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chore: extract AST check from convert.ts to ast-checks.ts #11748

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chore: extract AST check from convert.ts to ast-checks.ts #11748

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744c678
Chore: Extract AST check from convert.ts to ast-checks.ts
Lonercode Nov 9, 2025
b52f216
chore: extract AST check from convert.ts to ast-checks.ts
Lonercode Nov 9, 2025
9270fc4
chore: add test for ast-checks.ts
Lonercode Nov 9, 2025
6ced6b3
chore: add test for ast-checks.ts
Lonercode Nov 9, 2025
65803e4
chore: add test for ast-checks.ts
Lonercode Nov 9, 2025
b628bfa
chore: add function in ast-checks to run ts node checks
Lonercode Nov 15, 2025
78f1686
chore: fix lint errors
Lonercode Nov 15, 2025
001ea12
chore: update test
Lonercode Nov 15, 2025
f696ce1
chore: address review
Lonercode Nov 19, 2025
5eb48ef
chore: review update
Lonercode Nov 19, 2025
37c500f
chore: update based on reviews
Lonercode Nov 27, 2025
dc4dcc0
Merge branch 'main' into extract-ast-checks-from-converter
Lonercode Nov 27, 2025
4e5902b
chore: minor fix
Lonercode Nov 27, 2025
91d2b00
Merge branch 'extract-ast-checks-from-converter' of https://github.co…
Lonercode Nov 27, 2025
336c584
chore: merge main and update code
Lonercode Nov 27, 2025
ee1ada9
chore: minor update
Lonercode Nov 27, 2025
29a9c73
chore: update based on reviews
Lonercode Nov 27, 2025
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70 changes: 70 additions & 0 deletions packages/typescript-estree/src/check-syntax-errors.ts
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Original file line number Diff line number Diff line change
@@ -0,0 +1,70 @@
import * as ts from 'typescript';

import type { TSNode } from './ts-estree';

import { checkModifiers } from './check-modifiers';
import { isValidAssignmentTarget, createError } from './node-utils';

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@fisker fisker Nov 27, 2025

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We should also define a

const SyntaxKind = ts.SyntaxKind;

here, https://github.com/Lonercode/typescript-eslint/blob/ee1ada9db5229902f70faa19dc27950dc457cc7d/packages/typescript-estree/src/convert.ts#L42

so other checks can be copied easier to here.

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@JoshuaKGoldberg JoshuaKGoldberg Nov 27, 2025

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Ehh should we? We don't generally do namespace property shorthands like that in the typescript-eslint monorepo. IMO it just adds a bit of clutter.

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@fisker fisker Nov 27, 2025 •
edited
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We'll add lots of cases in switch, better align with convert.ts.

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@fisker fisker Nov 27, 2025

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At least keep it before it's done?

const SyntaxKind = ts.SyntaxKind;

export function checkSyntaxError(tsNode: ts.Node): void {
checkModifiers(tsNode);

const node = tsNode as TSNode;

switch (node.kind) {
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@JoshuaKGoldberg JoshuaKGoldberg Nov 28, 2025

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[Refactor] I don't think this is a positive change for the logic? Converter functions generally directly call the checkFor* logic they need. For example, for-in and for-of statements directly call checkForStatementDeclaration. Now this new checkSyntaxError function has to again switch on node.kind. That's extra code structure and work.

@fisker please correct me if I'm wrong here, but I think it'd still be in the spirit of the issue to have checkForStatementDeclaration be a standalone function separated out from convert.ts, and still called directly?

As in, the diffs to convert.ts would look more like:

+ import { checkForStatementDeclaration } from "./checks/...";
...
      case SyntaxKind.ForInStatement:
-       this.#checkForStatementDeclaration(node.initializer, node.kind);
+       checkForStatementDeclaration(node.initializer, node.kind);
        return this.createNode<TSESTree.ForInStatement>(node, {
...
-  #checkForStatementDeclaration(...) { ... }

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@fisker fisker Nov 28, 2025 •
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Take this

typescript-eslint/packages/typescript-estree/src/convert.ts

Lines 802 to 811 in 16cf0f7

if (
node.caseBlock.clauses.filter(
switchCase => switchCase.kind === SyntaxKind.DefaultClause,
).length > 1
) {
this.#throwError(
node,
"A 'default' clause cannot appear more than once in a 'switch' statement.",
);
}
as example, normally the check just few lines (there are even simpler checks, eg: 1). Not every node need such long code like SyntaxKind.ForInStatement.

If we call from covert.ts directly after the case ..., we'll have lot of lines to add. and forcing many functions to import/export.

I think a single call like checkModifiers() used did and duplicate the big switch(){} in check-syntax-error.ts is much easier to maintain.

Most kind of node check will inline, instead of separate function.

