Revert "[clang][Modules] Reporting Errors for Duplicating Link Declar… (#157154)

…ations in `modulemap`s (#148959)"

This reverts commit 538e9e8 for two
reasons.

1. Link decls in submodules can make sense even if the submodule is not
explicit. We need to review the error check. This PR reverts the check
so we still allow link decls in submodules.
2. It is not a fatal error to have duplicating link decls. The linker
deduplicates them anyways.

rdar://159467837

Author: qiongsiwu

clang/include/clang/Basic/DiagnosticLexKinds.td

@@ -912,11 +912,6 @@ def err_mmap_nested_submodule_id : Error<
   "qualified module name can only be used to define modules at the top level">;
 def err_mmap_expected_feature : Error<"expected a feature name">;
 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 err_mmap_submodule_link_decl
-    : Error<"link declaration is not allowed in submodules">;
 def warn_mmap_unknown_attribute : Warning<"unknown attribute '%0'">,
   InGroup<IgnoredAttributes>;
 def warn_mmap_mismatched_private_submodule : Warning<

clang/lib/Lex/ModuleMapFile.cpp

@@ -118,8 +118,7 @@ struct ModuleMapFileParser {
   std::optional<ExcludeDecl> parseExcludeDecl(clang::SourceLocation LeadingLoc);
   std::optional<UmbrellaDirDecl>
   parseUmbrellaDirDecl(SourceLocation UmbrellaLoc);
-  std::optional<LinkDecl>
-  parseLinkDecl(llvm::StringMap<SourceLocation> &SeenLinkDecl, bool Allowed);
+  std::optional<LinkDecl> parseLinkDecl();
 
   SourceLocation consumeToken();
   void skipUntil(MMToken::TokenKind K);
@@ -326,7 +325,6 @@ std::optional<ModuleDecl> ModuleMapFileParser::parseModuleDecl(bool TopLevel) {
   SourceLocation LBraceLoc = consumeToken();
 
   bool Done = false;
-  llvm::StringMap<SourceLocation> SeenLinkDecl;
   do {
     std::optional<Decl> SubDecl;
     switch (Tok.Kind) {
@@ -407,9 +405,7 @@ std::optional<ModuleDecl> ModuleMapFileParser::parseModuleDecl(bool TopLevel) {
       break;
 
     case MMToken::LinkKeyword:
-      // Link decls are only allowed in top level modules or explicit
-      // submodules.
-      SubDecl = parseLinkDecl(SeenLinkDecl, TopLevel || MDecl.Explicit);
+      SubDecl = parseLinkDecl();
       break;
 
     default:
@@ -826,8 +822,7 @@ ModuleMapFileParser::parseUmbrellaDirDecl(clang::SourceLocation UmbrellaLoc) {
 ///
 ///   module-declaration:
 ///     'link' 'framework'[opt] string-literal
-std::optional<LinkDecl> ModuleMapFileParser::parseLinkDecl(
-    llvm::StringMap<SourceLocation> &SeenLinkDecl, bool Allowed) {
+std::optional<LinkDecl> ModuleMapFileParser::parseLinkDecl() {
   assert(Tok.is(MMToken::LinkKeyword));
   LinkDecl LD;
   LD.Location = consumeToken();
@@ -843,33 +838,12 @@ std::optional<LinkDecl> ModuleMapFileParser::parseLinkDecl(
   if (!Tok.is(MMToken::StringLiteral)) {
     Diags.Report(Tok.getLocation(), diag::err_mmap_expected_library_name)
         << LD.Framework << SourceRange(LD.Location);
-    consumeToken();
     HadError = true;
     return std::nullopt;
   }
 
-  StringRef Library = Tok.getString();
-
-  LD.Library = Library;
+  LD.Library = Tok.getString();
   consumeToken();
-
-  // Make sure we eat all the tokens when we report the errors so parsing
-  // can continue.
-  if (!Allowed) {
-    Diags.Report(LD.Location, diag::err_mmap_submodule_link_decl);
-    HadError = true;
-    return std::nullopt;
-  }
-
-  auto [It, Inserted] =
-      SeenLinkDecl.insert(std::make_pair(Library, LD.Location));
-  if (!Inserted) {
-    Diags.Report(LD.Location, diag::warn_mmap_link_redeclaration) << Library;
-    Diags.Report(It->second, diag::note_mmap_prev_link_declaration);
-    HadError = true;
-    return std::nullopt;
-  }
-
   return std::move(LD);
 }