Revert "Revert the error check for link decls in submodules as that is a feature as indicated by the test case clang/test/Modules/autolink.m"

This reverts commit 3286622.

Author: qiongsiwu

clang/include/clang/Basic/DiagnosticLexKinds.td

@@ -911,6 +911,8 @@ def err_mmap_expected_feature : Error<"expected a feature name">;
 def err_mmap_expected_attribute : Error<"expected an attribute name">;
 def err_mmap_link_redecalration : Error<"redeclaration of link library '%0'">;
 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

@@ -853,6 +853,12 @@ std::optional<LinkDecl> ModuleMapFileParser::parseLinkDecl(
 
   // Make sure we eat all the tokens when we report the errors so parsing
   // can continue.
+  if (!TopLevel) {
+    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) {

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

@@ -8,7 +8,7 @@ module A {
 
   module B {
     header "B.h"
-    link "libraryA"
+    link "libraryB"
   }
 
   link "libraryA"
@@ -41,9 +41,7 @@ module C {
 // RUN: not clang-scan-deps -compilation-database %t/cdb.json -format \
 // RUN:   experimental-full 2>&1 | FileCheck %s
 
-// Note that the link declaration in submodule B does not conflict with the
-// first link declaration in module A, since we only check link declaration
-// duplications within the current module.
-// CHECK:      module.modulemap:10:3: error: redeclaration of link library 'libraryA'
+// CHECK:      module.modulemap:6:5: error: link decl is not allowed in submodules
+// CHECK-NEXT: module.modulemap:10:3: error: redeclaration of link library 'libraryA'
 // CHECK-NEXT: module.modulemap:9:3: note: previously declared here
-// CHECK-NOT:  module.modulemap:15:3: error: redeclaration of link library 'libraryA'
+// CHECK-NOT: module.modulemap:15:3: error: redeclaration of link library 'libraryA'