[Typechecker] We could also have a subscript when diagnosing SettableConflict, so guard against that

Author: theblixguy

lib/Sema/TypeCheckProtocol.cpp

@@ -2116,10 +2116,11 @@ diagnoseMatch(ModuleDecl *module, NormalProtocolConformance *conformance,
     auto witness = match.Witness;
     auto diag =
         diags.diagnose(witness, diag::protocol_witness_settable_conflict);
-    auto VD = cast<VarDecl>(witness);
-    if (VD->hasStorage()) {
-      auto PBD = VD->getParentPatternBinding();
-      diag.fixItReplace(PBD->getStartLoc(), getTokenText(tok::kw_var));
+    if (auto VD = dyn_cast<VarDecl>(witness)) {
+      if (VD->hasStorage()) {
+        auto PBD = VD->getParentPatternBinding();
+        diag.fixItReplace(PBD->getStartLoc(), getTokenText(tok::kw_var));
+      }
     }
     break;
   }
@@ -2166,7 +2167,7 @@ diagnoseMatch(ModuleDecl *module, NormalProtocolConformance *conformance,
   case MatchKind::RethrowsConflict: {
     auto witness = match.Witness;
     auto diag =
-        diags.diagnose(match.Witness, diag::protocol_witness_rethrows_conflict);
+        diags.diagnose(witness, diag::protocol_witness_rethrows_conflict);
     auto FD = cast<FuncDecl>(witness);
     diag.fixItReplace(FD->getThrowsLoc(), getTokenText(tok::kw_rethrows));
     break;

test/decl/protocol/req/witness_fix_its.swift

@@ -26,3 +26,11 @@ struct ConformsToFoo: Foo { // expected-error {{type 'ConformsToFoo' does not co
   var bar5: Int { return 0 } // expected-note {{candidate is not settable, but protocol requires it}}{{none}}
   subscript(_ pos: Int) -> Int { return 0 } // expected-note {{candidate operates on an instance, not a type as required}}{{3-3=static}}
 }
+
+protocol Foo1 {
+  subscript(value: Bool) -> Bool { get set } // expected-note {{protocol requires subscript with type '(Bool) -> Bool'; do you want to add a stub?}}
+}
+
+struct ConformsToFoo1: Foo1 { // expected-error {{type 'ConformsToFoo1' does not conform to protocol 'Foo1'}}
+  subscript(value: Bool) -> Bool { return false } // expected-note {{candidate is not settable, but protocol requires it}}{{none}}
+}