discard never aggregate inferences

src/compiler/checker.ts

@@ -26447,7 +26447,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
         if (inference.indexes) {
             const eraseSelfMapper = makeArrayTypeMapper([constraint.type, typeParameter], [allKeysAllKeysUnknownType, stringNumberSymbolType]);
-            return instantiateType(getIntersectionType(inference.indexes), eraseSelfMapper);
+            const aggregateInference = instantiateType(getIntersectionType(inference.indexes), eraseSelfMapper);
+            if (!(getReducedType(aggregateInference).flags & TypeFlags.Never)) {
+                return aggregateInference;
+            }
         }
         return unknownType;
     }
@@ -26900,8 +26903,6 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                         return;
                     }
                     if (!inference.isFixed) {
-                        // Instantiates instance of `type PartialInference<T, Keys extends string> = ({[K in Keys]: {[K1 in K]: T}})[Keys];`
-                        // Where `T` is `source` and `Keys` is `target.indexType`
                         const partialInferenceTypeSymbol = getGlobalPartialInferenceSymbol();
                         if (partialInferenceTypeSymbol) {
                             if ((target as IndexedAccessType).indexType.flags & TypeFlags.Instantiable) {
@@ -26911,6 +26912,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                                 }
                             }
                             else {
+                                // Instantiates instance of `type PartialInference<T, Keys extends PropertyKey> = ({[K in Keys]: {[K1 in K]: T}})[Keys];`
+                                // Where `T` is `source` and `Keys` is `target.indexType`
                                 inference.indexes = append(inference.indexes, getTypeAliasInstantiation(partialInferenceTypeSymbol, [source, (target as IndexedAccessType).indexType]));
                             }
                         }
@@ -27591,9 +27594,13 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 }
                 else if (inference.indexes) {
                     const eraseSelfMapper = makeUnaryTypeMapper(inference.typeParameter, allKeysUnknownType);
-                    let aggregateInference = instantiateType(getIntersectionType(inference.indexes), mergeTypeMappers(eraseSelfMapper, context.nonFixingMapper));
+                    let aggregateInference: Type | undefined = instantiateType(getIntersectionType(inference.indexes), mergeTypeMappers(eraseSelfMapper, context.nonFixingMapper));
+                    if (getReducedType(aggregateInference).flags & TypeFlags.Never) {
+                        // `never` inference isn't that useful of an inference given its assignable to every other type
+                        aggregateInference = undefined;
+                    }
                     const constraint = getConstraintOfTypeParameter(inference.typeParameter);
-                    if (constraint) {
+                    if (aggregateInference && constraint) {
                         const instantiatedConstraint = instantiateType(constraint, context.nonFixingMapper);
                         if (instantiatedConstraint.flags & TypeFlags.Union && !context.compareTypes(aggregateInference, getTypeWithThisArgument(instantiatedConstraint, aggregateInference))) {
                             const discriminantProps = findDiscriminantProperties(getPropertiesOfType(aggregateInference), instantiatedConstraint);

