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/**
* @fileoverview A rule to control the use of single variable declarations.
* @author Ian Christian Myers
*/
"use strict";
//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------
const astUtils = require("./utils/ast-utils");
//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------
/**
* Determines whether the given node is in a statement list.
* @param {ASTNode} node node to check
* @returns {boolean} `true` if the given node is in a statement list
*/
function isInStatementList(node) {
return astUtils.STATEMENT_LIST_PARENTS.has(node.parent.type);
}
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
/** @type {import('../types').Rule.RuleModule} */
module.exports = {
meta: {
type: "suggestion",
docs: {
description:
"Enforce variables to be declared either together or separately in functions",
recommended: false,
frozen: true,
url: "https://eslint.org/docs/latest/rules/one-var",
},
fixable: "code",
schema: [
{
oneOf: [
{
enum: ["always", "never", "consecutive"],
},
{
type: "object",
properties: {
separateRequires: {
type: "boolean",
},
var: {
enum: ["always", "never", "consecutive"],
},
let: {
enum: ["always", "never", "consecutive"],
},
const: {
enum: ["always", "never", "consecutive"],
},
},
additionalProperties: false,
},
{
type: "object",
properties: {
initialized: {
enum: ["always", "never", "consecutive"],
},
uninitialized: {
enum: ["always", "never", "consecutive"],
},
},
additionalProperties: false,
},
],
},
],
messages: {
combineUninitialized:
"Combine this with the previous '{{type}}' statement with uninitialized variables.",
combineInitialized:
"Combine this with the previous '{{type}}' statement with initialized variables.",
splitUninitialized:
"Split uninitialized '{{type}}' declarations into multiple statements.",
splitInitialized:
"Split initialized '{{type}}' declarations into multiple statements.",
splitRequires:
"Split requires to be separated into a single block.",
combine: "Combine this with the previous '{{type}}' statement.",
split: "Split '{{type}}' declarations into multiple statements.",
},
},
create(context) {
const MODE_ALWAYS = "always";
const MODE_NEVER = "never";
const MODE_CONSECUTIVE = "consecutive";
const mode = context.options[0] || MODE_ALWAYS;
const options = {};
if (typeof mode === "string") {
// simple options configuration with just a string
options.var = { uninitialized: mode, initialized: mode };
options.let = { uninitialized: mode, initialized: mode };
options.const = { uninitialized: mode, initialized: mode };
} else if (typeof mode === "object") {
// options configuration is an object
options.separateRequires = !!mode.separateRequires;
options.var = { uninitialized: mode.var, initialized: mode.var };
options.let = { uninitialized: mode.let, initialized: mode.let };
options.const = {
uninitialized: mode.const,
initialized: mode.const,
};
if (Object.hasOwn(mode, "uninitialized")) {
options.var.uninitialized = mode.uninitialized;
options.let.uninitialized = mode.uninitialized;
options.const.uninitialized = mode.uninitialized;
}
if (Object.hasOwn(mode, "initialized")) {
options.var.initialized = mode.initialized;
options.let.initialized = mode.initialized;
options.const.initialized = mode.initialized;
}
}
const sourceCode = context.sourceCode;
//--------------------------------------------------------------------------
// Helpers
//--------------------------------------------------------------------------
const functionStack = [];
const blockStack = [];
/**
* Increments the blockStack counter.
* @returns {void}
* @private
*/
function startBlock() {
blockStack.push({
let: { initialized: false, uninitialized: false },
const: { initialized: false, uninitialized: false },
});
}
/**
* Increments the functionStack counter.
* @returns {void}
* @private
*/
function startFunction() {
functionStack.push({ initialized: false, uninitialized: false });
startBlock();
}
/**
* Decrements the blockStack counter.
* @returns {void}
* @private
*/
function endBlock() {
blockStack.pop();
}
/**
* Decrements the functionStack counter.
* @returns {void}
* @private
*/
function endFunction() {
functionStack.pop();
endBlock();
}
/**
* Check if a variable declaration is a require.
* @param {ASTNode} decl variable declaration Node
* @returns {bool} if decl is a require, return true; else return false.
* @private
*/
function isRequire(decl) {
return (
decl.init &&
decl.init.type === "CallExpression" &&
decl.init.callee.name === "require"
);
}
/**
* Records whether initialized/uninitialized/required variables are defined in current scope.
