[PATCH] D126735: [clang-tidy] Silence modernize-redundant-void-arg in the case of vexing parses

[George Burgess IV via Phabricator via cfe-commits]

george.burgess.iv created this revision.
george.burgess.iv added reviewers: LegalizeAdulthood, aaron.ballman.
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Clang's `-Wvexing-parse` is enabled by default <https://godbolt.org/z/5Ec4f69sv>. When the vexing statement was _intended_ to be interpreted as a function that takes zero arguments, the function's declaration can be rewritten as `T foo(void);` to silence `-Wvexing-parse`. This workaround seems to upset `clang-tidy`.

Given my own lack of understanding of the corners of C++ parsing, I'm... not entirely confident that this patch catches everything && has no unintended side-effects. The bits that `-Wvexing-parse` depends upon are stored within `DeclaratorChunk::FunctionTypeInfo`s, which seem to only exist during AST formation, so it's not clear to me how to directly get at that information from clang-tidy.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D126735

Files:
  clang-tools-extra/clang-tidy/modernize/RedundantVoidArgCheck.cpp
  clang-tools-extra/test/clang-tidy/checkers/modernize-redundant-void-arg.cpp


Index: clang-tools-extra/test/clang-tidy/checkers/modernize-redundant-void-arg.cpp
===================================================================
--- clang-tools-extra/test/clang-tidy/checkers/modernize-redundant-void-arg.cpp
+++ clang-tools-extra/test/clang-tidy/checkers/modernize-redundant-void-arg.cpp
@@ -592,3 +592,9 @@
   (void)a;
 }
 #undef return_t
+
+// Explicitly specifying `(void)` is a way to sidestep -Wvexing-parse, so we
+// should not warn about it here.
+void most_vexing_parse() {
+  int foo(void);
+}
Index: clang-tools-extra/clang-tidy/modernize/RedundantVoidArgCheck.cpp
===================================================================
--- clang-tools-extra/clang-tidy/modernize/RedundantVoidArgCheck.cpp
+++ clang-tools-extra/clang-tidy/modernize/RedundantVoidArgCheck.cpp
@@ -109,9 +109,13 @@
     }
     removeVoidArgumentTokens(Result, SourceRange(Start, End),
                              "function definition");
-  } else
+  } else if (!Function->getLexicalDeclContext()->isFunctionOrMethod()) {
+    // Only do this if our decl context is outside of a function or method;
+    // otherwise, the user may have explicitly written `(void)` to avoid Most
+    // Vexing Parse warnings.
     removeVoidArgumentTokens(Result, SourceRange(Start, End),
                              "function declaration");
+  }
 }
 
 bool isMacroIdentifier(const IdentifierTable &Idents, const Token &ProtoToken) {


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