[PATCH] D110392: [clang-format] Left/Right alignment fixer can cause false positive replacements when they don't actually change anything

[MyDeveloperDay via Phabricator via cfe-commits]

MyDeveloperDay created this revision.
MyDeveloperDay added reviewers: curdeius, HazardyKnusperkeks.
MyDeveloperDay added projects: clang, clang-format.
MyDeveloperDay requested review of this revision.

Earlier during the development of D69764: [clang-format] Add Left/Right Const fixer capability <https://reviews.llvm.org/D69764> I felt it was no longer necessary to ensure we were not trying to change code which didn't need to change and we felt this could be removed, however I'd like to bring this back for now as I am seeing some false positives in terms of the "replacements"

What I see is the generation of a replacement which is a "No Op" on the original code, I think this comes about because of the merging of replacements:

  static const a;
  ->
  const static a;
  ->
  static const a;

The replacements don't really merge, in such a way as to identify when we have gone back to the original

Also remove the Penalty as I'm not using it (and it became marked as set and no used, I'd rather get rid of it if it means nothing)

I think we need to do this step for now, as many people use the --output-replacements-xml to identify that the file "needs a clang-format"

The same can be seen with the -n or --dry-run option as this uses the replacements to drive the error/warning output.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D110392

Files:
  clang/lib/Format/QualifierAlignmentFixer.cpp
  clang/unittests/Format/QualifierFixerTest.cpp


Index: clang/unittests/Format/QualifierFixerTest.cpp
===================================================================
--- clang/unittests/Format/QualifierFixerTest.cpp
+++ clang/unittests/Format/QualifierFixerTest.cpp
@@ -806,5 +806,18 @@
                "Foo(unsigned const char *bytes)", Style);
 }
 
+TEST_F(QualifierFixerTest, NoOpQualifierReplacements) {
+
+  FormatStyle Style = getLLVMStyle();
+  Style.QualifierAlignment = FormatStyle::QAS_Custom;
+  Style.QualifierOrder = {"static", "const", "type"};
+
+  ReplacementCount = 0;
+  EXPECT_EQ(ReplacementCount, 0);
+  verifyFormat("static const uint32 foo[] = {0, 31};",
+               "static const uint32 foo[] = {0, 31};", Style);
+  EXPECT_EQ(ReplacementCount, 0);
+}
+
 } // namespace format
 } // namespace clang
Index: clang/lib/Format/QualifierAlignmentFixer.cpp
===================================================================
--- clang/lib/Format/QualifierAlignmentFixer.cpp
+++ clang/lib/Format/QualifierAlignmentFixer.cpp
@@ -67,14 +67,12 @@
                                     NextStartColumn, LastStartColumn);
   llvm::Optional<std::string> CurrentCode = None;
   tooling::Replacements Fixes;
-  unsigned Penalty = 0;
   for (size_t I = 0, E = Passes.size(); I < E; ++I) {
     std::pair<tooling::Replacements, unsigned> PassFixes = Passes[I](*Env);
     auto NewCode = applyAllReplacements(
         CurrentCode ? StringRef(*CurrentCode) : Code, PassFixes.first);
     if (NewCode) {
       Fixes = Fixes.merge(PassFixes.first);
-      Penalty += PassFixes.second;
       if (I + 1 < E) {
         CurrentCode = std::move(*NewCode);
         Env = std::make_unique<Environment>(
@@ -84,7 +82,21 @@
       }
     }
   }
-  return {Fixes, Penalty};
+
+  // Don't make replacements that replace nothing.
+  tooling::Replacements NonNoOpFixes;
+
+  for (auto I = Fixes.begin(), E = Fixes.end(); I != E; ++I) {
+    StringRef OriginalCode = Code.substr(I->getOffset(), I->getLength());
+
+    if (!OriginalCode.equals(I->getReplacementText())) {
+      auto Err = NonNoOpFixes.add(*I);
+      if (Err)
+        llvm::errs() << "Error removing no op replacements : "
+                     << llvm::toString(std::move(Err)) << "\n";
+    }
+  }
+  return {NonNoOpFixes, 0};
 }
 
 static void replaceToken(const SourceManager &SourceMgr,


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