[modules] Don't leak -M flags for dependency file generation into the module

build process when we implicitly build a module. Previously, we'd create the
specified .d file once for each implicitly-built module and then finally
overwrite it with the correct contents after the requested build completes.
(This fails if you use stdout as a dependency file, which is what the provided
testcase does, and is how I discovered this brokenness.)

llvm-svn: 244412

1 files changed, 3 insertions, 1 deletions

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 4e7b08a..5133ffc 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -944,8 +944,10 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
     FullSourceLoc(ImportLoc, ImportingInstance.getSourceManager()));
 
   // If we're collecting module dependencies, we need to share a collector
-  // between all of the module CompilerInstances.
+  // between all of the module CompilerInstances. Other than that, we don't
+  // want to produce any dependency output from the module build.
   Instance.setModuleDepCollector(ImportingInstance.getModuleDepCollector());
+  Invocation->getDependencyOutputOpts() = DependencyOutputOptions();
 
   // Get or create the module map that we'll use to build this module.
   std::string InferredModuleMapContent;