8000 feat(eslint-plugin): [no-unnecessary-condition] check switch cases (#… · ronami/typescript-eslint@682299e · GitHub
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abrahamguokirkwaiblinger
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feat(eslint-plugin): [no-unnecessary-condition] check switch cases (typescript-eslint#9912)
* add new feature without testing it * add tests & cleanup * forgot to update the docs * refine report location * type-validate operator * WIP tests * refine tests * remove unused import * clarify docs Co-authored-by: Kirk Waiblinger <kirk.waiblinger@gmail.com> * lint --------- Co-authored-by: Kirk Waiblinger <kirk.waiblinger@gmail.com>
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‎packages/eslint-plugin/docs/rules/no-unnecessary-condition.mdx

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@@ -16,6 +16,7 @@ The following expressions are checked:
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- Arguments to the `&&`, `||` and `?:` (ternary) operators
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- Conditions for `if`, `for`, `while`, and `do-while` statements
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- `case`s in `switch` statements
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- Base values of optional chain expressions
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## Examples

‎packages/eslint-plugin/src/rules/no-unnecessary-condition.ts

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@@ -363,15 +363,18 @@ export default createRule<Options, MessageId>({
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'===',
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'!=',
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'!==',
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]);
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function checkIfBinaryExpressionIsNecessaryConditional(
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node: TSESTree.BinaryExpression,
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] as const);
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type BoolOperator = Parameters<typeof BOOL_OPERATORS.has>[0];
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const isBoolOperator = (operator: string): operator is BoolOperator =>
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(BOOL_OPERATORS as Set<string>).has(operator);
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function checkIfBoolExpressionIsNecessaryConditional(
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node: TSESTree.Node,
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left: TSESTree.Node,
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right: TSESTree.Node,
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operator: BoolOperator,
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): void {
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if (!BOOL_OPERATORS.has(node.operator)) {
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return;
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}
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const leftType = getConstrainedTypeAtLocation(services, node.left);
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const rightType = getConstrainedTypeAtLocation(services, node.right);
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const leftType = getConstrainedTypeAtLocation(services, left);
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const rightType = getConstrainedTypeAtLocation(services, right);
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if (isLiteral(leftType) && isLiteral(rightType)) {
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context.report({ node, messageId: 'literalBooleanExpression' });
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return;
@@ -390,7 +393,7 @@ export default createRule<Options, MessageId>({
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ts.TypeFlags.TypeVariable;
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// Allow loose comparison to nullish values.
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if (node.operator === '==' || node.operator === '!=') {
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if (operator === '==' || operator === '!=') {
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flag |= NULL | UNDEFINED | VOID;
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}
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@@ -719,13 +722,34 @@ export default createRule<Options, MessageId>({
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return {
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AssignmentExpression: checkAssignmentExpression,
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BinaryExpression: checkIfBinaryExpressionIsNecessaryConditional,
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BinaryExpression(node): void {
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const { operator } = node;
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if (isBoolOperator(operator)) {
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checkIfBoolExpressionIsNecessaryConditional(
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node,
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node.left,
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node.right,
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operator,
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);
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}
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},
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CallExpression: checkCallExpression,
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ConditionalExpression: (node): void => checkNode(node.test),
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DoWhileStatement: checkIfLoopIsNecessaryConditional,
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ForStatement: checkIfLoopIsNecessaryConditional,
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IfStatement: (node): void => checkNode(node.test),
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LogicalExpression: checkLogicalExpressionForUnnecessaryConditionals,
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SwitchCase({ test, parent }): void {
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// only check `case ...:`, not `default:`
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if (test) {
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checkIfBoolExpressionIsNecessaryConditional(
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test,
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parent.discriminant,
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test,
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'===',
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);
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}
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},
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WhileStatement: checkIfLoopIsNecessaryConditional,
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'MemberExpression[optional = true]': checkOptionalMemberExpression,
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'CallExpression[optional = true]': checkOptionalCallExpression,

‎packages/eslint-plugin/tests/rules/no-unnecessary-condition.test.ts

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@@ -75,6 +75,10 @@ for (let i = 0; b1 && b2; i++) {
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}
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const t1 = b1 && b2 ? 'yes' : 'no';
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for (;;) {}
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switch (b1) {
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case true:
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default:
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}
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`,
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`
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declare function foo(): number | void;
@@ -910,6 +914,10 @@ for (let i = 0; b1 && b2; i++) {
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}
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const t1 = b1 && b2 ? 'yes' : 'no';
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const t1 = b2 && b1 ? 'yes' : 'no';
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switch (b1) {
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case true:
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default:
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}
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`,
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output: null,
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errors: [
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ruleError(12, 17, 'alwaysTruthy'),
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ruleError(15, 12, 'alwaysTruthy'),
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ruleError(16, 18, 'alwaysTruthy'),
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ruleError(18, 8, 'literalBooleanExpression'),
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],
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},
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// Ensure that it's complaining about the right things

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