[PATCH] D72405: Allow /D flags absent during PCH creation under msvc-compat

[Zachary Henkel via Phabricator via cfe-commits]

zahen created this revision.
zahen added reviewers: rnk, thakis, hans.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

Before this patch adding a new /D flag when compiling a source file that consumed a PCH with clang-cl would issue a diagnostic and then fail.  With the patch, the diagnostic is still issued but the definition is accepted.  This matches the msvc behavior.  The fuzzy-pch-msvc.c is a clone of the existing fuzzy-pch.c tests with some msvc specific rework.

msvc diagnostic:

  warning C4605: '/DBAR=int' specified on current command line, but was not specified when precompiled header was built

Output of the CHECK-BAR test prior to the code change:

  <built-in>(1,9): warning: definition of macro 'BAR' does not match definition in precompiled header [-Wclang-cl-pch]
  #define BAR int
          ^
  D:\repos\llvm\llvm-project\clang\test\PCH\fuzzy-pch-msvc.c(12,1): error: unknown type name 'BAR'
  BAR bar = 17;
  ^
  D:\repos\llvm\llvm-project\clang\test\PCH\fuzzy-pch-msvc.c(23,4): error: BAR was not defined
  #  error BAR was not defined
     ^
  1 warning and 2 errors generated.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72405

Files:
  clang/lib/Lex/PPDirectives.cpp
  clang/test/PCH/fuzzy-pch-msvc.c


Index: clang/test/PCH/fuzzy-pch-msvc.c
===================================================================
--- /dev/null
+++ clang/test/PCH/fuzzy-pch-msvc.c
@@ -0,0 +1,32 @@
+// Test -D and -U interaction with a PCH when running clang-cl.
+
+// RUN: %clang_cl -DFOO -Yc %S/variables.h
+// RUN: %clang_cl -c -DBAR=int -Wno-microsoft-include -Yuvariables.h %s
+// RUN: %clang_cl -c -DFOO -DBAR=int -Wno-microsoft-include -Yuvariables.h %s
+// RUN: not %clang_cl -c -DFOO=blah -DBAR=int -Wno-microsoft-include -Yuvariables.h %s 2> %t.err
+// RUN: FileCheck -check-prefix=CHECK-FOO %s < %t.err
+// RUN: not %clang_cl -c -UFOO -DBAR=int -Wno-microsoft-include -Yuvariables.h %s 2> %t.err
+// RUN: FileCheck -check-prefix=CHECK-NOFOO %s < %t.err
+
+// RUN: not %clang_cl -c -DBAR=int -WX -Wno-microsoft-include -Yuvariables.h %s 2> %t.err
+// RUN: FileCheck -check-prefix=CHECK-BAR %s < %t.err
+
+#include "variables.h"
+
+BAR bar = 17;
+
+#ifndef FOO
+#  error FOO was not defined
+#endif
+
+#if FOO != 1
+#  error FOO has the wrong definition
+#endif
+
+#ifndef BAR
+#  error BAR was not defined
+#endif
+
+// CHECK-FOO: definition of macro 'FOO' differs between the precompiled header ('1') and the command line ('blah')
+// CHECK-NOFOO: macro 'FOO' was defined in the precompiled header but undef'd on the command line
+// CHECK-BAR: error: definition of macro 'BAR' does not match definition in precompiled header [-Werror,-Wclang-cl-pch]
Index: clang/lib/Lex/PPDirectives.cpp
===================================================================
--- clang/lib/Lex/PPDirectives.cpp
+++ clang/lib/Lex/PPDirectives.cpp
@@ -2727,7 +2727,9 @@
                              /*Syntactic=*/LangOpts.MicrosoftExt))
       Diag(MI->getDefinitionLoc(), diag::warn_pp_macro_def_mismatch_with_pch)
           << MacroNameTok.getIdentifierInfo();
-    return;
+    // Issue the diagnostic but allow the change under msvc compatability mode
+    if (!getLangOpts().MSVCCompat)
+      return;
   }
 
   // Finally, if this identifier already had a macro defined for it, verify that


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