[Dependency Scanning] Unique collected cross-import overlay files with a set

Resolves rdar://146141228

Author: artemcm

include/swift/AST/ModuleDependencies.h

@@ -966,7 +966,7 @@ class ModuleDependencyInfo {
   llvm::StringMap<llvm::SmallSetVector<Identifier, 4>>
   collectCrossImportOverlayNames(
       ASTContext &ctx, StringRef moduleName,
-      std::vector<std::pair<std::string, std::string>> &overlayFiles) const;
+      std::set<std::pair<std::string, std::string>> &overlayFiles) const;
 };
 
 using ModuleDependencyVector =

lib/AST/ModuleLoader.cpp

@@ -208,7 +208,7 @@ void ModuleLoader::findOverlayFiles(SourceLoc diagLoc, ModuleDecl *module,
 llvm::StringMap<llvm::SmallSetVector<Identifier, 4>>
 ModuleDependencyInfo::collectCrossImportOverlayNames(
     ASTContext &ctx, StringRef moduleName,
-    std::vector<std::pair<std::string, std::string>> &overlayFiles) const {
+    std::set<std::pair<std::string, std::string>> &overlayFiles) const {
   using namespace llvm::sys;
   using namespace file_types;
   std::optional<std::string> modulePath;
@@ -260,7 +260,7 @@ ModuleDependencyInfo::collectCrossImportOverlayNames(
       ModuleDecl::collectCrossImportOverlay(ctx, file, moduleName,
                                             bystandingModule);
     result[bystandingModule] = std::move(overlayNames);
-    overlayFiles.push_back({moduleName.str(), file.str()});
+    overlayFiles.insert({moduleName.str(), file.str()});
   });
   return result;
 }

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -556,7 +556,7 @@ ModuleDependencyScanner::getNamedSwiftModuleDependencyInfo(
 static void discoverCrossImportOverlayFiles(
     StringRef mainModuleName, ModuleDependenciesCache &cache,
     ASTContext &scanASTContext, llvm::SetVector<Identifier> &newOverlays,
-    std::vector<std::pair<std::string, std::string>> &overlayFiles) {
+    std::set<std::pair<std::string, std::string>> &overlayFiles) {
   auto mainModuleInfo = cache.findKnownDependency(ModuleDependencyID{
       mainModuleName.str(), ModuleDependencyKind::SwiftSource});
 
@@ -1275,7 +1275,7 @@ void ModuleDependencyScanner::resolveCrossImportOverlayDependencies(
     llvm::function_ref<void(ModuleDependencyID)> action) {
   // Modules explicitly imported. Only these can be secondary module.
   llvm::SetVector<Identifier> newOverlays;
-  std::vector<std::pair<std::string, std::string>> overlayFiles;
+  std::set<std::pair<std::string, std::string>> overlayFiles;
   discoverCrossImportOverlayFiles(mainModuleName, cache, ScanASTContext,
                                   newOverlays, overlayFiles);
 

test/ScanDependencies/unique_fine_grained_cross_import_overlays.swift

@@ -0,0 +1,20 @@
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/module-cache)
+// RUN: split-file %s %t
+
+// Run a dependency scan on a source file that imports both constituents of a cross-import overlay to ensure the cross-import overlay dependency is registered
+// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/module-cache %t/A.swift %t/B.swift -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -I %S/Inputs/CHeaders/ExtraCModules -module-name FineGrainedCrossImportTestModule -enable-cross-import-overlays
+
+// Check the contents of the JSON output
+// RUN: %validate-json %t/deps.json | %FileCheck %s
+
+//--- A.swift
+import E
+import SubE
+
+//--- B.swift
+import E
+import SubE
+
+// CHECK: "swift": "_cross_import_E"
+// CHECK-COUNT-1: -swift-module-cross-import