[ModuleInterface] Always use the real name for modules not imported directly

In AliasModuleNames, avoid wrongfully printing aliased names for modules
that were not aliased. This can happen in the case of modules indirectly
imported via a reexport.

rdar://102262019

Author: xymus

include/swift/AST/PrintOptions.h

@@ -19,6 +19,7 @@
 #include "swift/AST/TypeOrExtensionDecl.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/SmallSet.h"
 #include <limits.h>
 #include <vector>
 
@@ -470,6 +471,14 @@ struct PrintOptions {
   /// with types sharing a name with a module.
   bool AliasModuleNames = false;
 
+  /// Name of the modules that have been aliased in AliasModuleNames mode.
+  /// Ideally we would use something other than a string to identify a module,
+  /// but since one alias can apply to more than one module, strings happen
+  /// to be pretty reliable. That is, unless there's an unexpected name
+  /// collision between two modules, which isn't supported by this workaround
+  /// yet.
+  llvm::SmallSet<StringRef, 4> *AliasModuleNamesTargets = nullptr;
+
   /// When printing an Optional<T>, rather than printing 'T?', print
   /// 'T!'. Used as a modifier only when we know we're printing
   /// something that was declared as an implicitly unwrapped optional
@@ -641,7 +650,10 @@ struct PrintOptions {
                                               bool preferTypeRepr,
                                               bool printFullConvention,
                                               bool printSPIs,
-                                              bool aliasModuleNames);
+                                              bool aliasModuleNames,
+                                              llvm::SmallSet<StringRef, 4>
+                                                *aliasModuleNamesTargets
+                                              );
 
   /// Retrieve the set of options suitable for "Generated Interfaces", which
   /// are a prettified representation of the public API of a module, to be

lib/AST/ASTPrinter.cpp

@@ -132,7 +132,10 @@ PrintOptions PrintOptions::printSwiftInterfaceFile(ModuleDecl *ModuleToPrint,
                                                    bool preferTypeRepr,
                                                    bool printFullConvention,
                                                    bool printSPIs,
-                                                   bool aliasModuleNames) {
+                                                   bool aliasModuleNames,
+                                                   llvm::SmallSet<StringRef, 4>
+                                                     *aliasModuleNamesTargets
+                                                   ) {
   PrintOptions result;
   result.IsForSwiftInterface = true;
   result.PrintLongAttrsOnSeparateLines = true;
@@ -154,6 +157,7 @@ PrintOptions PrintOptions::printSwiftInterfaceFile(ModuleDecl *ModuleToPrint,
       OpaqueReturnTypePrintingMode::StableReference;
   result.PreferTypeRepr = preferTypeRepr;
   result.AliasModuleNames = aliasModuleNames;
+  result.AliasModuleNamesTargets = aliasModuleNamesTargets;
   if (printFullConvention)
     result.PrintFunctionRepresentationAttrs =
       PrintOptions::FunctionRepresentationMode::Full;
@@ -5393,7 +5397,8 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
       }
     }
 
-    if (Options.AliasModuleNames) {
+    if (Options.AliasModuleNames && Options.AliasModuleNamesTargets &&
+        Options.AliasModuleNamesTargets->contains(Name.str())) {
       auto nameTwine = MODULE_DISAMBIGUATING_PREFIX + Name.str();
       Name = Mod->getASTContext().getIdentifier(nameTwine.str());
     }

lib/Frontend/ModuleInterfaceSupport.cpp

@@ -49,7 +49,9 @@ version::Version swift::InterfaceFormatVersion({1, 0});
 /// construct \p M.
 static void printToolVersionAndFlagsComment(raw_ostream &out,
                                             ModuleInterfaceOptions const &Opts,
-                                            ModuleDecl *M) {
+                                            ModuleDecl *M,
+                                            llvm::SmallSet<StringRef, 4>
+                                              &AliasModuleNamesTargets) {
   auto &Ctx = M->getASTContext();
   auto ToolsVersion =
       getSwiftInterfaceCompilerVersionForCurrentCompiler(Ctx);
@@ -62,9 +64,8 @@ static void printToolVersionAndFlagsComment(raw_ostream &out,
 
