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/**
* @fileoverview Rule to replace assignment expressions with logical operator assignment
* @author Daniel Martens
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("./utils/ast-utils.js");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
const baseTypes = new Set(["Identifier", "Super", "ThisExpression"]);
/**
* Returns true iff either "undefined" or a void expression (eg. "void 0")
* @param {ASTNode} expression Expression to check
* @param {import('eslint-scope').Scope} scope Scope of the expression
* @returns {boolean} True iff "undefined" or "void ..."
*/
function isUndefined(expression, scope) {
if (expression.type === "Identifier" && expression.name === "undefined") {
return astUtils.isReferenceToGlobalVariable(scope, expression);
}
return (
expression.type === "UnaryExpression" &&
expression.operator === "void" &&
expression.argument.type === "Literal" &&
expression.argument.value === 0
);
}
/**
* Returns true iff the reference is either an identifier or member expression
* @param {ASTNode} expression Expression to check
* @returns {boolean} True for identifiers and member expressions
*/
function isReference(expression) {
return (
(expression.type === "Identifier" && expression.name !== "undefined") ||
expression.type === "MemberExpression"
);
}
/**
* Returns true iff the expression checks for nullish with loose equals.
* Examples: value == null, value == void 0
* @param {ASTNode} expression Test condition
* @param {import('eslint-scope').Scope} scope Scope of the expression
* @returns {boolean} True iff implicit nullish comparison
*/
function isImplicitNullishComparison(expression, scope) {
if (
expression.type !== "BinaryExpression" ||
expression.operator !== "=="
) {
return false;
}
const reference = isReference(expression.left) ? "left" : "right";
const nullish = reference === "left" ? "right" : "left";
return (
isReference(expression[reference]) &&
(astUtils.isNullLiteral(expression[nullish]) ||
isUndefined(expression[nullish], scope))
);
}
/**
* Condition with two equal comparisons.
* @param {ASTNode} expression Condition
* @returns {boolean} True iff matches ? === ? || ? === ?
*/
function isDoubleComparison(expression) {
return (
expression.type === "LogicalExpression" &&
expression.operator === "||" &&
expression.left.type === "BinaryExpression" &&
expression.left.operator === "===" &&
expression.right.type === "BinaryExpression" &&
expression.right.operator === "==="
);
}
/**
* Returns true iff the expression checks for undefined and null.
* Example: value === null || value === undefined
* @param {ASTNode} expression Test condition
* @param {import('eslint-scope').Scope} scope Scope of the expression
* @returns {boolean} True iff explicit nullish comparison
*/
function isExplicitNullishComparison(expression, scope) {
if (!isDoubleComparison(expression)) {
return false;
}
const leftReference = isReference(expression.left.left) ? "left" : "right";
const leftNullish = leftReference === "left" ? "right" : "left";
const rightReference = isReference(expression.right.left)
? "left"
: "right";
const rightNullish = rightReference === "left" ? "right" : "left";
return (
astUtils.isSameReference(
expression.left[leftReference],
expression.right[rightReference],
) &&
((astUtils.isNullLiteral(expression.left[leftNullish]) &&
isUndefined(expression.right[rightNullish], scope)) ||
(isUndefined(expression.left[leftNullish], scope) &&
astUtils.isNullLiteral(expression.right[rightNullish])))
);
}
/**
* Returns true for Boolean(arg) calls
* @param {ASTNode} expression Test condition
* @param {import('eslint-scope').Scope} scope Scope of the expression
* @returns {boolean} Whether the expression is a boolean cast
*/
function isBooleanCast(expression, scope) {
return (
expression.type === "CallExpression" &&
expression.callee.name === "Boolean" &&
expression.arguments.length === 1 &&
astUtils.isReferenceToGlobalVariable(scope, expression.callee)
);
}
/**
* Returns true for:
* truthiness checks: value, Boolean(value), !!value
* falsiness checks: !value, !Boolean(value)
* nullish checks: value == null, value === undefined || value === null
* @param {ASTNode} expression Test condition
* @param {import('eslint-scope').Scope} scope Scope of the expression
* @returns {?{ reference: ASTNode, operator: '??'|'||'|'&&'}} Null if not a known existence
*/
