Respect the module ABI name when mangling for the debugger

The mangled name produced for the debugger should match the one emitted
in reflection metadata, otherwise LLDB will not be able to lookup types
when the module is compiled with the -module-abi-name flag.

rdar://125848324

Author: augusto2112

include/swift/Strings.h

@@ -26,6 +26,9 @@ constexpr static const StringLiteral SWIFT_ONONE_SUPPORT = "SwiftOnoneSupport";
 constexpr static const StringLiteral SWIFT_CONCURRENCY_NAME = "_Concurrency";
 /// The name of the Concurrency Shims Clang module
 constexpr static const StringLiteral SWIFT_CONCURRENCY_SHIMS_NAME = "_SwiftConcurrencyShims";
+/// The unique ABI prefix that swift-syntax uses when it's built as part of the
+/// compiler.
+constexpr static const StringLiteral SWIFT_MODULE_ABI_NAME_PREFIX = "Compiler";
 /// The name of the Distributed module, which supports that extension.
 constexpr static const StringLiteral SWIFT_DISTRIBUTED_NAME = "Distributed";
 /// The name of the StringProcessing module, which supports that extension.

lib/AST/ASTMangler.cpp

@@ -2514,10 +2514,19 @@ void ASTMangler::appendModule(const ModuleDecl *module,
   // For example, if a module Foo has 'import Bar', and '-module-alias Bar=Baz'
   // was passed, the name 'Baz' will be used for mangling besides loading.
   StringRef ModName = module->getRealName().str();
-  if (RespectOriginallyDefinedIn &&
-      module->getABIName() != module->getName()) { // check if the ABI name is set
+
+  // If RespectOriginallyDefinedIn is not set, ignore the ABI name only for
+  // _Concurrency and swift-syntax (which adds "Compiler" as a prefix when
+  // building swift-syntax as part of the compiler).
+  // TODO: Mangling for the debugger should respect originally defined in, but
+  // as of right now there is not enough information in the mangled name to
+  // reconstruct AST types from mangled names when using that attribute.
+  if ((RespectOriginallyDefinedIn ||
+       (module->getName().str() != SWIFT_CONCURRENCY_NAME &&
+        !module->getABIName().str().starts_with(
+            SWIFT_MODULE_ABI_NAME_PREFIX))) &&
+      module->getABIName() != module->getName())
     ModName = module->getABIName().str();
-  }
 
   // Try the special 'swift' substitution.
   if (ModName == STDLIB_NAME) {

test/DebugInfo/module_abi_name.swift

@@ -0,0 +1,13 @@
+// RUN: %target-swift-frontend -primary-file %s -emit-ir -g -module-name=Hello -module-abi-name Goodbye -emit-ir -o - | %FileCheck %s
+
+class SomeClass {}
+// CHECK: DICompositeType(tag: DW_TAG_structure_type, name: "SomeClass",{{.*}}runtimeLang: DW_LANG_Swift, identifier: "$s7Goodbye9SomeClassCD"
+
+@available(macOS 10.13, *)
+@_originallyDefinedIn(module: "ThirdModule", OSX 10.12)
+class DefinedElsewhere {}
+// CHECK: DICompositeType(tag: DW_TAG_structure_type, name: "DefinedElsewhere",{{.*}}runtimeLang: DW_LANG_Swift, identifier: "$s7Goodbye16DefinedElsewhereCD")
+
+let v1 = SomeClass()
+let v2 = DefinedElsewhere()
+