[clang][Modules] Reporting Errors for Duplicating Link Declarations in modulemaps

[qiongsiwu]

This PR teaches the modulemap parsing logic to report warnings that default to errors if the parsing logic sees duplicating link declarations in the same module. Specifically, duplicating link declarations means multiple link declarations with the same string-literal in the same module. No errors are reported if a same link declaration exist in a submodule and its enclosing module.

The warning can be disabled with -Wno-module-link-redeclaration.

rdar://155880064

[qiongsiwu]

A different approach we can take is to deduplicate link libraries per module silently, and avoid adding any error checks. I think that is probably fine since there are no correctness issues. But I think it is also beneficial to report to the user that their modulemap contains duplicating link declarations. @Bigcheese @jansvoboda11 what do you think?

[jansvoboda11]

I think a hard error is a bit too much initially, maybe let's introduce a warning first and then tighten the screws later?

[qiongsiwu]

I think a hard error is a bit too much initially, maybe let's introduce a warning first and then tighten the screws later?

Thanks for the comment! While I agree that having a hard error initially may be harsh, I think we should go with an error for two reasons:

1. I am not seeing duplicates in SDKs.
2. Having an error will prevent duplicates getting accidentally added to the SDKs.

I'd like to keep this an error if there are no objections.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Qiongsi Wu (qiongsiwu)

Changes

This PR teaches the modulemap parsing logic to report errors if the parsing logic sees duplicating link declarations in the same module. Specifically, duplicating link declarations means multiple link declarations with the same string-literal in the same module. No errors are reported if a same link declaration exist in a submodule and its enclosing module.

rdar://155880064

---

Full diff: https://github.com/llvm/llvm-project/pull/148959.diff

3 Files Affected:

• (modified) clang/include/clang/Basic/DiagnosticLexKinds.td (+4)
• (modified) clang/lib/Lex/ModuleMapFile.cpp (+30-4)
• (added) clang/test/ClangScanDeps/link-libraries-diag-dup.c (+57)

diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
index 723f5d48b4f5f..b4dcb35454585 100644
--- a/clang/include/clang/Basic/DiagnosticLexKinds.td
+++ b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -909,6 +909,10 @@ 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 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<
diff --git a/clang/lib/Lex/ModuleMapFile.cpp b/clang/lib/Lex/ModuleMapFile.cpp
index 183e919d14c22..08bba8c16e2d6 100644
--- a/clang/lib/Lex/ModuleMapFile.cpp
+++ b/clang/lib/Lex/ModuleMapFile.cpp
@@ -118,7 +118,8 @@ struct ModuleMapFileParser {
   std::optional<ExcludeDecl> parseExcludeDecl(clang::SourceLocation LeadingLoc);
   std::optional<UmbrellaDirDecl>
   parseUmbrellaDirDecl(SourceLocation UmbrellaLoc);
-  std::optional<LinkDecl> parseLinkDecl();
+  std::optional<LinkDecl>
+  parseLinkDecl(llvm::StringMap<SourceLocation> &SeenLinkDecl, bool Allowed);
 
   SourceLocation consumeToken();
   void skipUntil(MMToken::TokenKind K);
@@ -325,6 +326,7 @@ 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) {
@@ -405,7 +407,9 @@ std::optional<ModuleDecl> ModuleMapFileParser::parseModuleDecl(bool TopLevel) {
       break;
 
     case MMToken::LinkKeyword:
-      SubDecl = parseLinkDecl();
+      // Link decls are only allowed in top level modules or explicit
+      // submodules.
+      SubDecl = parseLinkDecl(SeenLinkDecl, TopLevel || MDecl.Explicit);
       break;
 
     default:
@@ -822,7 +826,8 @@ ModuleMapFileParser::parseUmbrellaDirDecl(clang::SourceLocation UmbrellaLoc) {
 ///
 ///   module-declaration:
 ///     'link' 'framework'[opt] string-literal
-std::optional<LinkDecl> ModuleMapFileParser::parseLinkDecl() {
+std::optional<LinkDecl> ModuleMapFileParser::parseLinkDecl(
+    llvm::StringMap<SourceLocation> &SeenLinkDecl, bool Allowed) {
   assert(Tok.is(MMToken::LinkKeyword));
   LinkDecl LD;
   LD.Location = consumeToken();
@@ -838,12 +843,33 @@ 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;
   }
 
