Fix issue in findMatchingDiscriminantType (#1800)

Author: ahejlsberg

internal/checker/relater.go

@@ -1052,11 +1052,11 @@ func (c *Checker) findMatchingDiscriminantType(source *Type, target *Type, isRel
 		if match := c.getMatchingUnionConstituentForType(target, source); match != nil {
 			return match
 		}
-		discriminantProperties := c.findDiscriminantProperties(c.getPropertiesOfType(source), target)
-		discriminator := &TypeDiscriminator{c: c, props: discriminantProperties, isRelatedTo: isRelatedTo}
-		discriminated := c.discriminateTypeByDiscriminableItems(target, discriminator)
-		if discriminated != target {
-			return discriminated
+		if discriminantProperties := c.findDiscriminantProperties(c.getPropertiesOfType(source), target); len(discriminantProperties) != 0 {
+			discriminator := &TypeDiscriminator{c: c, props: discriminantProperties, isRelatedTo: isRelatedTo}
+			if discriminated := c.discriminateTypeByDiscriminableItems(target, discriminator); discriminated != target {
+				return discriminated
+			}
 		}
 	}
 	return nil

testdata/baselines/reference/submodule/compiler/jsxElementType.errors.txt

@@ -24,9 +24,8 @@ jsxElementType.tsx(78,1): error TS2339: Property 'boop' does not exist on type '
 jsxElementType.tsx(79,1): error TS2339: Property 'my-undeclared-custom-element' does not exist on type 'JSX.IntrinsicElements'.
 jsxElementType.tsx(91,2): error TS2786: 'ReactNativeFlatList' cannot be used as a JSX component.
   Its type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not a valid JSX element type.
-    Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '((props: any) => React18ReactNode) | (new (props: any) => Component<any, any, any>)'.
-      Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '(props: any) => React18ReactNode'.
-        Target signature provides too few arguments. Expected 2 or more, but got 1.
+    Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '(props: any) => React18ReactNode'.
+      Target signature provides too few arguments. Expected 2 or more, but got 1.
 jsxElementType.tsx(95,11): error TS2322: Type '{}' is not assignable to type 'LibraryManagedAttributes<T, {}>'.
 jsxElementType.tsx(98,2): error TS2304: Cannot find name 'Unresolved'.
 jsxElementType.tsx(99,2): error TS2304: Cannot find name 'Unresolved'.
@@ -177,9 +176,8 @@ jsxElementType.tsx(111,19): error TS2322: Type '{ a: string; b: string; }' is no
      ~~~~~~~~~~~~~~~~~~~
 !!! error TS2786: 'ReactNativeFlatList' cannot be used as a JSX component.
 !!! error TS2786:   Its type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not a valid JSX element type.
-!!! error TS2786:     Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '((props: any) => React18ReactNode) | (new (props: any) => Component<any, any, any>)'.
-!!! error TS2786:       Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '(props: any) => React18ReactNode'.
-!!! error TS2786:         Target signature provides too few arguments. Expected 2 or more, but got 1.
+!!! error TS2786:     Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '(props: any) => React18ReactNode'.
+!!! error TS2786:       Target signature provides too few arguments. Expected 2 or more, but got 1.
 
     // testing higher-order component compat
     function f1<T extends (props: {}) => React.ReactElement<any>>(Component: T) {

