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Improve error messages for discriminated union incompatible members
Fixes #62737 When assigning objects with wider discriminator unions to discriminated union types, TypeScript now identifies the actual incompatible types from the source union, rather than showing a misleading error about a compatible type. Before: Type '"foo"' is not assignable to type '"bar"' After: The type(s) '"baz"' are not present in the discriminator 'discriminator' of the target. This change: - Adds detection for discriminated union assignment errors - Reports which specific types from the source are missing in the target - Includes the discriminator property name in the error message - Adds comprehensive test cases
1 parent 4ef2378 commit 180b94d

12 files changed

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‎src/compiler/checker.ts‎

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@@ -23096,6 +23096,41 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
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}
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}
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if (reportErrors) {
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// Check if we're dealing with a discriminated union case where we can provide better error messages
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if (target.flags & TypeFlags.Union && source.flags & TypeFlags.Object) {
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const discriminantProps = findDiscriminantProperties(getPropertiesOfType(source), target);
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if (discriminantProps && discriminantProps.length > 0) {
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// For each discriminant property, check if the source property type contains values
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// not present in any constituent of the target union
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for (const prop of discriminantProps) {
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const sourcePropType = getTypeOfSymbol(prop);
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if (sourcePropType.flags & TypeFlags.Union) {
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// Get all discriminant values from the target union for this property
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const targetDiscriminantTypes: Type[] = [];
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for (const constituent of (target as UnionType).types) {
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const constituentPropType = getTypeOfPropertyOfType(constituent, prop.escapedName);
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if (constituentPropType) {
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forEachType(constituentPropType, t => { targetDiscriminantTypes.push(t); });
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}
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}
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const targetDiscriminantUnion = getUnionType(targetDiscriminantTypes);
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// Find source types that are not assignable to the target discriminant union
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const incompatibleTypes: Type[] = [];
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for (const sourceType of (sourcePropType as UnionType).types) {
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if (!isTypeAssignableTo(sourceType, targetDiscriminantUnion)) {
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incompatibleTypes.push(sourceType);
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}
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}
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if (incompatibleTypes.length > 0) {
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const incompatibleTypesStr = incompatibleTypes.map(t => typeToString(t)).join(" | ");
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const propName = symbolToString(prop);
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reportError(Diagnostics.Type_0_is_not_assignable_to_type_1_The_type_s_2_are_not_present_in_the_discriminator_3_of_the_target, typeToString(source), typeToString(target), incompatibleTypesStr, propName);
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return Ternary.False;
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}
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}
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}
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}
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}
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// Elaborate only if we can find a best matching type in the target union
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const bestMatchingType = getBestMatchingType(source, target, isRelatedTo);
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if (bestMatchingType) {

‎src/compiler/diagnosticMessages.json‎

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"category": "Error",
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"code": 2882
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},
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"Type '{0}' is not assignable to type '{1}'. The types of '{2}' are incompatible between these types.": {
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"category": "Error",
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"code": 2883
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},
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"Type '{0}' is not assignable to type '{1}'. The type(s) '{2}' are not present in the discriminator '{3}' of the target.": {
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"category": "Error",
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"code": 2884
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},
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"Import declaration '{0}' is using private name '{1}'.": {
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"category": "Error",

‎tests/baselines/reference/discriminatedUnionIncompatibleMemberErrorMessage.errors.txt‎

