Introducing -Wheader-guard, a warning that checks header guards actually work

properly.  This warning checks that the #ifndef and #define directives at
the beginning of a header refer to the same macro name.  Includes a fix-it
hint to correct the header guard.

llvm-svn: 183867

2 files changed, 36 insertions, 5 deletions

diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index 947011d7075..0cfdac92d23 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -626,6 +626,10 @@ void Preprocessor::HandleDirective(Token &Result) {
   CurPPLexer->ParsingPreprocessorDirective = true;
   if (CurLexer) CurLexer->SetKeepWhitespaceMode(false);
 
+  bool ImmediatelyAfterTopLevelIfndef =
+      CurPPLexer->MIOpt.getImmediatelyAfterTopLevelIfndef();
+  CurPPLexer->MIOpt.resetImmediatelyAfterTopLevelIfndef();
+
   ++NumDirectives;
 
   // We are about to read a token.  For the multiple-include optimization FA to
@@ -713,7 +717,7 @@ void Preprocessor::HandleDirective(Token &Result) {
 
     // C99 6.10.3 - Macro Replacement.
     case tok::pp_define:
-      return HandleDefineDirective(Result);
+      return HandleDefineDirective(Result, ImmediatelyAfterTopLevelIfndef);
     case tok::pp_undef:
       return HandleUndefDirective(Result);
 
@@ -1760,7 +1764,8 @@ bool Preprocessor::ReadMacroDefinitionArgList(MacroInfo *MI, Token &Tok) {
 
 /// HandleDefineDirective - Implements \#define.  This consumes the entire macro
 /// line then lets the caller lex the next real token.
-void Preprocessor::HandleDefineDirective(Token &DefineTok) {
+void Preprocessor::HandleDefineDirective(Token &DefineTok,
+                                         bool ImmediatelyAfterHeaderGuard) {
   ++NumDefined;
 
   Token MacroNameTok;
@@ -1786,6 +1791,11 @@ void Preprocessor::HandleDefineDirective(Token &DefineTok) {
   // marking each of the identifiers as being used as macro arguments.  Also,
   // check other constraints on the first token of the macro body.
   if (Tok.is(tok::eod)) {
+    if (ImmediatelyAfterHeaderGuard) {
+      // Save this macro information since it may part of a header guard.
+      CurPPLexer->MIOpt.SetDefinedMacro(MacroNameTok.getIdentifierInfo(),
+                                        MacroNameTok.getLocation());
+    }
     // If there is no body to this macro, we have no special handling here.
   } else if (Tok.hasLeadingSpace()) {
     // This is a normal token with leading space.  Clear the leading space
@@ -2076,7 +2086,7 @@ void Preprocessor::HandleIfdefDirective(Token &Result, bool isIfndef,
     // handle.
     if (!ReadAnyTokensBeforeDirective && MI == 0) {
       assert(isIfndef && "#ifdef shouldn't reach here");
-      CurPPLexer->MIOpt.EnterTopLevelIFNDEF(MII);
+      CurPPLexer->MIOpt.EnterTopLevelIfndef(MII, MacroNameTok.getLocation());
     } else
       CurPPLexer->MIOpt.EnterTopLevelConditional();
   }
@@ -2122,7 +2132,7 @@ void Preprocessor::HandleIfDirective(Token &IfToken,
   // directive seen, handle it for the multiple-include optimization.
   if (CurPPLexer->getConditionalStackDepth() == 0) {
     if (!ReadAnyTokensBeforeDirective && IfNDefMacro && ConditionalTrue)
-      CurPPLexer->MIOpt.EnterTopLevelIFNDEF(IfNDefMacro);
+      CurPPLexer->MIOpt.EnterTopLevelIfndef(IfNDefMacro, ConditionalBegin);
     else
       CurPPLexer->MIOpt.EnterTopLevelConditional();
   }
diff --git a/clang/lib/Lex/PPLexerChange.cpp b/clang/lib/Lex/PPLexerChange.cpp
index 64373362461..e521032bca3 100644
--- a/clang/lib/Lex/PPLexerChange.cpp
+++ b/clang/lib/Lex/PPLexerChange.cpp
@@ -244,8 +244,29 @@ bool Preprocessor::HandleEndOfFile(Token &Result, bool isEndOfMacro) {
           CurPPLexer->MIOpt.GetControllingMacroAtEndOfFile()) {
       // Okay, this has a controlling macro, remember in HeaderFileInfo.
       if (const FileEntry *FE =
-            SourceMgr.getFileEntryForID(CurPPLexer->getFileID()))
+            SourceMgr.getFileEntryForID(CurPPLexer->getFileID())) {
         HeaderInfo.SetFileControllingMacro(FE, ControllingMacro);
+        if (const IdentifierInfo *DefinedMacro =
+              CurPPLexer->MIOpt.GetDefinedMacro()) {
+          if (!ControllingMacro->hasMacroDefinition() &&
+              DefinedMacro != ControllingMacro &&
+              HeaderInfo.FirstTimeLexingFile(FE)) {
+            // Emit a warning for a bad header guard.
+            Diag(CurPPLexer->MIOpt.GetMacroLocation(),
+                 diag::warn_header_guard)
+                << CurPPLexer->MIOpt.GetMacroLocation()
+                << ControllingMacro;
+            Diag(CurPPLexer->MIOpt.GetDefinedLocation(),
+                 diag::note_header_guard)
+                << CurPPLexer->MIOpt.GetDefinedLocation()
+                << DefinedMacro
+                << ControllingMacro
+                << FixItHint::CreateReplacement(
+                       CurPPLexer->MIOpt.GetDefinedLocation(),
+                       ControllingMacro->getName());
+          }
+        }
+      }
     }
   }