[clang][DependencyScanner] Include the working directory in the context hash

The working directory is included in the PCM, but is not currently
part of the context hash. This causes problems because different
builds of a PCM with exactly the same command line can end up with
different binary content for a PCM. If a build system tracks tasks by
both working directory and command line, it may build a given PCM
multiple times, causing a "module file out of date" error when loading
the PCM due to different sizes.

Author: Bigcheese

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

@@ -316,7 +316,8 @@ void ModuleDepCollector::applyDiscoveredDependencies(CompilerInvocation &CI) {
 
 static std::string getModuleContextHash(const ModuleDeps &MD,
                                         const CowCompilerInvocation &CI,
-                                        bool EagerLoadModules) {
+                                        bool EagerLoadModules,
+                                        llvm::vfs::FileSystem &VFS) {
   llvm::HashBuilder<llvm::TruncatedBLAKE3<16>, llvm::endianness::native>
       HashBuilder;
   SmallString<32> Scratch;
@@ -325,6 +326,9 @@ static std::string getModuleContextHash(const ModuleDeps &MD,
   // will be readable.
   HashBuilder.add(getClangFullRepositoryVersion());
   HashBuilder.add(serialization::VERSION_MAJOR, serialization::VERSION_MINOR);
+  llvm::ErrorOr<std::string> CWD = VFS.getCurrentWorkingDirectory();
+  if (CWD)
+    HashBuilder.add(*CWD);
 
   // Hash the BuildInvocation without any input files.
   SmallString<0> ArgVec;
@@ -356,7 +360,8 @@ static std::string getModuleContextHash(const ModuleDeps &MD,
 
 void ModuleDepCollector::associateWithContextHash(
     const CowCompilerInvocation &CI, ModuleDeps &Deps) {
-  Deps.ID.ContextHash = getModuleContextHash(Deps, CI, EagerLoadModules);
+  Deps.ID.ContextHash = getModuleContextHash(
+      Deps, CI, EagerLoadModules, ScanInstance.getVirtualFileSystem());
   bool Inserted = ModuleDepsByID.insert({Deps.ID, &Deps}).second;
   (void)Inserted;
   assert(Inserted && "duplicate module mapping");

clang/test/ClangScanDeps/working-dir.m

@@ -0,0 +1,107 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s|DIR|%/t|g" %t/build/compile-commands.json.in > %t/build/compile-commands.json
+// RUN: clang-scan-deps -compilation-database %t/build/compile-commands.json \
+// RUN:   -j 1 -format experimental-full --optimize-args=all > %t/deps.db
+// RUN: cat %t/deps.db | sed 's:\\\\\?:/:g' | FileCheck %s -DPREFIX=%/t
+
+// Check that there are two separate modules hashes. One for each working dir.
+
+// CHECK:      {
+// CHECK-NEXT:   "modules": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-module-deps":
+// CHECK-NEXT:       "clang-modulemap-file":
+// CHECK-NEXT:       "command-line": [
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK:            ],
+// CHECK-NEXT:       "name": "A"
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-module-deps":
+// CHECK-NEXT:       "clang-modulemap-file":
+// CHECK-NEXT:       "command-line": [
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK:            ],
+// CHECK-NEXT:       "name": "A"
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-module-deps":
+// CHECK:            ],
+// CHECK-NEXT:       "clang-modulemap-file":
+// CHECK-NEXT:       "command-line": [
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK:            ],
+// CHECK-NEXT:       "name": "B"
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-module-deps":
+// CHECK:            ],
+// CHECK-NEXT:       "clang-modulemap-file":
+// CHECK-NEXT:       "command-line": [
+// CHECK:            ],
+// CHECK-NEXT:       "context-hash": "{{.*}}",
+// CHECK-NEXT:       "file-deps": [
+// CHECK:            ],
+// CHECK-NEXT:       "name": "B"
+// CHECK-NEXT:     }
+// CHECK-NEXT:   ],
+// CHECK-NEXT:   "translation-units": [
+// CHECK:        ]
+// CHECK:      }
+
+//--- build/compile-commands.json.in
+
+[
+{
+  "directory": "DIR/build",
+  "command": "clang -c DIR/A.m -IDIR/modules/A -IDIR/modules/B -fmodules -fmodules-cache-path=DIR/module-cache -fimplicit-module-maps",
+  "file": "DIR/A.m"
+},
+{
+  "directory": "DIR",
+  "command": "clang -c DIR/B.m -IDIR/modules/A -IDIR/modules/B -fmodules -fmodules-cache-path=DIR/module-cache -fimplicit-module-maps",
+  "file": "DIR/B.m"
+}
+]
+
+
+//--- modules/A/module.modulemap
+
+module A {
+  umbrella header "A.h"
+}
+
+//--- modules/A/A.h
+
+typedef int A_t;
+
+//--- modules/B/module.modulemap
+
+module B {
+  umbrella header "B.h"
+}
+
+//--- modules/B/B.h
+
+#include <A.h>
+
+typedef int B_t;
+
+//--- A.m
+
+#include <B.h>
+
+A_t a = 0;
+
+//--- B.m
+
+#include <B.h>
+
+B_t b = 0;