Improve diagnostics if friend function redefines file-level function.

Clang makes check for function redefinition after it merged the new
declaration with the existing one. As a result, it produces poor
diagnostics in the case of a friend function defined inline, as in
the code:
```
    void func() {}
    class C { friend void func() {} };
```
Error message in this case states that `inline declaration of 'func'
follows non-inline definition`, which is misleading, as `func` does
not have explicit `inline` specifier.

With this changes compiler reports function redefinition if the new
function is a friend defined inline and it does not have explicit
`inline` specifier.

Differential Revision: https://reviews.llvm.org/D26065

llvm-svn: 304964

1 files changed, 6 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 3e2306361cd..313552e23bc 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -638,7 +638,12 @@ bool Sema::MergeCXXFunctionDecl(FunctionDecl *New, FunctionDecl *Old,
     Diag(Old->getLocation(), diag::note_previous_declaration);
     Invalid = true;
   } else if (!Old->getMostRecentDecl()->isInlined() && New->isInlined() &&
-             Old->isDefined(Def)) {
+             Old->isDefined(Def) &&
+             // If a friend function is inlined but does not have 'inline'
+             // specifier, it is a definition. Do not report attribute conflict
+             // in this case, redefinition will be diagnosed later.
+             (New->isInlineSpecified() ||
+              New->getFriendObjectKind() == Decl::FOK_None)) {
     // C++11 [dcl.fcn.spec]p4:
     //   If the definition of a function appears in a translation unit before its
     //   first declaration as inline, the program is ill-formed.