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Avoid creating closures

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This commit is contained in:
Anders Hejlsberg
2024-03-01 21:40:28 -08:00
parent 703253ae6b
commit c7f1c3d309
1 changed files with 37 additions and 38 deletions
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75
src/compiler/checker.ts
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@@ -37421,49 +37421,48 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
});
if (bailedEarly || !singleReturn || functionHasImplicitReturn(func)) return undefined;
}
return checkIfExpressionRefinesAnyParameter(func, singleReturn);
}
return checkIfExpressionRefinesAnyParameter(singleReturn);
function checkIfExpressionRefinesAnyParameter(func: FunctionLikeDeclaration, expr: Expression): TypePredicate | undefined {
expr = skipParentheses(expr, /*excludeJSDocTypeAssertions*/ true);
const returnType = checkExpressionCached(expr);
if (!(returnType.flags & TypeFlags.Boolean)) return undefined;
function checkIfExpressionRefinesAnyParameter(expr: Expression): TypePredicate | undefined {
expr = skipParentheses(expr, /*excludeJSDocTypeAssertions*/ true);
const returnType = checkExpressionCached(expr);
if (!(returnType.flags & TypeFlags.Boolean)) return undefined;
return forEach(func.parameters, (param, i) => {
const initType = getTypeOfSymbol(param.symbol);
if (!initType || initType.flags & TypeFlags.Boolean || !isIdentifier(param.name) || isSymbolAssigned(param.symbol)) {
// Refining "x: boolean" to "x is true" or "x is false" isn't useful.
return;
}
const trueType = checkIfExpressionRefinesParameter(func, expr, param, initType);
if (trueType) {
return createTypePredicate(TypePredicateKind.Identifier, unescapeLeadingUnderscores(param.name.escapedText), i, trueType);
}
});
}
return forEach(func.parameters, (param, i) => {
const initType = getTypeOfSymbol(param.symbol);
if (!initType || initType.flags & TypeFlags.Boolean || !isIdentifier(param.name) || isSymbolAssigned(param.symbol)) {
// Refining "x: boolean" to "x is true" or "x is false" isn't useful.
return;
}
const trueType = checkIfExpressionRefinesParameter(expr, param, initType);
if (trueType) {
return createTypePredicate(TypePredicateKind.Identifier, unescapeLeadingUnderscores(param.name.escapedText), i, trueType);
}
});
}
function checkIfExpressionRefinesParameter(func: FunctionLikeDeclaration, expr: Expression, param: ParameterDeclaration, initType: Type): Type | undefined {
const antecedent = (expr as Expression & { flowNode?: FlowNode; }).flowNode ||
expr.parent.kind === SyntaxKind.ReturnStatement && (expr.parent as ReturnStatement).flowNode ||
{ flags: FlowFlags.Start };
const trueCondition: FlowCondition = {
flags: FlowFlags.TrueCondition,
node: expr,
antecedent,
};
function checkIfExpressionRefinesParameter(expr: Expression, param: ParameterDeclaration, initType: Type): Type | undefined {
const antecedent = (expr as Expression & { flowNode?: FlowNode; }).flowNode ||
expr.parent.kind === SyntaxKind.ReturnStatement && (expr.parent as ReturnStatement).flowNode ||
{ flags: FlowFlags.Start };
const trueCondition: FlowCondition = {
flags: FlowFlags.TrueCondition,
node: expr,
antecedent,
};
const trueType = getFlowTypeOfReference(param.name, initType, initType, func, trueCondition);
if (trueType === initType) return undefined;
const trueType = getFlowTypeOfReference(param.name, initType, initType, func, trueCondition);
if (trueType === initType) return undefined;
// "x is T" means that x is T if and only if it returns true. If it returns false then x is not T.
// This means that if the function is called with an argument of type trueType, there can't be anything left in the `else` branch. It must reduce to `never`.
const falseCondition: FlowCondition = {
...trueCondition,
flags: FlowFlags.FalseCondition,
};
const falseSubtype = getFlowTypeOfReference(param.name, trueType, trueType, func, falseCondition);
return falseSubtype.flags & TypeFlags.Never ? trueType : undefined;
}
// "x is T" means that x is T if and only if it returns true. If it returns false then x is not T.
// This means that if the function is called with an argument of type trueType, there can't be anything left in the `else` branch. It must reduce to `never`.
const falseCondition: FlowCondition = {
...trueCondition,
flags: FlowFlags.FalseCondition,
};
const falseSubtype = getFlowTypeOfReference(param.name, trueType, trueType, func, falseCondition);
return falseSubtype.flags & TypeFlags.Never ? trueType : undefined;
}
/**