testdata/baselines/reference/submodule/compiler/jsxElementType.errors.txt.diff

@@ -18,18 +18,7 @@
      Type '{ excessProp: true; }' is not assignable to type 'IntrinsicAttributes & IntrinsicClassAttributes<RenderStringClass> & Readonly<{ children?: ReactNode; }> & Readonly<{ title: string; }>'.
        Property 'excessProp' does not exist on type 'IntrinsicAttributes & IntrinsicClassAttributes<RenderStringClass> & Readonly<{ children?: ReactNode; }> & Readonly<{ title: string; }>'.
  jsxElementType.tsx(78,1): error TS2339: Property 'boop' does not exist on type 'JSX.IntrinsicElements'.
- jsxElementType.tsx(79,1): error TS2339: Property 'my-undeclared-custom-element' does not exist on type 'JSX.IntrinsicElements'.
- jsxElementType.tsx(91,2): error TS2786: 'ReactNativeFlatList' cannot be used as a JSX component.
-   Its type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not a valid JSX element type.
--    Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '(props: any) => React18ReactNode'.
--      Target signature provides too few arguments. Expected 2 or more, but got 1.
-+    Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '((props: any) => React18ReactNode) | (new (props: any) => Component<any, any, any>)'.
-+      Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '(props: any) => React18ReactNode'.
-+        Target signature provides too few arguments. Expected 2 or more, but got 1.
- jsxElementType.tsx(95,11): error TS2322: Type '{}' is not assignable to type 'LibraryManagedAttributes<T, {}>'.
- jsxElementType.tsx(98,2): error TS2304: Cannot find name 'Unresolved'.
- jsxElementType.tsx(99,2): error TS2304: Cannot find name 'Unresolved'.
-@@= skipped -129, +125 lines =@@
+@@= skipped -129, +124 lines =@@
      <RenderStringClass />;
       ~~~~~~~~~~~~~~~~~
  !!! error TS2769: No overload matches this call.
@@ -59,16 +48,4 @@
 +!!! related TS2771 react16.d.ts:357:13: The last overload is declared here.
 
