commit 8eeb16f5d1008a3d3fc89e88d92b3bcebc36bba2
author Richard Smith <richard-llvm@metafoo.co.uk> Mon Sep 10 20:31:03 2018 +0000
committer Richard Smith <richard-llvm@metafoo.co.uk> Mon Sep 10 20:31:03 2018 +0000
tree 515beea70adb40b91987b18587c4634a9ba4af7d
parent 6dc896812423b7201492a116895df6c8c9601acf

Enhance -Wc++14-compat for class template argument deduction to list the
deduced type (if known).

llvm-svn: 341858

clang/include/clang/Basic/DiagnosticSemaKinds.td

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 3ff595c..b253a88 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2153,7 +2153,8 @@
   "deduction guide declared %0 by intervening access specifier">;
 def warn_cxx14_compat_class_template_argument_deduction : Warning<
   "class template argument deduction is incompatible with C++ standards "
-  "before C++17">, InGroup<CXXPre17Compat>, DefaultIgnore;
+  "before C++17%select{|; for compatibility, use explicit type name %1}0">,
+  InGroup<CXXPre17Compat>, DefaultIgnore;
 
 // C++14 deduced return types
 def err_auto_fn_deduction_failure : Error<

clang/lib/Sema/SemaInit.cpp

diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 18a7aab..a25818f 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -9139,13 +9139,13 @@
     return QualType();
   }
 
-  Diag(TSInfo->getTypeLoc().getBeginLoc(),
-       diag::warn_cxx14_compat_class_template_argument_deduction)
-      << TSInfo->getTypeLoc().getSourceRange();
-
   // Can't deduce from dependent arguments.
-  if (Expr::hasAnyTypeDependentArguments(Inits))
+  if (Expr::hasAnyTypeDependentArguments(Inits)) {
+    Diag(TSInfo->getTypeLoc().getBeginLoc(),
+         diag::warn_cxx14_compat_class_template_argument_deduction)
+        << TSInfo->getTypeLoc().getSourceRange() << 0;
     return Context.DependentTy;
+  }
 
   // FIXME: Perform "exact type" matching first, per CWG discussion?
   //        Or implement this via an implied 'T(T) -> T' deduction guide?
@@ -9348,5 +9348,10 @@
   // C++ [dcl.type.class.deduct]p1:
   //  The placeholder is replaced by the return type of the function selected
   //  by overload resolution for class template deduction.
-  return SubstAutoType(TSInfo->getType(), Best->Function->getReturnType());
+  QualType DeducedType =
+      SubstAutoType(TSInfo->getType(), Best->Function->getReturnType());
+  Diag(TSInfo->getTypeLoc().getBeginLoc(),
+       diag::warn_cxx14_compat_class_template_argument_deduction)
+      << TSInfo->getTypeLoc().getSourceRange() << 1 << DeducedType;
+  return DeducedType;
 }

clang/test/SemaCXX/cxx14-compat.cpp

diff --git a/clang/test/SemaCXX/cxx14-compat.cpp b/clang/test/SemaCXX/cxx14-compat.cpp
index 8b3dee8..d70f477 100644
--- a/clang/test/SemaCXX/cxx14-compat.cpp
+++ b/clang/test/SemaCXX/cxx14-compat.cpp
@@ -16,7 +16,7 @@
 enum { e [[]] }; // expected-warning {{incompatible with C++ standards before C++17}}
 
 template<typename T = int> struct X {};
-X x; // expected-warning {{class template argument deduction is incompatible with C++ standards before C++17}}
+X x; // expected-warning {{class template argument deduction is incompatible with C++ standards before C++17; for compatibility, use explicit type name 'X<int>'}}
 
 template<template<typename> class> struct Y {};
 Y<X> yx; // ok, not class template argument deduction