[clang-tidy] fix PR39583 - ignoring ParenCast for string-literals in pro-bounds-array-to-pointer-decay

[JonasToth]

Summary

The fix to the issue that const char* p = ("foo") is diagnosed as decay
is to ignored the ParenCast.
Resolves PR39583

[aaron.ballman]

clang-tidy/cppcoreguidelines/ProBoundsArrayToPointerDecayCheck.cpp

65

I think you want ignoringParens() instead, no?

[JonasToth]

clang-tidy/cppcoreguidelines/ProBoundsArrayToPointerDecayCheck.cpp

65

That doesn't seem to compile, it only applies to QualType. There is ignoringParenCasts and ignoringParenImpCasts that match on everything. Ignoring the imp-casts is not what we want.

[aaron.ballman]

clang-tidy/cppcoreguidelines/ProBoundsArrayToPointerDecayCheck.cpp

65

Neither is ignoring the paren casts because that covers actual casts like reinterpret_cast. There is an Expr::IgnoreParens(), so I'm betting that the ignoringParens() matcher just needs an overload for Expr.

[JonasToth]

• use ignoringParens instead

[aaron.ballman]

LGTM aside from a minor commenting nit.

test/clang-tidy/cppcoreguidelines-pro-bounds-array-to-pointer-decay.cpp

44

Remove "Cast" as this is not a cast. It's a ParenExpr.

[JonasToth]

• use ignoringParens instead

[JonasToth]

• fix comment

clang-tidy/cppcoreguidelines/ProBoundsArrayToPointerDecayCheck.cpp

void ProBoundsArrayToPointerDecayCheck::registerMatchers(MatchFinder *Finder) {
   if (!getLangOpts().CPlusPlus)
     return;
 
   // The only allowed array to pointer decay
   // 1) just before array subscription
   // 2) inside a range-for over an array
   // 3) if it converts a string literal to a pointer
   Finder->addMatcher(
-      implicitCastExpr(unless(hasParent(arraySubscriptExpr())),
-                       unless(hasParentIgnoringImpCasts(explicitCastExpr())),
-                       unless(isInsideOfRangeBeginEndStmt()),
-                       unless(hasSourceExpression(stringLiteral())))
+      implicitCastExpr(
+          unless(hasParent(arraySubscriptExpr())),
+          unless(hasSourceExpression(ignoringParens(stringLiteral()))))
           .bind("cast"),
       this);
 }
 
 void ProBoundsArrayToPointerDecayCheck::check(
     const MatchFinder::MatchResult &Result) {
   const auto *MatchedCast = Result.Nodes.getNodeAs<ImplicitCastExpr>("cast");
   if (MatchedCast->getCastKind() != CK_ArrayToPointerDecay)

test/clang-tidy/cppcoreguidelines-pro-bounds-array-to-pointer-decay.cpp

void f() {
 
   pointerfun(a + s() - 10); // Convert to &a[g() - 10];
   // CHECK-MESSAGES: :[[@LINE-1]]:14: warning: do not implicitly decay an array into a pointer
 
   gsl::array_view<int> av(a);
   arrayviewfun(av); // OK
 
   int i = a[0];      // OK
+  int j = a[(1 + 2)];// OK
   pointerfun(&a[0]); // OK
 
   for (auto &e : a) // OK, iteration internally decays array to pointer
     e = 1;
 }
 
 const char *g() {
   return "clang"; // OK, decay string literal to pointer
 }
+const char *g2() {
+    return ("clang"); // OK, ParenCast hides the literal-pointer decay
+}
 
 void f2(void *const *);
 void bug25362() {
   void *a[2];
   f2(static_cast<void *const*>(a)); // OK, explicit cast
 }