unsafe { Flags::from_bits_unchecked(0b11) },
+            (Flags::A | Flags::B)
+        );
+        assert_eq!(
+            unsafe { Flags::from_bits_unchecked(0b1000) },
+            (extra | Flags::empty())
+        );
+        assert_eq!(
+            unsafe { Flags::from_bits_unchecked(0b1001) },
+            (extra | Flags::A)
+        );
+
+        let extra = unsafe { EmptyFlags::from_bits_unchecked(0b1000) };
+        assert_eq!(
+            unsafe { EmptyFlags::from_bits_unchecked(0b1000) },
+            (extra | EmptyFlags::empty())
+        );
     }
 
     #[test]
@@ -1031,6 +1064,9 @@
         assert!(!Flags::ABC.is_empty());
 
         assert!(!AnotherSetOfFlags::ANOTHER_FLAG.is_empty());
+
+        assert!(EmptyFlags::empty().is_empty());
+        assert!(EmptyFlags::all().is_empty());
     }
 
     #[test]
@@ -1039,7 +1075,15 @@
         assert!(!Flags::A.is_all());
         assert!(Flags::ABC.is_all());
 
+        let extra = unsafe { Flags::from_bits_unchecked(0b1000) };
+        assert!(!extra.is_all());
+        assert!(!(Flags::A | extra).is_all());
+        assert!((Flags::ABC | extra).is_all());
+
         assert!(AnotherSetOfFlags::ANOTHER_FLAG.is_all());
+
+        assert!(EmptyFlags::all().is_all());
+        assert!(EmptyFlags::empty().is_all());
     }
 
     #[test]
@@ -1081,6 +1125,8 @@
         assert!(Flags::ABC.contains(e2));
 
         assert!(AnotherSetOfFlags::ANOTHER_FLAG.contains(AnotherSetOfFlags::ANOTHER_FLAG));
+
+        assert!(EmptyFlags::empty().contains(EmptyFlags::empty()));
     }
 
     #[test]
@@ -1142,6 +1188,188 @@
     }
 
     #[test]
+    fn test_set_ops_basic() {
+        let ab = Flags::A.union(Flags::B);
+        let ac = Flags::A.union(Flags::C);
+        let bc = Flags::B.union(Flags::C);
+        assert_eq!(ab.bits, 0b011);
+        assert_eq!(bc.bits, 0b110);
+        assert_eq!(ac.bits, 0b101);
+
+        assert_eq!(ab, Flags::B.union(Flags::A));
+        assert_eq!(ac, Flags::C.union(Flags::A));
+        assert_eq!(bc, Flags::C.union(Flags::B));
+
+        assert_eq!(ac, Flags::A | Flags::C);
+        assert_eq!(bc, Flags::B | Flags::C);
+        assert_eq!(ab.union(bc), Flags::ABC);
+
+        assert_eq!(ac, Flags::A | Flags::C);
+        assert_eq!(bc, Flags::B | Flags::C);
+
+        assert_eq!(ac.union(bc), ac | bc);
+        assert_eq!(ac.union(bc), Flags::ABC);
+        assert_eq!(bc.union(ac), Flags::ABC);
+
+        assert_eq!(ac.intersection(bc), ac & bc);
+        assert_eq!(ac.intersection(bc), Flags::C);
+        assert_eq!(bc.intersection(ac), Flags::C);
+
+        assert_eq!(ac.difference(bc), ac - bc);
+        assert_eq!(bc.difference(ac), bc - ac);
+        assert_eq!(ac.difference(bc), Flags::A);
+        assert_eq!(bc.difference(ac), Flags::B);
+
+        assert_eq!(bc.complement(), !bc);
+        assert_eq!(bc.complement(), Flags::A);
+        assert_eq!(ac.symmetric_difference(bc), Flags::A.union(Flags::B));
+        assert_eq!(bc.symmetric_difference(ac), Flags::A.union(Flags::B));
+    }
+
+    #[test]
+    fn test_set_ops_const() {
+        // These just test that these compile and don't cause use-site panics
+        // (would be possible if we had some sort of UB)
+        const INTERSECT: Flags = Flags::all().intersection(Flags::C);
+        const UNION: Flags = Flags::A.union(Flags::C);
+        const DIFFERENCE: Flags = Flags::all().difference(Flags::A);
+        const COMPLEMENT: Flags = Flags::C.complement();
+        const SYM_DIFFERENCE: Flags = UNION.symmetric_difference(DIFFERENCE);
+        assert_eq!(INTERSECT, Flags::C);
+        assert_eq!(UNION, Flags::A | Flags::C);
+        assert_eq!(DIFFERENCE, Flags::all() - Flags::A);
+        assert_eq!(COMPLEMENT, !Flags::C);
+        assert_eq!(SYM_DIFFERENCE, (Flags::A | Flags::C) ^ (Flags::all() - Flags::A));
+    }
+
+    #[test]
+    fn test_set_ops_unchecked() {
+        let extra = unsafe { Flags::from_bits_unchecked(0b1000) };
+        let e1 = Flags::A.union(Flags::C).union(extra);
+        let e2 = Flags::B.union(Flags::C);
+        assert_eq!(e1.bits, 0b1101);