   // Insert additional -module-alias flags
   if (Opts.AliasModuleNames) {
-    llvm::SmallSet<StringRef, 2> aliasTargets;
     StringRef moduleName = M->getNameStr();
-    aliasTargets.insert(M->getNameStr());
+    AliasModuleNamesTargets.insert(M->getNameStr());
     out << " -module-alias " << MODULE_DISAMBIGUATING_PREFIX <<
            moduleName << "=" << moduleName;
 
@@ -77,7 +78,7 @@ static void printToolVersionAndFlagsComment(raw_ostream &out,
     M->getMissingImportedModules(imports);
     for (ImportedModule import: imports) {
       StringRef importedName = import.importedModule->getNameStr();
-      if (aliasTargets.insert(importedName).second) {
+      if (AliasModuleNamesTargets.insert(importedName).second) {
         out << " -module-alias " << MODULE_DISAMBIGUATING_PREFIX <<
                importedName << "=" << importedName;
       }
@@ -782,12 +783,14 @@ bool swift::emitSwiftInterface(raw_ostream &out,
                                ModuleDecl *M) {
   assert(M);
 
-  printToolVersionAndFlagsComment(out, Opts, M);
+  llvm::SmallSet<StringRef, 4> aliasModuleNamesTargets;
+  printToolVersionAndFlagsComment(out, Opts, M, aliasModuleNamesTargets);
+
   printImports(out, Opts, M);
 
   const PrintOptions printOptions = PrintOptions::printSwiftInterfaceFile(
       M, Opts.PreserveTypesAsWritten, Opts.PrintFullConvention, Opts.PrintSPIs,
-      Opts.AliasModuleNames);
+      Opts.AliasModuleNames, &aliasModuleNamesTargets);
   InheritedProtocolCollector::PerTypeMap inheritedProtocolMap;
 
   SmallVector<Decl *, 16> topLevelDecls;

test/ModuleInterface/ambiguous-aliases-workaround.swift

@@ -3,12 +3,19 @@
 // RUN: %empty-directory(%t)
 // RUN: split-file %s %t
 
+// RUN: %target-swift-frontend -emit-module -module-name ExportedLib \
+// RUN:     -swift-version 5 -enable-library-evolution \
+// RUN:     -o %t/ExportedLib.swiftmodule \
+// RUN:     -emit-module-interface-path %t/ExportedLib.swiftinterface \
+// RUN:     %t/ExportedLib.swift
+// RUN: %target-swift-typecheck-module-from-interface(%t/ExportedLib.swiftinterface)
+
 // RUN: %target-swift-frontend -emit-module -module-name AmbiguousLib \
 // RUN:     -swift-version 5 -enable-library-evolution \
 // RUN:     -o %t/AmbiguousLib.swiftmodule \
 // RUN:     -emit-module-interface-path %t/AmbiguousLib.swiftinterface \
-// RUN:     %t/AmbiguousLib.swift
-// RUN: %target-swift-typecheck-module-from-interface(%t/AmbiguousLib.swiftinterface)
+// RUN:     %t/AmbiguousLib.swift -I%t
+// RUN: %target-swift-typecheck-module-from-interface(%t/AmbiguousLib.swiftinterface) -I%t
 
 // RUN: %target-swift-frontend -emit-module -module-name AmbiguousClientName \
 // RUN:     -swift-version 5 -enable-library-evolution \
@@ -40,10 +47,17 @@ struct UnderlyingType {};
 void underlyingFunc() {}
 
 //--- SomeClangModule.h
+
 struct CType {};
 
+//--- ExportedLib.swift
+
+public struct RexportedStruct {}
+
 //--- AmbiguousLib.swift
 
+@_exported import ExportedLib
+
 // 1. AmbiguousLib defined a type named AmbiguousLib
 public struct AmbiguousLib {
     public struct Nested {}
@@ -73,6 +87,8 @@ public func refToStdlib(_ a: Swift.Int) {}
 public func refToUnderlying(_ a: UnderlyingType) {}
 public func refToC(_ a: CType) {}
 
+public func refToReexport(_ a: RexportedStruct) {}
+
 //--- OverlayClient.swift
 
 import AmbiguousClientName