Add -Wmodule-build to make it easy to see when modules are (re)built

Warning is default ignore, and not in -Wall.

llvm-svn: 207975

3 files changed, 27 insertions, 0 deletions

diff --git a/clang/include/clang/Basic/DiagnosticFrontendKinds.td b/clang/include/clang/Basic/DiagnosticFrontendKinds.td
index 7b500eed5c0..674d6d6c42f 100644
--- a/clang/include/clang/Basic/DiagnosticFrontendKinds.td
+++ b/clang/include/clang/Basic/DiagnosticFrontendKinds.td
@@ -167,6 +167,8 @@ def warn_module_config_macro_undef : Warning<
   InGroup<ConfigMacros>;
 def note_module_def_undef_here : Note<
   "macro was %select{defined|#undef'd}0 here">;
+def warn_module_build : Warning<"building module '%0' as '%1'">,
+  InGroup<DiagGroup<"module-build">>, DefaultIgnore;
 
 def err_missing_vfs_overlay_file : Error<
   "virtual filesystem overlay file '%0' not found">, DefaultFatal;
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index d7b526b2da2..4a75186d975 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1219,6 +1219,9 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
         return ModuleLoadResult();
       }
 
+      getDiagnostics().Report(ImportLoc, diag::warn_module_build)
+          << ModuleName << ModuleFileName;
+
       // Check whether we have already attempted to build this module (but
       // failed).
       if (getPreprocessorOpts().FailedModules &&
diff --git a/clang/test/Modules/Wmodule-build.m b/clang/test/Modules/Wmodule-build.m
new file mode 100644
index 00000000000..74e020965c4
--- /dev/null
+++ b/clang/test/Modules/Wmodule-build.m
@@ -0,0 +1,22 @@
+// REQUIRES: shell
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: echo '// A' > %t/A.h
+// RUN: echo '// B' > %t/B.h
+// RUN: echo 'module A { header "A.h" }' > %t/module.modulemap
+// RUN: echo 'module B { header "B.h" }' >> %t/module.modulemap
+
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fsyntax-only %s -verify \
+// RUN:            -I %t -Wmodule-build
+
+@import A; // expected-warning{{building module 'A' as}}
+@import B; // expected-warning{{building module 'B' as}}
+@import A; // no diagnostic
+@import B; // no diagnostic
+
+// RUN: echo ' ' >> %t/B.h
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -fsyntax-only %s -I %t \
+// RUN:            -Wmodule-build 2>&1 | FileCheck %s
+
+// CHECK-NOT: building module 'A'
+// CHECK: building module 'B'