function getExistence(expression, scope) {
const isNegated =
expression.type === "UnaryExpression" && expression.operator === "!";
const base = isNegated ? expression.argument : expression;
switch (true) {
case isReference(base):
return { reference: base, operator: isNegated ? "||" : "&&" };
case base.type === "UnaryExpression" &&
base.operator === "!" &&
isReference(base.argument):
return { reference: base.argument, operator: "&&" };
case isBooleanCast(base, scope) && isReference(base.arguments[0]):
return {
reference: base.arguments[0],
operator: isNegated ? "||" : "&&",
};
case isImplicitNullishComparison(expression, scope):
return {
reference: isReference(expression.left)
? expression.left
: expression.right,
operator: "??",
};
case isExplicitNullishComparison(expression, scope):
return {
reference: isReference(expression.left.left)
? expression.left.left
: expression.left.right,
operator: "??",
};
default:
return null;
}
}
/**
* Returns true iff the node is inside a with block
* @param {ASTNode} node Node to check
* @returns {boolean} True iff passed node is inside a with block
*/
function isInsideWithBlock(node) {
if (node.type === "Program") {
return false;
}
return node.parent.type === "WithStatement" && node.parent.body === node
? true
: isInsideWithBlock(node.parent);
}
/**
* Gets the leftmost operand of a consecutive logical expression.
* @param {SourceCode} sourceCode The ESLint source code object
* @param {LogicalExpression} node LogicalExpression
* @returns {Expression} Leftmost operand
*/
function getLeftmostOperand(sourceCode, node) {
let left = node.left;
while (
left.type === "LogicalExpression" &&
left.operator === node.operator
) {
if (astUtils.isParenthesised(sourceCode, left)) {
/*
* It should have associativity,
* but ignore it if use parentheses to make the evaluation order clear.
*/
return left;
}
left = left.left;
}
return left;
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../types').Rule.RuleModule} */
module.exports = {
meta: {
type: "suggestion",
docs: {
description:
"Require or disallow logical assignment operator shorthand",
recommended: false,
frozen: true,
url: "https://eslint.org/docs/latest/rules/logical-assignment-operators",
},
schema: {
type: "array",
oneOf: [
{
items: [
{ const: "always" },
{
type: "object",
properties: {
enforceForIfStatements: {
type: "boolean",
},
},
additionalProperties: false,
},
],
minItems: 0, // 0 for allowing passing no options
maxItems: 2,
},
{
items: [{ const: "never" }],
minItems: 1,
maxItems: 1,
},
],
},
fixable: "code",
hasSuggestions: true,
messages: {
assignment:
"Assignment (=) can be replaced with operator assignment ({{operator}}).",
useLogicalOperator:
"Convert this assignment to use the operator {{ operator }}.",
logical:
"Logical expression can be replaced with an assignment ({{ operator }}).",
convertLogical:
"Replace this logical expression with an assignment with the operator {{ operator }}.",
if: "'if' statement can be replaced with a logical operator assignment with operator {{ operator }}.",
convertIf:
"Replace this 'if' statement with a logical assignment with operator {{ operator }}.",
unexpected:
"Unexpected logical operator assignment ({{operator}}) shorthand.",
separate:
"Separate the logical assignment into an assignment with a logical operator.",
},
},
create(context) {
const mode = context.options[0] === "never" ? "never" : "always";
const checkIf =
mode === "always" &&
context.options.length > 1 &&
context.options[1].enforceForIfStatements;
const sourceCode = context.sourceCode;
const isStrict = sourceCode.getScope(sourceCode.ast).isStrict;
/**
* Returns false if the access could be a getter
* @param {ASTNode} node Assignment expression
* @returns {boolean} True iff the fix is safe
*/
function cannotBeGetter(node) {
return (
node.type === "Identifier" &&
(isStrict || !isInsideWithBlock(node))
);
}
/**
* Check whether only a single property is accessed
* @param {ASTNode} node reference
* @returns {boolean} True iff a single property is accessed
*/
function accessesSingleProperty(node) {
if (!isStrict && isInsideWithBlock(node)) {
return node.type === "Identifier";
}
return (
node.type === "MemberExpression" &&
baseTypes.has(node.object.type) &&
(!node.computed ||
(node.property.type !== "MemberExpression" &&
node.property.type !== "ChainExpression"))
);
}
/**
* Adds a fixer or suggestion whether on the fix is safe.