tests/baselines/reference/indexAccessCombinedInference2.symbols

@@ -0,0 +1,138 @@
+//// [tests/cases/compiler/indexAccessCombinedInference2.ts] ////
+
+=== indexAccessCombinedInference2.ts ===
+type TLArrowShape = {
+>TLArrowShape : Symbol(TLArrowShape, Decl(indexAccessCombinedInference2.ts, 0, 0))
+
+  type: "arrow";
+>type : Symbol(type, Decl(indexAccessCombinedInference2.ts, 0, 21))
+
+  id: string;
+>id : Symbol(id, Decl(indexAccessCombinedInference2.ts, 1, 16))
+
+  x: number;
+>x : Symbol(x, Decl(indexAccessCombinedInference2.ts, 2, 13))
+
+  y: number;
+>y : Symbol(y, Decl(indexAccessCombinedInference2.ts, 3, 12))
+
+  props: {
+>props : Symbol(props, Decl(indexAccessCombinedInference2.ts, 4, 12))
+
+    dir: 1 | -1;
+>dir : Symbol(dir, Decl(indexAccessCombinedInference2.ts, 5, 10))
+
+  };
+};
+
+type NodeShape = {
+>NodeShape : Symbol(NodeShape, Decl(indexAccessCombinedInference2.ts, 8, 2))
+
+  type: "node";
+>type : Symbol(type, Decl(indexAccessCombinedInference2.ts, 10, 18))
+
+  id: string;
+>id : Symbol(id, Decl(indexAccessCombinedInference2.ts, 11, 15))
+
+  x: number;
+>x : Symbol(x, Decl(indexAccessCombinedInference2.ts, 12, 13))
+
+  y: number;
+>y : Symbol(y, Decl(indexAccessCombinedInference2.ts, 13, 12))
+
+  props: {
+>props : Symbol(props, Decl(indexAccessCombinedInference2.ts, 14, 12))
+
+    nodeType: string;
+>nodeType : Symbol(nodeType, Decl(indexAccessCombinedInference2.ts, 15, 10))
+
+  };
+};
+
+type TLShape = TLArrowShape | NodeShape;
+>TLShape : Symbol(TLShape, Decl(indexAccessCombinedInference2.ts, 18, 2))
+>TLArrowShape : Symbol(TLArrowShape, Decl(indexAccessCombinedInference2.ts, 0, 0))
+>NodeShape : Symbol(NodeShape, Decl(indexAccessCombinedInference2.ts, 8, 2))
+
+export type TLShapePartial<T extends TLShape = TLShape> = T extends T
+>TLShapePartial : Symbol(TLShapePartial, Decl(indexAccessCombinedInference2.ts, 20, 40))
+>T : Symbol(T, Decl(indexAccessCombinedInference2.ts, 22, 27))
+>TLShape : Symbol(TLShape, Decl(indexAccessCombinedInference2.ts, 18, 2))
+>TLShape : Symbol(TLShape, Decl(indexAccessCombinedInference2.ts, 18, 2))
+>T : Symbol(T, Decl(indexAccessCombinedInference2.ts, 22, 27))
+>T : Symbol(T, Decl(indexAccessCombinedInference2.ts, 22, 27))
+
+  ? {
+      id: string;
+>id : Symbol(id, Decl(indexAccessCombinedInference2.ts, 23, 5))
+
+      type: T["type"];
+>type : Symbol(type, Decl(indexAccessCombinedInference2.ts, 24, 17))
+>T : Symbol(T, Decl(indexAccessCombinedInference2.ts, 22, 27))
+
+      props?: Partial<T["props"]>;
+>props : Symbol(props, Decl(indexAccessCombinedInference2.ts, 25, 22))
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(indexAccessCombinedInference2.ts, 22, 27))
+
+    } & Partial<Omit<T, "type" | "id" | "props">>
+>Partial : Symbol(Partial, Decl(lib.es5.d.ts, --, --))
+>Omit : Symbol(Omit, Decl(lib.es5.d.ts, --, --))
+>T : Symbol(T, Decl(indexAccessCombinedInference2.ts, 22, 27))
+
+  : never;
+
+declare class Editor {
+>Editor : Symbol(Editor, Decl(indexAccessCombinedInference2.ts, 28, 10))
+
+  updateShape<T extends TLShape = TLShape>(
+>updateShape : Symbol(Editor.updateShape, Decl(indexAccessCombinedInference2.ts, 30, 22))
+>T : Symbol(T, Decl(indexAccessCombinedInference2.ts, 31, 14))
+>TLShape : Symbol(TLShape, Decl(indexAccessCombinedInference2.ts, 18, 2))
+>TLShape : Symbol(TLShape, Decl(indexAccessCombinedInference2.ts, 18, 2))
+
+    partial: TLShapePartial<T> | null | undefined,
