[clang] [clang][scan] Report module dependencies in topological order (PR #107474)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Jan Svoboda (jansvoboda11)

<details>
<summary>Changes</summary>

Clients of the dependency scanner may benefit from being able to process modular dependencies in topological order. The scanner already processes dependencies in this order, so it makes sense to make it easy for clients by providing an API with that guarantee.

This is a cherry-pick of a change reviewed downstream: https://github.com/swiftlang/llvm-project/pull/9197

---
Full diff: https://github.com/llvm/llvm-project/pull/107474.diff


1 Files Affected:

- (modified) clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp (+6-5) 


``````````diff
diff --git a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
index 370d834846859f..c775adc0ddd73c 100644
--- a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
+++ b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -569,12 +569,11 @@ ModuleDepCollectorPP::handleTopLevelModule(const Module *M) {
     return {};
 
   // If this module has been handled already, just return its ID.
-  auto ModI = MDC.ModularDeps.insert({M, nullptr});
-  if (!ModI.second)
-    return ModI.first->second->ID;
+  if (auto ModI = MDC.ModularDeps.find(M); ModI != MDC.ModularDeps.end())
+    return ModI->second->ID;
 
-  ModI.first->second = std::make_unique<ModuleDeps>();
-  ModuleDeps &MD = *ModI.first->second;
+  auto OwnedMD = std::make_unique<ModuleDeps>();
+  ModuleDeps &MD = *OwnedMD;
 
   MD.ID.ModuleName = M->getFullModuleName();
   MD.IsSystem = M->IsSystem;
@@ -650,6 +649,8 @@ ModuleDepCollectorPP::handleTopLevelModule(const Module *M) {
 
   MD.BuildInfo = std::move(CI);
 
+  MDC.ModularDeps.insert({M, std::move(OwnedMD)});
+
   return MD.ID;
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/107474