Relate non-augmenting subtypes without resorting to structural comparison

src/compiler/checker.ts

@@ -17195,12 +17195,13 @@ namespace ts {
 
         function getNormalizedType(type: Type, writing: boolean): Type {
             while (true) {
-                const t = isFreshLiteralType(type) ? (<FreshableType>type).regularType :
+                let t = isFreshLiteralType(type) ? (<FreshableType>type).regularType :
                     getObjectFlags(type) & ObjectFlags.Reference && (<TypeReference>type).node ? createTypeReference((<TypeReference>type).target, getTypeArguments(<TypeReference>type)) :
                     type.flags & TypeFlags.UnionOrIntersection ? getReducedType(type) :
                     type.flags & TypeFlags.Substitution ? writing ? (<SubstitutionType>type).baseType : (<SubstitutionType>type).substitute :
                     type.flags & TypeFlags.Simplifiable ? getSimplifiedType(type, writing) :
                     type;
+                t = getSingleBaseForNonAugmentingSubtype(t) || t;
                 if (t === type) break;
                 type = t;
             }
@@ -17702,8 +17703,10 @@ namespace ts {
 
                 function reportErrorResults(source: Type, target: Type, result: Ternary, isComparingJsxAttributes: boolean) {
                     if (!result && reportErrors) {
-                        source = originalSource.aliasSymbol ? originalSource : source;
-                        target = originalTarget.aliasSymbol ? originalTarget : target;
+                        const sourceHasBase = !!getSingleBaseForNonAugmentingSubtype(originalSource);
+                        const targetHasBase = !!getSingleBaseForNonAugmentingSubtype(originalTarget);
+                        source = (originalSource.aliasSymbol || sourceHasBase) ? originalSource : source;
+                        target = (originalTarget.aliasSymbol || targetHasBase) ? originalTarget : target;
                         let maybeSuppress = overrideNextErrorInfo > 0;
                         if (maybeSuppress) {
                             overrideNextErrorInfo--;
@@ -19956,6 +19959,30 @@ namespace ts {
             return isArrayType(type) || !(type.flags & TypeFlags.Nullable) && isTypeAssignableTo(type, anyReadonlyArrayType);
         }
 
+        function getSingleBaseForNonAugmentingSubtype(type: Type) {
+            if (!(getObjectFlags(type) & ObjectFlags.Reference) || !(getObjectFlags((type as TypeReference).target) & ObjectFlags.ClassOrInterface)) {
+                return undefined;
+            }
+            if (getObjectFlags(type) & ObjectFlags.IdenticalBaseTypeCalculated) {
+                return getObjectFlags(type) & ObjectFlags.IdenticalBaseTypeExists ? (type as TypeReference).cachedEquivalentBaseType : undefined;
+            }
+            (type as TypeReference).objectFlags |= ObjectFlags.IdenticalBaseTypeCalculated;
+            const target = (type as TypeReference).target as InterfaceType;
+            const bases = getBaseTypes(target);
+            if (bases.length !== 1) {
+                return undefined;
+            }
+            if (getMembersOfSymbol(type.symbol).size) {
+                return undefined; // If the interface has any members, they may subtype members in the base, so we should do a full structural comparison
+            }
+            let instantiatedBase = !length(target.typeParameters) ? bases[0] : instantiateType(bases[0], createTypeMapper(target.typeParameters!, getTypeArguments(type as TypeReference).slice(0, target.typeParameters!.length)));
+            if (length(getTypeArguments(type as TypeReference)) > length(target.typeParameters)) {
+                instantiatedBase = getTypeWithThisArgument(instantiatedBase, last(getTypeArguments(type as TypeReference)));
+            }
+            (type as TypeReference).objectFlags |= ObjectFlags.IdenticalBaseTypeExists;
+            return (type as TypeReference).cachedEquivalentBaseType = instantiatedBase;
+        }
+
         function isEmptyArrayLiteralType(type: Type): boolean {
             const elementType = getElementTypeOfArrayType(type);
             return strictNullChecks ? elementType === implicitNeverType : elementType === undefinedWideningType;

src/compiler/types.ts

@@ -5220,6 +5220,12 @@ namespace ts {
         IsNeverIntersectionComputed = 1 << 26, // IsNeverLike flag has been computed
         /* @internal */
         IsNeverIntersection = 1 << 27, // Intersection reduces to never
+
+        // Flags that require TypeFlags.Reference
+        /* @internal */
+        IdenticalBaseTypeCalculated = 1 << 26, // has had `getSingleBaseForNonAugmentingSubtype` invoked on it already
+        /* @internal */
+        IdenticalBaseTypeExists = 1 << 27, // has a defined cachedEquivalentBaseType member
     }
 
     /* @internal */
@@ -5281,6 +5287,8 @@ namespace ts {
         resolvedTypeArguments?: readonly Type[];  // Resolved type reference type arguments
         /* @internal */
         literalType?: TypeReference;  // Clone of type with ObjectFlags.ArrayLiteral set
+        /* @internal */
+        cachedEquivalentBaseType?: Type; // Only set on references to class or interfaces with a single base type and no augmentations
     }
 
     export interface DeferredTypeReference extends TypeReference {

tests/baselines/reference/arrayLiterals3.errors.txt

@@ -8,9 +8,8 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(17,5): error
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(33,5): error TS2322: Type 'number[]' is not assignable to type '[number, number, number]'.
   Target requires 3 element(s) but source may have fewer.
 tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error TS2322: Type '(string | number)[]' is not assignable to type 'myArray'.
-  The types returned by 'pop()' are incompatible between these types.
-    Type 'string | number' is not assignable to type 'Number'.
-      Type 'string' is not assignable to type 'Number'.
+  Type 'string | number' is not assignable to type 'Number'.
+    Type 'string' is not assignable to type 'Number'.
 
