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Add Support for Using Aliased Discriminants in Conditional Statements (#56173)
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‎src/compiler/checker.ts

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@@ -27244,6 +27244,10 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
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case SyntaxKind.ElementAccessExpression:
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// The resolvedSymbol property is initialized by checkPropertyAccess or checkElementAccess before we get here.
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return isConstantReference((node as AccessExpression).expression) && isReadonlySymbol(getNodeLinks(node).resolvedSymbol || unknownSymbol);
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case SyntaxKind.ObjectBindingPattern:
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case SyntaxKind.ArrayBindingPattern:
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const rootDeclaration = getRootDeclaration(node.parent);
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return isVariableDeclaration(rootDeclaration) && isVarConstLike(rootDeclaration);
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}
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return false;
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}

‎tests/baselines/reference/controlFlowAliasedDiscriminants.errors.txt

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controlFlowAliasedDiscriminants.ts(39,9): error TS18048: 'data1' is possibly 'undefined'.
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controlFlowAliasedDiscriminants.ts(40,9): error TS18048: 'data2' is possibly 'undefined'.
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controlFlowAliasedDiscriminants.ts(65,9): error TS18048: 'bar2' is possibly 'undefined'.
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controlFlowAliasedDiscriminants.ts(66,9): error TS18048: 'bar3' is possibly 'undefined'.
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controlFlowAliasedDiscriminants.ts(86,14): error TS1360: Type 'string | number' does not satisfy the expected type 'string'.
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Type 'number' is not assignable to type 'string'.
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controlFlowAliasedDiscriminants.ts(98,19): error TS1360: Type 'string | number' does not satisfy the expected type 'string'.
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Type 'number' is not assignable to type 'string'.
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==== controlFlowAliasedDiscriminants.ts (6 errors) ====
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type UseQueryResult<T> = {
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isSuccess: false;
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data: undefined;
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} | {
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isSuccess: true;
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data: T
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};
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function useQuery(): UseQueryResult<number> {
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return {
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isSuccess: false,
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data: undefined,
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};
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}
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const { data: data1, isSuccess: isSuccess1 } = useQuery();
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const { data: data2, isSuccess: isSuccess2 } = useQuery();
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const { data: data3, isSuccess: isSuccess3 } = useQuery();
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if (isSuccess1 && isSuccess2 && isSuccess3) {
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data1.toExponential(); // should ok
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data2.toExponential(); // should ok
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data3.toExponential(); // should ok
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}
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const areSuccess = isSuccess1 && isSuccess2 && isSuccess3;
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if (areSuccess) {
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data1.toExponential(); // should ok
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data2.toExponential(); // should ok
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data3.toExponential(); // should ok
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}
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{
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let { data: data1, isSuccess: isSuccess1 } = useQuery();
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let { data: data2, isSuccess: isSuccess2 } = useQuery();
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const { data: data3, isSuccess: isSuccess3 } = useQuery();
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const areSuccess = isSuccess1 && isSuccess2 && isSuccess3;
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if (areSuccess) {
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data1.toExponential(); // should error
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~~~~~
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!!! error TS18048: 'data1' is possibly 'undefined'.
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data2.toExponential(); // should error
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~~~~~
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!!! error TS18048: 'data2' is possibly 'undefined'.
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data3.toExponential(); // should ok
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}
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}
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declare function getArrayResult(): [true, number] | [false, undefined];
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{
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const [foo1, bar1] = getArrayResult();
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const [foo2, bar2] = getArrayResult();
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const [foo3, bar3] = getArrayResult();
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const arrayAllSuccess = foo1 && foo2 && foo3;
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if (arrayAllSuccess) {
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bar1.toExponential(); // should ok
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bar2.toExponential(); // should ok
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bar3.toExponential(); // should ok
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}
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}
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{
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const [foo1, bar1] = getArrayResult();
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let [foo2, bar2] = getArrayResult();
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let [foo3, bar3] = getArrayResult();
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const arrayAllSuccess = foo1 && foo2 && foo3;
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if (arrayAllSuccess) {
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bar1.toExponential(); // should ok
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bar2.toExponential(); // should error
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~~~~
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!!! error TS18048: 'bar2' is possibly 'undefined'.
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bar3.toExponential(); // should error
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~~~~
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!!! error TS18048: 'bar3' is possibly 'undefined'.
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}
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}
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type Nested = {
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type: 'string';
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resp: {
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data: string
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}
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} | {
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type: 'number';
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resp: {
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data: number;
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}
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}
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{
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let resp!: Nested;
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const { resp: { data }, type } = resp;
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if (type === 'string') {
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data satisfies string;
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~~~~~~~~~
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!!! error TS1360: Type 'string | number' does not satisfy the expected type 'string'.
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!!! error TS1360: Type 'number' is not assignable to type 'string'.
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}
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if (resp.type === 'string') {
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resp.resp.data satisfies string;
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}
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}
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{
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let resp!: Nested;
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const { resp: { data: dataAlias }, type } = resp;
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if (type === 'string') {
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dataAlias satisfies string;
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~~~~~~~~~
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!!! error TS1360: Type 'string | number' does not satisfy the expected type 'string'.
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!!! error TS1360: Type 'number' is not assignable to type 'string'.
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}
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if (resp.type === 'string') {
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resp.resp.data satisfies string;
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}
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}
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‎tests/baselines/reference/controlFlowAliasedDiscriminants.js

