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fix(instrumentor): Do not run the arithmetic operator mutator on obvious string concatenations #2648

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merged 4 commits into from Dec 8, 2020
Merged

fix(instrumentor): Do not run the arithmetic operator mutator on obvious string concatenations #2648

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dd57842
bug(instrumentor): Do not run the arithmetic operator mutator on obvi…
Garethp Dec 7, 2020
e269cb4
Update for template literals
Garethp Dec 7, 2020
4bbed7a
bug(instrumentor): Add more tests and fix e2e
Garethp Dec 8, 2020
1ca2098
bug(instrumentor): Fixing up the e2e test
Garethp Dec 8, 2020
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16 changes: 13 additions & 3 deletions packages/instrumenter/src/mutators/arithmetic-operator-mutator.ts
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Expand Up @@ -18,7 +18,7 @@ export class ArithmeticOperatorMutator implements NodeMutator {
public name = 'ArithmeticOperator';

public mutate(path: NodePath): NodeMutation[] {
if (path.isBinaryExpression() && this.isSupported(path.node.operator)) {
if (path.isBinaryExpression() && this.isSupported(path.node.operator, path.node)) {
const mutatedOperator = this.operators[path.node.operator];
const replacement = types.cloneNode(path.node, false);
replacement.operator = mutatedOperator;
Expand All @@ -28,7 +28,17 @@ export class ArithmeticOperatorMutator implements NodeMutator {
return [];
}

private isSupported(operator: string): operator is keyof typeof ArithmeticOperators {
return Object.keys(this.operators).includes(operator);
private isSupported(operator: string, node: types.BinaryExpression): operator is keyof typeof ArithmeticOperators {
if (!Object.keys(this.operators).includes(operator)) {
return false;
}

const stringTypes = ['StringLiteral', 'TemplateLiteral'];
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On further thought, this should probably be a whitelist not a blacklist. It's a bit weird, but something like:

const log = (thingToLog) => console.log(thingToLog);
const concat = 1 + log;
console.log(concat)

Will result in "1(thingToLog) => console.log(thingToLog)". What do you think @nicojs, should we do a whitelist of things that actually make sense for an ArithmeticOperator, or keep it simple and only make exceptions for strings and template strings?

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I think a whitelist can become big and hard(er) to maintain. I personally think this is fine to start with. It's better than what we have now.


if (stringTypes.includes(node.right.type) || stringTypes.includes(node.left.type)) {
return false;
}

return true;
}
}
10 changes: 10 additions & 0 deletions packages/instrumenter/test/unit/mutators/arithmatic-operator-mutator.spec.ts
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Expand Up @@ -23,4 +23,14 @@ describe(ArithmeticOperatorMutator.name, () => {
expectJSMutation(sut, 'a / b', 'a * b');
expectJSMutation(sut, 'a % b', 'a * b');
});

it('should not mutate string literal concatenation', () => {
expectJSMutation(sut, '"a" + "b"');
expectJSMutation(sut, 'const a = 1; "a" + a');
expectJSMutation(sut, '3 + "a"');

expectJSMutation(sut, '`a` + `b`');
expectJSMutation(sut, 'const a = 1; `a` + a');
expectJSMutation(sut, '3 + `a`');
});
});