+>partial : Symbol(partial, Decl(indexAccessCombinedInference2.ts, 31, 43))
+>TLShapePartial : Symbol(TLShapePartial, Decl(indexAccessCombinedInference2.ts, 20, 40))
+>T : Symbol(T, Decl(indexAccessCombinedInference2.ts, 31, 14))
+
+  ): T;
+>T : Symbol(T, Decl(indexAccessCombinedInference2.ts, 31, 14))
+}
+
+declare const x: number;
+>x : Symbol(x, Decl(indexAccessCombinedInference2.ts, 36, 13))
+
+declare const y: number;
+>y : Symbol(y, Decl(indexAccessCombinedInference2.ts, 37, 13))
+
+declare const editor: Editor;
+>editor : Symbol(editor, Decl(indexAccessCombinedInference2.ts, 38, 13))
+>Editor : Symbol(Editor, Decl(indexAccessCombinedInference2.ts, 28, 10))
+
+declare const node1: NodeShape;
+>node1 : Symbol(node1, Decl(indexAccessCombinedInference2.ts, 40, 13))
+>NodeShape : Symbol(NodeShape, Decl(indexAccessCombinedInference2.ts, 8, 2))
+
+const node2 = editor.updateShape({ ...node1, x, y });
+>node2 : Symbol(node2, Decl(indexAccessCombinedInference2.ts, 41, 5))
+>editor.updateShape : Symbol(Editor.updateShape, Decl(indexAccessCombinedInference2.ts, 30, 22))
+>editor : Symbol(editor, Decl(indexAccessCombinedInference2.ts, 38, 13))
+>updateShape : Symbol(Editor.updateShape, Decl(indexAccessCombinedInference2.ts, 30, 22))
+>node1 : Symbol(node1, Decl(indexAccessCombinedInference2.ts, 40, 13))
+>x : Symbol(x, Decl(indexAccessCombinedInference2.ts, 41, 44))
+>y : Symbol(y, Decl(indexAccessCombinedInference2.ts, 41, 47))
+
+declare const shape1: TLShape;
+>shape1 : Symbol(shape1, Decl(indexAccessCombinedInference2.ts, 43, 13))
+>TLShape : Symbol(TLShape, Decl(indexAccessCombinedInference2.ts, 18, 2))
+
+const shape2 = editor.updateShape({ ...shape1, x, y });
+>shape2 : Symbol(shape2, Decl(indexAccessCombinedInference2.ts, 44, 5))
+>editor.updateShape : Symbol(Editor.updateShape, Decl(indexAccessCombinedInference2.ts, 30, 22))
+>editor : Symbol(editor, Decl(indexAccessCombinedInference2.ts, 38, 13))
+>updateShape : Symbol(Editor.updateShape, Decl(indexAccessCombinedInference2.ts, 30, 22))
+>shape1 : Symbol(shape1, Decl(indexAccessCombinedInference2.ts, 43, 13))
+>x : Symbol(x, Decl(indexAccessCombinedInference2.ts, 44, 46))
+>y : Symbol(y, Decl(indexAccessCombinedInference2.ts, 44, 49))
+

tests/baselines/reference/indexAccessCombinedInference2.types

@@ -0,0 +1,168 @@
+//// [tests/cases/compiler/indexAccessCombinedInference2.ts] ////
+
+=== indexAccessCombinedInference2.ts ===
+type TLArrowShape = {
+>TLArrowShape : TLArrowShape
+>             : ^^^^^^^^^^^^
+
+  type: "arrow";
+>type : "arrow"
+>     : ^^^^^^^
+
+  id: string;
+>id : string
+>   : ^^^^^^
+
+  x: number;
+>x : number
+>  : ^^^^^^
+
+  y: number;
+>y : number
+>  : ^^^^^^
+
+  props: {
+>props : { dir: 1 | -1; }
+>      : ^^^^^^^      ^^^
+
+    dir: 1 | -1;
+>dir : 1 | -1
+>    : ^^^^^^
+>-1 : -1
+>   : ^^
+>1 : 1
+>  : ^
+
+  };
+};
+
+type NodeShape = {
+>NodeShape : NodeShape
+>          : ^^^^^^^^^
+
+  type: "node";
+>type : "node"
+>     : ^^^^^^
+
+  id: string;
+>id : string
+>   : ^^^^^^
+
+  x: number;
+>x : number
+>  : ^^^^^^
+
+  y: number;
+>y : number
+>  : ^^^^^^
+
+  props: {
+>props : { nodeType: string; }
+>      : ^^^^^^^^^^^^      ^^^
+
+    nodeType: string;
+>nodeType : string
+>         : ^^^^^^
+
+  };
+};
+
+type TLShape = TLArrowShape | NodeShape;
+>TLShape : TLShape
+>        : ^^^^^^^
+
+export type TLShapePartial<T extends TLShape = TLShape> = T extends T
+>TLShapePartial : TLShapePartial<T>
+>               : ^^^^^^^^^^^^^^^^^
+
+  ? {
+      id: string;
+>id : string
+>   : ^^^^^^
