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feat(eslint-plugin): [prefer-nullish-coalescing]: add support for assignment expressions #5234

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merged 6 commits into from
Nov 16, 2022
Merged

feat(eslint-plugin): [prefer-nullish-coalescing]: add support for assignment expressions #5234

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dcb43d0
feat(eslint-plugin) [prefer-nullish-coalescing]: add support for assi…
JoshuaKGoldberg Jun 23, 2022
5603522
fix: updated all rule docs
JoshuaKGoldberg Jun 23, 2022
5b7c106
WIP: Merge branch 'main'
JoshuaKGoldberg Oct 25, 2022
4b965a4
WIP: progress on tests
JoshuaKGoldberg Oct 25, 2022
ce35f24
Finish fixing tests
JoshuaKGoldberg Oct 26, 2022
9678f6c
Fix rule description
JoshuaKGoldberg Oct 26, 2022
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15 changes: 13 additions & 2 deletions packages/eslint-plugin/docs/rules/prefer-nullish-coalescing.md
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
---
description: 'Enforce using the nullish coalescing operator instead of logical chaining.'
description: 'Enforce using the nullish coalescing operator instead of logical assignments or chaining.'
---

> 🛑 This file is source code, not the primary documentation location! 🛑
Expand All @@ -9,7 +9,10 @@ description: 'Enforce using the nullish coalescing operator instead of logical c
The `??` nullish coalescing runtime operator allows providing a default value when dealing with `null` or `undefined`.
Because the nullish coalescing operator _only_ coalesces when the original value is `null` or `undefined`, it is much safer than relying upon logical OR operator chaining `||`, which coalesces on any _falsy_ value.

This rule reports when an `||` operator can be safely replaced with a `??`.
This rule reports when you can safely replace:

- An `||` operator with `??`
- An `||=` operator with `??=`

## Options

Expand Down Expand Up @@ -69,7 +72,10 @@ declare const b: string | null;

if (a || b) {
}
if ((a ||= b)) {
}
while (a || b) {}
while ((a ||= b)) {}
do {} while (a || b);
for (let i = 0; a || b; i += 1) {}
a || b ? true : false;
Expand All @@ -83,7 +89,10 @@ declare const b: string | null;

if (a ?? b) {
}
if ((a ??= b)) {
}
while (a ?? b) {}
while ((a ??= b)) {}
do {} while (a ?? b);
for (let i = 0; a ?? b; i += 1) {}
a ?? b ? true : false;
Expand All @@ -106,6 +115,7 @@ declare const c: string | null;
declare const d: string | null;

a || (b && c);
a ||= b && c;
(a && b) || c || d;
a || (b && c) || d;
a || (b && c && d);
Expand All @@ -120,6 +130,7 @@ declare const c: string | null;
declare const d: string | null;

a ?? (b && c);
a ??= b && c;
(a && b) ?? c ?? d;
a ?? (b && c) ?? d;
a ?? (b && c && d);
Expand Down
149 changes: 87 additions & 62 deletions packages/eslint-plugin/src/rules/prefer-nullish-coalescing.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -23,17 +23,17 @@ export default util.createRule<Options, MessageIds>({
type: 'suggestion',
docs: {
description:
'Enforce using the nullish coalescing operator instead of logical chaining',
'Enforce using the nullish coalescing operator instead of logical assignments or chaining',
recommended: 'strict',
requiresTypeChecking: true,
},
hasSuggestions: true,
messages: {
preferNullishOverOr:
'Prefer using nullish coalescing operator (`??`) instead of a logical or (`||`), as it is a safer operator.',
'Prefer using nullish coalescing operator (`??{{ equals }}`) instead of a logical {{ description }} (`||{{ equals }}`), as it is a safer operator.',
preferNullishOverTernary:
'Prefer using nullish coalescing operator (`??`) instead of a ternary expression, as it is simpler to read.',
suggestNullish: 'Fix to nullish coalescing operator (`??`).',
'Prefer using nullish coalescing operator (`??{{ equals }}`) instead of a ternary expression, as it is simpler to read.',
suggestNullish: 'Fix to nullish coalescing operator (`??{{ equals }}`).',
},
schema: [
{
Expand Down Expand Up @@ -74,6 +74,75 @@ export default util.createRule<Options, MessageIds>({
const sourceCode = context.getSourceCode();
const checker = parserServices.program.getTypeChecker();

