Introduce an opt-in warning when a module is being implicitly built

from sources.

llvm-svn: 140746

clang/include/clang/Basic/DiagnosticCommonKinds.td

@@ -63,6 +63,8 @@ def err_module_not_found : Error<"module '%0' not found">, DefaultFatal;
 def err_module_not_built : Error<"could not build module '%0'">, DefaultFatal;
 def err_module_cycle : Error<"cyclic dependency in module '%0': %1">, 
   DefaultFatal;
+def warn_module_build : Warning<"building module '%0' from source">, 
+  InGroup<ModuleBuild>, DefaultIgnore;
 
 // Sema && Lex
 def ext_longlong : Extension<

clang/include/clang/Basic/DiagnosticGroups.td

@@ -85,6 +85,7 @@ def : DiagGroup<"newline-eof">;
 def LongLong : DiagGroup<"long-long">;
 def MismatchedTags : DiagGroup<"mismatched-tags">;
 def MissingFieldInitializers : DiagGroup<"missing-field-initializers">;
+def ModuleBuild : DiagGroup<"module-build">;
 def NullDereference : DiagGroup<"null-dereference">;
 def InitializerOverrides : DiagGroup<"initializer-overrides">;
 def NonNull : DiagGroup<"nonnull">;

clang/lib/Frontend/CompilerInstance.cpp

@@ -752,6 +752,8 @@ ModuleKey CompilerInstance::loadModule(SourceLocation ImportLoc,
       return 0;
     }
     
+    getDiagnostics().Report(ModuleNameLoc, diag::warn_module_build)
+      << ModuleName.getName();
     BuildingModule = true;
     compileModule(*this, ModuleName.getName(), ModuleFileName, UmbrellaHeader);
     ModuleFile = PP->getHeaderSearchInfo().lookupModule(ModuleName.getName());

clang/test/Modules/on-demand-build-warnings.m

@@ -0,0 +1,5 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fno-objc-infer-related-result-type -Wmodule-build -fmodule-cache-path %t -F %S/Inputs -DFOO -verify %s
+
+__import_module__ Module; // expected-warning{{building module 'Module' from source}}
+