[clangd] [Modules] Fixes to correctly handle module dependencies (#142090)

Simple module import dependencies, see
[module_dependencies.test](https://github.com/llvm/llvm-project/compare/main...fleeting-xx:llvm-project:fix_clangd_dependent_modules#diff-5510681cbe5b7ed3a72c5e683184e83fa66e911e9abb0e6670b01b87b3ca7b1a),
were not being correctly handled due to a couple of issues.

- The `MDB.getRequiredModules()` call returned a
`std::vector<std::string>` and all `StringRefs` were to entries in that
temporary value. So the `StringRef` elements in
`getAllRequiredModules()`'s return value were bound to values that went
out of scope.
- `ModulesBuilder::ModulesBuilderImpl::getOrBuildModuleFile()` was
iterating over each module dependency name, but only using the original
module name and path for various checks and module compilation.

In addition to fixing the above issues I added support for Windows paths
in modules.test and added a new unit test, module_dependencies.test,
which demonstrates the failure in the previous state and works correctly
after the fixes have been applied.

Please let me know if I've missed anything.

Co-authored-by: Dan Baker <dan@requires.coffee>

clang-tools-extra/clangd/ModulesBuilder.cpp

@@ -84,8 +84,7 @@ public:
 
   // We shouldn't adjust the compilation commands based on
   // FailedPrerequisiteModules.
-  void adjustHeaderSearchOptions(HeaderSearchOptions &Options) const override {
-  }
+  void adjustHeaderSearchOptions(HeaderSearchOptions &Options) const override {}
 
   // FailedPrerequisiteModules can never be reused.
   bool
@@ -430,21 +429,21 @@ private:
 /// Collect the directly and indirectly required module names for \param
 /// ModuleName in topological order. The \param ModuleName is guaranteed to
 /// be the last element in \param ModuleNames.
-llvm::SmallVector<StringRef> getAllRequiredModules(PathRef RequiredSource,
-                                                   CachingProjectModules &MDB,
-                                                   StringRef ModuleName) {
-  llvm::SmallVector<llvm::StringRef> ModuleNames;
+llvm::SmallVector<std::string> getAllRequiredModules(PathRef RequiredSource,
+                                                     CachingProjectModules &MDB,
+                                                     StringRef ModuleName) {
+  llvm::SmallVector<std::string> ModuleNames;
   llvm::StringSet<> ModuleNamesSet;
 
   auto VisitDeps = [&](StringRef ModuleName, auto Visitor) -> void {
     ModuleNamesSet.insert(ModuleName);
 
-    for (StringRef RequiredModuleName : MDB.getRequiredModules(
+    for (const std::string &RequiredModuleName : MDB.getRequiredModules(
              MDB.getSourceForModuleName(ModuleName, RequiredSource)))
       if (ModuleNamesSet.insert(RequiredModuleName).second)
         Visitor(RequiredModuleName, Visitor);
 
-    ModuleNames.push_back(ModuleName);
+    ModuleNames.push_back(ModuleName.str());
   };
   VisitDeps(ModuleName, VisitDeps);
 
@@ -494,13 +493,13 @@ llvm::Error ModulesBuilder::ModulesBuilderImpl::getOrBuildModuleFile(
   // Get Required modules in topological order.
   auto ReqModuleNames = getAllRequiredModules(RequiredSource, MDB, ModuleName);
   for (llvm::StringRef ReqModuleName : ReqModuleNames) {
-    if (BuiltModuleFiles.isModuleUnitBuilt(ModuleName))
+    if (BuiltModuleFiles.isModuleUnitBuilt(ReqModuleName))
       continue;
 
     if (auto Cached = Cache.getModule(ReqModuleName)) {
       if (IsModuleFileUpToDate(Cached->getModuleFilePath(), BuiltModuleFiles,
                                TFS.view(std::nullopt))) {
-        log("Reusing module {0} from {1}", ModuleName,
+        log("Reusing module {0} from {1}", ReqModuleName,
             Cached->getModuleFilePath());
         BuiltModuleFiles.addModuleFile(std::move(Cached));
         continue;
@@ -508,14 +507,16 @@ llvm::Error ModulesBuilder::ModulesBuilderImpl::getOrBuildModuleFile(
       Cache.remove(ReqModuleName);
     }
 
+    std::string ReqFileName =
+        MDB.getSourceForModuleName(ReqModuleName, RequiredSource);
     llvm::Expected<ModuleFile> MF = buildModuleFile(
-        ModuleName, ModuleUnitFileName, getCDB(), TFS, BuiltModuleFiles);
+        ReqModuleName, ReqFileName, getCDB(), TFS, BuiltModuleFiles);
     if (llvm::Error Err = MF.takeError())
       return Err;
 