* @param {{ messageId: string, node: ASTNode }} descriptor Report descriptor without fix or suggest
* @param {{ messageId: string, fix: Function }} suggestion Adds the fix or the whole suggestion as only element in "suggest" to suggestion
* @param {boolean} shouldBeFixed Fix iff the condition is true
* @returns {Object} Descriptor with either an added fix or suggestion
*/
function createConditionalFixer(descriptor, suggestion, shouldBeFixed) {
if (shouldBeFixed) {
return {
...descriptor,
fix: suggestion.fix,
};
}
return {
...descriptor,
suggest: [suggestion],
};
}
/**
* Returns the operator token for assignments and binary expressions
* @param {ASTNode} node AssignmentExpression or BinaryExpression
* @returns {import('eslint').AST.Token} Operator token between the left and right expression
*/
function getOperatorToken(node) {
return sourceCode.getFirstTokenBetween(
node.left,
node.right,
token => token.value === node.operator,
);
}
if (mode === "never") {
return {
// foo ||= bar
AssignmentExpression(assignment) {
if (
!astUtils.isLogicalAssignmentOperator(
assignment.operator,
)
) {
return;
}
const descriptor = {
messageId: "unexpected",
node: assignment,
data: { operator: assignment.operator },
};
const suggestion = {
messageId: "separate",
*fix(ruleFixer) {
if (
sourceCode.getCommentsInside(assignment)
.length > 0
) {
return;
}
const operatorToken = getOperatorToken(assignment);
// -> foo = bar
yield ruleFixer.replaceText(operatorToken, "=");
const assignmentText = sourceCode.getText(
assignment.left,
);
const operator = assignment.operator.slice(0, -1);
// -> foo = foo || bar
yield ruleFixer.insertTextAfter(
operatorToken,
` ${assignmentText} ${operator}`,
);
const precedence =
astUtils.getPrecedence(assignment.right) <=
astUtils.getPrecedence({
type: "LogicalExpression",
operator,
});
// ?? and || / && cannot be mixed but have same precedence
const mixed =
assignment.operator === "??=" &&
astUtils.isLogicalExpression(assignment.right);
if (
!astUtils.isParenthesised(
sourceCode,
assignment.right,
) &&
(precedence || mixed)
) {
// -> foo = foo || (bar)
yield ruleFixer.insertTextBefore(
assignment.right,
"(",
);
yield ruleFixer.insertTextAfter(
assignment.right,
")",
);
}
},
};
context.report(
createConditionalFixer(
descriptor,
suggestion,
cannotBeGetter(assignment.left),
),
);
},
};
}
return {
// foo = foo || bar
"AssignmentExpression[operator='='][right.type='LogicalExpression']"(
assignment,
) {
const leftOperand = getLeftmostOperand(
sourceCode,
assignment.right,
);
if (!astUtils.isSameReference(assignment.left, leftOperand)) {
return;
}
const descriptor = {
messageId: "assignment",
node: assignment,
data: { operator: `${assignment.right.operator}=` },
};
const suggestion = {
messageId: "useLogicalOperator",
data: { operator: `${assignment.right.operator}=` },
*fix(ruleFixer) {
if (
sourceCode.getCommentsInside(assignment).length > 0
) {
return;
}
// No need for parenthesis around the assignment based on precedence as the precedence stays the same even with changed operator
const assignmentOperatorToken =
getOperatorToken(assignment);
// -> foo ||= foo || bar
yield ruleFixer.insertTextBefore(
assignmentOperatorToken,
assignment.right.operator,
);
// -> foo ||= bar
const logicalOperatorToken = getOperatorToken(
leftOperand.parent,
);
const firstRightOperandToken =
sourceCode.getTokenAfter(logicalOperatorToken);
yield ruleFixer.removeRange([
leftOperand.parent.range[0],
firstRightOperandToken.range[0],
]);
},
};
context.report(
createConditionalFixer(
descriptor,
suggestion,
cannotBeGetter(assignment.left),
),
);
},
// foo || (foo = bar)
'LogicalExpression[right.type="AssignmentExpression"][right.operator="="]'(