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discriminatedUnionIncompatibleMemberErrorMessage.ts(12,7): error TS2322: Type '{ discriminator: UnionType; }' is not assignable to type 'Discriminated'.
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Type '{ discriminator: UnionType; }' is not assignable to type 'Discriminated'. The type(s) '"baz"' are not present in the discriminator 'discriminator' of the target.
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discriminatedUnionIncompatibleMemberErrorMessage.ts(17,7): error TS2322: Type '{ discriminator: WiderUnion; }' is not assignable to type 'Discriminated'.
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Type '{ discriminator: WiderUnion; }' is not assignable to type 'Discriminated'. The type(s) '"baz" | "qux"' are not present in the discriminator 'discriminator' of the target.
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discriminatedUnionIncompatibleMemberErrorMessage.ts(26,7): error TS2322: Type '{ kind: ShapeKind; }' is not assignable to type 'Shape'.
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Type '{ kind: ShapeKind; }' is not assignable to type 'Shape'. The type(s) '"triangle"' are not present in the discriminator 'kind' of the target.
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discriminatedUnionIncompatibleMemberErrorMessage.ts(33,7): error TS2322: Type '{ discriminator: UnionType; }' is not assignable to type 'Discriminated2'.
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Type '{ discriminator: UnionType; }' is not assignable to type 'Discriminated2'. The type(s) '"baz"' are not present in the discriminator 'discriminator' of the target.
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==== discriminatedUnionIncompatibleMemberErrorMessage.ts (4 errors) ====
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// Test case for issue #62737
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// Improve error messages when assigning objects with wider discriminator unions to discriminated union types
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// Basic case - single incompatible type
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type Discriminated =
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| { discriminator: "foo" }
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| { discriminator: "bar" };
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type UnionType = "foo" | "bar" | "baz";
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const obj = { discriminator: "foo" as UnionType };
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const err: Discriminated = obj; // Error: "baz" is not present in discriminator
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~~~
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!!! error TS2322: Type '{ discriminator: UnionType; }' is not assignable to type 'Discriminated'.
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!!! error TS2322: Type '{ discriminator: UnionType; }' is not assignable to type 'Discriminated'. The type(s) '"baz"' are not present in the discriminator 'discriminator' of the target.
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// Multiple incompatible types
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type WiderUnion = "foo" | "bar" | "baz" | "qux";
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const obj2 = { discriminator: "foo" as WiderUnion };
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const err2: Discriminated = obj2; // Error: "baz" | "qux" are not present in discriminator
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~~~~
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!!! error TS2322: Type '{ discriminator: WiderUnion; }' is not assignable to type 'Discriminated'.
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!!! error TS2322: Type '{ discriminator: WiderUnion; }' is not assignable to type 'Discriminated'. The type(s) '"baz" | "qux"' are not present in the discriminator 'discriminator' of the target.
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// Different discriminator property name
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type Shape =
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| { kind: "circle"; radius: number }
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| { kind: "square"; side: number };
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type ShapeKind = "circle" | "square" | "triangle";
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const shape = { kind: "circle" as ShapeKind };
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const err3: Shape = shape; // Error: "triangle" is not present in discriminator "kind"
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~~~~
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!!! error TS2322: Type '{ kind: ShapeKind; }' is not assignable to type 'Shape'.
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!!! error TS2322: Type '{ kind: ShapeKind; }' is not assignable to type 'Shape'. The type(s) '"triangle"' are not present in the discriminator 'kind' of the target.
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// From issue #62603
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type Discriminated2 =
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| { discriminator: "foo" }
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| { discriminator: "bar" };
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const unexpectedError: Discriminated2 = { discriminator: "foo" } as { discriminator: UnionType };
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~~~~~~~~~~~~~~~
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!!! error TS2322: Type '{ discriminator: UnionType; }' is not assignable to type 'Discriminated2'.
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!!! error TS2322: Type '{ discriminator: UnionType; }' is not assignable to type 'Discriminated2'. The type(s) '"baz"' are not present in the discriminator 'discriminator' of the target.
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‎tests/baselines/reference/discriminatedUnionIncompatibleMemberErrorMessage.js‎

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//// [tests/cases/compiler/discriminatedUnionIncompatibleMemberErrorMessage.ts] ////
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//// [discriminatedUnionIncompatibleMemberErrorMessage.ts]
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// Test case for issue #62737
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// Improve error messages when assigning objects with wider discriminator unions to discriminated union types
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// Basic case - single incompatible type
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type Discriminated =
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| { discriminator: "foo" }
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| { discriminator: "bar" };
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type UnionType = "foo" | "bar" | "baz";
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const obj = { discriminator: "foo" as UnionType };
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const err: Discriminated = obj; // Error: "baz" is not present in discriminator
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// Multiple incompatible types
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type WiderUnion = "foo" | "bar" | "baz" | "qux";
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const obj2 = { discriminator: "foo" as WiderUnion };
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const err2: Discriminated = obj2; // Error: "baz" | "qux" are not present in discriminator
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// Different discriminator property name
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type Shape =
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| { kind: "circle"; radius: number }
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| { kind: "square"; side: number };
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type ShapeKind = "circle" | "square" | "triangle";
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const shape = { kind: "circle" as ShapeKind };
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const err3: Shape = shape; // Error: "triangle" is not present in discriminator "kind"
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// From issue #62603
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type Discriminated2 =
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| { discriminator: "foo" }
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| { discriminator: "bar" };
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const unexpectedError: Discriminated2 = { discriminator: "foo" } as { discriminator: UnionType };
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//// [discriminatedUnionIncompatibleMemberErrorMessage.js]
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"use strict";
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// Test case for issue #62737
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// Improve error messages when assigning objects with wider discriminator unions to discriminated union types
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var obj = { discriminator: "foo" };
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var err = obj; // Error: "baz" is not present in discriminator
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var obj2 = { discriminator: "foo" };
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var err2 = obj2; // Error: "baz" | "qux" are not present in discriminator
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var shape = { kind: "circle" };
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var err3 = shape; // Error: "triangle" is not present in discriminator "kind"
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var unexpectedError = { discriminator: "foo" };

