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fix(eslint-plugin): [no-unnecessary-type-assertion] combine template literal check with const variable check #8820

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Merged
merged 7 commits into from
May 28, 2024
Merged

fix(eslint-plugin): [no-unnecessary-type-assertion] combine template literal check with const variable check #8820

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f53f6cd
add failing tests
abrahamguo Apr 2, 2024
99a1a0b
remove unrelated test, and implement fix
abrahamguo Apr 2, 2024
a7255dd
clean up
abrahamguo Apr 2, 2024
5c856cd
improve name
abrahamguo Apr 2, 2024
e3f52f5
clarify name and comment
abrahamguo Apr 2, 2024
fc1fb1d
invert check
abrahamguo Apr 2, 2024
d8f2fe7
revert name
abrahamguo Apr 2, 2024
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30 changes: 15 additions & 15 deletions packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -108,23 +108,23 @@ export default createRule<Options, MessageIds>({
);
}

function isLiteralVariableDeclarationChangingTypeWithConst(
node: TSESTree.TSAsExpression | TSESTree.TSTypeAssertion,
): boolean {
/**
* If the type assertion is on a template literal WITH expressions we
* should keep the `const` casting
* @see https://github.com/typescript-eslint/typescript-eslint/issues/8737
*/
if (node.expression.type === AST_NODE_TYPES.TemplateLiteral) {
return node.expression.expressions.length === 0;
}

function isImplicitlyNarrowedConstDeclaration({
expression,
parent,
}: TSESTree.TSAsExpression | TSESTree.TSTypeAssertion): boolean {
// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
const maybeDeclarationNode = node.parent.parent!;
const maybeDeclarationNode = parent.parent!;
const isTemplateLiteralWithExpressions =
expression.type === AST_NODE_TYPES.TemplateLiteral &&
expression.expressions.length !== 0;
return (
maybeDeclarationNode.type === AST_NODE_TYPES.VariableDeclaration &&
maybeDeclarationNode.kind === 'const'
maybeDeclarationNode.kind === 'const' &&
/**
* Even on `const` variable declarations, template literals with expressions can sometimes be widened without a type assertion.
* @see https://github.com/typescript-eslint/typescript-eslint/issues/8737
*/
!isTemplateLiteralWithExpressions
);
}

Expand Down Expand Up @@ -267,7 +267,7 @@ export default createRule<Options, MessageIds>({
const typeIsUnchanged = isTypeUnchanged(uncastType, castType);

const wouldSameTypeBeInferred = castType.isLiteral()
? isLiteralVariableDeclarationChangingTypeWithConst(node)
? isImplicitlyNarrowedConstDeclaration(node)
: !isConstAssertion(node.typeAnnotation);

if (typeIsUnchanged && wouldSameTypeBeInferred) {
Expand Down
5 changes: 3 additions & 2 deletions packages/eslint-plugin/tests/rules/no-unnecessary-type-assertion.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -284,14 +284,15 @@ function bar(items: string[]) {
},
// https://github.com/typescript-eslint/typescript-eslint/issues/8737
`
const myString = 'foo';
let myString = 'foo';
const templateLiteral = \`\${myString}-somethingElse\` as const;
`,
// https://github.com/typescript-eslint/typescript-eslint/issues/8737
`
const myString = 'foo';
let myString = 'foo';
const templateLiteral = <const>\`\${myString}-somethingElse\`;
`,
'let a = `a` as const;',
{
code: `
declare const foo: {
Expand Down
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