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fix(eslint-plugin): [no-unnecessary-type-assertion] should report readonly class properties with a literal initializer #10618

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Merged
merged 9 commits into from
Jan 28, 2025
Merged

fix(eslint-plugin): [no-unnecessary-type-assertion] should report readonly class properties with a literal initializer #10618

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62b77e7
fix: handle readonly class properties
y-hsgw Jan 6, 2025
80b23fd
test: add test
y-hsgw Jan 6, 2025
1a8112d
Merge branch 'main' of https://github.com/y-hsgw/typescript-eslint in…
y-hsgw Jan 15, 2025
d20d458
test: add valid case
y-hsgw Jan 17, 2025
b0924e7
fix: check that template literals nodes have no expressions in them
y-hsgw Jan 17, 2025
d000227
test: split invalid test
y-hsgw Jan 21, 2025
cc7a718
refactor: create isImplicitlyNarrowedLiteralDeclaration function
y-hsgw Jan 21, 2025
6f2326b
test: add test
y-hsgw Jan 24, 2025
a320eaf
test: remove test
y-hsgw Jan 27, 2025
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33 changes: 21 additions & 12 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 @@ -156,23 +156,32 @@ export default createRule<Options, MessageIds>({
);
}

function isImplicitlyNarrowedConstDeclaration({
function isTemplateLiteralWithExpressions(expression: TSESTree.Expression) {
return (
expression.type === AST_NODE_TYPES.TemplateLiteral &&
expression.expressions.length !== 0
);
}

function isImplicitlyNarrowedLiteralDeclaration({
expression,
parent,
}: TSESTree.TSAsExpression | TSESTree.TSTypeAssertion): boolean {
/**
* 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
*/
if (isTemplateLiteralWithExpressions(expression)) {
return false;
}

// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
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' &&
/**
* 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
(maybeDeclarationNode.type === AST_NODE_TYPES.VariableDeclaration &&
maybeDeclarationNode.kind === 'const') ||
(parent.type === AST_NODE_TYPES.PropertyDefinition && parent.readonly)
);
}

Expand Down Expand Up @@ -225,7 +234,7 @@ export default createRule<Options, MessageIds>({
const typeIsUnchanged = isTypeUnchanged(uncastType, castType);

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

if (typeIsUnchanged && wouldSameTypeBeInferred) {
Expand Down
98 changes: 98 additions & 0 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 @@ -151,6 +151,28 @@ const y: number = x!;
const x: number | null = null;
class Foo {
prop: number = x!;
}
`,
`
class T {
a = 'a' as const;
}
`,
`
class T {
a = 3 as 3;
}
`,
`
const foo = 'foo';

class T {
readonly test = \`\${foo}\` as const;
}
`,
`
class T {
readonly a = { foo: 'foo' } as const;
}
`,
`
Expand Down Expand Up @@ -1138,6 +1160,82 @@ var x = 1;
},
{
code: `
class T {
readonly a = 'a' as const;
}
`,
errors: [
{
line: 3,
messageId: 'unnecessaryAssertion',
},
],
output: `
class T {
readonly a = 'a';
}
`,
},
{
code: `
class T {
readonly a = 3 as 3;
}
`,
errors: [
{
line: 3,
messageId: 'unnecessaryAssertion',
},
],
output: `
class T {
readonly a = 3;
}
`,
},
{
code: `
type S = 10;

class T {
readonly a = 10 as S;
}
`,
errors: [
{
line: 5,
messageId: 'unnecessaryAssertion',
},
],
output: `
type S = 10;

class T {
readonly a = 10;
}
`,
},
{
code: `
class T {
readonly a = (3 + 5) as number;
}
`,
errors: [
{
line: 3,
messageId: 'unnecessaryAssertion',
},
],
output: `
class T {
readonly a = (3 + 5);
}
`,
},
{
code: `
const a = '';
const b: string | undefined = (a ? undefined : a)!;
`,
Expand Down
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