loplugin:redundantcast: Avoid double warnings on some const_cast

Change-Id: I1e6140fef55054899dd32465726e804fc6006394

2 files changed, 10 insertions, 7 deletions

diff --git a/compilerplugins/clang/redundantcast.cxx b/compilerplugins/clang/redundantcast.cxx
index 6d18f2abffd8..c7561a7a6bae 100644
--- a/compilerplugins/clang/redundantcast.cxx
+++ b/compilerplugins/clang/redundantcast.cxx
@@ -107,6 +107,12 @@ bool isVoidPointer(QualType type) {
         && type->getAs<clang::PointerType>()->getPointeeType()->isVoidType();
 }
 
+bool isRedundantConstCast(CXXConstCastExpr const * expr) {
+    return expr->getTypeAsWritten().getCanonicalType().getTypePtr()
+        == (expr->getSubExprAsWritten()->getType().getCanonicalType()
+            .getTypePtr());
+}
+
 class RedundantCast:
     public RecursiveASTVisitor<RedundantCast>, public loplugin::RewritePlugin
 {
@@ -168,7 +174,7 @@ bool RedundantCast::VisitImplicitCastExpr(const ImplicitCastExpr * expr) {
         {
             auto e = dyn_cast<CXXConstCastExpr>(
                 expr->getSubExpr()->IgnoreParenImpCasts());
-            if (e != nullptr) {
+            if (e != nullptr && !isRedundantConstCast(e)) {
                 auto t1 = e->getSubExpr()->getType().getCanonicalType();
                 auto t2 = expr->getType().getCanonicalType();
                 bool ObjCLifetimeConversion;
@@ -392,10 +398,7 @@ bool RedundantCast::VisitCXXConstCastExpr(CXXConstCastExpr const * expr) {
     if (ignoreLocation(expr)) {
         return true;
     }
-    if (expr->getTypeAsWritten().getCanonicalType().getTypePtr()
-        == (expr->getSubExprAsWritten()->getType().getCanonicalType()
-            .getTypePtr()))
-    {
+    if (isRedundantConstCast(expr)) {
         report(
             DiagnosticsEngine::Warning, "redundant const_cast from %0 to %1",
             expr->getExprLoc())
diff --git a/compilerplugins/clang/test/redundantcast.cxx b/compilerplugins/clang/test/redundantcast.cxx
index 7af9716fa27c..e8be3013cd86 100644
--- a/compilerplugins/clang/test/redundantcast.cxx
+++ b/compilerplugins/clang/test/redundantcast.cxx
@@ -19,8 +19,8 @@ int main() {
     f1(const_cast<char * const>(p1)); // expected-error {{redundant const_cast from 'char *' to 'char *const' [loplugin:redundantcast]}}
     f1(const_cast<char *>(p2));
     f1(const_cast<char * const>(p2));
-    f2(const_cast<char *>(p1)); // expected-error {{redundant const_cast from 'char *' to 'char *', result is implictly cast to 'const char *' [loplugin:redundantcast]}} expected-error {{redundant const_cast from 'char *' to 'char *' [loplugin:redundantcast]}}
-    f2(const_cast<char * const>(p1)); // expected-error {{redundant const_cast from 'char *' to 'char *', result is implictly cast to 'const char *' [loplugin:redundantcast]}} expected-error {{redundant const_cast from 'char *' to 'char *const' [loplugin:redundantcast]}}
+    f2(const_cast<char *>(p1)); // expected-error {{redundant const_cast from 'char *' to 'char *' [loplugin:redundantcast]}}
+    f2(const_cast<char * const>(p1)); //  expected-error {{redundant const_cast from 'char *' to 'char *const' [loplugin:redundantcast]}}
     f2(const_cast<char const *>(p1));
     f2(const_cast<char const * const>(p1));
     f2(const_cast<char *>(p2)); // expected-error {{redundant const_cast from 'const char *' to 'char *', result is implictly cast to 'const char *' [loplugin:redundantcast]}}