[ImportResolution] Deduplicate top-level clang modules from import list

Importing clang submodules results in an implicit import of the
top-level module as well. This can result in the same TLM being imported
many different times, if multiple submodules are imported from the same
module. This deduplicates these imports.

Other imports are not expected to be duplicated, so care is taken to
only deduplicate clang TLM imports.

Author: hnrklssn

lib/Sema/ImportResolution.cpp

@@ -163,6 +163,11 @@ class ImportResolver final : public DeclVisitor<ImportResolver> {
   /// The list of fully bound imports.
   SmallVector<AttributedImport<ImportedModule>, 16> boundImports;
 
+  /// Set of imported top-level clang modules. We normally don't expect
+  /// duplicated imports, but importing multiple submodules of the same clang
+  /// TLM would cause the same TLM to be imported once per submodule.
+  SmallPtrSet<const ModuleDecl*, 16> seenClangTLMs;
+
   /// All imported modules which should be considered when cross-importing.
   /// This is basically the transitive import graph, but with only top-level
   /// modules and without reexports from Objective-C modules.
@@ -388,14 +393,16 @@ void ImportResolver::bindImport(UnboundImport &&I) {
 
   I.validateOptions(topLevelModule, SF);
 
-  if (topLevelModule && topLevelModule != M) {
-    // If we have distinct submodule and top-level module, add both.
-    addImport(I, M);
-    addImport(I, topLevelModule.get());
-  }
-  else {
-    // Add only the import itself.
+  if (!M->isNonSwiftModule() || topLevelModule != M ||
+      seenClangTLMs.insert(M).second) {
     addImport(I, M);
+    if (topLevelModule && topLevelModule != M &&
+        seenClangTLMs.insert(topLevelModule.get()).second) {
+      // If we have distinct submodule and top-level module, add both.
+      // Importing the submodule ensures that it gets loaded, but the decls
+      // are imported to the TLM, so import that for visibility.
+      addImport(I, topLevelModule.get());
+    }
   }
 
   crossImport(M, I);

test/Interop/C/swiftify-import/clang-includes-indirect-explicit-modules.swift

@@ -156,9 +156,7 @@ d1_t b2d(void * _Nonnull __sized_by(size), int size);
 // DUMP-NEXT:   D1
 // DUMP-NEXT:   A1
 // DUMP-NEXT:   C1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B2
 // DUMP-CXX-NEXT:   CxxShim
 // DUMP-CXX-NEXT:   Cxx
@@ -174,9 +172,7 @@ d1_t b2d(void * _Nonnull __sized_by(size), int size);
 // DUMP-NEXT:   D1
 // DUMP-NEXT:   A1
 // DUMP-NEXT:   C1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B2
 // DUMP-CXX-NEXT:   CxxShim
 // DUMP-CXX-NEXT:   Cxx
@@ -192,9 +188,7 @@ d1_t b2d(void * _Nonnull __sized_by(size), int size);
 // DUMP-NEXT:   D1
 // DUMP-NEXT:   A1
 // DUMP-NEXT:   C1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B2
 // DUMP-CXX-NEXT:   CxxShim
 // DUMP-CXX-NEXT:   Cxx

test/Interop/C/swiftify-import/clang-includes-redundant-imports.swift

@@ -38,17 +38,12 @@ import A2.B2.C2
 // DUMP-NEXT:   SwiftOnoneSupport
 // DUMP-NEXT:   A1
 // DUMP-NEXT:   B1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   C1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   D1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   E1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B2
 // DUMP-NEXT:   A2
 // DUMP-NEXT:   C2
-// DUMP-NEXT:   A2
 
 public func callUnsafe(_ p: UnsafeMutableRawPointer) {
   let _ = a1(p, 13)
@@ -301,10 +296,7 @@ c2_t b2_2(void * _Nonnull __sized_by(size), int size);
 // DUMP-NEXT:   D1
 // DUMP-NEXT:   A1
 // DUMP-NEXT:   C1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B1
-// DUMP-NEXT:   A1
-// DUMP-NEXT:   A1
 // DUMP-CXX-NEXT:   CxxShim
 // DUMP-CXX-NEXT:   Cxx
 // DUMP-NEXT:   _StringProcessing
@@ -320,10 +312,7 @@ c2_t b2_2(void * _Nonnull __sized_by(size), int size);
 // DUMP-NEXT:   D1
 // DUMP-NEXT:   A1
 // DUMP-NEXT:   C1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B1
-// DUMP-NEXT:   A1
-// DUMP-NEXT:   A1
 // DUMP-CXX-NEXT:   CxxShim
 // DUMP-CXX-NEXT:   Cxx
 // DUMP-NEXT:   _StringProcessing
@@ -352,10 +341,7 @@ e2_t c2(void * _Nonnull __sized_by(size), int size);
 // DUMP-NEXT:   D1
 // DUMP-NEXT:   A1
 // DUMP-NEXT:   C1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B1
-// DUMP-NEXT:   A1
-// DUMP-NEXT:   A1
 // DUMP-CXX-NEXT:   CxxShim
 // DUMP-CXX-NEXT:   Cxx
 // DUMP-NEXT:   _StringProcessing
@@ -380,10 +366,7 @@ e2_t d2(void * _Nonnull __sized_by(size), int size);
 // DUMP-NEXT:   D1
 // DUMP-NEXT:   A1
 // DUMP-NEXT:   C1
-// DUMP-NEXT:   A1
 // DUMP-NEXT:   B1
-// DUMP-NEXT:   A1
-// DUMP-NEXT:   A1
 // DUMP-CXX-NEXT:   CxxShim
 // DUMP-CXX-NEXT:   Cxx
 // DUMP-NEXT:   _StringProcessing