Now that macro expansion notes are real notes and go through the same

formatting as any other diagnostic, they will be properly line wrapped and
otherwise pretty printed. Let's take advantage of that and the new factoring to
add some helpful information to them (much like template backtrace notes and
other notes): the name of the macro whose expansion is being noted. This makes
a world of difference if caret diagnostics are disabled, making the expansion
notes actually useful in this case. It also helps ensure that in edge cases the
information the user needs is present. Consider:

% nl -ba t5.cc
     1  #define M(x, y, z) \
     2    y
     3
     4  M(
     5    1,
     6    2,
     7    3);

We now produce:
% ./bin/clang -fsyntax-only t5.cc
t5.cc:6:3: error: expected unqualified-id
  2,
  ^
t5.cc:2:3: note: expanded from macro: M
  y
  ^
1 error generated.

Without the added information in the note, the name of the macro being expanded
would never be shown.

This also deletes a FIXME to use the diagnostic formatting. It's not yet clear
to me that we *can* do this reasonably, and the production of this message was
my primary goal here anyways.

I'd love any comments or suggestions on improving these notes, their wording,
etc. Currently, I need to make them provide more helpful information in the
presence of a token-pasting buffer, and I'm pondering adding something along
the lines of "expanded from argument N of macro: ...".

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142127 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 23 insertions, 2 deletions

diff --git a/lib/Frontend/TextDiagnostic.cpp b/lib/Frontend/TextDiagnostic.cpp
index 7b3ebc4cd6..8dab0afcac 100644
--- a/lib/Frontend/TextDiagnostic.cpp
+++ b/lib/Frontend/TextDiagnostic.cpp
@@ -689,6 +689,9 @@ void TextDiagnostic::emitMacroExpansionsAndCarets(
   emitMacroExpansionsAndCarets(OneLevelUp, Level, Ranges, Hints, MacroDepth,
                                OnMacroInst + 1);
 
+  // Save the original location so we can find the spelling of the macro call.
+  SourceLocation MacroLoc = Loc;
+
   // Map the location.
   Loc = getImmediateMacroCalleeLoc(SM, Loc);
 
@@ -726,9 +729,27 @@ void TextDiagnostic::emitMacroExpansionsAndCarets(
     return;
   }
 
-  // FIXME: Format an actual diagnostic rather than a hard coded string.
+  // Walk past macro argument expanions.
+  while (SM.isMacroArgExpansion(MacroLoc))
+    MacroLoc = SM.getImmediateExpansionRange(MacroLoc).first;
+
+  // Find the spelling location of the start of the non-argument expansion
+  // range. This is where the macro name was spelled in order to begin
+  // expanding this macro.
+  MacroLoc = SM.getSpellingLoc(SM.getImmediateExpansionRange(MacroLoc).first);
+
+  // Dig out the buffer where the macro name was spelled and the extents of the
+  // name so that we can render it into the expansion note.
+  std::pair<FileID, unsigned> ExpansionInfo = SM.getDecomposedLoc(MacroLoc);
+  unsigned MacroTokenLength = Lexer::MeasureTokenLength(MacroLoc, SM, LangOpts);
+  StringRef ExpansionBuffer = SM.getBufferData(ExpansionInfo.first);
+
+  llvm::SmallString<100> MessageStorage;
+  llvm::raw_svector_ostream Message(MessageStorage);
+  Message << "expanded from macro: "
+          << ExpansionBuffer.substr(ExpansionInfo.second, MacroTokenLength);
   emitDiagnostic(SM.getSpellingLoc(Loc), DiagnosticsEngine::Note,
-                 "expanded from:",
+                 Message.str(),
                  Ranges, ArrayRef<FixItHint>());
 }