PR23334: Perform semantic checking of lambda capture initialization in the right context.

Previously we'd try to perform checks on the captures from the middle of
parsing the lambda's body, at the point where we detected that a variable
needed to be captured. This was wrong in a number of subtle ways. In
PR23334, we couldn't correctly handle the list of potential odr-uses
resulting from the capture, and our attempt to recover from that resulted
in a use-after-free.

We now defer building the initialization expression until we leave the lambda
body and return to the enclosing context, where the initialization does the
right thing. This patch only covers lambda-expressions, but we should apply
the same change to blocks and captured statements too.

llvm-svn: 235921

1 files changed, 17 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 58e78387fd8..e11b4e14c58 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -10587,6 +10587,23 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
         Context.adjustDeducedFunctionResultType(
             FD, SubstAutoType(ResultType.getType(), Context.VoidTy));
       }
+    } else if (getLangOpts().CPlusPlus11 && isLambdaCallOperator(FD)) {
+      auto *LSI = getCurLambda();
+      if (LSI->HasImplicitReturnType) {
+        deduceClosureReturnType(*LSI);
+
+        // C++11 [expr.prim.lambda]p4:
+        //   [...] if there are no return statements in the compound-statement
+        //   [the deduced type is] the type void
+        QualType RetType =
+            LSI->ReturnType.isNull() ? Context.VoidTy : LSI->ReturnType;
+
+        // Update the return type to the deduced type.
+        const FunctionProtoType *Proto =
+            FD->getType()->getAs<FunctionProtoType>();
+        FD->setType(Context.getFunctionType(RetType, Proto->getParamTypes(),
+                                            Proto->getExtProtoInfo()));
+      }
     }
 
     // The only way to be included in UndefinedButUsed is if there is an