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fix(eslint-plugin): [no-unnecessary-type-assertion] allow non-null assertion for void type #8912

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merged 2 commits into from
Apr 22, 2024
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fix(eslint-plugin): [no-unnecessary-type-assertion] allow non-null assertion for void type #8912

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cde11af
fix(eslint-plugin): [no-unnecessary-type-assertion] allow non-null as…
yeonjuan Apr 13, 2024
198ce1a
Update packages/eslint-plugin/src/rules/no-unnecessary-type-assertion.ts
JoshuaKGoldberg Apr 22, 2024
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12 changes: 10 additions & 2 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 @@ -189,7 +189,7 @@ export default createRule<Options, MessageIds>({

const type = getConstrainedTypeAtLocation(services, node.expression);

if (!isNullableType(type)) {
if (!isNullableType(type) && !isTypeFlagSet(type, ts.TypeFlags.Void)) {
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question - should void just be part of isNullableType?

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@kirkwaiblinger A quick check shows that modifying isNullableType seems to work fine. However, if we do modify this function, it would be nice to add some tests to other rules that use it. What do you think about creating a separate issue?

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Agreed!

if (
node.expression.type === AST_NODE_TYPES.Identifier &&
isPossiblyUsedBeforeAssigned(node.expression)
Expand Down Expand Up @@ -217,6 +217,7 @@ export default createRule<Options, MessageIds>({
ts.TypeFlags.Undefined,
);
const typeIncludesNull = isTypeFlagSet(type, ts.TypeFlags.Null);
const typeIncludesVoid = isTypeFlagSet(type, ts.TypeFlags.Void);

const contextualTypeIncludesUndefined = isTypeFlagSet(
contextualType,
Expand All @@ -226,6 +227,10 @@ export default createRule<Options, MessageIds>({
contextualType,
ts.TypeFlags.Null,
);
const contextualTypeIncludesVoid = isTypeFlagSet(
contextualType,
ts.TypeFlags.Void,
);

// make sure that the parent accepts the same types
// i.e. assigning `string | null | undefined` to `string | undefined` is invalid
Expand All @@ -235,8 +240,11 @@ export default createRule<Options, MessageIds>({
const isValidNull = typeIncludesNull
? contextualTypeIncludesNull
: true;
const isValidVoid = typeIncludesVoid
? contextualTypeIncludesVoid
: true;

if (isValidUndefined && isValidNull) {
if (isValidUndefined && isValidNull && isValidVoid) {
context.report({
node,
messageId: 'contextuallyUnnecessary',
Expand Down
22 changes: 22 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 @@ -88,6 +88,10 @@ let foo: number = bar!;
declare const a: { data?: unknown };
const x = a.data!;
`,
`
declare function foo(arg?: number): number | void;
const bar: number = foo()!;
`,
{
code: `
Expand Down Expand Up @@ -692,6 +696,24 @@ y = 0;
},
{
code: `
declare function foo(arg?: number): number | void;
const bar: number | void = foo()!;
`,
output: `
declare function foo(arg?: number): number | void;
const bar: number | void = foo();
`,
errors: [
{
messageId: 'contextuallyUnnecessary',
line: 3,
column: 28,
endColumn: 34,
},
],
},
{
code: `
declare function foo(): number;
const a = foo()!;
`,
Expand Down