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feat: report more cases with ?? in no-constant-binary-expression #16826

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merged 8 commits into from Feb 13, 2023
Merged

feat: report more cases with ?? in no-constant-binary-expression #16826

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0d2e7ad
feat: update rule for unnecessary nullish coalescing operator
nissy-dev Jan 25, 2023
8971e90
docs: add incorrect cases
nissy-dev Jan 26, 2023
7c91ba8
fix: update logic by review
nissy-dev Feb 4, 2023
6237476
Update docs/src/rules/no-constant-binary-expression.md
nissy-dev Feb 11, 2023
5fad3e6
wip
nissy-dev Feb 12, 2023
0a2fe3e
fix: update logic for false negative
nissy-dev Feb 12, 2023
fbcc0bb
fix; remove unnecessary diff
nissy-dev Feb 12, 2023
feb2cad
Update tests/lib/rules/no-constant-binary-expression.js
nissy-dev Feb 13, 2023
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6 changes: 6 additions & 0 deletions lib/rules/no-constant-binary-expression.js
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Expand Up @@ -45,6 +45,12 @@ function hasConstantNullishness(scope, node) {
return (functionName === "Boolean" || functionName === "String" || functionName === "Number") &&
isReferenceToGlobalVariable(scope, node.callee);
}
case "LogicalExpression": {
const isLeftConstant = hasConstantNullishness(scope, node.left);
const isRightConstant = hasConstantNullishness(scope, node.right);

return isLeftConstant || isRightConstant;
}
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These would be false positives, as the left-hand sides of these ?? do not have constant nullishness so the expressions neither always nor never short-circuit:

const first = (foo && true) ?? bar;
//             ^^^^^^^^^^^ Unexpected constant nullishness on the left-hand side of a `??` expression.

const second = null ?? foo ?? bar;
//             ^^^^^^^^^^^ Unexpected constant nullishness on the left-hand side of a `??` expression.

const third = foo ?? null ?? bar;
//            ^^^^^^^^^^^ Unexpected constant nullishness on the left-hand side of a `??` expression.

We should check if the operator is ?? and if its right side is non-nullish.

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Thank you for review! I tried to fix in 7c91ba8.

case "AssignmentExpression":
if (node.operator === "=") {
return hasConstantNullishness(scope, node.right);
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8 changes: 7 additions & 1 deletion tests/lib/rules/no-constant-binary-expression.js
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Expand Up @@ -308,6 +308,12 @@ ruleTester.run("no-constant-binary-expression", rule, {
{ code: "x === /[a-z]/", errors: [{ messageId: "alwaysNew" }] },

// It's not obvious what this does, but it compares the old value of `x` to the new object.
{ code: "x === (x = {})", errors: [{ messageId: "alwaysNew" }] }
{ code: "x === (x = {})", errors: [{ messageId: "alwaysNew" }] },

{ code: "window.abc && false && anything", errors: [{ messageId: "constantShortCircuit" }] },
{ code: "window.abc || true || anything", errors: [{ messageId: "constantShortCircuit" }] },
{ code: "window.abc ?? 'non-nullish' ?? 'non-nullish'", errors: [{ messageId: "constantShortCircuit" }] },
{ code: "window.abc ?? undefined ?? 'non-nullish'", errors: [{ messageId: "constantShortCircuit" }] },
{ code: "window.abc ?? null ?? 'non-nullish'", errors: [{ messageId: "constantShortCircuit" }] }
]
});