1 files changed, 106 insertions, 0 deletions
diff --git a/clang-tools-extra/clang-tidy/performance/ImplicitCastInLoopCheck.cpp b/clang-tools-extra/clang-tidy/performance/ImplicitCastInLoopCheck.cpp
new file mode 100644
index 00000000000..1752e2d0f10
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+++ b/clang-tools-extra/clang-tidy/performance/ImplicitCastInLoopCheck.cpp
@@ -0,0 +1,106 @@
+//===--- ImplicitCastInLoopCheck.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 "ImplicitCastInLoopCheck.h"
+
+#include "clang/AST/ASTContext.h"
+#include "clang/AST/Decl.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Lex/Lexer.h"
+
+namespace clang {
+
+using namespace ast_matchers;
+
+namespace tidy {
+namespace performance {
+
+namespace {
+// Checks if the stmt is a ImplicitCastExpr with a CastKind that is not a NoOp.
+// The subtelty is that in some cases (user defined conversions), we can
+// get to ImplicitCastExpr inside each other, with the outer one a NoOp. In this
+// case we skip the first cast expr.
+bool IsNonTrivialImplicitCast(const Stmt* ST) {
+  if (const auto* ICE = dyn_cast<ImplicitCastExpr>(ST)) {
+    return (ICE->getCastKind() != CK_NoOp) ||
+            IsNonTrivialImplicitCast(ICE->getSubExpr());
+  }
+  return false;
+}
+} // namespace
+
+void ImplicitCastInLoopCheck::registerMatchers(
+    ast_matchers::MatchFinder* Finder) {
+  // We look for const ref loop variables that (optionally inside an
+  // ExprWithCleanup) materialize a temporary, and contain a implicit cast. The
+  // check on the implicit cast is done in check() because we can't access
+  // implicit cast subnode via matchers: has() skips casts and materialize!
+  // We also bind on the call to operator* to get the proper type in the
+  // diagnostic message.
+  // Note that when the implicit cast is done through a user defined cast
+  // operator, the node is a CXXMemberCallExpr, not a CXXOperatorCallExpr, so
+  // it should not get caught by the cxxOperatorCallExpr() matcher.
+  Finder->addMatcher(
+      cxxForRangeStmt(hasLoopVariable(
+          varDecl(hasType(qualType(references(qualType(isConstQualified())))),
+                  hasInitializer(expr(hasDescendant(cxxOperatorCallExpr().bind(
+                                          "operator-call")))
+                                     .bind("init")))
+              .bind("faulty-var"))),
+      this);
+}
+
+void ImplicitCastInLoopCheck::check(
+    const ast_matchers::MatchFinder::MatchResult &Result) {
+  const auto* VD = Result.Nodes.getNodeAs<VarDecl>("faulty-var");
+  const auto* Init = Result.Nodes.getNodeAs<Expr>("init");
+  const auto* OperatorCall =
+      Result.Nodes.getNodeAs<CXXOperatorCallExpr>("operator-call");
+
+  if (const auto* Cleanup = dyn_cast<ExprWithCleanups>(Init)) {
+    Init = Cleanup->getSubExpr();
+  }
+  const auto* Materialized = dyn_cast<MaterializeTemporaryExpr>(Init);
+  if (!Materialized) {
+    return;
+  }
+
+  // We ignore NoOp casts. Those are generated if the * operator on the
+  // iterator returns a value instead of a reference, and the loop variable
+  // is a reference. This situation is fine (it probably produces the same
+  // code at the end).
+  if (IsNonTrivialImplicitCast(Materialized->getTemporary())) {
+    ReportAndFix(Result.Context, VD, OperatorCall);
+  }
+}
+
+void ImplicitCastInLoopCheck::ReportAndFix(
+    const ASTContext *Context, const VarDecl *VD,
+    const CXXOperatorCallExpr *OperatorCall) {
+  // We only match on const ref, so we should print a const ref version of the
+  // type.
+  QualType ConstType = OperatorCall->getType().withConst();
+  QualType ConstRefType = Context->getLValueReferenceType(ConstType);
+  const char Message[] =
+      "the type of the loop variable '%0' is different from the one returned "
+      "by the iterator and generates an implicit cast; you can either "
+      "change the type to the correct one ('%1' but 'const auto&' is always a "
+      "valid option) or remove the reference to make it explicit that you are "
+      "creating a new value";
+  PrintingPolicy Policy(Context->getLangOpts());
+  Policy.SuppressTagKeyword = true;
+
+  diag(VD->getLocStart(), Message) << VD->getName()
+                                   << ConstRefType.getAsString(Policy);
+}
+
+} // namespace performance
+} // namespace tidy
+} // namespace clang