+        assert_eq!(e1.union(e2), (Flags::ABC | extra));
+        assert_eq!(e1.intersection(e2), Flags::C);
+        assert_eq!(e1.difference(e2), Flags::A | extra);
+        assert_eq!(e2.difference(e1), Flags::B);
+        assert_eq!(e2.complement(), Flags::A);
+        assert_eq!(e1.complement(), Flags::B);
+        assert_eq!(e1.symmetric_difference(e2), Flags::A | Flags::B | extra); // toggle
+    }
+
+    #[test]
+    fn test_set_ops_exhaustive() {
+        // Define a flag that contains gaps to help exercise edge-cases,
+        // especially around "unknown" flags (e.g. ones outside of `all()`
+        // `from_bits_unchecked`).
+        // - when lhs and rhs both have different sets of unknown flags.
+        // - unknown flags at both ends, and in the middle
+        // - cases with "gaps".
+        bitflags! {
+            struct Test: u16 {
+                // Intentionally no `A`
+                const B = 0b000000010;
+                // Intentionally no `C`
+                const D = 0b000001000;
+                const E = 0b000010000;
+                const F = 0b000100000;
+                const G = 0b001000000;
+                // Intentionally no `H`
+                const I = 0b100000000;
+            }
+        }
+        let iter_test_flags =
+            || (0..=0b111_1111_1111).map(|bits| unsafe { Test::from_bits_unchecked(bits) });
+
+        for a in iter_test_flags() {
+            assert_eq!(
+                a.complement(),
+                Test::from_bits_truncate(!a.bits),
+                "wrong result: !({:?})",
+                a,
+            );
+            assert_eq!(a.complement(), !a, "named != op: !({:?})", a);
+            for b in iter_test_flags() {
+                // Check that the named operations produce the expected bitwise
+                // values.
+                assert_eq!(
+                    a.union(b).bits,
+                    a.bits | b.bits,
+                    "wrong result: `{:?}` | `{:?}`",
+                    a,
+                    b,
+                );
+                assert_eq!(
+                    a.intersection(b).bits,
+                    a.bits & b.bits,
+                    "wrong result: `{:?}` & `{:?}`",
+                    a,
+                    b,
+                );
+                assert_eq!(
+                    a.symmetric_difference(b).bits,
+                    a.bits ^ b.bits,
+                    "wrong result: `{:?}` ^ `{:?}`",
+                    a,
+                    b,
+                );
+                assert_eq!(
+                    a.difference(b).bits,
+                    a.bits & !b.bits,
+                    "wrong result: `{:?}` - `{:?}`",
+                    a,
+                    b,
+                );
+                // Note: Difference is checked as both `a - b` and `b - a`
+                assert_eq!(
+                    b.difference(a).bits,
+                    b.bits & !a.bits,
+                    "wrong result: `{:?}` - `{:?}`",
+                    b,
+                    a,
+                );
+                // Check that the named set operations are equivalent to the
+                // bitwise equivalents
+                assert_eq!(a.union(b), a | b, "named != op: `{:?}` | `{:?}`", a, b,);
+                assert_eq!(
+                    a.intersection(b),
+                    a & b,
+                    "named != op: `{:?}` & `{:?}`",
+                    a,
+                    b,
+                );
+                assert_eq!(
+                    a.symmetric_difference(b),
+                    a ^ b,
+                    "named != op: `{:?}` ^ `{:?}`",
+                    a,
+                    b,
+                );
+                assert_eq!(a.difference(b), a - b, "named != op: `{:?}` - `{:?}`", a, b,);
+                // Note: Difference is checked as both `a - b` and `b - a`
+                assert_eq!(b.difference(a), b - a, "named != op: `{:?}` - `{:?}`", b, a,);
+                // Verify that the operations which should be symmetric are
+                // actually symmetric.