      // Host element types still work
-     <div />;
-@@= skipped -42, +38 lines =@@
-      ~~~~~~~~~~~~~~~~~~~
- !!! error TS2786: 'ReactNativeFlatList' cannot be used as a JSX component.
- !!! error TS2786:   Its type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not a valid JSX element type.
--!!! error TS2786:     Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '(props: any) => React18ReactNode'.
--!!! error TS2786:       Target signature provides too few arguments. Expected 2 or more, but got 1.
-+!!! error TS2786:     Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '((props: any) => React18ReactNode) | (new (props: any) => Component<any, any, any>)'.
-+!!! error TS2786:       Type '(props: {}, ref: ForwardedRef<typeof ReactNativeFlatList>) => null' is not assignable to type '(props: any) => React18ReactNode'.
-+!!! error TS2786:         Target signature provides too few arguments. Expected 2 or more, but got 1.
-     
-     // testing higher-order component compat
-     function f1<T extends (props: {}) => React.ReactElement<any>>(Component: T) {
+     <div />;

testdata/baselines/reference/submodule/compiler/jsxFragmentWrongType.errors.txt

@@ -1,9 +1,7 @@
 a.tsx(6,28): error TS2322: Type '{ children: () => string; }' is not assignable to type '{ children?: ReactNode; }'.
   Types of property 'children' are incompatible.
     Type '() => string' is not assignable to type 'ReactNode'.
-      Type '() => string' is not assignable to type 'ReactElement<any, string | JSXElementConstructor<any>> | ReactFragment | ReactPortal'.
 a.tsx(7,47): error TS2322: Type '() => string' is not assignable to type 'ReactNode'.
-  Type '() => string' is not assignable to type 'ReactElement<any, string | JSXElementConstructor<any>> | ReactFragment | ReactPortal'.
 
 
 ==== a.tsx (2 errors) ====
@@ -17,10 +15,8 @@ a.tsx(7,47): error TS2322: Type '() => string' is not assignable to type 'ReactN
 !!! error TS2322: Type '{ children: () => string; }' is not assignable to type '{ children?: ReactNode; }'.
 !!! error TS2322:   Types of property 'children' are incompatible.
 !!! error TS2322:     Type '() => string' is not assignable to type 'ReactNode'.
-!!! error TS2322:       Type '() => string' is not assignable to type 'ReactElement<any, string | JSXElementConstructor<any>> | ReactFragment | ReactPortal'.
     const jsxWithReactFragment = <React.Fragment>{test}</React.Fragment>;
                                                   ~~~~
 !!! error TS2322: Type '() => string' is not assignable to type 'ReactNode'.
-!!! error TS2322:   Type '() => string' is not assignable to type 'ReactElement<any, string | JSXElementConstructor<any>> | ReactFragment | ReactPortal'.
 !!! related TS6212 a.tsx:7:47: Did you mean to call this expression?
 

testdata/baselines/reference/submodule/compiler/jsxFragmentWrongType.errors.txt.diff

@@ -3,34 +3,20 @@ potentiallyUncalledDecorators.ts(35,1): error TS1329: 'noArgs' accepts too few a
 potentiallyUncalledDecorators.ts(37,5): error TS1329: 'noArgs' accepts too few arguments to be used as a decorator here. Did you mean to call it first and write '@noArgs()'?
 potentiallyUncalledDecorators.ts(38,5): error TS1329: 'noArgs' accepts too few arguments to be used as a decorator here. Did you mean to call it first and write '@noArgs()'?
 potentiallyUncalledDecorators.ts(41,2): error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof B'.
-  Type 'OmniDecorator' is not assignable to type 'typeof B'.
-    Type 'OmniDecorator' provides no match for the signature 'new (): B'.
 potentiallyUncalledDecorators.ts(43,6): error TS1271: Decorator function return type is 'OmniDecorator' but is expected to be 'void' or 'any'.
 potentiallyUncalledDecorators.ts(44,6): error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | TypedPropertyDescriptor<() => void>'.
-  Type 'OmniDecorator' has no properties in common with type 'TypedPropertyDescriptor<() => void>'.
 potentiallyUncalledDecorators.ts(47,2): error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof C'.
-  Type 'OmniDecorator' is not assignable to type 'typeof C'.
-    Type 'OmniDecorator' provides no match for the signature 'new (): C'.
 potentiallyUncalledDecorators.ts(49,5): error TS1329: 'oneOptional' accepts too few arguments to be used as a decorator here. Did you mean to call it first and write '@oneOptional()'?
 potentiallyUncalledDecorators.ts(50,5): error TS1329: 'oneOptional' accepts too few arguments to be used as a decorator here. Did you mean to call it first and write '@oneOptional()'?
 potentiallyUncalledDecorators.ts(53,2): error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof D'.
-  Type 'OmniDecorator' is not assignable to type 'typeof D'.
-    Type 'OmniDecorator' provides no match for the signature 'new (): D'.
 potentiallyUncalledDecorators.ts(55,6): error TS1271: Decorator function return type is 'OmniDecorator' but is expected to be 'void' or 'any'.
 potentiallyUncalledDecorators.ts(56,6): error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | TypedPropertyDescriptor<() => void>'.
