[CS] Avoid crashing if we have no contextual type for initialization

For `CTP_Initialization`, there's no contextual
type to record if the pattern is not a
`TypedPattern`. As such, tweak
`RequirementFailure::getDeclRef` to handle this
case.

We probably ought to reconsider how we handle
contextual types here, using a ContextualType
locator when there is no contextual type recorded
seems a bit weird, though in most cases we want
to treat initializations the same regardless of
if a TypedPattern was used. For now I'm leaving
that as future work.

rdar://111009224

Author: hamishknight

lib/Sema/CSDiagnostics.cpp

@@ -313,7 +313,21 @@ ValueDecl *RequirementFailure::getDeclRef() const {
       return cast<ValueDecl>(getDC()->getParent()->getAsDecl());
     }
 
-    return getAffectedDeclFromType(contextualTy);
+    // We check for a contextual type here because we form a
+    // ContextualType(CTP_Initialization) LocatorPathElt for pattern bindings
+    // when there is no TypedPattern present. In such a case, there will be
+    // no recorded contextual type (though the pattern may produce a type that
+    // could be considered contextual).
+    if (contextualTy) {
+      // If the contextual type is e.g a tuple, we may not be able to resolve
+      // a decl. Fall through to getting the 'owner type' in that case.
+      if (auto *D = getAffectedDeclFromType(contextualTy))
+        return D;
+    } else {
+      assert((contextualPurpose == CTP_Initialization ||
+              contextualPurpose == CTP_Unused) &&
+             "Should have had a contextual type");
+    }
   }
 
   if (getLocator()->isFirstElement<LocatorPathElt::CoercionOperand>())

test/Constraints/patterns.swift

@@ -658,3 +658,69 @@ enum LotsOfOptional {
 func testLotsOfNil(_ x: LotsOfOptional) {
   if case .yup(nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil) = x {}
 }
+
+// https://github.com/apple/swift/issues/66752
+// FIXME: We ought to improve the diagnostics here
+func issue66752(_ x: Result<String, Error>) {
+  let _ = {
+    if case .failure() = x {}
+    // expected-error@-1 {{type '()' cannot conform to 'Error}}
+    // expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
+    // expected-note@-3 {{required by generic enum 'Result' where 'Failure' = '()'}}
+  }
+  let _ = {
+    if case (.failure(), let y) = (x, 0) {}
+    // expected-error@-1 {{type '()' cannot conform to 'Error}}
+    // expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
+    // expected-note@-3 {{required by generic enum 'Result' where 'Failure' = '()'}}
+  }
+  if case .failure() = x {}
+  // expected-error@-1 {{type '()' cannot conform to 'Error}}
+  // expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
+  // expected-note@-3 {{required by generic enum 'Result' where 'Failure' = '()'}}
+  
+  if case (.failure(), let y) = (x, 0) {}
+  // expected-error@-1 {{type '()' cannot conform to 'Error}}
+  // expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
+  // expected-note@-3 {{required by generic enum 'Result' where 'Failure' = '()'}}
+}
+
+// https://github.com/apple/swift/issues/66750
+// FIXME: We ought to improve the diagnostics here
+func issue66750(_ x: Result<String, Error>) {
+  let _ = {
+    switch x {
+    case .success:
+      "a"
+    case .failure():
+      // expected-error@-1 {{type '()' cannot conform to 'Error}}
+      // expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
+      // expected-note@-3 {{required by generic enum 'Result' where 'Failure' = '()'}}
+      "b"
+    }
+  }
+  let _ = {
+    switch (x, 0) {
+    case (.success, let y):
+      "a"
+    case (.failure(), let y):
+      // expected-error@-1 {{type '()' cannot conform to 'Error}}
+      // expected-note@-2 {{only concrete types such as structs, enums and classes can conform to protocols}}
+      // expected-note@-3 {{required by generic enum 'Result' where 'Failure' = '()'}}
+      "b"
+    }
+  }
+  switch x {
+  case .success:
+    break
+  case .failure(): // expected-error {{tuple pattern cannot match values of the non-tuple type 'any Error'}}
+    break
+  }
+  switch (x, 0) {
+  case (.success, let y):
+    break
+  case (.failure(), let y):
+    // expected-error@-1 {{tuple pattern cannot match values of the non-tuple type 'any Error'}}
+    break
+  }
+}