Improve 0-argument -Wvexing-parse diagnostic by adding notes with fix-its:

 - If the declarator is at the start of a line, and the previous line contained
   another declarator and ended with a comma, then that comma was probably a
   typo for a semicolon:

   int n = 0, m = 1, l = 2, // k = 5;
   myImportantFunctionCall(); // oops!

 - If removing the parentheses would correctly initialize the object, then
   produce a note suggesting that fix.

 - Otherwise, if there is a simple initializer we can suggest which performs
   value-initialization, then provide a note suggesting a correction to that
   initializer.

Sema::Declarator now tracks the location of the comma prior to the declarator in
the declaration, if there is one, to facilitate providing the note. The code to
determine an appropriate initializer from the -Wuninitialized warning has been
factored out to allow use in both that and -Wvexing-parse.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@148072 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 33 insertions, 2 deletions

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index dc8d6ec8cf..4dcf1db2cf 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -4921,8 +4921,39 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
       if (!T->isVoidType() && C.Fun.NumArgs == 0 && !C.Fun.isVariadic &&
           !C.Fun.TrailingReturnType &&
           C.Fun.getExceptionSpecType() == EST_None) {
-        Diag(C.Loc, diag::warn_empty_parens_are_function_decl)
-          << SourceRange(C.Loc, C.EndLoc);
+        SourceRange ParenRange(C.Loc, C.EndLoc);
+        Diag(C.Loc, diag::warn_empty_parens_are_function_decl) << ParenRange;
+
+        // If the declaration looks like:
+        //   T var1,
+        //   f();
+        // and name lookup finds a function named 'f', then the ',' was
+        // probably intended to be a ';'.
+        if (!D.isFirstDeclarator() && D.getIdentifier()) {
+          FullSourceLoc Comma(D.getCommaLoc(), SourceMgr);
+          FullSourceLoc Name(D.getIdentifierLoc(), SourceMgr);
+          if (Comma.getFileID() != Name.getFileID() ||
+              Comma.getSpellingLineNumber() != Name.getSpellingLineNumber()) {
+            LookupResult Result(*this, D.getIdentifier(), SourceLocation(),
+                                LookupOrdinaryName);
+            if (LookupName(Result, S))
+              Diag(D.getCommaLoc(), diag::note_empty_parens_function_call)
+                << FixItHint::CreateReplacement(D.getCommaLoc(), ";") << NewFD;
+          }
+        }
+        const CXXRecordDecl *RD = T->getAsCXXRecordDecl();
+        // Empty parens mean value-initialization, and no parens mean default
+        // initialization. These are equivalent if the default constructor is
+        // user-provided, or if zero-initialization is a no-op.
+        if (RD && (RD->isEmpty() || RD->hasUserProvidedDefaultConstructor()))
+          Diag(C.Loc, diag::note_empty_parens_default_ctor)
+            << FixItHint::CreateRemoval(ParenRange);
+        else if (const char *Init = getFixItZeroInitializerForType(T))
+          Diag(C.Loc, diag::note_empty_parens_zero_initialize)
+            << FixItHint::CreateReplacement(ParenRange, Init);
+        else if (LangOpts.CPlusPlus0x)
+          Diag(C.Loc, diag::note_empty_parens_zero_initialize)
+            << FixItHint::CreateReplacement(ParenRange, "{}");
       }
     }