* @param {string} statementType node.kind, one of: "var", "let", or "const"
* @param {ASTNode[]} declarations List of declarations
* @param {Object} currentScope The scope being investigated
* @returns {void}
* @private
*/
function recordTypes(statementType, declarations, currentScope) {
for (let i = 0; i < declarations.length; i++) {
if (declarations[i].init === null) {
if (
options[statementType] &&
options[statementType].uninitialized === MODE_ALWAYS
) {
currentScope.uninitialized = true;
}
} else {
if (
options[statementType] &&
options[statementType].initialized === MODE_ALWAYS
) {
if (
options.separateRequires &&
isRequire(declarations[i])
) {
currentScope.required = true;
} else {
currentScope.initialized = true;
}
}
}
}
}
/**
* Determines the current scope (function or block)
* @param {string} statementType node.kind, one of: "var", "let", or "const"
* @returns {Object} The scope associated with statementType
*/
function getCurrentScope(statementType) {
let currentScope;
if (statementType === "var") {
currentScope = functionStack.at(-1);
} else if (statementType === "let") {
currentScope = blockStack.at(-1).let;
} else if (statementType === "const") {
currentScope = blockStack.at(-1).const;
}
return currentScope;
}
/**
* Counts the number of initialized and uninitialized declarations in a list of declarations
* @param {ASTNode[]} declarations List of declarations
* @returns {Object} Counts of 'uninitialized' and 'initialized' declarations
* @private
*/
function countDeclarations(declarations) {
const counts = { uninitialized: 0, initialized: 0 };
for (let i = 0; i < declarations.length; i++) {
if (declarations[i].init === null) {
counts.uninitialized++;
} else {
counts.initialized++;
}
}
return counts;
}
/**
* Determines if there is more than one var statement in the current scope.
* @param {string} statementType node.kind, one of: "var", "let", or "const"
* @param {ASTNode[]} declarations List of declarations
* @returns {boolean} Returns true if it is the first var declaration, false if not.
* @private
*/
function hasOnlyOneStatement(statementType, declarations) {
const declarationCounts = countDeclarations(declarations);
const currentOptions = options[statementType] || {};
const currentScope = getCurrentScope(statementType);
const hasRequires = declarations.some(isRequire);
if (
currentOptions.uninitialized === MODE_ALWAYS &&
currentOptions.initialized === MODE_ALWAYS
) {
if (currentScope.uninitialized || currentScope.initialized) {
if (!hasRequires) {
return false;
}
}
}
if (declarationCounts.uninitialized > 0) {
if (
currentOptions.uninitialized === MODE_ALWAYS &&
currentScope.uninitialized
) {
return false;
}
}
if (declarationCounts.initialized > 0) {
if (
currentOptions.initialized === MODE_ALWAYS &&
currentScope.initialized
) {
if (!hasRequires) {
return false;
}
}
}
if (currentScope.required && hasRequires) {
return false;
}
recordTypes(statementType, declarations, currentScope);
return true;
}
/**
* Fixer to join VariableDeclaration's into a single declaration
* @param {VariableDeclarator[]} declarations The `VariableDeclaration` to join
* @returns {Function} The fixer function
*/
function joinDeclarations(declarations) {
const declaration = declarations[0];
const body = Array.isArray(declaration.parent.parent.body)
? declaration.parent.parent.body
: [];
const currentIndex = body.findIndex(
node => node.range[0] === declaration.parent.range[0],
);
const previousNode = body[currentIndex - 1];
return fixer => {
const type = sourceCode.getTokenBefore(declaration);
const prevSemi = sourceCode.getTokenBefore(type);
const res = [];
if (
previousNode &&
previousNode.kind === sourceCode.getText(type)
) {
if (prevSemi.value === ";") {
res.push(fixer.replaceText(prevSemi, ","));
} else {
res.push(fixer.insertTextAfter(prevSemi, ","));
}
res.push(fixer.replaceText(type, ""));
}
return res;
};
}
/**
* Fixer to split a VariableDeclaration into individual declarations
* @param {VariableDeclaration} declaration The `VariableDeclaration` to split
* @returns {Function|null} The fixer function
*/
function splitDeclarations(declaration) {
const { parent } = declaration;
// don't autofix code such as: if (foo) var x, y;
if (
!isInStatementList(
parent.type === "ExportNamedDeclaration"
? parent
: declaration,
)
) {
return null;
}
return fixer =>
declaration.declarations
.map(declarator => {
const tokenAfterDeclarator =
sourceCode.getTokenAfter(declarator);
if (tokenAfterDeclarator === null) {
return null;
}
const afterComma = sourceCode.getTokenAfter(
tokenAfterDeclarator,
{ includeComments: true },
);
if (tokenAfterDeclarator.value !== ",") {
return null;
}
const exportPlacement =
declaration.parent.type === "ExportNamedDeclaration"
? "export "
: "";
/*
* `var x,y`
* tokenAfterDeclarator ^^ afterComma
*/
if (
afterComma.range[0] ===
tokenAfterDeclarator.range[1]
) {
return fixer.replaceText(
tokenAfterDeclarator,
`; ${exportPlacement}${declaration.kind} `,
);
}
/*
* `var x,
* tokenAfterDeclarator ^
* y`
* ^ afterComma
*/
if (
afterComma.loc.start.line >
tokenAfterDeclarator.loc.end.line ||
afterComma.type === "Line" ||
afterComma.type === "Block"
) {
let lastComment = afterComma;
while (
lastComment.type === "Line" ||
lastComment.type === "Block"
) {
lastComment = sourceCode.getTokenAfter(
lastComment,
{ includeComments: true },
);
}
return fixer.replaceTextRange(
[
tokenAfterDeclarator.range[0],
lastComment.range[0],
],
`;${sourceCode.text.slice(tokenAfterDeclarator.range[1], lastComment.range[0])}${exportPlacement}${declaration.kind} `,
);
}
return fixer.replaceText(
tokenAfterDeclarator,
`; ${exportPlacement}${declaration.kind}`,
);
})
.filter(x => x);
}
/**
* Checks a given VariableDeclaration node for errors.