‎tests/baselines/reference/discriminatedUnionIncompatibleMemberErrorMessage.symbols‎

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//// [tests/cases/compiler/discriminatedUnionIncompatibleMemberErrorMessage.ts] ////
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=== discriminatedUnionIncompatibleMemberErrorMessage.ts ===
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// Test case for issue #62737
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// Improve error messages when assigning objects with wider discriminator unions to discriminated union types
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// Basic case - single incompatible type
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type Discriminated =
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>Discriminated : Symbol(Discriminated, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 0, 0))
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| { discriminator: "foo" }
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>discriminator : Symbol(discriminator, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 5, 5))
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| { discriminator: "bar" };
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>discriminator : Symbol(discriminator, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 6, 5))
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type UnionType = "foo" | "bar" | "baz";
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>UnionType : Symbol(UnionType, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 6, 29))
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const obj = { discriminator: "foo" as UnionType };
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>obj : Symbol(obj, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 10, 5))
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>discriminator : Symbol(discriminator, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 10, 13))
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>UnionType : Symbol(UnionType, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 6, 29))
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const err: Discriminated = obj; // Error: "baz" is not present in discriminator
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>err : Symbol(err, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 11, 5))
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>Discriminated : Symbol(Discriminated, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 0, 0))
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>obj : Symbol(obj, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 10, 5))
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// Multiple incompatible types
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type WiderUnion = "foo" | "bar" | "baz" | "qux";
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>WiderUnion : Symbol(WiderUnion, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 11, 31))
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const obj2 = { discriminator: "foo" as WiderUnion };
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>obj2 : Symbol(obj2, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 15, 5))
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>discriminator : Symbol(discriminator, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 15, 14))
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>WiderUnion : Symbol(WiderUnion, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 11, 31))
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const err2: Discriminated = obj2; // Error: "baz" | "qux" are not present in discriminator
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>err2 : Symbol(err2, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 16, 5))
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>Discriminated : Symbol(Discriminated, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 0, 0))
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>obj2 : Symbol(obj2, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 15, 5))
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// Different discriminator property name
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type Shape =
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>Shape : Symbol(Shape, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 16, 33))
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| { kind: "circle"; radius: number }
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>kind : Symbol(kind, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 20, 5))
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>radius : Symbol(radius, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 20, 21))
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| { kind: "square"; side: number };
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>kind : Symbol(kind, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 21, 5))
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>side : Symbol(side, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 21, 21))
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type ShapeKind = "circle" | "square" | "triangle";
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>ShapeKind : Symbol(ShapeKind, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 21, 37))
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const shape = { kind: "circle" as ShapeKind };
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>shape : Symbol(shape, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 24, 5))
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>kind : Symbol(kind, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 24, 15))
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>ShapeKind : Symbol(ShapeKind, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 21, 37))
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const err3: Shape = shape; // Error: "triangle" is not present in discriminator "kind"
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>err3 : Symbol(err3, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 25, 5))
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>Shape : Symbol(Shape, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 16, 33))
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>shape : Symbol(shape, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 24, 5))
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// From issue #62603
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type Discriminated2 =
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>Discriminated2 : Symbol(Discriminated2, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 25, 26))
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| { discriminator: "foo" }
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>discriminator : Symbol(discriminator, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 29, 5))
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| { discriminator: "bar" };
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>discriminator : Symbol(discriminator, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 30, 5))
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const unexpectedError: Discriminated2 = { discriminator: "foo" } as { discriminator: UnionType };
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>unexpectedError : Symbol(unexpectedError, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 32, 5))
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>Discriminated2 : Symbol(Discriminated2, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 25, 26))
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>discriminator : Symbol(discriminator, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 32, 41))
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>discriminator : Symbol(discriminator, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 32, 69))
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>UnionType : Symbol(UnionType, Decl(discriminatedUnionIncompatibleMemberErrorMessage.ts, 6, 29))
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‎tests/baselines/reference/discriminatedUnionIncompatibleMemberErrorMessage.types‎