+                assert_eq!(a.union(b), b.union(a), "asymmetry: `{:?}` | `{:?}`", a, b,);
+                assert_eq!(
+                    a.intersection(b),
+                    b.intersection(a),
+                    "asymmetry: `{:?}` & `{:?}`",
+                    a,
+                    b,
+                );
+                assert_eq!(
+                    a.symmetric_difference(b),
+                    b.symmetric_difference(a),
+                    "asymmetry: `{:?}` ^ `{:?}`",
+                    a,
+                    b,
+                );
+            }
+        }
+    }
+
+    #[test]
     fn test_set() {
         let mut e1 = Flags::A | Flags::C;
         e1.set(Flags::B, true);
@@ -1168,8 +1396,6 @@
         assert_eq!(m1, e1);
     }
 
-
-    #[cfg(bitflags_const_fn)]
     #[test]
     fn test_const_fn() {
         const _M1: Flags = Flags::empty();
@@ -1260,6 +1486,11 @@
     }
 
     #[test]
+    fn test_default() {
+        assert_eq!(Flags::empty(), Flags::default());
+    }
+
+    #[test]
     fn test_debug() {
         assert_eq!(format!("{:?}", Flags::A | Flags::B), "A | B");
         assert_eq!(format!("{:?}", Flags::empty()), "(empty)");
@@ -1267,7 +1498,13 @@
         let extra = unsafe { Flags::from_bits_unchecked(0xb8) };
         assert_eq!(format!("{:?}", extra), "0xb8");
         assert_eq!(format!("{:?}", Flags::A | extra), "A | 0xb8");
-        assert_eq!(format!("{:?}", Flags::ABC | extra), "A | B | C | ABC | 0xb8");
+
+        assert_eq!(
+            format!("{:?}", Flags::ABC | extra),
+            "A | B | C | ABC | 0xb8"
+        );
+
+        assert_eq!(format!("{:?}", EmptyFlags::empty()), "(empty)");
     }
 
     #[test]
@@ -1311,8 +1548,7 @@
             pub struct PublicFlags: i8 {
                 const X = 0;
             }
-        }
-        bitflags! {
+
             struct PrivateFlags: i8 {
                 const Y = 0;
             }
@@ -1427,4 +1663,71 @@
         assert_eq!(format!("{:?}", Flags::empty()), "NONE");
         assert_eq!(format!("{:?}", Flags::SOME), "SOME");
     }
+
+    #[test]
+    fn test_empty_bitflags() {
+        bitflags! {}
+    }
+
+    #[test]
+    fn test_u128_bitflags() {
+        bitflags! {
+            struct Flags128: u128 {
+                const A = 0x0000_0000_0000_0000_0000_0000_0000_0001;
+                const B = 0x0000_0000_0000_1000_0000_0000_0000_0000;
+                const C = 0x8000_0000_0000_0000_0000_0000_0000_0000;
+                const ABC = Self::A.bits | Self::B.bits | Self::C.bits;
+            }
+        }
+
+        assert_eq!(Flags128::ABC, Flags128::A | Flags128::B | Flags128::C);
+        assert_eq!(Flags128::A.bits, 0x0000_0000_0000_0000_0000_0000_0000_0001);
+        assert_eq!(Flags128::B.bits, 0x0000_0000_0000_1000_0000_0000_0000_0000);
+        assert_eq!(Flags128::C.bits, 0x8000_0000_0000_0000_0000_0000_0000_0000);
+        assert_eq!(
+            Flags128::ABC.bits,
+            0x8000_0000_0000_1000_0000_0000_0000_0001
+        );
+        assert_eq!(format!("{:?}", Flags128::A), "A");
+        assert_eq!(format!("{:?}", Flags128::B), "B");
+        assert_eq!(format!("{:?}", Flags128::C), "C");
+        assert_eq!(format!("{:?}", Flags128::ABC), "A | B | C | ABC");
+    }
+
+    #[test]
+    fn test_serde_bitflags_serialize() {
+        let flags = SerdeFlags::A | SerdeFlags::B;
+
+        let serialized = serde_json::to_string(&flags).unwrap();
+
+        assert_eq!(serialized, r#"{"bits":3}"#);
+    }
+
+    #[test]
+    fn test_serde_bitflags_deserialize() {