* @param {ASTNode} node The VariableDeclaration node to check
* @returns {void}
* @private
*/
function checkVariableDeclaration(node) {
const parent = node.parent;
const type = node.kind;
if (!options[type]) {
return;
}
const declarations = node.declarations;
const declarationCounts = countDeclarations(declarations);
const mixedRequires =
declarations.some(isRequire) && !declarations.every(isRequire);
if (options[type].initialized === MODE_ALWAYS) {
if (options.separateRequires && mixedRequires) {
context.report({
node,
messageId: "splitRequires",
});
}
}
// consecutive
const nodeIndex =
(parent.body &&
parent.body.length > 0 &&
parent.body.indexOf(node)) ||
0;
if (nodeIndex > 0) {
const previousNode = parent.body[nodeIndex - 1];
const isPreviousNodeDeclaration =
previousNode.type === "VariableDeclaration";
const declarationsWithPrevious = declarations.concat(
previousNode.declarations || [],
);
if (
isPreviousNodeDeclaration &&
previousNode.kind === type &&
!(
declarationsWithPrevious.some(isRequire) &&
!declarationsWithPrevious.every(isRequire)
)
) {
const previousDeclCounts = countDeclarations(
previousNode.declarations,
);
if (
options[type].initialized === MODE_CONSECUTIVE &&
options[type].uninitialized === MODE_CONSECUTIVE
) {
context.report({
node,
messageId: "combine",
data: {
type,
},
fix: joinDeclarations(declarations),
});
} else if (
options[type].initialized === MODE_CONSECUTIVE &&
declarationCounts.initialized > 0 &&
previousDeclCounts.initialized > 0
) {
context.report({
node,
messageId: "combineInitialized",
data: {
type,
},
fix: joinDeclarations(declarations),
});
} else if (
options[type].uninitialized === MODE_CONSECUTIVE &&
declarationCounts.uninitialized > 0 &&
previousDeclCounts.uninitialized > 0
) {
context.report({
node,
messageId: "combineUninitialized",
data: {
type,
},
fix: joinDeclarations(declarations),
});
}
}
}
// always
if (!hasOnlyOneStatement(type, declarations)) {
if (
options[type].initialized === MODE_ALWAYS &&
options[type].uninitialized === MODE_ALWAYS
) {
context.report({
node,
messageId: "combine",
data: {
type,
},
fix: joinDeclarations(declarations),
});
} else {
if (
options[type].initialized === MODE_ALWAYS &&
declarationCounts.initialized > 0
) {
context.report({
node,
messageId: "combineInitialized",
data: {
type,
},
fix: joinDeclarations(declarations),
});
}
if (
options[type].uninitialized === MODE_ALWAYS &&
declarationCounts.uninitialized > 0
) {
if (
node.parent.left === node &&
(node.parent.type === "ForInStatement" ||
node.parent.type === "ForOfStatement")
) {
return;
}
context.report({
node,
messageId: "combineUninitialized",
data: {
type,
},
fix: joinDeclarations(declarations),
});
}
}
}
// never
if (parent.type !== "ForStatement" || parent.init !== node) {
const totalDeclarations =
declarationCounts.uninitialized +
declarationCounts.initialized;
if (totalDeclarations > 1) {
if (
options[type].initialized === MODE_NEVER &&
options[type].uninitialized === MODE_NEVER
) {
// both initialized and uninitialized
context.report({
node,
messageId: "split",
data: {
type,
},
fix: splitDeclarations(node),
});
} else if (
options[type].initialized === MODE_NEVER &&
declarationCounts.initialized > 0
) {
// initialized
context.report({
node,
messageId: "splitInitialized",
data: {
type,
},
fix: splitDeclarations(node),
});
} else if (
options[type].uninitialized === MODE_NEVER &&
declarationCounts.uninitialized > 0
) {
// uninitialized
context.report({
node,
messageId: "splitUninitialized",
data: {
type,
},
fix: splitDeclarations(node),
});
}
}
}
}
//--------------------------------------------------------------------------
// Public API
//--------------------------------------------------------------------------
return {
Program: startFunction,
FunctionDeclaration: startFunction,
FunctionExpression: startFunction,
ArrowFunctionExpression: startFunction,
StaticBlock: startFunction, // StaticBlock creates a new scope for `var` variables
BlockStatement: startBlock,
ForStatement: startBlock,
ForInStatement: startBlock,
ForOfStatement: startBlock,
SwitchStatement: startBlock,
VariableDeclaration: checkVariableDeclaration,
"ForStatement:exit": endBlock,
"ForOfStatement:exit": endBlock,
"ForInStatement:exit": endBlock,
"SwitchStatement:exit": endBlock,
"BlockStatement:exit": endBlock,
"Program:exit": endFunction,
"FunctionDeclaration:exit": endFunction,
"FunctionExpression:exit": endFunction,
"ArrowFunctionExpression:exit": endFunction,
"StaticBlock:exit": endFunction,
};
},
};
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