Suggest automated replacements of C-style casts with C++ casts.

Summary:
This patch implements a subset of possible replacements of C-style
casts with const_cast/static_cast/reinterpret_cast. This should cover a large
portion of cases in real code. Handling of a few more cases may be implemented
eventually.

Reviewers: sbenza, djasper

Reviewed By: djasper

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D4478

llvm-svn: 212924

1 files changed, 92 insertions, 10 deletions

diff --git a/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp b/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp
index 59914e02fb9..7f8a965a11f 100644
--- a/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp
+++ b/clang-tools-extra/clang-tidy/google/AvoidCStyleCastsCheck.cpp
@@ -8,8 +8,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "AvoidCStyleCastsCheck.h"
+#include "clang/AST/ASTContext.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Lex/Lexer.h"
 
 using namespace clang::ast_matchers;
 
@@ -24,27 +26,107 @@ AvoidCStyleCastsCheck::registerMatchers(ast_matchers::MatchFinder *Finder) {
           // Filter out (EnumType)IntegerLiteral construct, which is generated
           // for non-type template arguments of enum types.
           // FIXME: Remove this once this is fixed in the AST.
-          unless(hasParent(substNonTypeTemplateParmExpr()))).bind("cast"),
+          unless(hasParent(substNonTypeTemplateParmExpr())),
+          // Avoid matches in template instantiations.
+          unless(hasAncestor(decl(
+              anyOf(recordDecl(ast_matchers::isTemplateInstantiation()),
+                    functionDecl(ast_matchers::isTemplateInstantiation()))))))
+          .bind("cast"),
       this);
 }
 
+bool needsConstCast(QualType SourceType, QualType DestType) {
+  SourceType = SourceType.getNonReferenceType();
+  DestType = DestType.getNonReferenceType();
+  while (SourceType->isPointerType() && DestType->isPointerType()) {
+    SourceType = SourceType->getPointeeType();
+    DestType = DestType->getPointeeType();
+    if (SourceType.isConstQualified() && !DestType.isConstQualified())
+      return true;
+  }
+  return false;
+}
+
+bool pointedTypesAreEqual(QualType SourceType, QualType DestType) {
+  SourceType = SourceType.getNonReferenceType();
+  DestType = DestType.getNonReferenceType();
+  while (SourceType->isPointerType() && DestType->isPointerType()) {
+    SourceType = SourceType->getPointeeType();
+    DestType = DestType->getPointeeType();
+  }
+  return SourceType.getUnqualifiedType() == DestType.getUnqualifiedType();
+}
 void AvoidCStyleCastsCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *CastExpr = Result.Nodes.getNodeAs<CStyleCastExpr>("cast");
 
-  // Ignore casts in macros for now.
-  if (CastExpr->getLocStart().isMacroID())
-    return;
-
   // Casting to void is an idiomatic way to mute "unused variable" and similar
   // warnings.
   if (CastExpr->getTypeAsWritten()->isVoidType())
     return;
 
-  diag(CastExpr->getLocStart(), "C-style casts are discouraged. Use "
-                                "static_cast/const_cast/reinterpret_cast "
-                                "instead.");
-  // FIXME: Suggest appropriate C++ cast. See [expr.cast] for cast notation
-  // semantics.
+  QualType SourceType =
+      CastExpr->getSubExprAsWritten()->getType().getCanonicalType();
+  QualType DestType = CastExpr->getTypeAsWritten().getCanonicalType();
+
+  auto ParenRange = CharSourceRange::getTokenRange(CastExpr->getLParenLoc(),
+                                                   CastExpr->getRParenLoc());
+  if (SourceType == DestType) {
+    diag(CastExpr->getLocStart(), "Redundant cast to the same type.")
+        << FixItHint::CreateRemoval(ParenRange);
+    return;
+  }
+
+  std::string DestTypeString = CastExpr->getTypeAsWritten().getAsString();
+
+  auto diag_builder =
+      diag(CastExpr->getLocStart(), "C-style casts are discouraged. %0");
+
+  auto ReplaceWithCast = [&](StringRef CastType) {
+    diag_builder << ("Use " + CastType + ".").str();
+    if (ParenRange.getBegin().isMacroID() || ParenRange.getEnd().isMacroID())
+      return;
+    diag_builder << FixItHint::CreateReplacement(
+                        ParenRange,
+                        (CastType + "<" + DestTypeString + ">(").str())
+                 << FixItHint::CreateInsertion(
+                        Lexer::getLocForEndOfToken(
+                            CastExpr->getSubExprAsWritten()->getLocEnd(), 0,
+                            *Result.SourceManager,
+                            Result.Context->getLangOpts()),
+                        ")");
+  };
+  // Suggest appropriate C++ cast. See [expr.cast] for cast notation semantics.
+  switch (CastExpr->getCastKind()) {
+  case CK_NoOp:
+    if (needsConstCast(SourceType, DestType) &&
+        pointedTypesAreEqual(SourceType, DestType)) {
+      ReplaceWithCast("const_cast");
+      return;
+    }
+    if (DestType->isReferenceType() &&
+        (SourceType.getNonReferenceType() ==
+             DestType.getNonReferenceType().withConst() ||
+         SourceType.getNonReferenceType() == DestType.getNonReferenceType())) {
+      ReplaceWithCast("const_cast");
+      return;
+    }
+    if (SourceType->isBuiltinType() && DestType->isBuiltinType()) {
+      ReplaceWithCast("static_cast");
+      return;
+    }
+    break;
+  case CK_BitCast:
+    // FIXME: Suggest const_cast<...>(reinterpret_cast<...>(...)) replacement.
+    if (!needsConstCast(SourceType, DestType)) {
+      ReplaceWithCast("reinterpret_cast");
+      return;
+    }
+    break;
+  default:
+    break;
+  }
+
+  diag_builder << "Use static_cast/const_cast/reinterpret_cast.";
 }
 
 } // namespace readability