logical,
) {
// Right side has to be parenthesized, otherwise would be parsed as (foo || foo) = bar which is illegal
if (
isReference(logical.left) &&
astUtils.isSameReference(logical.left, logical.right.left)
) {
const descriptor = {
messageId: "logical",
node: logical,
data: { operator: `${logical.operator}=` },
};
const suggestion = {
messageId: "convertLogical",
data: { operator: `${logical.operator}=` },
*fix(ruleFixer) {
if (
sourceCode.getCommentsInside(logical).length > 0
) {
return;
}
const parentPrecedence = astUtils.getPrecedence(
logical.parent,
);
const requiresOuterParenthesis =
logical.parent.type !== "ExpressionStatement" &&
(parentPrecedence === -1 ||
astUtils.getPrecedence({
type: "AssignmentExpression",
}) < parentPrecedence);
if (
!astUtils.isParenthesised(
sourceCode,
logical,
) &&
requiresOuterParenthesis
) {
yield ruleFixer.insertTextBefore(logical, "(");
yield ruleFixer.insertTextAfter(logical, ")");
}
// Also removes all opening parenthesis
yield ruleFixer.removeRange([
logical.range[0],
logical.right.range[0],
]); // -> foo = bar)
// Also removes all ending parenthesis
yield ruleFixer.removeRange([
logical.right.range[1],
logical.range[1],
]); // -> foo = bar
const operatorToken = getOperatorToken(
logical.right,
);
yield ruleFixer.insertTextBefore(
operatorToken,
logical.operator,
); // -> foo ||= bar
},
};
const fix =
cannotBeGetter(logical.left) ||
accessesSingleProperty(logical.left);
context.report(
createConditionalFixer(descriptor, suggestion, fix),
);
}
},
// if (foo) foo = bar
"IfStatement[alternate=null]"(ifNode) {
if (!checkIf) {
return;
}
const hasBody = ifNode.consequent.type === "BlockStatement";
if (hasBody && ifNode.consequent.body.length !== 1) {
return;
}
const body = hasBody
? ifNode.consequent.body[0]
: ifNode.consequent;
const scope = sourceCode.getScope(ifNode);
const existence = getExistence(ifNode.test, scope);
if (
body.type === "ExpressionStatement" &&
body.expression.type === "AssignmentExpression" &&
body.expression.operator === "=" &&
existence !== null &&
astUtils.isSameReference(
existence.reference,
body.expression.left,
)
) {
const descriptor = {
messageId: "if",
node: ifNode,
data: { operator: `${existence.operator}=` },
};
const suggestion = {
messageId: "convertIf",
data: { operator: `${existence.operator}=` },
*fix(ruleFixer) {
if (
sourceCode.getCommentsInside(ifNode).length > 0
) {
return;
}
const firstBodyToken =
sourceCode.getFirstToken(body);
const prevToken = sourceCode.getTokenBefore(ifNode);
if (
prevToken !== null &&
prevToken.value !== ";" &&
prevToken.value !== "{" &&
firstBodyToken.type !== "Identifier" &&
firstBodyToken.type !== "Keyword"
) {
// Do not fix if the fixed statement could be part of the previous statement (eg. fn() if (a == null) (a) = b --> fn()(a) ??= b)
return;
}
const operatorToken = getOperatorToken(
body.expression,
);
yield ruleFixer.insertTextBefore(
operatorToken,
existence.operator,
); // -> if (foo) foo ||= bar
yield ruleFixer.removeRange([
ifNode.range[0],
body.range[0],
]); // -> foo ||= bar
yield ruleFixer.removeRange([
body.range[1],
ifNode.range[1],
]); // -> foo ||= bar, only present if "if" had a body
const nextToken = sourceCode.getTokenAfter(
body.expression,
);
if (
hasBody &&
nextToken !== null &&
nextToken.value !== ";"
) {
yield ruleFixer.insertTextAfter(ifNode, ";");
}
},
};
const shouldBeFixed =
cannotBeGetter(existence.reference) ||
(ifNode.test.type !== "LogicalExpression" &&
accessesSingleProperty(existence.reference));
context.report(
createConditionalFixer(
descriptor,
suggestion,
shouldBeFixed,
),
);
}
},
};
},
};
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