// todo: rename to something more specific?
function checkAssignmentOrLogicalExpression(
node: TSESTree.AssignmentExpression | TSESTree.LogicalExpression,
description: string,
equals: string,
): void {
const tsNode = parserServices.esTreeNodeToTSNodeMap.get(node);
const type = checker.getTypeAtLocation(tsNode.left);
const isNullish = util.isNullableType(type, { allowUndefined: true });
if (!isNullish) {
return;
}

if (ignoreConditionalTests === true && isConditionalTest(node)) {
return;
}

if (
ignoreMixedLogicalExpressions === true &&
isMixedLogicalExpression(node)
) {
return;
}

const barBarOperator = util.nullThrows(
sourceCode.getTokenAfter(
node.left,
token =>
token.type === AST_TOKEN_TYPES.Punctuator &&
token.value === node.operator,
),
util.NullThrowsReasons.MissingToken('operator', node.type),
);

function* fix(
fixer: TSESLint.RuleFixer,
): IterableIterator<TSESLint.RuleFix> {
if (node.parent && util.isLogicalOrOperator(node.parent)) {
// '&&' and '??' operations cannot be mixed without parentheses (e.g. a && b ?? c)
if (
node.left.type === AST_NODE_TYPES.LogicalExpression &&
!util.isLogicalOrOperator(node.left.left)
) {
yield fixer.insertTextBefore(node.left.right, '(');
} else {
yield fixer.insertTextBefore(node.left, '(');
}
yield fixer.insertTextAfter(node.right, ')');
}
yield fixer.replaceText(
barBarOperator,
node.operator.replace('||', '??'),
);
}

context.report({
data: { equals, description },
node: barBarOperator,
messageId: 'preferNullishOverOr',
suggest: [
{
data: { equals },
messageId: 'suggestNullish',
fix,
},
],
});
}

return {
ConditionalExpression(node: TSESTree.ConditionalExpression): void {
if (ignoreTernaryTests) {
Expand Down Expand Up @@ -103,7 +172,7 @@ export default util.createRule<Options, MessageIds>({
node.test.right.left,
node.test.right.right,
];
if (node.test.operator === '||') {
if (['||', '||='].includes(node.test.operator)) {
if (
node.test.left.operator === '===' &&
node.test.right.operator === '==='
Expand Down Expand Up @@ -205,10 +274,13 @@ export default util.createRule<Options, MessageIds>({

if (isFixable) {
context.report({
// TODO: also account for = in the ternary clause
data: { equals: '' },
node,
messageId: 'preferNullishOverTernary',
suggest: [
{
data: { equals: '' },
messageId: 'suggestNullish',
fix(fixer: TSESLint.RuleFixer): TSESLint.RuleFix {
const [left, right] =
Expand All @@ -231,64 +303,15 @@ export default util.createRule<Options, MessageIds>({
});
}
},

'AssignmentExpression[operator = "||="]'(
node: TSESTree.AssignmentExpression,
): void {
checkAssignmentOrLogicalExpression(node, 'assignment', '=');
},
'LogicalExpression[operator = "||"]'(
node: TSESTree.LogicalExpression,
): void {
const tsNode = parserServices.esTreeNodeToTSNodeMap.get(node);
const type = checker.getTypeAtLocation(tsNode.left);
const isNullish = util.isNullableType(type, { allowUndefined: true });
if (!isNullish) {
return;
}

if (ignoreConditionalTests === true && isConditionalTest(node)) {
return;
}

const isMixedLogical = isMixedLogicalExpression(node);
if (ignoreMixedLogicalExpressions === true && isMixedLogical) {
return;
}

const barBarOperator = util.nullThrows(
sourceCode.getTokenAfter(
node.left,
token =>
token.type === AST_TOKEN_TYPES.Punctuator &&
token.value === node.operator,
),
util.NullThrowsReasons.MissingToken('operator', node.type),
);

function* fix(
fixer: TSESLint.RuleFixer,
): IterableIterator<TSESLint.RuleFix> {
if (node.parent && util.isLogicalOrOperator(node.parent)) {
// '&&' and '??' operations cannot be mixed without parentheses (e.g. a && b ?? c)
if (
node.left.type === AST_NODE_TYPES.LogicalExpression &&
!util.isLogicalOrOperator(node.left.left)
) {
yield fixer.insertTextBefore(node.left.right, '(');
} else {
yield fixer.insertTextBefore(node.left, '(');
}
yield fixer.insertTextAfter(node.right, ')');
}
yield fixer.replaceText(barBarOperator, '??');
}

context.report({
node: barBarOperator,
messageId: 'preferNullishOverOr',
suggest: [
{
messageId: 'suggestNullish',
fix,
},
],
});
checkAssignmentOrLogicalExpression(node, 'or', '');
},
};
},
Expand Down Expand Up @@ -331,7 +354,9 @@ function isConditionalTest(node: TSESTree.Node): boolean {
return false;
}

function isMixedLogicalExpression(node: TSESTree.LogicalExpression): boolean {
function isMixedLogicalExpression(
node: TSESTree.AssignmentExpression | TSESTree.LogicalExpression,
): boolean {
const seen = new Set<TSESTree.Node | undefined>();
const queue = [node.parent, node.left, node.right];
for (const current of queue) {
Expand All @@ -343,7 +368,7 @@ function isMixedLogicalExpression(node: TSESTree.LogicalExpression): boolean {
if (current && current.type === AST_NODE_TYPES.LogicalExpression) {
if (current.operator === '&&') {
return true;
} else if (current.operator === '||') {
} else if (['||', '||='].includes(current.operator)) {
// check the pieces of the node to catch cases like `a || b || c && d`
queue.push(current.parent, current.left, current.right);
}
Expand Down