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//// [tests/cases/compiler/discriminatedUnionIncompatibleMemberErrorMessage.ts] ////
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=== discriminatedUnionIncompatibleMemberErrorMessage.ts ===
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// Test case for issue #62737
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// Improve error messages when assigning objects with wider discriminator unions to discriminated union types
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// Basic case - single incompatible type
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type Discriminated =
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>Discriminated : Discriminated
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> : ^^^^^^^^^^^^^
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| { discriminator: "foo" }
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>discriminator : "foo"
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> : ^^^^^
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| { discriminator: "bar" };
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>discriminator : "bar"
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> : ^^^^^
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type UnionType = "foo" | "bar" | "baz";
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>UnionType : UnionType
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> : ^^^^^^^^^
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const obj = { discriminator: "foo" as UnionType };
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>obj : { discriminator: UnionType; }
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> : ^^^^^^^^^^^^^^^^^ ^^^
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>{ discriminator: "foo" as UnionType } : { discriminator: UnionType; }
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> : ^^^^^^^^^^^^^^^^^ ^^^
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>discriminator : UnionType
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> : ^^^^^^^^^
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>"foo" as UnionType : UnionType
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> : ^^^^^^^^^
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>"foo" : "foo"
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> : ^^^^^
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const err: Discriminated = obj; // Error: "baz" is not present in discriminator
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>err : Discriminated
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> : ^^^^^^^^^^^^^
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>obj : { discriminator: UnionType; }
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> : ^^^^^^^^^^^^^^^^^ ^^^
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// Multiple incompatible types
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type WiderUnion = "foo" | "bar" | "baz" | "qux";
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>WiderUnion : WiderUnion
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> : ^^^^^^^^^^
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const obj2 = { discriminator: "foo" as WiderUnion };
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>obj2 : { discriminator: WiderUnion; }
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> : ^^^^^^^^^^^^^^^^^ ^^^
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>{ discriminator: "foo" as WiderUnion } : { discriminator: WiderUnion; }
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> : ^^^^^^^^^^^^^^^^^ ^^^
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>discriminator : WiderUnion
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> : ^^^^^^^^^^
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>"foo" as WiderUnion : WiderUnion
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> : ^^^^^^^^^^
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>"foo" : "foo"
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> : ^^^^^
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const err2: Discriminated = obj2; // Error: "baz" | "qux" are not present in discriminator
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>err2 : Discriminated
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> : ^^^^^^^^^^^^^
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>obj2 : { discriminator: WiderUnion; }
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> : ^^^^^^^^^^^^^^^^^ ^^^
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// Different discriminator property name
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type Shape =
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>Shape : Shape
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> : ^^^^^
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| { kind: "circle"; radius: number }
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>kind : "circle"
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> : ^^^^^^^^
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>radius : number
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> : ^^^^^^
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| { kind: "square"; side: number };
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>kind : "square"
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> : ^^^^^^^^
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>side : number
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> : ^^^^^^
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type ShapeKind = "circle" | "square" | "triangle";
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>ShapeKind : ShapeKind
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> : ^^^^^^^^^
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const shape = { kind: "circle" as ShapeKind };
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>shape : { kind: ShapeKind; }
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> : ^^^^^^^^ ^^^
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>{ kind: "circle" as ShapeKind } : { kind: ShapeKind; }
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> : ^^^^^^^^ ^^^
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>kind : ShapeKind
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> : ^^^^^^^^^
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>"circle" as ShapeKind : ShapeKind
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> : ^^^^^^^^^
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>"circle" : "circle"
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> : ^^^^^^^^
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const err3: Shape = shape; // Error: "triangle" is not present in discriminator "kind"
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>err3 : Shape
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> : ^^^^^
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>shape : { kind: ShapeKind; }
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> : ^^^^^^^^ ^^^
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// From issue #62603
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type Discriminated2 =
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>Discriminated2 : Discriminated2
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> : ^^^^^^^^^^^^^^
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| { discriminator: "foo" }
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>discriminator : "foo"
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> : ^^^^^
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| { discriminator: "bar" };
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>discriminator : "bar"
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> : ^^^^^
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const unexpectedError: Discriminated2 = { discriminator: "foo" } as { discriminator: UnionType };
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>unexpectedError : Discriminated2
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> : ^^^^^^^^^^^^^^
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>{ discriminator: "foo" } as { discriminator: UnionType } : { discriminator: UnionType; }
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> : ^^^^^^^^^^^^^^^^^ ^^^
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>{ discriminator: "foo" } : { discriminator: "foo"; }
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> : ^^^^^^^^^^^^^^^^^^^^^^^^^
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>discriminator : "foo"
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> : ^^^^^
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>"foo" : "foo"
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> : ^^^^^
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>discriminator : UnionType
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> : ^^^^^^^^^
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