Take array-to-pointer decay into account in loplugin:redundantcast

Change-Id: I3c5bace180605d1a72a74feb1bf9f9b184a16d83
Reviewed-on: https://gerrit.libreoffice.org/63545
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

compilerplugins/clang/redundantcast.cxx

@@ -358,6 +358,28 @@ bool RedundantCast::VisitCXXStaticCastExpr(CXXStaticCastExpr const * expr) {
             << expr->getSourceRange();
         return true;
     }
+    if (auto const impl = dyn_cast<ImplicitCastExpr>(expr->getSubExpr())) {
+        if (impl->getCastKind() == CK_ArrayToPointerDecay && impl->getType() == t2)
+            //TODO: instead of exact QualType match, allow some variation?
+        {
+            auto const fn = handler.getMainFileName();
+            if (!(loplugin::isSamePathname(
+                      fn, SRCDIR "/sal/qa/rtl/strings/test_ostring_concat.cxx")
+                  || loplugin::isSamePathname(
+                      fn, SRCDIR "/sal/qa/rtl/strings/test_ostring_stringliterals.cxx")
+                  || loplugin::isSamePathname(
+                      fn, SRCDIR "/sal/qa/rtl/strings/test_oustring_concat.cxx")
+                  || loplugin::isSamePathname(
+                      fn, SRCDIR "/sal/qa/rtl/strings/test_oustring_stringliterals.cxx")))
+            {
+                report(
+                    DiagnosticsEngine::Warning, "redundant static_cast from %0 to %1",
+                    expr->getExprLoc())
+                    << expr->getSubExprAsWritten()->getType() << t2 << expr->getSourceRange();
+            }
+            return true;
+        }
+    }
     auto const t3 = expr->getType();
     auto const c1 = t1.getCanonicalType();
     auto const c3 = t3.getCanonicalType();
@@ -471,6 +493,30 @@ bool RedundantCast::VisitCXXReinterpretCastExpr(
     if (ignoreLocation(expr)) {
         return true;
     }
+    if (auto const sub = dyn_cast<ImplicitCastExpr>(expr->getSubExpr())) {
+        if (sub->getCastKind() == CK_ArrayToPointerDecay && sub->getType() == expr->getType())
+            //TODO: instead of exact QualType match, allow some variation?
+        {
+            if (loplugin::TypeCheck(sub->getType()).Pointer().Const().Char()) {
+                if (auto const lit = dyn_cast<clang::StringLiteral>(expr->getSubExprAsWritten())) {
+                    if (lit->getKind() == clang::StringLiteral::UTF8) {
+                        // Don't warn about
+                        //
+                        //   redundant_cast<char const *>(u8"...")
+                        //
+                        // in pre-C++2a code:
+                        return true;
+                    }
+                }
+            }
+            report(
+                DiagnosticsEngine::Warning, "redundant reinterpret_cast from %0 to %1",
+                expr->getExprLoc())
+                << expr->getSubExprAsWritten()->getType() << expr->getTypeAsWritten()
+                << expr->getSourceRange();
+            return true;
+        }
+    }
     if (expr->getSubExpr()->getType()->isVoidPointerType()) {
         auto t = expr->getType()->getAs<clang::PointerType>();
         if (t == nullptr || !t->getPointeeType()->isObjectType()) {

compilerplugins/clang/test/redundantcast.cxx

@@ -386,6 +386,12 @@ void testIntermediaryStaticCast() {
     d = int(d) + 1.0; // expected-error {{suspicious functional cast from 'double' to 'int', result is implicitly cast to 'double' [loplugin:redundantcast]}}
 };
 
+void testArrayDecay() {
+    (void) static_cast<char const *>(""); // expected-error {{redundant static_cast from 'const char [1]' to 'const char *' [loplugin:redundantcast]}}
+    (void) reinterpret_cast<char const *>(""); // expected-error {{redundant reinterpret_cast from 'const char [1]' to 'const char *' [loplugin:redundantcast]}}
+    (void) reinterpret_cast<char const *>(u8"");
+}
+
 int main() {
     testConstCast();
     testStaticCast();
@@ -395,6 +401,7 @@ int main() {
     testReinterpretConstCast();
     testDynamicCast();
     testIntermediaryStaticCast();
+    testArrayDecay();
 }
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */

vcl/workben/vcldemo.cxx

@@ -523,8 +523,8 @@ public:
                 const char *mpString;
             } const aRuns[] = {
 #define SET(font,string) { font, reinterpret_cast<const char *>(string) }
-                SET("sans", "a"),           // logical font - no 'sans' font.
-                SET("opensymbol", "#$%"),   // font fallback - $ is missing.
+                {"sans", "a"},           // logical font - no 'sans' font.
+                {"opensymbol", "#$%"},   // font fallback - $ is missing.
                 SET("sans", pInvalid),      // unicode invalid character
                 // tdf#96266 - stacking diacritics
                 SET("carlito", pDiacritic1),