Initial version of misc-unused-using-decl check.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@266735 91177308-0d34-0410-b5e6-96231b3b80d8

clang-tidy/misc/CMakeLists.txt

@@ -32,10 +32,11 @@ add_clang_library(clangTidyMiscModule
   SwappedArgumentsCheck.cpp
   ThrowByValueCatchByReferenceCheck.cpp
   UndelegatedConstructor.cpp
+  UniqueptrResetReleaseCheck.cpp
   UnusedAliasDeclsCheck.cpp
   UnusedParametersCheck.cpp
   UnusedRAIICheck.cpp
-  UniqueptrResetReleaseCheck.cpp
+  UnusedUsingDeclsCheck.cpp
   VirtualNearMissCheck.cpp
 
   LINK_LIBS

clang-tidy/misc/MiscTidyModule.cpp

@@ -44,6 +44,7 @@
 #include "UnusedAliasDeclsCheck.h"
 #include "UnusedParametersCheck.h"
 #include "UnusedRAIICheck.h"
+#include "UnusedUsingDeclsCheck.h"
 #include "VirtualNearMissCheck.h"
 
 namespace clang {
@@ -118,6 +119,8 @@ public:
     CheckFactories.registerCheck<UnusedParametersCheck>(
         "misc-unused-parameters");
     CheckFactories.registerCheck<UnusedRAIICheck>("misc-unused-raii");
+    CheckFactories.registerCheck<UnusedUsingDeclsCheck>(
+        "misc-unused-using-decls");
     CheckFactories.registerCheck<VirtualNearMissCheck>(
         "misc-virtual-near-miss");
   }

clang-tidy/misc/UnusedAliasDeclsCheck.h

@@ -11,6 +11,7 @@
 #define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_UNUSED_ALIAS_DECLS_H
 
 #include "../ClangTidy.h"
+#include "llvm/ADT/DenseMap.h"
 
 namespace clang {
 namespace tidy {

clang-tidy/misc/UnusedUsingDeclsCheck.cpp

@@ -0,0 +1,73 @@
+//===--- UnusedUsingDeclsCheck.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 "UnusedUsingDeclsCheck.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 misc {
+
+void UnusedUsingDeclsCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(usingDecl(isExpansionInMainFile()).bind("using"), this);
+  Finder->addMatcher(recordType(hasDeclaration(namedDecl().bind("used"))),
+                     this);
+}
+
+void UnusedUsingDeclsCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *Using = Result.Nodes.getNodeAs<UsingDecl>("using")) {
+    // FIXME: Implement the correct behavior for using declarations with more
+    // than one shadow.
+    if (Using->shadow_size() != 1)
+      return;
+    const auto* TargetDecl = Using->shadow_begin()->getTargetDecl();
+
+    // FIXME: Handle other target types.
+    if (!isa<RecordDecl>(TargetDecl))
+      return;
+
+    FoundDecls[TargetDecl] = Using;
+    FoundRanges[TargetDecl] = CharSourceRange::getCharRange(
+        Using->getLocStart(),
+        Lexer::findLocationAfterToken(
+            Using->getLocEnd(), tok::semi, *Result.SourceManager,
+            Result.Context->getLangOpts(),
+            /*SkipTrailingWhitespaceAndNewLine=*/true));
+    return;
+  }
+
+  // Mark using declarations as used by setting FoundDecls' value to zero. As
+  // the AST is walked in order, usages are only marked after a the
+  // corresponding using declaration has been found.
+  // FIXME: This currently doesn't look at whether the type reference is
+  // actually found with the help of the using declaration.
+  if (const auto *Used = Result.Nodes.getNodeAs<NamedDecl>("used")) {
+    if (FoundDecls.find(Used) != FoundDecls.end())
+      FoundDecls[Used] = nullptr;
+  }
+}
+
+void UnusedUsingDeclsCheck::onEndOfTranslationUnit() {
+  for (const auto &FoundDecl : FoundDecls) {
+    if (FoundDecl.second == nullptr)
+      continue;
+    diag(FoundDecl.second->getLocation(), "using decl %0 is unused")
+        << FoundDecl.second
+        << FixItHint::CreateRemoval(FoundRanges[FoundDecl.first]);
+  }
+  FoundDecls.clear();
+}
+
+} // namespace misc
+} // namespace tidy
+} // namespace clang

clang-tidy/misc/UnusedUsingDeclsCheck.h

@@ -0,0 +1,41 @@
+//===--- UnusedUsingDeclsCheck.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_MISC_UNUSED_USING_DECLS_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_UNUSED_USING_DECLS_H
+
+#include "../ClangTidy.h"
+#include "llvm/ADT/DenseMap.h"
+
+namespace clang {
+namespace tidy {
+namespace misc {
+
+/// Finds unused using declarations.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/misc-unused-using-decls.html
+class UnusedUsingDeclsCheck : public ClangTidyCheck {
+public:
+  UnusedUsingDeclsCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  void onEndOfTranslationUnit() override;
+
+private:
+  llvm::DenseMap<const NamedDecl*, const UsingDecl*> FoundDecls;
+  llvm::DenseMap<const NamedDecl*, CharSourceRange> FoundRanges;
+};
+
+} // namespace misc
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MISC_UNUSED_USING_DECLS_H

docs/clang-tidy/checks/list.rst

@@ -80,6 +80,7 @@ Clang-Tidy Checks
    misc-unused-alias-decls
    misc-unused-parameters
    misc-unused-raii
+   misc-unused-using-decls
    misc-virtual-near-miss
    modernize-deprecated-headers
    modernize-loop-convert

docs/clang-tidy/checks/misc-unused-using-decls.rst

@@ -0,0 +1,14 @@
+.. title:: clang-tidy - misc-unused-using-decls
+
+misc-unused-using-decls
+=======================
+
+Finds unused ``using`` declarations.
+
+Example:
+
+.. code:: c++
+
+  namespace n { class C; }
+  using n::C;  // Never actually used.
+

test/clang-tidy/misc-unused-using-decls.cpp

@@ -0,0 +1,27 @@
+// RUN: %check_clang_tidy %s misc-unused-using-decls %t
+
+// ----- Definitions -----
+template <typename T> class vector {};
+namespace n {
+class A;
+class B;
+class C;
+class D { public: static int i; };
+}
+
+// ----- Using declarations -----
+// eol-comments aren't removed (yet)
+using n::A; // A
+// CHECK-MESSAGES: :[[@LINE-1]]:10: warning: using decl 'A' is unused
+// CHECK-FIXES: {{^}}// A
+using n::B;
+using n::C;
+using n::D;
+
+// ----- Usages -----
+void f(B b);
+void g() {
+  vector<C> data;
+  D::i = 1;
+}
+