Add misc-unused-alias-decls check that currently finds unused namespace

alias declarations. In the future, we might want to reuse it to also
fine unsed using declarations and such.

llvm-svn: 243754

1 files changed, 63 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/misc/UnusedAliasDeclsCheck.cpp b/clang-tools-extra/clang-tidy/misc/UnusedAliasDeclsCheck.cpp
new file mode 100644
index 00000000000..a56c1bfa8bd
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/misc/UnusedAliasDeclsCheck.cpp
@@ -0,0 +1,63 @@
+//===--- UnusedAliasDeclsCheck.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 "UnusedAliasDeclsCheck.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 {
+
+// FIXME: Move this to ASTMatchers.h.
+const ast_matchers::internal::VariadicDynCastAllOfMatcher<
+    Decl, NamespaceAliasDecl> namespaceAliasDecl;
+
+void UnusedAliasDeclsCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(namespaceAliasDecl().bind("alias"), this);
+  Finder->addMatcher(nestedNameSpecifier().bind("nns"), this);
+}
+
+void UnusedAliasDeclsCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *AliasDecl = Result.Nodes.getNodeAs<Decl>("alias")) {
+    // We cannot do anything about headers (yet), as the alias declarations used
+    // in one header could be used by some other translation unit.
+    if (!Result.SourceManager->isInMainFile(AliasDecl->getLocation()))
+      return;
+
+    FoundDecls[AliasDecl] = CharSourceRange::getCharRange(
+        AliasDecl->getLocStart(),
+        Lexer::findLocationAfterToken(
+            AliasDecl->getLocEnd(), tok::semi, *Result.SourceManager,
+            Result.Context->getLangOpts(),
+            /*SkipTrailingWhitespaceAndNewLine=*/true));
+    return;
+  }
+
+  if (const auto *NestedName =
+          Result.Nodes.getNodeAs<NestedNameSpecifier>("nns")) {
+    if (const auto *AliasDecl = NestedName->getAsNamespaceAlias()) {
+      FoundDecls[AliasDecl] = CharSourceRange();
+    }
+  }
+}
+
+void UnusedAliasDeclsCheck::onEndOfTranslationUnit() {
+  for (const auto &FoundDecl : FoundDecls) {
+    if (!FoundDecl.second.isValid())
+      continue;
+    diag(FoundDecl.first->getLocation(), "this namespace alias decl is unused")
+        << FixItHint::CreateRemoval(FoundDecl.second);
+  }
+}
+
+} // namespace tidy
+} // namespace clang