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A fix for array methods strangely breaks the compiler #36591
Description
Although neither reduce nor reduceRight method doesn't directly relate to the errors, looks like the errors (which were not discovered by gulp runtests-parallel) are caused by a bug of the compiler. For instance, the following function should return Statement[] when nodes is MutableNodeArray<Statement>, but actually returns Node[]. This is strange.
export function visitNodes<T extends Node>(nodes: NodeArray<T> | undefined, visitor: Visitor, test?: (node: Node) => boolean, start?: number, count?: number): NodeArray<T>;Looks like the errors indicate a bug of the compiler.
This issue is requested by Nathan Shively-Sanders (@sandersn) .
TypeScript Version: 3.7.x-dev.201xxxxx
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Expected behavior:
pass
Actual behavior:
src/services/codefixes/helpers.ts:127:45 - error TS2345: Argument of type 'NodeArray<Node> | undefined' is not assignable to parameter of type 'NodeArray<Modifier> | undefined'.
Type 'NodeArray<Node>' is not assignable to type 'NodeArray<Modifier>'.
Type 'Node' is not assignable to type 'Modifier'.
Type 'Node' is not assignable to type 'Token<SyntaxKind.StaticKeyword>'.
Types of property 'kind' are incompatible.
Type 'SyntaxKind' is not assignable to type 'SyntaxKind.StaticKeyword'.
127 outputMethod(signature, getSynthesizedDeepClones(modifiers, /*includeTrivia*/ false), getSynthesizedDeepClone(name, /*includeTrivia*/ false));
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/services/refactors/extractSymbol.ts:1259:40 - error TS2345: Argument of type 'Node[]' is not assignable to parameter of type 'readonly Statement[]'.
Property '_statementBrand' is missing in type 'Node' but required in type 'Statement'.
1259 return { body: createBlock(rewrittenStatements, /*multiLine*/ true), returnValueProperty };
~~~~~~~~~~~~~~~~~~~
built/local/compiler.d.ts:2048:9
2048 _statementBrand: any;
~~~~~~~~~~~~~~~
'_statementBrand' is declared here.
https://travis-ci.org/microsoft/TypeScript/jobs/644727907#L419-L441
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sandersn commentedon Jul 23, 2020
Repros in 3.8 but not in 4.0. Must have gotten fixed during one of the assignability, inference or overload resolution tweaks.
Aside: I never got a standalone repro; the most reliable method I found was to edit transformFunctionBody in extractSymbol in the following way: