[clang][scan] Report module dependencies in topological order

clang/include/clang-c/Dependencies.h

@@ -478,6 +478,16 @@ CINDEX_LINKAGE size_t clang_experimental_DepGraph_getNumModules(CXDepGraph);
 CINDEX_LINKAGE CXDepGraphModule
 clang_experimental_DepGraph_getModule(CXDepGraph, size_t Index);
 
+/**
+ * \returns the \c CXDepGraphModule object at the given \p Index in
+ * a topologically sorted list.
+ *
+ * The \c CXDepGraphModule object is only valid to use while \c CXDepGraph is
+ * valid. Must be disposed with \c clang_experimental_DepGraphModule_dispose.
+ */
+CINDEX_LINKAGE CXDepGraphModule
+clang_experimental_DepGraph_getModuleTopological(CXDepGraph, size_t Index);
+
 CINDEX_LINKAGE void clang_experimental_DepGraphModule_dispose(CXDepGraphModule);
 
 /**

clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp

@@ -640,12 +640,11 @@ 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;
@@ -756,6 +755,8 @@ ModuleDepCollectorPP::handleTopLevelModule(const Module *M) {
 
   MD.BuildInfo = std::move(CI);
 
+  MDC.ModularDeps.insert({M, std::move(OwnedMD)});
+
   return MD.ID;
 }
 

clang/test/ClangScanDeps/modules-order-c-api.c

@@ -10,6 +10,13 @@
 // RUN: diff %t/output1 %t/output2
 // RUN: diff %t/output1 %t/output3
 
+// And that module dependencies are in topological order.
+// RUN: FileCheck --input-file %t/output1 %s
+// CHECK:     modules
+// CHECK-DAG:     name: FromMod1
+// CHECK-DAG:     name: FromMod2
+// CHECK:         name: FromMain1
+
 //--- module.modulemap
 module FromMain1 { header "FromMain1.h" }
 module FromMain2 { header "FromMain2.h" }

clang/tools/c-index-test/core_main.cpp

@@ -801,7 +801,8 @@ static int scanDeps(ArrayRef<const char *> Args, std::string WorkingDirectory,
     llvm::outs() << "modules:\n";
     for (size_t I = 0, E = clang_experimental_DepGraph_getNumModules(Graph);
          I < E; ++I) {
-      CXDepGraphModule Mod = clang_experimental_DepGraph_getModule(Graph, I);
+      CXDepGraphModule Mod =
+          clang_experimental_DepGraph_getModuleTopological(Graph, I);
       const char *Name = clang_experimental_DepGraphModule_getName(Mod);
       const char *ContextHash =
           clang_experimental_DepGraphModule_getContextHash(Mod);

clang/tools/libclang/CDependencies.cpp

@@ -545,6 +545,12 @@ size_t clang_experimental_DepGraph_getNumModules(CXDepGraph Graph) {
 
 CXDepGraphModule clang_experimental_DepGraph_getModule(CXDepGraph Graph,
                                                        size_t Index) {
+  return clang_experimental_DepGraph_getModuleTopological(Graph, Index);
+}
+
+CXDepGraphModule
+clang_experimental_DepGraph_getModuleTopological(CXDepGraph Graph,
+                                                 size_t Index) {
   TranslationUnitDeps &TUDeps = unwrap(Graph)->TUDeps;
   return wrap(new DependencyGraphModule{&TUDeps.ModuleGraph[Index]});
 }

clang/tools/libclang/libclang.map

@@ -519,6 +519,7 @@ LLVM_16 {
     clang_experimental_DepGraph_dispose;
     clang_experimental_DepGraph_getDiagnostics;
     clang_experimental_DepGraph_getModule;
+    clang_experimental_DepGraph_getModuleTopological;
     clang_experimental_DepGraph_getNumModules;
     clang_experimental_DepGraph_getNumTUCommands;
     clang_experimental_DepGraph_getTUCommand;