+
+      type: T["type"];
+>type : T["type"]
+>     : ^^^^^^^^^
+
+      props?: Partial<T["props"]>;
+>props : Partial<T["props"]> | undefined
+>      : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+    } & Partial<Omit<T, "type" | "id" | "props">>
+  : never;
+
+declare class Editor {
+>Editor : Editor
+>       : ^^^^^^
+
+  updateShape<T extends TLShape = TLShape>(
+>updateShape : <T extends TLShape = TLShape>(partial: TLShapePartial<T> | null | undefined) => T
+>            : ^ ^^^^^^^^^       ^^^^^^^^^^^^       ^^                                    ^^^^^ 
+
+    partial: TLShapePartial<T> | null | undefined,
+>partial : TLShapePartial<T> | null | undefined
+>        : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+  ): T;
+}
+
+declare const x: number;
+>x : number
+>  : ^^^^^^
+
+declare const y: number;
+>y : number
+>  : ^^^^^^
+
+declare const editor: Editor;
+>editor : Editor
+>       : ^^^^^^
+
+declare const node1: NodeShape;
+>node1 : NodeShape
+>      : ^^^^^^^^^
+
+const node2 = editor.updateShape({ ...node1, x, y });
+>node2 : { type: "node"; x: number; y: number; id: string; props: { nodeType: string; }; }
+>      : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^      ^^^^^^^^^                     ^^^
+>editor.updateShape({ ...node1, x, y }) : { type: "node"; x: number; y: number; id: string; props: { nodeType: string; }; }
+>                                       : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^      ^^^^^^^^^                     ^^^
+>editor.updateShape : <T extends TLShape = TLShape>(partial: TLShapePartial<T> | null | undefined) => T
+>                   : ^ ^^^^^^^^^       ^^^^^^^^^^^^       ^^                                    ^^^^^ 
+>editor : Editor
+>       : ^^^^^^
+>updateShape : <T extends TLShape = TLShape>(partial: TLShapePartial<T> | null | undefined) => T
+>            : ^ ^^^^^^^^^       ^^^^^^^^^^^^       ^^                                    ^^^^^ 
+>{ ...node1, x, y } : { x: number; y: number; type: "node"; id: string; props: { nodeType: string; }; }
+>                   : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^      ^^^^^^      ^^^^^^^^^                     ^^^
+>node1 : NodeShape
+>      : ^^^^^^^^^
+>x : number
+>  : ^^^^^^
+>y : number
+>  : ^^^^^^
+
+declare const shape1: TLShape;
+>shape1 : TLShape
+>       : ^^^^^^^
+
+const shape2 = editor.updateShape({ ...shape1, x, y });
+>shape2 : TLShape
+>       : ^^^^^^^
+>editor.updateShape({ ...shape1, x, y }) : TLShape
+>                                        : ^^^^^^^
+>editor.updateShape : <T extends TLShape = TLShape>(partial: TLShapePartial<T> | null | undefined) => T
+>                   : ^ ^^^^^^^^^       ^^^^^^^^^^^^       ^^                                    ^^^^^ 
+>editor : Editor
+>       : ^^^^^^
+>updateShape : <T extends TLShape = TLShape>(partial: TLShapePartial<T> | null | undefined) => T
+>            : ^ ^^^^^^^^^       ^^^^^^^^^^^^       ^^                                    ^^^^^ 
+>{ ...shape1, x, y } : { x: number; y: number; type: "arrow"; id: string; props: { dir: 1 | -1; }; } | { x: number; y: number; type: "node"; id: string; props: { nodeType: string; }; }
+>                    : ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^       ^^^^^^      ^^^^^^^^^                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^      ^^^^^^      ^^^^^^^^^                     ^^^
+>shape1 : TLShape
+>       : ^^^^^^^
+>x : number
+>  : ^^^^^^
+>y : number
+>  : ^^^^^^
+