-    log("Built module {0} to {1}", ModuleName, MF->getModuleFilePath());
+    log("Built module {0} to {1}", ReqModuleName, MF->getModuleFilePath());
     auto BuiltModuleFile = std::make_shared<const ModuleFile>(std::move(*MF));
-    Cache.add(ModuleName, BuiltModuleFile);
+    Cache.add(ReqModuleName, BuiltModuleFile);
     BuiltModuleFiles.addModuleFile(std::move(BuiltModuleFile));
   }
 

clang-tools-extra/clangd/test/module_dependencies.test

@@ -0,0 +1,92 @@
+# A smoke test to check that a simple dependency chain for modules can work.
+#
+# RUN: rm -fr %t
+# RUN: mkdir -p %t
+# RUN: split-file %s %t
+#
+# RUN: sed -e "s|DIR|%/t|g" %t/compile_commands.json.tmpl > %t/compile_commands.json.tmp
+# RUN: sed -e "s|CLANG_CC|%clang|g" %t/compile_commands.json.tmp > %t/compile_commands.json
+# RUN: sed -e "s|DIR|%/t|g" %t/definition.jsonrpc.tmpl > %t/definition.jsonrpc.tmp
+#
+# On Windows, we need the URI in didOpen to look like "uri":"file:///C:/..."
+# (with the extra slash in the front), so we add it here.
+# RUN: sed -E -e 's|"file://([A-Z]):/|"file:///\1:/|g' %/t/definition.jsonrpc.tmp > %/t/definition.jsonrpc
+#
+# RUN: clangd -experimental-modules-support -lit-test < %t/definition.jsonrpc \
+# RUN:      | FileCheck -strict-whitespace %t/definition.jsonrpc
+
+#--- A-frag.cppm
+export module A:frag;
+export void printA() {}
+
+#--- A.cppm
+export module A;
+export import :frag;
+
+#--- Use.cpp
+import A;
+void foo() {
+    print
+}
+
+#--- compile_commands.json.tmpl
+[
+    {
+      "directory": "DIR",
+      "command": "CLANG_CC -fprebuilt-module-path=DIR -std=c++20 -o DIR/main.cpp.o -c DIR/Use.cpp",
+      "file": "DIR/Use.cpp"
+    },
+    {
+      "directory": "DIR",
+      "command": "CLANG_CC -std=c++20 DIR/A.cppm --precompile -o DIR/A.pcm",
+      "file": "DIR/A.cppm"
+    },
+    {
+      "directory": "DIR",
+      "command": "CLANG_CC -std=c++20 DIR/A-frag.cppm --precompile -o DIR/A-frag.pcm",
+      "file": "DIR/A-frag.cppm"
+    }
+]
+
+#--- definition.jsonrpc.tmpl
+{
+  "jsonrpc": "2.0",
+  "id": 0,
+  "method": "initialize",
+  "params": {
+    "processId": 123,
+    "rootPath": "clangd",
+    "capabilities": {
+      "textDocument": {
+        "completion": {
+          "completionItem": {
+            "snippetSupport": true
+          }
+        }
+      }
+    },
+    "trace": "off"
+  }
+}
+---
+{
+  "jsonrpc": "2.0",
+  "method": "textDocument/didOpen",
+  "params": {
+    "textDocument": {
+      "uri": "file://DIR/Use.cpp",
+      "languageId": "cpp",
+      "version": 1,
+      "text": "import A;\nvoid foo() {\n    print\n}\n"
+    }
+  }
+}
+
+# CHECK: "message"{{.*}}printA{{.*}}(fix available)
+
+---
+{"jsonrpc":"2.0","id":1,"method":"textDocument/completion","params":{"textDocument":{"uri":"file://DIR/Use.cpp"},"context":{"triggerKind":1},"position":{"line":2,"character":6}}}
+---
+{"jsonrpc":"2.0","id":2,"method":"shutdown"}
+---
+{"jsonrpc":"2.0","method":"exit"}

clang-tools-extra/clangd/test/modules.test

@@ -1,16 +1,16 @@
 # A smoke test to check the modules can work basically.
 #
-# Windows have different escaping modes.
-# FIXME: We should add one for windows.
-# UNSUPPORTED: system-windows
-#
 # RUN: rm -fr %t
 # RUN: mkdir -p %t
 # RUN: split-file %s %t
 #
 # RUN: sed -e "s|DIR|%/t|g" %t/compile_commands.json.tmpl > %t/compile_commands.json.tmp
 # RUN: sed -e "s|CLANG_CC|%clang|g" %t/compile_commands.json.tmp > %t/compile_commands.json
-# RUN: sed -e "s|DIR|%/t|g" %t/definition.jsonrpc.tmpl > %t/definition.jsonrpc
+# RUN: sed -e "s|DIR|%/t|g" %t/definition.jsonrpc.tmpl > %t/definition.jsonrpc.tmp
+#
+# On Windows, we need the URI in didOpen to look like "uri":"file:///C:/..."
+# (with the extra slash in the front), so we add it here.
+# RUN: sed -E -e 's|"file://([A-Z]):/|"file:///\1:/|g' %/t/definition.jsonrpc.tmp > %/t/definition.jsonrpc
 #
 # RUN: clangd -experimental-modules-support -lit-test < %t/definition.jsonrpc \
 # RUN:      | FileCheck -strict-whitespace %t/definition.jsonrpc