[clang-scan-deps] ignore top-level module dependencies that aren't actually imported

[arphaman]

Summary

Whenever -fmodule-name=top_level_module name is parsed, and clang actually tries to import top_level_module, the headers are imported textually and the module isn't actually built. However, the dependency scanner could still record it as a potential dependency if the module was reimported and thus recorded by the preprocessor callbacks. This patch avoids collecting this kind of module as a dependency by verifying that we don't collect top level modules without actual PCM files.

[jansvoboda11]

LGTM!

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

 void ModuleDepCollectorPP::EndOfMainFile() {
   FileID MainFileID = Instance.getSourceManager().getMainFileID();
   MDC.MainFile = std::string(
       Instance.getSourceManager().getFileEntryForID(MainFileID)->getName());
 
   if (!Instance.getPreprocessorOpts().ImplicitPCHInclude.empty())
     MDC.FileDeps.push_back(Instance.getPreprocessorOpts().ImplicitPCHInclude);
 
-  for (const Module *M : DirectModularDeps)
+  for (const Module *M : DirectModularDeps) {
+    // A top-level module might not be actually imported as a module when
+    // -fmodule-name is used to compile a translation unit that imports this
+    // module. In that case it can be skipped. The appropriate header
+    // dependencies will still be reported as expected.
+    if (!M->getASTFile())
+      continue;
     handleTopLevelModule(M);
+  }
 
   MDC.Consumer.handleDependencyOutputOpts(*MDC.Opts);
 
   for (auto &&I : MDC.ModularDeps)
     MDC.Consumer.handleModuleDependency(I.second);
 
   for (auto &&I : MDC.FileDeps)
     MDC.Consumer.handleFileDependency(I);

clang/test/ClangScanDeps/Inputs/header3.h

+// import another header from the same module
+#include "header.h"

clang/test/ClangScanDeps/Inputs/module.modulemap

 module header1 {
   header "header.h"
 }
 
 module header2 {
     header "header2.h"
 }
+
+module header3 {
+  header "header.h"
+  header "header3.h"
+}

clang/test/ClangScanDeps/Inputs/module_fmodule_name_cdb.json

+[
+{
+  "directory": "DIR",
+  "command": "clang -E DIR/modules-fmodule-name-no-module-built.m -IInputs -D INCLUDE_HEADER2 -MD -MF DIR/modules_cdb.d -fmodules -fcxx-modules -fmodules-cache-path=DIR/module-cache -fimplicit-modules -fmodule-name=header3 -fimplicit-module-maps",
+  "file": "DIR/modules-fmodule-name-no-module-built.m"
+}
+]

clang/test/ClangScanDeps/modules-fmodule-name-no-module-built.m

+// RUN: rm -rf %t.dir
+// RUN: rm -rf %t.cdb
+// RUN: mkdir -p %t.dir
+// RUN: cp %s %t.dir/modules-fmodule-name-no-module-built.m
+// RUN: mkdir %t.dir/Inputs
+// RUN: cp %S/Inputs/header.h %t.dir/Inputs/header.h
+// RUN: cp %S/Inputs/header2.h %t.dir/Inputs/header2.h
+// RUN: cp %S/Inputs/header3.h %t.dir/Inputs/header3.h
+// RUN: cp %S/Inputs/module.modulemap %t.dir/Inputs/module.modulemap
+// RUN: sed -e "s|DIR|%/t.dir|g" %S/Inputs/module_fmodule_name_cdb.json > %t.cdb
+
+// RUN: echo %t.dir > %t.result
+// RUN: clang-scan-deps -compilation-database %t.cdb -j 1 -format experimental-full \
+// RUN:   -generate-modules-path-args -mode preprocess-minimized-sources >> %t.result
+// RUN: cat %t.result | sed 's:\\\\\?:/:g' | FileCheck --check-prefixes=CHECK %s
+
+#import "header3.h"
+#import "header.h"
+
+// CHECK: [[PREFIX:.*]]
+// CHECK-NEXT: {
+// CHECK-NEXT:   "modules": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-module-deps": []
+// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/Inputs/module.modulemap",
+// CHECK-NEXT:       "command-line": [
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "[[HASH_H2:[A-Z0-9]+]]",
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/Inputs/header2.h",
+// CHECK-NEXT:         "[[PREFIX]]/Inputs/module.modulemap"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "name": "header2"
+// CHECK-NEXT:     }
+// CHECK-NEXT:   ],
+// CHECK-NEXT:   "translation-units": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-context-hash": "[[HASH_TU:[A-Z0-9]+]]",
+// CHECK-NEXT:       "clang-module-deps": [
+// CHECK-NEXT:         {
+// CHECK-NEXT:           "context-hash": "[[HASH_H2]]",
+// CHECK-NEXT:           "module-name": "header2"
+// CHECK-NEXT:         }
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "command-line": [
+// CHECK-NEXT:         "-fno-implicit-modules"
+// CHECK-NEXT:         "-fno-implicit-module-maps"
+// CHECK-NEXT:         "-fmodule-file=[[PREFIX]]/module-cache{{(_clangcl)?}}/[[HASH_H2]]/header2-{{[A-Z0-9]+}}.pcm"
+// CHECK-NEXT:         "-fmodule-map-file=[[PREFIX]]/Inputs/module.modulemap"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/modules-fmodule-name-no-module-built.m"
+// CHECK-NEXT:         "[[PREFIX]]/Inputs/header3.h"
+// CHECK-NEXT:         "[[PREFIX]]/Inputs/header.h"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "input-file": "[[PREFIX]]/modules-fmodule-name-no-module-built.m"
+// CHECK-NEXT:     }
+// CHECK-NEXT:   ]
+// CHECK-NEXT: }