[clang-tools-extra] [clangd] [Modules] Fix to correctly handle module dependencies (PR #142828)

[via cfe-commits]

https://github.com/fleeting-xx created 
https://github.com/llvm/llvm-project/pull/142828

This is a re-application of llvm/llvm-project#142090 without the unit test 
changes. A subsequent PR will follow that adds a unit test for module 
dependencies.

### Changes
- Fix dangling string references in the return value of getAllRequiredModules()
- Change a couple of calls in getOrBuildModuleFile() to use the loop variable 
instead of the ModuleName parameter.

@ChuanqiXu9 for review

>From 63c7b6ea7927750c0559098ac9d74f34d03b4863 Mon Sep 17 00:00:00 2001
From: fleeting-xx <bake...@gmail.com>
Date: Wed, 4 Jun 2025 12:57:48 -0500
Subject: [PATCH] [clangd] [Modules] Fix to correctly handle module
 dependencies

- Fix dangling string references in the return value of
  getAllRequiredModules()
- Change a couple of calls in getOrBuildModuleFile() to use the loop
  variable instead of the ModuleName parameter.
---
 clang-tools-extra/clangd/ModulesBuilder.cpp | 22 +++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/clang-tools-extra/clangd/ModulesBuilder.cpp 
b/clang-tools-extra/clangd/ModulesBuilder.cpp
index bf77f43bd28bb..d88aa01aad05d 100644
--- a/clang-tools-extra/clangd/ModulesBuilder.cpp
+++ b/clang-tools-extra/clangd/ModulesBuilder.cpp
@@ -430,10 +430,10 @@ class CachingProjectModules : public ProjectModules {
 /// 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 {
@@ -444,7 +444,7 @@ llvm::SmallVector<StringRef> getAllRequiredModules(PathRef 
RequiredSource,
       if (ModuleNamesSet.insert(RequiredModuleName).second)
         Visitor(RequiredModuleName, Visitor);
 
-    ModuleNames.push_back(ModuleName);
+    ModuleNames.push_back(ModuleName.str());
   };
   VisitDeps(ModuleName, VisitDeps);
 
@@ -494,13 +494,13 @@ 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 +508,16 @@ 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));
   }
 

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