+        let deserialized: SerdeFlags = serde_json::from_str(r#"{"bits":12}"#).unwrap();
+
+        let expected = SerdeFlags::C | SerdeFlags::D;
+
+        assert_eq!(deserialized.bits, expected.bits);
+    }
+
+    #[test]
+    fn test_serde_bitflags_roundtrip() {
+        let flags = SerdeFlags::A | SerdeFlags::B;
+
+        let deserialized: SerdeFlags = serde_json::from_str(&serde_json::to_string(&flags).unwrap()).unwrap();
+
+        assert_eq!(deserialized.bits, flags.bits);
+    }
+
+    bitflags! {
+        #[derive(serde::Serialize, serde::Deserialize)]
+        struct SerdeFlags: u32 {
+            const A = 1;
+            const B = 2;
+            const C = 4;
+            const D = 8;
+        }
+    }
 }
diff --git a/tests/basic.rs b/tests/basic.rs
new file mode 100644
index 0000000..73a52be
--- /dev/null
+++ b/tests/basic.rs
@@ -0,0 +1,20 @@
+#![no_std]
+
+use bitflags::bitflags;
+
+bitflags! {
+    /// baz
+    struct Flags: u32 {
+        const A = 0b00000001;
+        #[doc = "bar"]
+        const B = 0b00000010;
+        const C = 0b00000100;
+        #[doc = "foo"]
+        const ABC = Flags::A.bits | Flags::B.bits | Flags::C.bits;
+    }
+}
+
+#[test]
+fn basic() {
+    assert_eq!(Flags::ABC, Flags::A | Flags::B | Flags::C);
+}
diff --git a/tests/compile-fail/.gitignore b/tests/compile-fail/.gitignore
new file mode 100644
index 0000000..4dd9abc
--- /dev/null
+++ b/tests/compile-fail/.gitignore
@@ -0,0 +1 @@
+*.stderr
diff --git a/tests/compile-fail/impls/copy.rs b/tests/compile-fail/impls/copy.rs
new file mode 100644
index 0000000..38f4822
--- /dev/null
+++ b/tests/compile-fail/impls/copy.rs
@@ -0,0 +1,10 @@
+use bitflags::bitflags;
+
+bitflags! {
+    #[derive(Clone, Copy)]
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-fail/impls/copy.stderr.beta b/tests/compile-fail/impls/copy.stderr.beta
new file mode 100644
index 0000000..0c13aa5
--- /dev/null
+++ b/tests/compile-fail/impls/copy.stderr.beta
@@ -0,0 +1,27 @@
+error[E0119]: conflicting implementations of trait `std::clone::Clone` for type `Flags`
+ --> $DIR/copy.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(Clone, Copy)]
+  | |              ----- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `std::marker::Copy` for type `Flags`
+ --> $DIR/copy.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(Clone, Copy)]
+  | |                     ---- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/tests/compile-fail/impls/eq.rs b/tests/compile-fail/impls/eq.rs
new file mode 100644
index 0000000..4abbd63
--- /dev/null
+++ b/tests/compile-fail/impls/eq.rs
@@ -0,0 +1,10 @@
+use bitflags::bitflags;
+
+bitflags! {
+    #[derive(PartialEq, Eq)]
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-fail/impls/eq.stderr.beta b/tests/compile-fail/impls/eq.stderr.beta
new file mode 100644
index 0000000..8a1a3b4
--- /dev/null
+++ b/tests/compile-fail/impls/eq.stderr.beta
@@ -0,0 +1,55 @@
+error[E0119]: conflicting implementations of trait `std::cmp::PartialEq` for type `Flags`
+ --> $DIR/eq.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(PartialEq, Eq)]
+  | |              --------- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `std::cmp::Eq` for type `Flags`
+ --> $DIR/eq.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(PartialEq, Eq)]
+  | |                         -- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `std::marker::StructuralPartialEq` for type `Flags`
+ --> $DIR/eq.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(PartialEq, Eq)]
