[clang-tidy] Add check readability-redundant-declaration

[danielmarjamaki]

Summary

This is a new check that warns about redundant variable declarations.

[danielmarjamaki]

For information, I am testing this on debian packages right now. I will see the results next week.

clang-tidy/readability/RedundantDeclarationCheck.cpp

22 ↗

(On Diff #71612)

I forgot to remove this FIXME comment, I will remove it.

41 ↗

(On Diff #71612)

Imho this is a clumpsy way to see if it's a "multivariable" declaration. Do you know if there is a better way?

50 ↗

(On Diff #71612)

Is there a better way to rewrite this ... I tried something like this without success:

auto D = diag(..);
if (!MultiVar)
    D << FixItHint..;

clang-tidy/readability/RedundantDeclarationCheck.h

19 ↗

(On Diff #71612)

I will fix this FIXME.

test/clang-tidy/readability-redundant-declaration.cpp

11 ↗

(On Diff #71612)

Ideally this would be changed to "extern int B;". I currently don't fix multivariable declarations.

[danielmarjamaki]

minor fixes

[Eugene.Zelenko]

Please mention this check in docs/ReleaseNotes.rst (in alphabetical order).

Will be good idea to detect redundant function prototypes.

However, I think this check should be part of Clang diagnostics. GCC has -Wredundant-decls for a long time.

[Eugene.Zelenko]

test/clang-tidy/readability-redundant-declaration.cpp

9 ↗

(On Diff #71614)

Please run Clang-format over test.

[danielmarjamaki]

However, I think this check should be part of Clang diagnostics. GCC has -Wredundant-decls for a long time.

I am not against that.

What is the criteria? When should it be in the compiler and when should it be in clang-tidy?

Personally I think it's natural that the compiler has warnings about dangerous code. This check is about readability.

[danielmarjamaki]

Will be good idea to detect redundant function prototypes.

Yes.

Should that have the same ID though? Is it better to have one readability-redundant-declaration or two separate readability-redundant-variable-declaration and readability-redundant-function-declaration?

[danielmarjamaki]

run clang-format on test. add release notes.

[alexfh]

If this kind of an error is not too frequent, it might make sense as a clang diagnostic, indeed. Having it in clang-tidy until then doesn't hurt, though.

clang-tidy/readability/RedundantDeclarationCheck.cpp

36 ↗

(On Diff #71775)

Don't check for system headers, clang-tidy takes care of this (and sometimes, warnings in system headers are interesting to the standard library maintainers).

38 ↗

(On Diff #71775)

Don't check for the same file. It will prevent fixing headers.

44 ↗

(On Diff #71775)

There should be a better way of checking for multi variable declarations.

58–64 ↗

(On Diff #71775)

No need to duplicate this code. Store the diagnostic builder and conditionally insert the fix:

{
  auto Diag = diag(...);
  if (x)
    Diag << FixItHint::....;
}
diag(..., Note);

[danielmarjamaki]

Fix review comments

[danielmarjamaki]

clang-tidy/readability/RedundantDeclarationCheck.cpp

39 ↗

(On Diff #72802)

I don't want to generate a fixit. because it could easily break the code. And it will probably depend on inclusion order.

45 ↗

(On Diff #72802)

I think this is better. But not perfect. Maybe there is still a better way.

59–65 ↗

(On Diff #72802)

Thanks! That works.

[danielmarjamaki]

Ping.

I am not very happy about how I detect multivariable declarations. But I really don't see any such info in the VarDecl. For instance, the AST dump does not show this info.

[alexfh]

clang-tidy/readability/RedundantDeclarationCheck.cpp

39 ↗

(On Diff #72802)

Yep, not generating fixes for redundant declarations in multiple headers totally makes sense (at least, by default).

45 ↗

(On Diff #72802)

I don't know whether there is a better way. I somewhat dislike iterating over all declarations here, but it only happens when we're about to generate a warning anyway. Good enough for the start.

60 ↗

(On Diff #72802)

It should be possible to just use D here.

[danielmarjamaki]

clang-tidy/readability/RedundantDeclarationCheck.cpp

60 ↗

(On Diff #72802)

Thanks. It's not possible:

RedundantDeclarationCheck.cpp:61:15: error: ‘const class clang::Decl’ has no member named ‘getName’
         << D->getName();
               ^

[aaron.ballman]

clang-tidy/readability/RedundantDeclarationCheck.cpp

60 ↗

(On Diff #72802)

diag(...) << cast<NamedDecl>(D) is required; the diagnostic engine properly handles quoting NamedDecl objects.

[danielmarjamaki]

changed cast<NamedDecl>(D)->getName() to cast<NamedDecl>(D)

[danielmarjamaki]

Ping.

[alexfh]

Sorry for the delay. I'm on vacation, returning on Monday.

The patch looks good when the comments are fixed.

clang-tidy/readability/RedundantDeclarationCheck.cpp

36 ↗

(On Diff #74478)

nit: No need for parentheses here.

41 ↗

(On Diff #74478)

VD is checked on the previous line, no need to repeat the check here.

