P0806R2 Implicit capture of this with a capture-default of [=] is

deprecated.

Add a -Wdeprecated warning for this in C++2a onwards. (In C++17 and
before, there isn't a reasonable alternative because [=,this] is
ill-formed.)

llvm-svn: 336480

1 files changed, 11 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index fcacc2a17c9..5e69feceda6 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -1548,6 +1548,17 @@ ExprResult Sema::BuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
 
       // Handle 'this' capture.
       if (From.isThisCapture()) {
+        // Capturing 'this' implicitly with a default of '[=]' is deprecated,
+        // because it results in a reference capture. Don't warn prior to
+        // C++2a; there's nothing that can be done about it before then.
+        if (getLangOpts().CPlusPlus2a && IsImplicit &&
+            CaptureDefault == LCD_ByCopy) {
+          Diag(From.getLocation(), diag::warn_deprecated_this_capture);
+          Diag(CaptureDefaultLoc, diag::note_deprecated_this_capture)
+              << FixItHint::CreateInsertion(
+                     getLocForEndOfToken(CaptureDefaultLoc), ", this");
+        }
+
         Captures.push_back(
             LambdaCapture(From.getLocation(), IsImplicit,
                           From.isCopyCapture() ? LCK_StarThis : LCK_This));