+  | |              --------- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0119]: conflicting implementations of trait `std::marker::StructuralEq` for type `Flags`
+ --> $DIR/eq.rs:3:1
+  |
+3 | / bitflags! {
+4 | |     #[derive(PartialEq, Eq)]
+  | |                         -- first implementation here
+5 | |     struct Flags: u32 {
+6 | |         const A = 0b00000001;
+7 | |     }
+8 | | }
+  | |_^ conflicting implementation for `Flags`
+  |
+  = note: this error originates in the derive macro `Eq` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/tests/compile-fail/non_integer_base/all_defined.rs b/tests/compile-fail/non_integer_base/all_defined.rs
new file mode 100644
index 0000000..c2856b1
--- /dev/null
+++ b/tests/compile-fail/non_integer_base/all_defined.rs
@@ -0,0 +1,123 @@
+use std::{
+    fmt::{
+        self,
+        Debug,
+        Display,
+        LowerHex,
+        UpperHex,
+        Octal,
+        Binary,
+    },
+    ops::{
+        BitAnd,
+        BitOr,
+        BitXor,
+        BitAndAssign,
+        BitOrAssign,
+        BitXorAssign,
+        Not,
+    },
+};
+
+use bitflags::bitflags;
+
+// Ideally we'd actually want this to work, but currently need something like `num`'s `Zero`
+// With some design work it could be made possible
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+struct MyInt(u8);
+
+impl BitAnd for MyInt {
+    type Output = Self;
+
+    fn bitand(self, other: Self) -> Self {
+        MyInt(self.0 & other.0)
+    }
+}
+
+impl BitOr for MyInt {
+    type Output = Self;
+
+    fn bitor(self, other: Self) -> Self {
+        MyInt(self.0 | other.0)
+    }
+}
+
+impl BitXor for MyInt {
+    type Output = Self;
+
+    fn bitxor(self, other: Self) -> Self {
+        MyInt(self.0 ^ other.0)
+    }
+}
+
+impl BitAndAssign for MyInt {
+    fn bitand_assign(&mut self, other: Self) {
+        self.0 &= other.0
+    }
+}
+
+impl BitOrAssign for MyInt {
+    fn bitor_assign(&mut self, other: Self) {
+        self.0 |= other.0
+    }
+}
+
+impl BitXorAssign for MyInt {
+    fn bitxor_assign(&mut self, other: Self) {
+        self.0 ^= other.0
+    }
+}
+
+impl Debug for MyInt {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Debug::fmt(&self.0, f)
+    }
+}
+
+impl Display for MyInt {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Display::fmt(&self.0, f)
+    }
+}
+
+impl LowerHex for MyInt {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        LowerHex::fmt(&self.0, f)
+    }
+}
+
+impl UpperHex for MyInt {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        UpperHex::fmt(&self.0, f)
+    }
+}
+
+impl Octal for MyInt {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Octal::fmt(&self.0, f)
+    }
+}
+
+impl Binary for MyInt {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Binary::fmt(&self.0, f)
+    }
+}
+
+impl Not for MyInt {
+    type Output = MyInt;
+
+    fn not(self) -> Self {
+        MyInt(!self.0)
+    }
+}
+
+bitflags! {
+    struct Flags128: MyInt {
+        const A = MyInt(0b0000_0001u8);
+        const B = MyInt(0b0000_0010u8);
+        const C = MyInt(0b0000_0100u8);
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-fail/non_integer_base/all_defined.stderr.beta b/tests/compile-fail/non_integer_base/all_defined.stderr.beta
new file mode 100644
index 0000000..1f0fb5c
--- /dev/null
+++ b/tests/compile-fail/non_integer_base/all_defined.stderr.beta
@@ -0,0 +1,27 @@
+error[E0308]: mismatched types
+   --> $DIR/all_defined.rs:115:1
+    |
+115 | / bitflags! {
+116 | |     struct Flags128: MyInt {
+117 | |         const A = MyInt(0b0000_0001u8);
+118 | |         const B = MyInt(0b0000_0010u8);
