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

Finds redundant variable and function declarations.

  extern int X;
  extern int X;  // <- redundant

Differential Revision: https://reviews.llvm.org/D24656

llvm-svn: 285689

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

@@ -16,6 +16,7 @@ add_clang_library(clangTidyReadabilityModule
   NonConstParameterCheck.cpp
   ReadabilityTidyModule.cpp
   RedundantControlFlowCheck.cpp
+  RedundantDeclarationCheck.cpp
   RedundantMemberInitCheck.cpp
   RedundantStringCStrCheck.cpp
   RedundantSmartptrGetCheck.cpp

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

@@ -23,6 +23,7 @@
 #include "NamedParameterCheck.h"
 #include "NonConstParameterCheck.h"
 #include "RedundantControlFlowCheck.h"
+#include "RedundantDeclarationCheck.h"
 #include "RedundantMemberInitCheck.h"
 #include "RedundantSmartptrGetCheck.h"
 #include "RedundantStringCStrCheck.h"
@@ -68,6 +69,8 @@ public:
         "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>(

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

@@ -0,0 +1,71 @@
+//===--- 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/clang-tidy/readability/RedundantDeclarationCheck.h

@@ -0,0 +1,35 @@
+//===--- 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/docs/ReleaseNotes.rst

@@ -129,6 +129,11 @@ Improvements to clang-tidy
   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

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

@@ -133,6 +133,7 @@ Clang-Tidy Checks
    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

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

@@ -0,0 +1,27 @@
+.. 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/test/clang-tidy/readability-redundant-declaration.cpp

@@ -0,0 +1,23 @@
+// 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() {}