 
 ==== tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts (7 errors) ====
@@ -65,7 +64,6 @@ tests/cases/conformance/expressions/arrayLiterals/arrayLiterals3.ts(34,5): error
     var c2: myArray = [...temp1, ...temp];            // Error cannot assign (number|string)[] to number[]
         ~~
 !!! error TS2322: Type '(string | number)[]' is not assignable to type 'myArray'.
-!!! error TS2322:   The types returned by 'pop()' are incompatible between these types.
-!!! error TS2322:     Type 'string | number' is not assignable to type 'Number'.
-!!! error TS2322:       Type 'string' is not assignable to type 'Number'.
+!!! error TS2322:   Type 'string | number' is not assignable to type 'Number'.
+!!! error TS2322:     Type 'string' is not assignable to type 'Number'.
 

tests/baselines/reference/assignmentCompatWithObjectMembersAccessibility.errors.txt

@@ -17,7 +17,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(81,5): error TS2322: Type 'Base' is not assignable to type '{ foo: string; }'.
   Property 'foo' is private in type 'Base' but not in type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(82,5): error TS2322: Type 'I' is not assignable to type '{ foo: string; }'.
-  Property 'foo' is private in type 'I' but not in type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(84,5): error TS2322: Type 'E' is not assignable to type '{ foo: string; }'.
   Property 'foo' is private in type 'E' but not in type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(86,5): error TS2322: Type '{ foo: string; }' is not assignable to type 'Base'.
@@ -27,23 +26,18 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(89,5): error TS2322: Type 'E' is not assignable to type 'Base'.
   Types have separate declarations of a private property 'foo'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(92,5): error TS2322: Type '{ foo: string; }' is not assignable to type 'I'.
-  Property 'foo' is private in type 'I' but not in type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(94,5): error TS2322: Type 'D' is not assignable to type 'I'.
-  Property 'foo' is private in type 'I' but not in type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(95,5): error TS2322: Type 'E' is not assignable to type 'I'.
-  Types have separate declarations of a private property 'foo'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(99,5): error TS2322: Type 'Base' is not assignable to type 'D'.
   Property 'foo' is private in type 'Base' but not in type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(100,5): error TS2322: Type 'I' is not assignable to type 'D'.
-  Property 'foo' is private in type 'I' but not in type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(101,5): error TS2322: Type 'E' is not assignable to type 'D'.
   Property 'foo' is private in type 'E' but not in type 'D'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(103,5): error TS2322: Type '{ foo: string; }' is not assignable to type 'E'.
   Property 'foo' is private in type 'E' but not in type '{ foo: string; }'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(104,5): error TS2322: Type 'Base' is not assignable to type 'E'.
   Types have separate declarations of a private property 'foo'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(105,5): error TS2322: Type 'I' is not assignable to type 'E'.
-  Types have separate declarations of a private property 'foo'.
 tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignmentCompatWithObjectMembersAccessibility.ts(106,5): error TS2322: Type 'D' is not assignable to type 'E'.
   Property 'foo' is private in type 'E' but not in type 'D'.
 
@@ -160,7 +154,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         a = i; // error
         ~
 !!! error TS2322: Type 'I' is not assignable to type '{ foo: string; }'.
-!!! error TS2322:   Property 'foo' is private in type 'I' but not in type '{ foo: string; }'.
         a = d;
         a = e; // error
         ~
@@ -185,16 +178,13 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         i = a; // error
         ~
 !!! error TS2322: Type '{ foo: string; }' is not assignable to type 'I'.
-!!! error TS2322:   Property 'foo' is private in type 'I' but not in type '{ foo: string; }'.
         i = b;
         i = d; // error
         ~
 !!! error TS2322: Type 'D' is not assignable to type 'I'.
-!!! error TS2322:   Property 'foo' is private in type 'I' but not in type 'D'.
         i = e; // error
         ~
 !!! error TS2322: Type 'E' is not assignable to type 'I'.
-!!! error TS2322:   Types have separate declarations of a private property 'foo'.
         i = i;
 
         d = a;
@@ -205,7 +195,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         d = i; // error
         ~
 !!! error TS2322: Type 'I' is not assignable to type 'D'.
-!!! error TS2322:   Property 'foo' is private in type 'I' but not in type 'D'.
         d = e; // error
         ~
 !!! error TS2322: Type 'E' is not assignable to type 'D'.
@@ -222,7 +211,6 @@ tests/cases/conformance/types/typeRelationships/assignmentCompatibility/assignme
         e = i; // errror
         ~
 !!! error TS2322: Type 'I' is not assignable to type 'E'.
-!!! error TS2322:   Types have separate declarations of a private property 'foo'.
         e = d; // errror
         ~
 !!! error TS2322: Type 'D' is not assignable to type 'E'.