61 ↗

(On Diff #74478)

Looks like it's better to make D NamedDecl and remove the cast here:

Finder->addMatcher(namedDecl(...
...
const auto *D = Result.Nodes.getNodeAs<NamedDecl>("Decl");

docs/clang-tidy/checks/readability-redundant-declaration.rst

6 ↗

(On Diff #74478)

I think, these points should be covered more thoroughly:

• kinds of declarations supported by the check (function declarations aren't mentioned);
• how declarations in different files are treated;
• limitations (e.g. declarations with multiple variables);
• a few words on the motivation for this check.

[alexfh]

clang-tools-extra/trunk/test/clang-tidy/readability-redundant-declaration.cpp

11

Just noticed: could you add a check line for the note ("previously declared here")? One should be enough.

17

Just noticed: this is a rather unspecific check pattern that can match any empty line anywhere in the file. Int way to make the check stricter is to add a unique trailing comment and then match it (anchored to the line start).

clang-tools-extra/trunk/clang-tidy/readability/CMakeLists.txt

add_clang_library(clangTidyReadabilityModule
   ImplicitBoolCastCheck.cpp
   InconsistentDeclarationParameterNameCheck.cpp
   MisplacedArrayIndexCheck.cpp
   NamedParameterCheck.cpp
   NamespaceCommentCheck.cpp
   NonConstParameterCheck.cpp
   ReadabilityTidyModule.cpp
   RedundantControlFlowCheck.cpp
+  RedundantDeclarationCheck.cpp
   RedundantMemberInitCheck.cpp
   RedundantStringCStrCheck.cpp
   RedundantSmartptrGetCheck.cpp
   RedundantStringInitCheck.cpp
   SimplifyBooleanExprCheck.cpp
   StaticDefinitionInAnonymousNamespaceCheck.cpp
   UniqueptrDeleteReleaseCheck.cpp
 

clang-tools-extra/trunk/clang-tidy/readability/ReadabilityTidyModule.cpp

 #include "FunctionSizeCheck.h"
 #include "IdentifierNamingCheck.h"
 #include "ImplicitBoolCastCheck.h"
 #include "InconsistentDeclarationParameterNameCheck.h"
 #include "MisplacedArrayIndexCheck.h"
 #include "NamedParameterCheck.h"
 #include "NonConstParameterCheck.h"
 #include "RedundantControlFlowCheck.h"
+#include "RedundantDeclarationCheck.h"
 #include "RedundantMemberInitCheck.h"
 #include "RedundantSmartptrGetCheck.h"
 #include "RedundantStringCStrCheck.h"
 #include "RedundantStringInitCheck.h"
 #include "SimplifyBooleanExprCheck.h"
 #include "StaticDefinitionInAnonymousNamespaceCheck.h"
 #include "UniqueptrDeleteReleaseCheck.h"
 
void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.registerCheck<StaticDefinitionInAnonymousNamespaceCheck>(
         "readability-static-definition-in-anonymous-namespace");
     CheckFactories.registerCheck<readability::NamedParameterCheck>(
         "readability-named-parameter");
     CheckFactories.registerCheck<NonConstParameterCheck>(
         "readability-non-const-parameter");
     CheckFactories.registerCheck<RedundantControlFlowCheck>(
         "readability-redundant-control-flow");
+    CheckFactories.registerCheck<RedundantDeclarationCheck>(
+        "readability-redundant-declaration");
     CheckFactories.registerCheck<RedundantSmartptrGetCheck>(
         "readability-redundant-smartptr-get");
     CheckFactories.registerCheck<RedundantStringCStrCheck>(
         "readability-redundant-string-cstr");
     CheckFactories.registerCheck<RedundantStringInitCheck>(
         "readability-redundant-string-init");
     CheckFactories.registerCheck<SimplifyBooleanExprCheck>(
         "readability-simplify-boolean-expr");

clang-tools-extra/trunk/clang-tidy/readability/RedundantDeclarationCheck.h

+//===--- RedundantDeclarationCheck.h - clang-tidy----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_REDUNDANT_DECLARATION_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_REDUNDANT_DECLARATION_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+/// Find redundant variable declarations.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/readability-redundant-declaration.html
+class RedundantDeclarationCheck : public ClangTidyCheck {
+public:
+  RedundantDeclarationCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_REDUNDANT_DECLARATION_H