-  LD.Library = Tok.getString();
+  StringRef Library = Tok.getString();
+
+  LD.Library = Library;
   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::err_mmap_link_redecalration) << Library;
+    Diags.Report(It->second, diag::note_mmap_prev_link_declaration);
+    HadError = true;
+    return std::nullopt;
+  }
+
   return std::move(LD);
 }
 
diff --git a/clang/test/ClangScanDeps/link-libraries-diag-dup.c b/clang/test/ClangScanDeps/link-libraries-diag-dup.c
new file mode 100644
index 0000000000000..6f9d4be4447a6
--- /dev/null
+++ b/clang/test/ClangScanDeps/link-libraries-diag-dup.c
@@ -0,0 +1,57 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+
+//--- module.modulemap
+module A {
+  umbrella header "A.h"
+
+  module B {
+    header "B.h"
+    link "libraryB"
+  }
+
+  explicit module D {
+    header "D.h"
+    link "libraryD"
+  }
+
+  link "libraryA"
+  link "libraryA"
+}
+
+module C {
+  header "C.h"
+  link "libraryA"
+}
+
+//--- A.h
+#include "B.h"
+//--- B.h
+// empty
+//--- C.h
+// empty
+//--- D.h
+// empty
+//--- TU.c
+#include "A.h"
+#include "C.h"
+#include "D.h"
+
+//--- cdb.json.template
+[{
+  "file": "DIR/TU.c",
+  "directory": "DIR",
+  "command": "clang -fmodules -fmodules-cache-path=DIR/cache -I DIR -c DIR/TU.c"
+}]
+
+// RUN: sed "s|DIR|%/t|g" %t/cdb.json.template > %t/cdb.json
+// 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
+// CHECK-NEXT: module.modulemap:15:3: error: redeclaration of link library 'libraryA'
+// CHECK-NEXT: module.modulemap:14:3: note: previously declared here
+// CHECK-NOT:  module.modulemap:20:3: error: redeclaration of link library 'libraryA'

[qiongsiwu]

Gentle ping for review. Thanks!

[qiongsiwu]

Ping for review. Thank you!

[Bigcheese]

I think it would be good to make this a warning that defaults to error to start with. That provides an easy way to disable it if anyone does hit it, but it still errors by default.

Otherwise the change looks good.

[llvm-ci]

LLVM Buildbot has detected a new failure on builder clang-aarch64-quick running on linaro-clang-aarch64-quick while building clang at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/21626

Here is the relevant piece of the build log for the reference

Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'LLVM-Unit :: Support/./SupportTests/188/385' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/unittests/Support/./SupportTests-LLVM-Unit-3861641-188-385.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=385 GTEST_SHARD_INDEX=188 /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/unittests/Support/./SupportTests
--

Script:
--
/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/unittests/Support/./SupportTests --gtest_filter=ProgramEnvTest.TestLockFileExclusive
--
../llvm/llvm/unittests/Support/ProgramTest.cpp:648: Failure
Value of: Finished
  Actual: false
Expected: true


../llvm/llvm/unittests/Support/ProgramTest.cpp:648
Value of: Finished
  Actual: false
Expected: true



********************

[qiongsiwu]

LLVM Buildbot has detected a new failure on builder clang-aarch64-quick running on linaro-clang-aarch64-quick while building clang at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/21626

Here is the relevant piece of the build log for the reference

This seems to be an intermittent failure. The following build https://lab.llvm.org/buildbot/#/builders/65/builds/21627 succeeded.