clang-tidy: Add initial check for "Don't use else after return".

As per the LLVM coding standards:
http://llvm.org/docs/CodingStandards.html#don-t-use-else-after-a-return

Initial version, probably still quite a bit to do until this is really
useful.

Review: http://reviews.llvm.org/D6927
llvm-svn: 226025

5 files changed, 108 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/readability/CMakeLists.txt b/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
index cf1248c196a..5d8031c3bf3 100644
--- a/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
+++ b/clang-tools-extra/clang-tidy/readability/CMakeLists.txt
@@ -2,6 +2,7 @@ set(LLVM_LINK_COMPONENTS support)
 
 add_clang_library(clangTidyReadabilityModule
   BracesAroundStatementsCheck.cpp
+  ElseAfterReturnCheck.cpp
   FunctionSize.cpp
   NamespaceCommentCheck.cpp
   ReadabilityTidyModule.cpp
diff --git a/clang-tools-extra/clang-tidy/readability/ElseAfterReturnCheck.cpp b/clang-tools-extra/clang-tidy/readability/ElseAfterReturnCheck.cpp
new file mode 100644
index 00000000000..9dd0c13f623
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/readability/ElseAfterReturnCheck.cpp
@@ -0,0 +1,46 @@
+//===--- ElseAfterReturnCheck.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 "ElseAfterReturnCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+
+void ElseAfterReturnCheck::registerMatchers(MatchFinder *Finder) {
+  // FIXME: Support continue, break and throw.
+  Finder->addMatcher(
+      ifStmt(
+          hasThen(stmt(anyOf(returnStmt(), compoundStmt(has(returnStmt()))))),
+          hasElse(stmt().bind("else"))).bind("if"),
+      this);
+}
+
+static FixItHint removeToken(SourceLocation Loc) {
+  return FixItHint::CreateRemoval(CharSourceRange::getTokenRange(Loc, Loc));
+}
+
+void ElseAfterReturnCheck::check(const MatchFinder::MatchResult &Result) {
+  const auto *If = Result.Nodes.getNodeAs<IfStmt>("if");
+  SourceLocation ElseLoc = If->getElseLoc();
+  DiagnosticBuilder Diag = diag(ElseLoc, "don't use else after return");
+  Diag << removeToken(ElseLoc);
+
+  // FIXME: Removing the braces isn't always safe. Do a more careful analysis.
+  // FIXME: Change clang-format to correctly un-indent the code.
+  if (const auto *CS = Result.Nodes.getNodeAs<CompoundStmt>("else"))
+    Diag << removeToken(CS->getLBracLoc()) << removeToken(CS->getRBracLoc());
+}
+
+} // namespace tidy
+} // namespace clang
+
diff --git a/clang-tools-extra/clang-tidy/readability/ElseAfterReturnCheck.h b/clang-tools-extra/clang-tidy/readability/ElseAfterReturnCheck.h
new file mode 100644
index 00000000000..2d2b4fb42a2
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/readability/ElseAfterReturnCheck.h
@@ -0,0 +1,30 @@
+//===--- ElseAfterReturnCheck.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_ELSE_AFTER_RETURN_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_ELSE_AFTER_RETURN_H
+
+#include "../ClangTidy.h"
+
+namespace clang {
+namespace tidy {
+
+class ElseAfterReturnCheck : public ClangTidyCheck {
+public:
+  ElseAfterReturnCheck(StringRef Name, ClangTidyContext *Context)
+      : ClangTidyCheck(Name, Context) {}
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+};
+
+} // namespace tidy
+} // namespace clang
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_ELSE_AFTER_RETURN_H
+
diff --git a/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp b/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
index 9e7187573c9..71bac790a58 100644
--- a/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
+++ b/clang-tools-extra/clang-tidy/readability/ReadabilityTidyModule.cpp
@@ -11,6 +11,7 @@
 #include "../ClangTidyModule.h"
 #include "../ClangTidyModuleRegistry.h"
 #include "BracesAroundStatementsCheck.h"
+#include "ElseAfterReturnCheck.h"
 #include "FunctionSize.h"
 #include "RedundantSmartptrGet.h"
 
@@ -23,6 +24,8 @@ public:
   void addCheckFactories(ClangTidyCheckFactories &CheckFactories) override {
     CheckFactories.registerCheck<BracesAroundStatementsCheck>(
         "readability-braces-around-statements");
+    CheckFactories.registerCheck<ElseAfterReturnCheck>(
+        "readability-else-after-return");
     CheckFactories.registerCheck<FunctionSizeCheck>(
         "readability-function-size");
     CheckFactories.registerCheck<RedundantSmartptrGet>(
diff --git a/clang-tools-extra/test/clang-tidy/readability-else-after-return.cpp b/clang-tools-extra/test/clang-tidy/readability-else-after-return.cpp
new file mode 100644
index 00000000000..c94e71ba118
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/readability-else-after-return.cpp
@@ -0,0 +1,28 @@
+// RUN: $(dirname %s)/check_clang_tidy.sh %s readability-else-after-return %t
+// REQUIRES: shell
+
+void f(int a) {
+  if (a > 0)
+    return;
+  else // comment
+// CHECK-MESSAGES: :[[@LINE-1]]:3: warning: don't use else after return
+// CHECK-FIXES: {{^}}  // comment
+    return;
+
+  if (a > 0) {
+    return;
+  } else { // comment
+// CHECK-MESSAGES: :[[@LINE-1]]:5: warning: don't use else after return
+// CHECK-FIXES:  } // comment
+    return;
+  }
+
+  if (a > 0) {
+    f(0);
+    if (a > 10)
+      return;
+  } else {
+    return;
+  }
+}
+