tests/baselines/reference/checkJsxChildrenProperty5.errors.txt

@@ -1,5 +1,5 @@
 tests/cases/conformance/jsx/file.tsx(20,10): error TS2741: Property 'children' is missing in type '{ a: number; b: string; }' but required in type 'Prop'.
-tests/cases/conformance/jsx/file.tsx(25,9): error TS2740: Type 'Element' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
+tests/cases/conformance/jsx/file.tsx(25,9): error TS2740: Type 'ReactElement<any>' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
 tests/cases/conformance/jsx/file.tsx(29,10): error TS2740: Type 'typeof Button' is missing the following properties from type 'Button': render, setState, forceUpdate, props, and 3 more.
 
 
@@ -33,7 +33,7 @@ tests/cases/conformance/jsx/file.tsx(29,10): error TS2740: Type 'typeof Button'
         <Comp a={10} b="hi">
             <Button />
             ~~~~~~~~~~
-!!! error TS2740: Type 'Element' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
+!!! error TS2740: Type 'ReactElement<any>' is missing the following properties from type 'Button': render, setState, forceUpdate, state, and 2 more.
 !!! related TS6500 tests/cases/conformance/jsx/file.tsx:6:5: The expected type comes from property 'children' which is declared here on type 'IntrinsicAttributes & Prop'
         </Comp>;
     let k2 =

tests/baselines/reference/classImplementsClass4.errors.txt

@@ -1,6 +1,6 @@
 tests/cases/compiler/classImplementsClass4.ts(5,7): error TS2720: Class 'C' incorrectly implements class 'A'. Did you mean to extend 'A' and inherit its members as a subclass?
   Property 'x' is missing in type 'C' but required in type 'A'.
-tests/cases/compiler/classImplementsClass4.ts(16,1): error TS2741: Property 'x' is missing in type 'C' but required in type 'C2'.
+tests/cases/compiler/classImplementsClass4.ts(16,1): error TS2741: Property 'x' is missing in type 'C' but required in type 'A'.
 
 
 ==== tests/cases/compiler/classImplementsClass4.ts (2 errors) ====
@@ -25,5 +25,5 @@ tests/cases/compiler/classImplementsClass4.ts(16,1): error TS2741: Property 'x'
     c = c2;
     c2 = c;
     ~~
-!!! error TS2741: Property 'x' is missing in type 'C' but required in type 'C2'.
+!!! error TS2741: Property 'x' is missing in type 'C' but required in type 'A'.
 !!! related TS2728 tests/cases/compiler/classImplementsClass4.ts:2:13: 'x' is declared here.

tests/baselines/reference/crashInsourcePropertyIsRelatableToTargetProperty.errors.txt

@@ -1,4 +1,4 @@
-tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts(9,5): error TS2741: Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'D'.
+tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts(9,5): error TS2741: Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'C'.
 
 
 ==== tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts (1 errors) ====
@@ -12,6 +12,6 @@ tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts(9,5): e
     }
     var a: D = foo("hi", []);
         ~
-!!! error TS2741: Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'D'.
+!!! error TS2741: Property 'x' is missing in type '(x: "hi", items: string[]) => typeof foo' but required in type 'C'.
 !!! related TS2728 tests/cases/compiler/crashInsourcePropertyIsRelatableToTargetProperty.ts:2:13: 'x' is declared here.
 

tests/baselines/reference/implementingAnInterfaceExtendingClassWithProtecteds.errors.txt

@@ -7,7 +7,7 @@ tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInte
 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts(21,7): error TS2420: Class 'Bar4' incorrectly implements interface 'I'.
   Property 'x' is protected but type 'Bar4' is not a class derived from 'Foo'.
 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts(26,7): error TS2420: Class 'Bar5' incorrectly implements interface 'I'.
-  Property 'y' is missing in type 'Bar5' but required in type 'I'.
+  Property 'y' is missing in type 'Foo' but required in type 'I'.
 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts(29,7): error TS2420: Class 'Bar6' incorrectly implements interface 'I'.
   Property 'y' is protected in type 'Bar6' but public in type 'I'.
 
@@ -54,7 +54,7 @@ tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInte
     class Bar5 extends Foo implements I { // error
           ~~~~
 !!! error TS2420: Class 'Bar5' incorrectly implements interface 'I'.
-!!! error TS2420:   Property 'y' is missing in type 'Bar5' but required in type 'I'.
+!!! error TS2420:   Property 'y' is missing in type 'Foo' but required in type 'I'.
 !!! related TS2728 tests/cases/conformance/interfaces/interfacesExtendingClasses/implementingAnInterfaceExtendingClassWithProtecteds.ts:6:5: 'y' is declared here.
     }