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//// [tests/cases/compiler/controlFlowAliasedDiscriminants.ts] ////
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//// [controlFlowAliasedDiscriminants.ts]
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type UseQueryResult<T> = {
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isSuccess: false;
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data: undefined;
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} | {
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isSuccess: true;
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data: T
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};
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function useQuery(): UseQueryResult<number> {
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return {
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isSuccess: false,
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data: undefined,
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};
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}
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const { data: data1, isSuccess: isSuccess1 } = useQuery();
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const { data: data2, isSuccess: isSuccess2 } = useQuery();
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const { data: data3, isSuccess: isSuccess3 } = useQuery();
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if (isSuccess1 && isSuccess2 && isSuccess3) {
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data1.toExponential(); // should ok
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data2.toExponential(); // should ok
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data3.toExponential(); // should ok
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}
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const areSuccess = isSuccess1 && isSuccess2 && isSuccess3;
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if (areSuccess) {
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data1.toExponential(); // should ok
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data2.toExponential(); // should ok
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data3.toExponential(); // should ok
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}
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{
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let { data: data1, isSuccess: isSuccess1 } = useQuery();
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let { data: data2, isSuccess: isSuccess2 } = useQuery();
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const { data: data3, isSuccess: isSuccess3 } = useQuery();
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const areSuccess = isSuccess1 && isSuccess2 && isSuccess3;
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if (areSuccess) {
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data1.toExponential(); // should error
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data2.toExponential(); // should error
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data3.toExponential(); // should ok
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}
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}
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declare function getArrayResult(): [true, number] | [false, undefined];
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{
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const [foo1, bar1] = getArrayResult();
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const [foo2, bar2] = getArrayResult();
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const [foo3, bar3] = getArrayResult();
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const arrayAllSuccess = foo1 && foo2 && foo3;
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if (arrayAllSuccess) {
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bar1.toExponential(); // should ok
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bar2.toExponential(); // should ok
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bar3.toExponential(); // should ok
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}
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}
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{
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const [foo1, bar1] = getArrayResult();
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let [foo2, bar2] = getArrayResult();
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let [foo3, bar3] = getArrayResult();
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const arrayAllSuccess = foo1 && foo2 && foo3;
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if (arrayAllSuccess) {
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bar1.toExponential(); // should ok
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bar2.toExponential(); // should error
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bar3.toExponential(); // should error
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}
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}
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type Nested = {
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type: 'string';
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resp: {
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data: string
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}
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} | {
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type: 'number';
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resp: {
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data: number;
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}
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}
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{
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let resp!: Nested;
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const { resp: { data }, type } = resp;
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if (type === 'string') {
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data satisfies string;
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}
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if (resp.type === 'string') {
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resp.resp.data satisfies string;
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}
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}
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{
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let resp!: Nested;
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const { resp: { data: dataAlias }, type } = resp;
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if (type === 'string') {
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dataAlias satisfies string;
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}
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if (resp.type === 'string') {
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resp.resp.data satisfies string;
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}
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}
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//// [controlFlowAliasedDiscriminants.js]
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function useQuery() {
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return {
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isSuccess: false,
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data: undefined,
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};
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}
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var _a = useQuery(), data1 = _a.data, isSuccess1 = _a.isSuccess;
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var _b = useQuery(), data2 = _b.data, isSuccess2 = _b.isSuccess;
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var _c = useQuery(), data3 = _c.data, isSuccess3 = _c.isSuccess;
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if (isSuccess1 && isSuccess2 && isSuccess3) {
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data1.toExponential(); // should ok
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data2.toExponential(); // should ok
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data3.toExponential(); // should ok
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}
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var areSuccess = isSuccess1 && isSuccess2 && isSuccess3;
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if (areSuccess) {
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data1.toExponential(); // should ok
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data2.toExponential(); // should ok
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data3.toExponential(); // should ok
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}
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{
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var _d = useQuery(), data1_1 = _d.data, isSuccess1_1 = _d.isSuccess;
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var _e = useQuery(), data2_1 = _e.data, isSuccess2_1 = _e.isSuccess;
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var _f = useQuery(), data3_1 = _f.data, isSuccess3_1 = _f.isSuccess;
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var areSuccess_1 = isSuccess1_1 && isSuccess2_1 && isSuccess3_1;
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if (areSuccess_1) {
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data1_1.toExponential(); // should error
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data2_1.toExponential(); // should error
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data3_1.toExponential(); // should ok
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}
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}
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{
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var _g = getArrayResult(), foo1 = _g[0], bar1 = _g[1];
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var _h = getArrayResult(), foo2 = _h[0], bar2 = _h[1];
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var _j = getArrayResult(), foo3 = _j[0], bar3 = _j[1];
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var arrayAllSuccess = foo1 && foo2 && foo3;
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if (arrayAllSuccess) {
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bar1.toExponential(); // should ok
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bar2.toExponential(); // should ok
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bar3.toExponential(); // should ok
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}
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}
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{
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var _k = getArrayResult(), foo1 = _k[0], bar1 = _k[1];
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var _l = getArrayResult(), foo2 = _l[0], bar2 = _l[1];
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var _m = getArrayResult(), foo3 = _m[0], bar3 = _m[1];
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var arrayAllSuccess = foo1 && foo2 && foo3;
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if (arrayAllSuccess) {
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bar1.toExponential(); // should ok
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bar2.toExponential(); // should error
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bar3.toExponential(); // should error
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}
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}
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{
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var resp = void 0;
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var data = resp.resp.data, type = resp.type;
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if (type === 'string') {
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data;
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}
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if (resp.type === 'string') {
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resp.resp.data;
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}
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}
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{
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var resp = void 0;
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var dataAlias = resp.resp.data, type = resp.type;
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if (type === 'string') {
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dataAlias;
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}
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if (resp.type === 'string') {
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resp.resp.data;
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}
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}

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