Allow discrimination to identical object types when discriminating contextual types

src/compiler/checker.ts

@@ -18264,8 +18264,18 @@ namespace ts {
                 }
             }
             const match = discriminable.indexOf(/*searchElement*/ true);
+            if (match === -1) {
+                return defaultValue;
+            }
             // make sure exactly 1 matches before returning it
-            return match === -1 || discriminable.indexOf(/*searchElement*/ true, match + 1) !== -1 ? defaultValue : target.types[match];
+            let nextMatch = discriminable.indexOf(/*searchElement*/ true, match + 1);
+            while (nextMatch !== -1) {
+                if (!isTypeIdenticalTo(target.types[match], target.types[nextMatch])) {
+                    return defaultValue;
+                }
+                nextMatch = discriminable.indexOf(/*searchElement*/ true, nextMatch + 1);
+            }
+            return target.types[match];
         }
 
         /**

src/compiler/types.ts

@@ -4184,7 +4184,7 @@ namespace ts {
     export const enum UnionReduction {
         None = 0,
         Literal,
-        Subtype
+        Subtype,
     }
 
     /* @internal */

tests/baselines/reference/inferenceUnionOfObjectsMappedContextualType.js

@@ -0,0 +1,25 @@
+//// [inferenceUnionOfObjectsMappedContextualType.ts]
+type Entity = {
+    someDate: Date | null;
+} & ({ id: string; } | { id: number; })
+
+type RowRendererMeta<TInput extends {}> = {
+    [key in keyof TInput]: { key: key; caption: string; formatter?: (value: TInput[key]) => string; };
+}
+
+type RowRenderer<TInput extends {}> = RowRendererMeta<TInput>[keyof RowRendererMeta<TInput>];
+
+const test: RowRenderer<Entity> = {
+    key: 'someDate',
+    caption: 'My Date',
+    formatter: (value) => value ? value.toString() : '-' // value: any
+}
+
+
+//// [inferenceUnionOfObjectsMappedContextualType.js]
+"use strict";
+var test = {
+    key: 'someDate',
+    caption: 'My Date',
+    formatter: function (value) { return value ? value.toString() : '-'; } // value: any
+};

tests/baselines/reference/inferenceUnionOfObjectsMappedContextualType.symbols

@@ -0,0 +1,56 @@
+=== tests/cases/compiler/inferenceUnionOfObjectsMappedContextualType.ts ===
+type Entity = {
+>Entity : Symbol(Entity, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 0, 0))
+
+    someDate: Date | null;
+>someDate : Symbol(someDate, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 0, 15))
+>Date : Symbol(Date, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.scripthost.d.ts, --, --))
+
+} & ({ id: string; } | { id: number; })
+>id : Symbol(id, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 2, 6))
+>id : Symbol(id, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 2, 24))
+
+type RowRendererMeta<TInput extends {}> = {
+>RowRendererMeta : Symbol(RowRendererMeta, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 2, 39))
+>TInput : Symbol(TInput, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 4, 21))
+
+    [key in keyof TInput]: { key: key; caption: string; formatter?: (value: TInput[key]) => string; };
+>key : Symbol(key, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 5, 5))
+>TInput : Symbol(TInput, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 4, 21))
+>key : Symbol(key, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 5, 28))
+>key : Symbol(key, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 5, 5))
+>caption : Symbol(caption, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 5, 38))
+>formatter : Symbol(formatter, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 5, 55))
+>value : Symbol(value, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 5, 69))
+>TInput : Symbol(TInput, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 4, 21))
+>key : Symbol(key, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 5, 5))
+}
+
+type RowRenderer<TInput extends {}> = RowRendererMeta<TInput>[keyof RowRendererMeta<TInput>];
+>RowRenderer : Symbol(RowRenderer, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 6, 1))
+>TInput : Symbol(TInput, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 8, 17))
+>RowRendererMeta : Symbol(RowRendererMeta, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 2, 39))
+>TInput : Symbol(TInput, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 8, 17))
+>RowRendererMeta : Symbol(RowRendererMeta, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 2, 39))
+>TInput : Symbol(TInput, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 8, 17))
+
+const test: RowRenderer<Entity> = {
+>test : Symbol(test, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 10, 5))
+>RowRenderer : Symbol(RowRenderer, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 6, 1))
+>Entity : Symbol(Entity, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 0, 0))
+
+    key: 'someDate',
+>key : Symbol(key, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 10, 35))
+
+    caption: 'My Date',
+>caption : Symbol(caption, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 11, 20))
+
+    formatter: (value) => value ? value.toString() : '-' // value: any
+>formatter : Symbol(formatter, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 12, 23))
+>value : Symbol(value, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 13, 16))
+>value : Symbol(value, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 13, 16))
+>value.toString : Symbol(Date.toString, Decl(lib.es5.d.ts, --, --))
+>value : Symbol(value, Decl(inferenceUnionOfObjectsMappedContextualType.ts, 13, 16))
+>toString : Symbol(Date.toString, Decl(lib.es5.d.ts, --, --))
+}
+

tests/baselines/reference/inferenceUnionOfObjectsMappedContextualType.types

@@ -0,0 +1,50 @@
+=== tests/cases/compiler/inferenceUnionOfObjectsMappedContextualType.ts ===
+type Entity = {
+>Entity : Entity
+
+    someDate: Date | null;
+>someDate : Date | null
+>null : null
+
+} & ({ id: string; } | { id: number; })
+>id : string
+>id : number
+
+type RowRendererMeta<TInput extends {}> = {
+>RowRendererMeta : RowRendererMeta<TInput>
+
+    [key in keyof TInput]: { key: key; caption: string; formatter?: (value: TInput[key]) => string; };
+>key : key
+>caption : string
+>formatter : ((value: TInput[key]) => string) | undefined
+>value : TInput[key]
+}
+
+type RowRenderer<TInput extends {}> = RowRendererMeta<TInput>[keyof RowRendererMeta<TInput>];
+>RowRenderer : RowRenderer<TInput>
+
+const test: RowRenderer<Entity> = {
+>test : RowRenderer<Entity>
+>{    key: 'someDate',    caption: 'My Date',    formatter: (value) => value ? value.toString() : '-' // value: any} : { key: "someDate"; caption: string; formatter: (value: Date | null) => string; }
+
+    key: 'someDate',
+>key : "someDate"
+>'someDate' : "someDate"
+
+    caption: 'My Date',
+>caption : string
+>'My Date' : "My Date"
+
+    formatter: (value) => value ? value.toString() : '-' // value: any
+>formatter : (value: Date | null) => string
+>(value) => value ? value.toString() : '-' : (value: Date | null) => string
+>value : Date | null
+>value ? value.toString() : '-' : string
+>value : Date | null
+>value.toString() : string
+>value.toString : () => string
+>value : Date
+>toString : () => string
+>'-' : "-"
+}
+

tests/cases/compiler/inferenceUnionOfObjectsMappedContextualType.ts

@@ -0,0 +1,16 @@
+// @strict: true
+type Entity = {
+    someDate: Date | null;
+} & ({ id: string; } | { id: number; })
+
+type RowRendererMeta<TInput extends {}> = {
+    [key in keyof TInput]: { key: key; caption: string; formatter?: (value: TInput[key]) => string; };
+}
+
+type RowRenderer<TInput extends {}> = RowRendererMeta<TInput>[keyof RowRendererMeta<TInput>];
+
+const test: RowRenderer<Entity> = {
+    key: 'someDate',
+    caption: 'My Date',
+    formatter: (value) => value ? value.toString() : '-' // value: any
+}