clang-tools-extra/trunk/clang-tidy/readability/RedundantDeclarationCheck.cpp

+//===--- RedundantDeclarationCheck.cpp - clang-tidy------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "RedundantDeclarationCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace readability {
+
+void RedundantDeclarationCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(namedDecl(anyOf(varDecl(), functionDecl())).bind("Decl"), this);
+}
+
+void RedundantDeclarationCheck::check(const MatchFinder::MatchResult &Result) {
+  const NamedDecl *D = Result.Nodes.getNodeAs<NamedDecl>("Decl");
+  const auto *Prev = D->getPreviousDecl();
+  if (!Prev)
+    return;
+  if (Prev->getLocation() == D->getLocation())
+    return;
+
+  const SourceManager &SM = *Result.SourceManager;
+
+  const bool DifferentHeaders =
+       !SM.isInMainFile(D->getLocation()) &&
+       !SM.isWrittenInSameFile(Prev->getLocation(), D->getLocation());
+
+  bool MultiVar = false;
+  if (const auto *VD = dyn_cast<VarDecl>(D)) {
+    if (VD->getPreviousDecl()->getStorageClass() == SC_Extern &&
+        VD->getStorageClass() != SC_Extern)
+      return;
+    // Is this a multivariable declaration?
+    for (const auto Other : VD->getDeclContext()->decls()) {
+      if (Other != D && Other->getLocStart() == VD->getLocStart()) {
+        MultiVar = true;
+        break;
+      }
+    }
+  } else {
+    const auto *FD = cast<FunctionDecl>(D);
+    if (FD->isThisDeclarationADefinition())
+      return;
+  }
+
+  SourceLocation EndLoc = Lexer::getLocForEndOfToken(
+      D->getSourceRange().getEnd(), 0, SM, Result.Context->getLangOpts());
+  {
+    auto Diag = diag(D->getLocation(), "redundant %0 declaration")
+                << D;
+    if (!MultiVar && !DifferentHeaders)
+      Diag << FixItHint::CreateRemoval(
+          SourceRange(D->getSourceRange().getBegin(), EndLoc));
+  }
+  diag(Prev->getLocation(), "previously declared here", DiagnosticIDs::Note);
+}
+
+} // namespace readability
+} // namespace tidy
+} // namespace clang

clang-tools-extra/trunk/docs/ReleaseNotes.rst

- New `readability-non-const-parameter
   a constant type instead.
 
 - New `readability-redundant-member-init
   <http://clang.llvm.org/extra/clang-tidy/checks/readability-redundant-member-init.html>`_ check
 
   Flags member initializations that are unnecessary because the same default
   constructor would be called if they were not present.
 
+- New `readability-redundant-declaration
+  <http://clang.llvm.org/extra/clang-tidy/checks/readability-redundant-declaration.html>`_ check
+
+  Warns about duplicate variable declarations.
+
 Fixed bugs:
 
 - `modernize-make-unique
   <http://clang.llvm.org/extra/clang-tidy/checks/modernize-make-unique.html>`_
   and `modernize-make-shared
   <http://clang.llvm.org/extra/clang-tidy/checks/modernize-make-shared.html>`_
   Calling ``make_{unique|shared}`` from within a member function of a type
   with a private or protected constructor would be ill-formed.

clang-tools-extra/trunk/docs/clang-tidy/checks/list.rst

.. toctree::
    readability-function-size
    readability-identifier-naming
    readability-implicit-bool-cast
    readability-inconsistent-declaration-parameter-name
    readability-misplaced-array-index
    readability-named-parameter
    readability-non-const-parameter
    readability-redundant-control-flow
+   readability-redundant-declaration
    readability-redundant-member-init
    readability-redundant-smartptr-get
    readability-redundant-string-cstr
    readability-redundant-string-init
    readability-simplify-boolean-expr
    readability-static-definition-in-anonymous-namespace
    readability-uniqueptr-delete-release

clang-tools-extra/trunk/docs/clang-tidy/checks/readability-redundant-declaration.rst

+.. title:: clang-tidy - readability-redundant-declaration
+
+readability-redundant-declaration
+=================================
+
+Finds redundant variable and function declarations.
+
+.. code-block:: c++
+
+  extern int X;
+  extern int X;
+
+becomes
+
+.. code-block:: c++
+
+  extern int X;
+
+Such redundant declarations can be removed without changing program behaviour.
+They can for instance be unintentional left overs from previous refactorings
+when code has been moved around. Having redundant declarations could in worst
+case mean that there are typos in the code that cause bugs.
+
+Normally the code can be automatically fixed, clang-tidy can remove the second
+declaration. However there are 2 cases when you need to fix the code manually:
+ * When the declarations are in different header files.
+ * When multiple variables are declared together.

clang-tools-extra/trunk/test/clang-tidy/readability-redundant-declaration.cpp

+// RUN: %check_clang_tidy %s readability-redundant-declaration %t
+
+extern int Xyz;
+extern int Xyz;
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: redundant 'Xyz' declaration [readability-redundant-declaration]
+// CHECK-FIXES: {{^}}{{$}}
+int Xyz = 123;
+
+extern int A;
+extern int A, B;
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: redundant 'A' declaration
+// CHECK-FIXES: {{^}}extern int A, B;{{$}}
+
+extern int Buf[10];
+extern int Buf[10];
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: redundant 'Buf' declaration
+// CHECK-FIXES: {{^}}{{$}}
+
+static int f();
+static int f();
+// CHECK-MESSAGES: :[[@LINE-1]]:12: warning: redundant 'f' declaration
+// CHECK-FIXES: {{^}}{{$}}
+static int f() {}