Sema: fix getPublicModuleName to look only at loaded modules

When onlyIfImported is true, we should return the public module name
only when the public facing module is already imported. Replace the
call to getModuleByIdentifier with getLoadedModule to prevent trigering
loading that module.

Also fix the test where the CHECK lined ended up matching itself from
the diagnostics output.

Author: xymus

lib/AST/Module.cpp

@@ -1923,15 +1923,11 @@ ImportedModule::removeDuplicates(SmallVectorImpl<ImportedModule> &imports) {
 }
 
 Identifier ModuleDecl::getPublicModuleName(bool onlyIfImported) const {
-  if (!PublicModuleName.empty()) {
-    if (!onlyIfImported)
-      return PublicModuleName;
+  if (!PublicModuleName.empty() &&
+      (!onlyIfImported ||
+       getASTContext().getLoadedModule(PublicModuleName)))
+    return PublicModuleName;
 
-    bool publicModuleIsImported =
-      getASTContext().getModuleByIdentifier(PublicModuleName);
-    if (publicModuleIsImported)
-      return PublicModuleName;
-  }
   return getName();
 }
 

test/Sema/public-module-name.swift

@@ -47,6 +47,7 @@
 // RUN:   -verify
 // RUN: not %target-swift-frontend -typecheck %t/ClientMiddle.swift -o %t -I %t \
 // RUN:   -enable-library-evolution -swift-version 6 \
+// RUN:   -diagnostic-style llvm \
 // RUN:   2>&1 | %FileCheck %t/ClientMiddle.swift
 
 /// Test more diagnostics referencing modules.
@@ -69,6 +70,7 @@
 // RUN:   -verify
 // RUN: not %target-swift-frontend -typecheck %t/ClientMiddle.swift -o %t -I %t \
 // RUN:   -enable-library-evolution -swift-version 6 \
+// RUN:   -diagnostic-style llvm \
 // RUN:   2>&1 | %FileCheck %t/ClientMiddle.swift
 
 // RUN: %target-swift-frontend -typecheck %t/ClientAccessLevelOnImports.swift -o %t -I %t \