Allow conditions to be decomposed with structured bindings
Summary:
This feature was discussed but not yet proposed. It allows a structured binding to appear as a //condition//
if (auto [ok, val] = f(...))
So the user can save an extra //condition// if the statement can test the value to-be-decomposed instead. Formally, it makes the value of the underlying object of the structured binding declaration also the value of a //condition// that is an initialized declaration.
Considering its logicality which is entirely evident from its trivial implementation, I think it might be acceptable to land it as an extension for now before I write the paper.
Reviewers: rsmith, faisalv, aaron.ballman
Reviewed By: rsmith
Subscribers: aaron.ballman, cfe-commits
Differential Revision: https://reviews.llvm.org/D39284
llvm-svn: 320011
diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index ade0655..959cb7a 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -1715,6 +1715,8 @@
/// type-specifier-seq declarator '=' assignment-expression
/// [C++11] type-specifier-seq declarator '=' initializer-clause
/// [C++11] type-specifier-seq declarator braced-init-list
+/// [Clang] type-specifier-seq ref-qualifier[opt] '[' identifier-list ']'
+/// brace-or-equal-initializer
/// [GNU] type-specifier-seq declarator simple-asm-expr[opt] attributes[opt]
/// '=' assignment-expression
///
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 00d2319..5a5874e 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -692,8 +692,9 @@
assert(D.isDecompositionDeclarator());
const DecompositionDeclarator &Decomp = D.getDecompositionDeclarator();
- // The syntax only allows a decomposition declarator as a simple-declaration
- // or a for-range-declaration, but we parse it in more cases than that.
+ // The syntax only allows a decomposition declarator as a simple-declaration,
+ // a for-range-declaration, or a condition in Clang, but we parse it in more
+ // cases than that.
if (!D.mayHaveDecompositionDeclarator()) {
Diag(Decomp.getLSquareLoc(), diag::err_decomp_decl_context)
<< Decomp.getSourceRange();
@@ -708,9 +709,12 @@
return nullptr;
}
- Diag(Decomp.getLSquareLoc(), getLangOpts().CPlusPlus17
- ? diag::warn_cxx14_compat_decomp_decl
- : diag::ext_decomp_decl)
+ Diag(Decomp.getLSquareLoc(),
+ !getLangOpts().CPlusPlus17
+ ? diag::ext_decomp_decl
+ : D.getContext() == Declarator::ConditionContext
+ ? diag::ext_decomp_decl_cond
+ : diag::warn_cxx14_compat_decomp_decl)
<< Decomp.getSourceRange();
// The semantic context is always just the current context.