loplugin:redundantcast handle dynamic_cast

Change-Id: I7855c76e820efce96778b1c19ec71dffcc4b4abb
Reviewed-on: https://gerrit.libreoffice.org/43621
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 44 insertions, 0 deletions

diff --git a/compilerplugins/clang/redundantcast.cxx b/compilerplugins/clang/redundantcast.cxx
index 30914a460dc4..c28878e9e536 100644
--- a/compilerplugins/clang/redundantcast.cxx
+++ b/compilerplugins/clang/redundantcast.cxx
@@ -128,6 +128,8 @@ public:
 
     bool VisitCXXFunctionalCastExpr(CXXFunctionalCastExpr const * expr);
 
+    bool VisitCXXDynamicCastExpr(CXXDynamicCastExpr const * expr);
+
     bool VisitCallExpr(CallExpr const * expr);
 
     bool VisitCXXDeleteExpr(CXXDeleteExpr const * expr);
@@ -676,6 +678,28 @@ bool RedundantCast::VisitCXXFunctionalCastExpr(CXXFunctionalCastExpr const * exp
     return true;
 }
 
+bool RedundantCast::VisitCXXDynamicCastExpr(CXXDynamicCastExpr const * expr) {
+    if (ignoreLocation(expr)) {
+        return true;
+    }
+    // ignore dynamic_cast<T1>(static_cast<T1>(void*)), it's necessary
+    if (auto subStaticCast = dyn_cast<CXXStaticCastExpr>(expr->getSubExpr())) {
+        if (loplugin::TypeCheck(subStaticCast->getSubExpr()->getType()).Pointer().Void())
+            return true;
+    }
+    // so far this only deals with dynamic casting from T to T
+    auto const sub = compat::getSubExprAsWritten(expr);
+    auto const t1 = expr->getTypeAsWritten();
+    auto const t2 = sub->getType();
+    if (t1.getCanonicalType() != t2.getCanonicalType())
+        return true;
+    report(
+        DiagnosticsEngine::Warning,
+        "redundant dynamic cast from %0 to %1", expr->getExprLoc())
+        << t2 << t1 << expr->getSourceRange();
+    return true;
+}
+
 bool RedundantCast::VisitCallExpr(CallExpr const * expr) {
     if (ignoreLocation(expr)) {
         return true;
diff --git a/compilerplugins/clang/test/redundantcast.cxx b/compilerplugins/clang/test/redundantcast.cxx
index ff3e8392906a..38c44f837cbc 100644
--- a/compilerplugins/clang/test/redundantcast.cxx
+++ b/compilerplugins/clang/test/redundantcast.cxx
@@ -325,6 +325,25 @@ void testReinterpretConstCast() {
     (void) reinterpret_cast<std::size_t>((const_cast<int const *>(&n))); // expected-error-re {{redundant const_cast from 'int *' to 'const int *' within reinterpret_cast to fundamental type 'std::size_t' (aka 'unsigned {{.+}}') [loplugin:redundantcast]}}
 }
 
+void testDynamicCast() {
+
+    struct S1 { virtual ~S1(); };
+    struct S2 final: S1 {};
+    struct S3: S1 {};
+
+    S1 * s1 = nullptr;
+    S2 * s2 = nullptr;
+    void * v1 = nullptr;
+
+    (void) dynamic_cast<S2 *>(s1);
+    (void) dynamic_cast<S1 *>(s2);
+    (void) dynamic_cast<S2 *>(s2); // expected-error {{redundant dynamic cast from 'S2 *' to 'S2 *' [loplugin:redundantcast]}}
+    (void) dynamic_cast<S3 *>(s2);
+    // used in some assert in vcl
+    (void) dynamic_cast<S1 *>(static_cast<S1*>(v1));
+    (void) dynamic_cast<S2 *>(static_cast<S2*>(s1));  // expected-error {{redundant dynamic cast from 'S2 *' to 'S2 *' [loplugin:redundantcast]}}
+}
+
 int main() {
     testConstCast();
     testStaticCast();
@@ -332,6 +351,7 @@ int main() {
     testCStyleCast();
     testCStyleCastOfTemplateMethodResult(nullptr);
     testReinterpretConstCast();
+    testDynamicCast();
 }
 
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