Remove the check against link decls in submodules.

Author: qiongsiwu

clang/include/clang/Basic/DiagnosticLexKinds.td

@@ -915,10 +915,6 @@ def err_mmap_expected_attribute : Error<"expected an attribute name">;
 def warn_mmap_link_redeclaration : Warning<"redeclaration of link library '%0'">,
   InGroup<DiagGroup<"module-link-redeclaration">>, DefaultError;
 def note_mmap_prev_link_declaration : Note<"previously declared here">;
-def warn_mmap_submodule_link_decl
-    : Warning<"link declaration is not allowed in submodules">,
-      InGroup<DiagGroup<"module-submodule-link-decl">>,
-      DefaultError;
 def warn_mmap_unknown_attribute : Warning<"unknown attribute '%0'">,
   InGroup<IgnoredAttributes>;
 def warn_mmap_mismatched_private_submodule : Warning<

clang/lib/Lex/ModuleMapFile.cpp

@@ -119,7 +119,7 @@ struct ModuleMapFileParser {
   std::optional<UmbrellaDirDecl>
   parseUmbrellaDirDecl(SourceLocation UmbrellaLoc);
   std::optional<LinkDecl>
-  parseLinkDecl(llvm::StringMap<SourceLocation> &SeenLinkDecl, bool Allowed);
+  parseLinkDecl(llvm::StringMap<SourceLocation> &SeenLinkDecl);
 
   SourceLocation consumeToken();
   void skipUntil(MMToken::TokenKind K);
@@ -409,7 +409,7 @@ std::optional<ModuleDecl> ModuleMapFileParser::parseModuleDecl(bool TopLevel) {
     case MMToken::LinkKeyword:
       // Link decls are only allowed in top level modules or explicit
       // submodules.
-      SubDecl = parseLinkDecl(SeenLinkDecl, TopLevel || MDecl.Explicit);
+      SubDecl = parseLinkDecl(SeenLinkDecl);
       break;
 
     default:
@@ -827,7 +827,7 @@ ModuleMapFileParser::parseUmbrellaDirDecl(clang::SourceLocation UmbrellaLoc) {
 ///   module-declaration:
 ///     'link' 'framework'[opt] string-literal
 std::optional<LinkDecl> ModuleMapFileParser::parseLinkDecl(
-    llvm::StringMap<SourceLocation> &SeenLinkDecl, bool Allowed) {
+    llvm::StringMap<SourceLocation> &SeenLinkDecl) {
   assert(Tok.is(MMToken::LinkKeyword));
   LinkDecl LD;
   LD.Location = consumeToken();
@@ -853,12 +853,8 @@ std::optional<LinkDecl> ModuleMapFileParser::parseLinkDecl(
   LD.Library = Library;
   consumeToken();
 
-  // Make sure we eat all the tokens when we report the errors so parsing
+  // Make sure we eat all the token when we report the errors so parsing
   // can continue.
-  if (!Allowed) {
-    Diags.Report(LD.Location, diag::warn_mmap_submodule_link_decl);
-  }
-
   auto [It, Inserted] =
       SeenLinkDecl.insert(std::make_pair(Library, LD.Location));
   if (!Inserted) {

clang/test/ClangScanDeps/link-libraries-diag-dup.c

@@ -14,8 +14,10 @@ module A {
   explicit module D {
     header "D.h"
     link "libraryD"
+    link "libraryD"
   }
 
+  link "libraryB"
   link "libraryA"
   link "libraryA"
 }
@@ -49,9 +51,10 @@ module C {
 // RUN: not clang-scan-deps -compilation-database %t/cdb.json -format \
 // RUN:   experimental-full 2>&1 | FileCheck %s
 
-// Note that module D does not report an error because it is explicit.
-// Therefore we can use CHECK-NEXT for the redeclaration error on line 15.
-// CHECK:      module.modulemap:6:5:  error: link declaration is not allowed in submodules [-Wmodule-submodule-link-decl]
-// CHECK-NEXT: module.modulemap:15:3: error: redeclaration of link library 'libraryA' [-Wmodule-link-redeclaration]
-// CHECK-NEXT: module.modulemap:14:3: note: previously declared here
-// CHECK-NOT:  module.modulemap:20:3: error: redeclaration of link library 'libraryA'
+// Note that the `link "libraryB"` in the top level module A does not
+// cause an issue because we only check within a module.
+// CHECK: 12:5: error: redeclaration of link library 'libraryD' [-Wmodule-link-redeclaration]
+// CHECK-NEXT: 11:5: note: previously declared here
+// CHECK-NEXT: 17:3: error: redeclaration of link library 'libraryA' [-Wmodule-link-redeclaration]
+// CHECK-NEXT: 16:3: note: previously declared here
+// CHECK-NOT: error: redeclaration of link library 'libraryB'