+119 | |         const C = MyInt(0b0000_0100u8);
+120 | |     }
+121 | | }
+    | |_^ expected struct `MyInt`, found integer
+    |
+    = note: this error originates in the macro `__impl_all_bitflags` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+   --> $DIR/all_defined.rs:115:1
+    |
+115 | / bitflags! {
+116 | |     struct Flags128: MyInt {
+117 | |         const A = MyInt(0b0000_0001u8);
+118 | |         const B = MyInt(0b0000_0010u8);
+119 | |         const C = MyInt(0b0000_0100u8);
+120 | |     }
+121 | | }
+    | |_^ expected struct `MyInt`, found integer
+    |
+    = note: this error originates in the macro `__impl_bitflags` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/tests/compile-fail/non_integer_base/all_missing.rs b/tests/compile-fail/non_integer_base/all_missing.rs
new file mode 100644
index 0000000..fff6b2c
--- /dev/null
+++ b/tests/compile-fail/non_integer_base/all_missing.rs
@@ -0,0 +1,13 @@
+use bitflags::bitflags;
+
+struct MyInt(u8);
+
+bitflags! {
+    struct Flags128: MyInt {
+        const A = MyInt(0b0000_0001);
+        const B = MyInt(0b0000_0010);
+        const C = MyInt(0b0000_0100);
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-fail/non_integer_base/all_missing.stderr.beta b/tests/compile-fail/non_integer_base/all_missing.stderr.beta
new file mode 100644
index 0000000..ee95f83
--- /dev/null
+++ b/tests/compile-fail/non_integer_base/all_missing.stderr.beta
@@ -0,0 +1,13 @@
+error[E0204]: the trait `Copy` may not be implemented for this type
+  --> $DIR/all_missing.rs:5:1
+   |
+5  | / bitflags! {
+6  | |     struct Flags128: MyInt {
+7  | |         const A = MyInt(0b0000_0001);
+8  | |         const B = MyInt(0b0000_0010);
+9  | |         const C = MyInt(0b0000_0100);
+10 | |     }
+11 | | }
+   | |_^ this field does not implement `Copy`
+   |
+   = note: this error originates in the derive macro `Copy` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/tests/compile-fail/visibility/private_field.rs b/tests/compile-fail/visibility/private_field.rs
new file mode 100644
index 0000000..a6a3912
--- /dev/null
+++ b/tests/compile-fail/visibility/private_field.rs
@@ -0,0 +1,13 @@
+mod example {
+    use bitflags::bitflags;
+
+    bitflags! {
+        pub struct Flags1: u32 {
+            const FLAG_A = 0b00000001;
+        }
+    }
+}
+
+fn main() {
+    let flag1 = example::Flags1::FLAG_A.bits;
+}
diff --git a/tests/compile-fail/visibility/private_field.stderr.beta b/tests/compile-fail/visibility/private_field.stderr.beta
new file mode 100644
index 0000000..58a0466
--- /dev/null
+++ b/tests/compile-fail/visibility/private_field.stderr.beta
@@ -0,0 +1,10 @@
+error[E0616]: field `bits` of struct `Flags1` is private
+  --> $DIR/private_field.rs:12:41
+   |
+12 |     let flag1 = example::Flags1::FLAG_A.bits;
+   |                                         ^^^^ private field
+   |
+help: a method `bits` also exists, call it with parentheses
+   |
+12 |     let flag1 = example::Flags1::FLAG_A.bits();
+   |                                             ^^
diff --git a/tests/compile-fail/visibility/private_flags.rs b/tests/compile-fail/visibility/private_flags.rs
new file mode 100644
index 0000000..85a5b18
--- /dev/null
+++ b/tests/compile-fail/visibility/private_flags.rs
@@ -0,0 +1,18 @@
+mod example {
+    use bitflags::bitflags;
+
+    bitflags! {
+        pub struct Flags1: u32 {
+            const FLAG_A = 0b00000001;
+        }
+
+        struct Flags2: u32 {
+            const FLAG_B = 0b00000010;
+        }
+    }
+}
+
+fn main() {
+    let flag1 = example::Flags1::FLAG_A;