-  Type 'OmniDecorator' has no properties in common with type 'TypedPropertyDescriptor<() => void>'.
 potentiallyUncalledDecorators.ts(59,2): error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof E'.
-  Type 'OmniDecorator' is not assignable to type 'typeof E'.
-    Type 'OmniDecorator' provides no match for the signature 'new (): E'.
 potentiallyUncalledDecorators.ts(61,6): error TS1271: Decorator function return type is 'OmniDecorator' but is expected to be 'void' or 'any'.
 potentiallyUncalledDecorators.ts(62,6): error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | TypedPropertyDescriptor<() => void>'.
-  Type 'OmniDecorator' has no properties in common with type 'TypedPropertyDescriptor<() => void>'.
 potentiallyUncalledDecorators.ts(65,2): error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof F'.
-  Type 'OmniDecorator' is not assignable to type 'typeof F'.
-    Type 'OmniDecorator' provides no match for the signature 'new (): F'.
 potentiallyUncalledDecorators.ts(67,6): error TS1271: Decorator function return type is 'OmniDecorator' but is expected to be 'void' or 'any'.
 potentiallyUncalledDecorators.ts(68,6): error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | TypedPropertyDescriptor<() => void>'.
-  Type 'OmniDecorator' has no properties in common with type 'TypedPropertyDescriptor<() => void>'.
 
 
 ==== potentiallyUncalledDecorators.ts (19 errors) ====
@@ -85,23 +71,18 @@ potentiallyUncalledDecorators.ts(68,6): error TS1270: Decorator function return
     @allRest
      ~~~~~~~
 !!! error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof B'.
-!!! error TS1270:   Type 'OmniDecorator' is not assignable to type 'typeof B'.
-!!! error TS1270:     Type 'OmniDecorator' provides no match for the signature 'new (): B'.
     class B {
         @allRest foo: any;
          ~~~~~~~
 !!! error TS1271: Decorator function return type is 'OmniDecorator' but is expected to be 'void' or 'any'.
         @allRest bar() { }
          ~~~~~~~
 !!! error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | TypedPropertyDescriptor<() => void>'.
-!!! error TS1270:   Type 'OmniDecorator' has no properties in common with type 'TypedPropertyDescriptor<() => void>'.
     }
 
     @oneOptional
      ~~~~~~~~~~~
 !!! error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof C'.
-!!! error TS1270:   Type 'OmniDecorator' is not assignable to type 'typeof C'.
-!!! error TS1270:     Type 'OmniDecorator' provides no match for the signature 'new (): C'.
     class C {
         @oneOptional foo: any;
         ~~~~~~~~~~~~
@@ -114,46 +95,37 @@ potentiallyUncalledDecorators.ts(68,6): error TS1270: Decorator function return
     @twoOptional
      ~~~~~~~~~~~
 !!! error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof D'.
-!!! error TS1270:   Type 'OmniDecorator' is not assignable to type 'typeof D'.
-!!! error TS1270:     Type 'OmniDecorator' provides no match for the signature 'new (): D'.
     class D {
         @twoOptional foo: any;
          ~~~~~~~~~~~
 !!! error TS1271: Decorator function return type is 'OmniDecorator' but is expected to be 'void' or 'any'.
         @twoOptional bar() { }
          ~~~~~~~~~~~
 !!! error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | TypedPropertyDescriptor<() => void>'.
-!!! error TS1270:   Type 'OmniDecorator' has no properties in common with type 'TypedPropertyDescriptor<() => void>'.
     }
 
     @threeOptional
      ~~~~~~~~~~~~~
 !!! error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof E'.
-!!! error TS1270:   Type 'OmniDecorator' is not assignable to type 'typeof E'.
-!!! error TS1270:     Type 'OmniDecorator' provides no match for the signature 'new (): E'.
     class E {
         @threeOptional foo: any;
          ~~~~~~~~~~~~~
 !!! error TS1271: Decorator function return type is 'OmniDecorator' but is expected to be 'void' or 'any'.
         @threeOptional bar() { }
          ~~~~~~~~~~~~~
 !!! error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | TypedPropertyDescriptor<() => void>'.
-!!! error TS1270:   Type 'OmniDecorator' has no properties in common with type 'TypedPropertyDescriptor<() => void>'.
     }
 
     @oneOptionalWithRest
      ~~~~~~~~~~~~~~~~~~~
 !!! error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | typeof F'.
-!!! error TS1270:   Type 'OmniDecorator' is not assignable to type 'typeof F'.
-!!! error TS1270:     Type 'OmniDecorator' provides no match for the signature 'new (): F'.
     class F {
         @oneOptionalWithRest foo: any;
          ~~~~~~~~~~~~~~~~~~~
 !!! error TS1271: Decorator function return type is 'OmniDecorator' but is expected to be 'void' or 'any'.
         @oneOptionalWithRest bar() { }
          ~~~~~~~~~~~~~~~~~~~
 !!! error TS1270: Decorator function return type 'OmniDecorator' is not assignable to type 'void | TypedPropertyDescriptor<() => void>'.
-!!! error TS1270:   Type 'OmniDecorator' has no properties in common with type 'TypedPropertyDescriptor<() => void>'.
     }
 
     @anyDec