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@Lonercode Lonercode Dec 3, 2025

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@JoshuaKGoldberg @fisker Would it prove more efficient to separate out checkForStatmentDeclaration? I thought the point of the issue was to extract those checks?

case SyntaxKind.ForInStatement:
case SyntaxKind.ForOfStatement: {
checkForStatementDeclaration(node);
break;
}
default: {
break;
}
Comment on lines +21 to +23
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@fisker fisker Nov 27, 2025

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Add this because ESLint complaint? Will this work?

Suggested change
default: {
break;
}
// No default

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@Lonercode Lonercode Nov 27, 2025

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I think it's valid, exiting with the default, for now at least.

}
}

function checkForStatementDeclaration(
node: ts.ForInStatement | ts.ForOfStatement,
): void {
const { initializer, kind } = node;
const loop = kind === SyntaxKind.ForInStatement ? 'for...in' : 'for...of';
if (ts.isVariableDeclarationList(initializer)) {
if (initializer.declarations.length !== 1) {
throw createError(
initializer,
`Only a single variable declaration is allowed in a '${loop}' statement.`,
);
}
const declaration = initializer.declarations[0];
if (declaration.initializer) {
throw createError(
declaration,
`The variable declaration of a '${loop}' statement cannot have an initializer.`,
);
} else if (declaration.type) {
throw createError(
declaration,
`The variable declaration of a '${loop}' statement cannot have a type annotation.`,
);
}
if (
kind === SyntaxKind.ForInStatement &&
initializer.flags & ts.NodeFlags.Using
) {
throw createError(
initializer,
"The left-hand side of a 'for...in' statement cannot be a 'using' declaration.",
);
}
} else if (
!isValidAssignmentTarget(initializer) &&
initializer.kind !== SyntaxKind.ObjectLiteralExpression &&
initializer.kind !== SyntaxKind.ArrayLiteralExpression
) {
throw createError(
initializer,
`The left-hand side of a '${loop}' statement must be a variable or a property access.`,
);
}
}
56 changes: 4 additions & 52 deletions packages/typescript-estree/src/convert.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ import type {
import type { SemanticOrSyntacticError } from './semantic-or-syntactic-errors';
import type { TSESTree, TSESTreeToTSNode, TSNode } from './ts-estree';

import { checkModifiers } from './check-modifiers';
import { checkSyntaxError } from './check-syntax-errors';
import { getDecorators, getModifiers } from './getModifiers';
import {
canContainDirective,
Expand Down Expand Up @@ -105,58 +105,12 @@ export class Converter {
this.options = { ...options };
}

#checkForStatementDeclaration(
initializer: ts.ForInitializer,
kind: ts.SyntaxKind.ForInStatement | ts.SyntaxKind.ForOfStatement,
): void {
const loop =
kind === ts.SyntaxKind.ForInStatement ? 'for...in' : 'for...of';
if (ts.isVariableDeclarationList(initializer)) {
if (initializer.declarations.length !== 1) {
this.#throwError(
initializer,
`Only a single variable declaration is allowed in a '${loop}' statement.`,
);
}
const declaration = initializer.declarations[0];
if (declaration.initializer) {
this.#throwError(
declaration,
`The variable declaration of a '${loop}' statement cannot have an initializer.`,
);
} else if (declaration.type) {
this.#throwError(
declaration,
`The variable declaration of a '${loop}' statement cannot have a type annotation.`,
);
}
if (
kind === ts.SyntaxKind.ForInStatement &&
initializer.flags & ts.NodeFlags.Using
) {
this.#throwError(
initializer,
"The left-hand side of a 'for...in' statement cannot be a 'using' declaration.",
);
}
} else if (
!isValidAssignmentTarget(initializer) &&
initializer.kind !== ts.SyntaxKind.ObjectLiteralExpression &&
initializer.kind !== ts.SyntaxKind.ArrayLiteralExpression
) {
this.#throwError(
initializer,
`The left-hand side of a '${loop}' statement must be a variable or a property access.`,
);
}
}

#checkModifiers(node: ts.Node): void {
#checkSyntaxError(node: ts.Node): void {
if (this.options.allowInvalidAST) {
return;
}

checkModifiers(node);
checkSyntaxError(node);
}

#throwError(
Expand Down Expand Up @@ -528,7 +482,7 @@ export class Converter {
return null;
}

this.#checkModifiers(node);
this.#checkSyntaxError(node);

const pattern = this.allowPattern;
if (allowPattern != null) {
Expand Down Expand Up @@ -896,7 +850,6 @@ export class Converter {
});

case SyntaxKind.ForInStatement:
this.#checkForStatementDeclaration(node.initializer, node.kind);
return this.createNode<TSESTree.ForInStatement>(node, {
type: AST_NODE_TYPES.ForInStatement,
body: this.convertChild(node.statement),
Expand All @@ -905,7 +858,6 @@ export class Converter {
});

case SyntaxKind.ForOfStatement: {
this.#checkForStatementDeclaration(node.initializer, node.kind);
return this.createNode<TSESTree.ForOfStatement>(node, {
type: AST_NODE_TYPES.ForOfStatement,
await: Boolean(
Expand Down