+    let flag2 = example::Flags2::FLAG_B;
+}
diff --git a/tests/compile-fail/visibility/private_flags.stderr.beta b/tests/compile-fail/visibility/private_flags.stderr.beta
new file mode 100644
index 0000000..d23f832
--- /dev/null
+++ b/tests/compile-fail/visibility/private_flags.stderr.beta
@@ -0,0 +1,18 @@
+error[E0603]: struct `Flags2` is private
+  --> $DIR/private_flags.rs:17:26
+   |
+17 |     let flag2 = example::Flags2::FLAG_B;
+   |                          ^^^^^^ private struct
+   |
+note: the struct `Flags2` is defined here
+  --> $DIR/private_flags.rs:4:5
+   |
+4  | /     bitflags! {
+5  | |         pub struct Flags1: u32 {
+6  | |             const FLAG_A = 0b00000001;
+7  | |         }
+...  |
+11 | |         }
+12 | |     }
+   | |_____^
+   = note: this error originates in the macro `bitflags` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/tests/compile-fail/visibility/pub_const.rs b/tests/compile-fail/visibility/pub_const.rs
new file mode 100644
index 0000000..b90f0ce
--- /dev/null
+++ b/tests/compile-fail/visibility/pub_const.rs
@@ -0,0 +1,9 @@
+use bitflags::bitflags;
+
+bitflags! {
+    pub struct Flags1: u32 {
+        pub const FLAG_A = 0b00000001;
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-fail/visibility/pub_const.stderr.beta b/tests/compile-fail/visibility/pub_const.stderr.beta
new file mode 100644
index 0000000..b01122c
--- /dev/null
+++ b/tests/compile-fail/visibility/pub_const.stderr.beta
@@ -0,0 +1,5 @@
+error: no rules expected the token `pub`
+ --> $DIR/pub_const.rs:5:9
+  |
+5 |         pub const FLAG_A = 0b00000001;
+  |         ^^^ no rules expected this token in macro call
diff --git a/tests/compile-pass/impls/convert.rs b/tests/compile-pass/impls/convert.rs
new file mode 100644
index 0000000..1f02982
--- /dev/null
+++ b/tests/compile-pass/impls/convert.rs
@@ -0,0 +1,17 @@
+use bitflags::bitflags;
+
+bitflags! {
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+impl From<u32> for Flags {
+    fn from(v: u32) -> Flags {
+        Flags::from_bits_truncate(v)
+    }
+}
+
+fn main() {
+
+}
diff --git a/tests/compile-pass/impls/default.rs b/tests/compile-pass/impls/default.rs
new file mode 100644
index 0000000..a97b653
--- /dev/null
+++ b/tests/compile-pass/impls/default.rs
@@ -0,0 +1,10 @@
+use bitflags::bitflags;
+
+bitflags! {
+    #[derive(Default)]
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-pass/impls/inherent_methods.rs b/tests/compile-pass/impls/inherent_methods.rs
new file mode 100644
index 0000000..3052c46
--- /dev/null
+++ b/tests/compile-pass/impls/inherent_methods.rs
@@ -0,0 +1,15 @@
+use bitflags::bitflags;
+
+bitflags! {
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+impl Flags {
+    pub fn new() -> Flags {
+        Flags::A
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-pass/redefinition/core.rs b/tests/compile-pass/redefinition/core.rs
new file mode 100644
index 0000000..4754921
--- /dev/null
+++ b/tests/compile-pass/redefinition/core.rs
@@ -0,0 +1,14 @@
+use bitflags::bitflags;
+
+// Checks for possible errors caused by overriding names used by `bitflags!` internally.
+
+mod core {}
+mod _core {}
+
+bitflags! {
+    struct Test: u8 {
+        const A = 1;
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-pass/redefinition/stringify.rs b/tests/compile-pass/redefinition/stringify.rs
new file mode 100644
index 0000000..b04f2f6
--- /dev/null
+++ b/tests/compile-pass/redefinition/stringify.rs
@@ -0,0 +1,19 @@
+use bitflags::bitflags;
+
+// Checks for possible errors caused by overriding names used by `bitflags!` internally.
+
+#[allow(unused_macros)]
+macro_rules! stringify {
+    ($($t:tt)*) => { "..." };
+}
+
+bitflags! {
+    struct Test: u8 {
+        const A = 1;
+    }
+}
+
+fn main() {
+    // Just make sure we don't call the redefined `stringify` macro
+    assert_eq!(format!("{:?}", Test::A), "A");
+}
diff --git a/tests/compile-pass/repr/c.rs b/tests/compile-pass/repr/c.rs
new file mode 100644
index 0000000..6feba36
--- /dev/null
+++ b/tests/compile-pass/repr/c.rs
@@ -0,0 +1,10 @@
+use bitflags::bitflags;
+
+bitflags! {
+    #[repr(C)]
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-pass/repr/transparent.rs b/tests/compile-pass/repr/transparent.rs
new file mode 100644
index 0000000..e38db4d
--- /dev/null
+++ b/tests/compile-pass/repr/transparent.rs
@@ -0,0 +1,10 @@
+use bitflags::bitflags;
+
+bitflags! {
+    #[repr(transparent)]
+    struct Flags: u32 {
+        const A = 0b00000001;
+    }
+}
+
+fn main() {}
diff --git a/tests/compile-pass/visibility/bits_field.rs b/tests/compile-pass/visibility/bits_field.rs
new file mode 100644
index 0000000..33a7967
--- /dev/null
+++ b/tests/compile-pass/visibility/bits_field.rs
@@ -0,0 +1,11 @@
+use bitflags::bitflags;
+
+bitflags! {
+    pub struct Flags1: u32 {
+        const FLAG_A = 0b00000001;
+    }
+}
+
+fn main() {
+    assert_eq!(0b00000001, Flags1::FLAG_A.bits);
+}
diff --git a/tests/compile-pass/visibility/pub_in.rs b/tests/compile-pass/visibility/pub_in.rs
new file mode 100644
index 0000000..c11050e
--- /dev/null
+++ b/tests/compile-pass/visibility/pub_in.rs
@@ -0,0 +1,19 @@
+mod a {
+    mod b {
+        use bitflags::bitflags;
+
+        bitflags! {
+            pub(in crate::a) struct Flags: u32 {
+                const FLAG_A = 0b00000001;
+            }
+        }
+    }
+
+    pub fn flags() -> u32 {
+        b::Flags::FLAG_A.bits()
+    }
+}
+
+fn main() {
+    assert_eq!(0b00000001, a::flags());
+}
diff --git a/tests/compile.rs b/tests/compile.rs
new file mode 100644
index 0000000..ed02d01
--- /dev/null
+++ b/tests/compile.rs
@@ -0,0 +1,63 @@
+use std::{
+    fs,
+    ffi::OsStr,
+    io,
+    path::Path,
+};
+
+use walkdir::WalkDir;
+
+#[test]
+fn fail() {
+    prepare_stderr_files("tests/compile-fail").unwrap();
+
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/compile-fail/**/*.rs");
+}
+
+#[test]
+fn pass() {
+    let t = trybuild::TestCases::new();
+    t.pass("tests/compile-pass/**/*.rs");
+}
+
+// Compiler messages may change between versions
+// We don't want to have to track these too closely for `bitflags`, but
+// having some message to check makes sure user-facing errors are sensical.
+// 
+// The approach we use is to run the test on all compilers, but only check stderr
+// output on beta (which is the next stable release). We do this by default ignoring
+// any `.stderr` files in the `compile-fail` directory, and copying `.stderr.beta` files
+// when we happen to be running on a beta compiler.
+fn prepare_stderr_files(path: impl AsRef<Path>) -> io::Result<()> {
+    for entry in WalkDir::new(path) {
+        let entry = entry?;
+
+        if entry.path().extension().and_then(OsStr::to_str) == Some("beta") {
+            let renamed = entry.path().with_extension("");
+
+            // Unconditionally remove a corresponding `.stderr` file for a `.stderr.beta`
+            // file if it exists. On `beta` compilers, we'll recreate it. On other compilers,
+            // we don't want to end up checking it anyways.
+            if renamed.exists() {
+                fs::remove_file(&renamed)?;
+            }
+
+            rename_beta_stderr(entry.path(), renamed)?;
+        }
+    }
+
+    Ok(())
+}
+
+#[rustversion::beta]
+fn rename_beta_stderr(from: impl AsRef<Path>, to: impl AsRef<Path>) -> io::Result<()> {
+    fs::copy(from, to)?;
+
+    Ok(())
+}
+
+#[rustversion::not(beta)]
+fn rename_beta_stderr(_: impl AsRef<Path>, _: impl AsRef<Path>) -> io::Result<()> {
+    Ok(())
+}