[Clang][ScanDeps] Use the virtual path for module maps

Make clang-scan-deps use the virtual path for module maps instead of the on disk
path. This is needed so that modulemap relative lookups are done correctly in
the actual module builds. The file dependencies still use the on disk path as
that's what matters for build invalidation.

Differential Revision: https://reviews.llvm.org/D114206

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

@@ -237,7 +237,13 @@ ModuleID ModuleDepCollectorPP::handleTopLevelModule(const Module *M) {
                                    .getHeaderSearchInfo()
                                    .getModuleMap()
                                    .getModuleMapFileForUniquing(M);
-  MD.ClangModuleMapFile = std::string(ModuleMap ? ModuleMap->getName() : "");
+
+  if (ModuleMap) {
+    StringRef Path = ModuleMap->tryGetRealPathName();
+    if (Path.empty())
+      Path = ModuleMap->getName();
+    MD.ClangModuleMapFile = std::string(Path);
+  }
 
   serialization::ModuleFile *MF =
       MDC.ScanInstance.getASTReader()->getModuleManager().lookup(

clang/test/ClangScanDeps/modulemap-via-vfs.m

@@ -0,0 +1,56 @@
+// RUN: rm -rf %t.dir
+// RUN: split-file %s %t.dir
+// RUN: sed -e "s|DIR|%/t.dir|g" %t.dir/build/compile-commands.json.in > %t.dir/build/compile-commands.json
+// RUN: sed -e "s|DIR|%/t.dir|g" %t.dir/build/vfs.yaml.in > %t.dir/build/vfs.yaml
+// RUN: clang-scan-deps -compilation-database %t.dir/build/compile-commands.json -j 1 -format experimental-full \
+// RUN:   -mode preprocess-minimized-sources -generate-modules-path-args > %t.db
+// RUN: %python %S/../../utils/module-deps-to-rsp.py %t.db --module-name=A > %t.A.cc1.rsp
+// RUN: cat %t.A.cc1.rsp | sed 's:\\\\\?:/:g' | FileCheck %s
+
+// CHECK-NOT: build/module.modulemap
+// CHECK: A/module.modulemap
+
+//--- build/compile-commands.json.in
+
+[
+{
+  "directory": "DIR",
+  "command": "clang DIR/main.m -Imodules/A -fmodules -fmodules-cache-path=module-cache -fimplicit-modules -fimplicit-module-maps -ivfsoverlay build/vfs.yaml",
+  "file": "DIR/main.m"
+}
+]
+
+//--- build/module.modulemap
+
+module A {
+  umbrella header "A.h"
+}
+
+//--- modules/A/A.h
+
+typedef int A_t;
+
+//--- build/vfs.yaml.in
+
+{
+  "version": 0,
+  "case-sensitive": "false",
+  "roots": [
+  {
+     "contents": [
+     {
+        "external-contents": "DIR/build/module.modulemap",
+        "name": "module.modulemap",
+        "type": "file"
+     }],
+     "name": "DIR/modules/A",
+     "type": "directory"
+  }
+  ]
+}
+
+//--- main.m
+
+@import A;
+
+A_t a = 0;