[clang][DependencyScanner] Include the working directory in the context hash (llvm#73719)

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causing a "module file out of date" error when loading the PCM due to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;