PR5803: clang++: Treat untyped 'C' inputs as C++.

- Patch by Andrzej K. Haczewski, with a tweak by me to emit a 'deprecated'
   diagnostic when we do this. We'll see what zee users say.

llvm-svn: 96511

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -88,6 +88,8 @@ def warn_ignoring_ftabstop_value : Warning<
 def warn_drv_missing_resource_library : Warning<
   "missing resource library '%0', link may fail">;
 def warn_drv_conflicting_deployment_targets : Warning<
-    "conflicting deployment targets, both MACOSX_DEPLOYMENT_TARGET '%0' and IPHONEOS_DEPLOYMENT_TARGET '%1' are present in environment">;
+  "conflicting deployment targets, both MACOSX_DEPLOYMENT_TARGET '%0' and IPHONEOS_DEPLOYMENT_TARGET '%1' are present in environment">;
+def warn_drv_treating_input_as_cxx : Warning<
+  "treating '%0' input as '%1' when in C++ mode, this behavior is deprecated">;
 
 }

clang/include/clang/Driver/Types.h

@@ -80,6 +80,10 @@ namespace types {
   /// getCompilationPhase - Return the \args N th compilation phase to
   /// be done for this type.
   phases::ID getCompilationPhase(ID Id, unsigned N);
+  
+  /// lookupCXXTypeForCType - Lookup CXX input type that corresponds to given
+  /// C type (used for clang++ emulation of g++ behaviour)
+  ID lookupCXXTypeForCType(ID Id);
 
 } // end namespace types
 } // end namespace driver

clang/lib/Driver/Driver.cpp

@@ -558,6 +558,17 @@ void Driver::BuildActions(const ArgList &Args, ActionList &Actions) const {
 
           if (Ty == types::TY_INVALID)
             Ty = types::TY_Object;
+
+          // If the driver is invoked as C++ compiler (like clang++ or c++) it
+          // should autodetect some input files as C++ for g++ compatibility.
+          if (CCCIsCXX) {
+            types::ID OldTy = Ty;
+            Ty = types::lookupCXXTypeForCType(Ty);
+
+            if (Ty != OldTy)
+              Diag(clang::diag::warn_drv_treating_input_as_cxx)
+                << getTypeName(OldTy) << getTypeName(Ty);
+          }
         }
 
         // -ObjC and -ObjC++ override the default language, but only for "source

clang/lib/Driver/Types.cpp

@@ -213,3 +213,19 @@ phases::ID types::getCompilationPhase(ID Id, unsigned N) {
 
   return phases::Link;
 }
+
+ID types::lookupCXXTypeForCType(ID Id) {
+  switch (Id) {
+  default:
+    return Id;
+    
+  case types::TY_C:
+    return types::TY_CXX;
+  case types::TY_PP_C:
+    return types::TY_PP_CXX;
+  case types::TY_CHeader:
+    return types::TY_CXXHeader;
+  case types::TY_PP_CHeader:
+    return types::TY_PP_CXXHeader;
+  }
+}

clang/test/Driver/clang-c-as-cxx.c

@@ -0,0 +1,6 @@
+// RUN: %clangxx -### %s 2>&1 | FileCheck %s
+//
+// PR5803
+//
+// CHECK: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated
+// CHECK: "-cc1" {{.*}} "-x" "c++"