Function with unparsed body is a definition

While a function body is being parsed, the function declaration is not considered
as a definition because it does not have a body yet. In some cases it leads to
incorrect interpretation, the case is presented in
https://bugs.llvm.org/show_bug.cgi?id=14785:
```
    template<typename T> struct Somewhat {
      void internal() const {}
      friend void operator+(int const &, Somewhat<T> const &) {}
    };
void operator+(int const &, Somewhat<char> const &x) { x.internal(); }
```
When statement `x.internal()` in the body of global `operator+` is parsed, the type
of `x` must be completed, so the instantiation of `Somewhat<char>` is started. It
instantiates the declaration of `operator+` defined inline, and makes a check for
redefinition. The check does not detect another definition because the declaration
of `operator+` is still not defining as does not have a body yet.

To solves this problem the function `isThisDeclarationADefinition` considers
a function declaration as a definition if it has flag `WillHaveBody` set.

This change fixes PR14785.

Differential Revision: https://reviews.llvm.org/D30375

This is a recommit of 305379, reverted in 305381, with small changes.

llvm-svn: 305903

1 files changed, 1 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index d6164b3..2f78d06 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -12232,6 +12232,7 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
 
   if (FD) {
     FD->setBody(Body);
+    FD->setWillHaveBody(false);
 
     if (getLangOpts().CPlusPlus14) {
       if (!FD->isInvalidDecl() && Body && !FD->isDependentContext() &&