source: frontend/node_modules/eslint/lib/rules/prefer-const.js

Last change on this file was 9af201e, checked in by MBK <marija.karapandzova@…>, 12 days ago

Fix frontend appearance
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1/**
2 * @fileoverview A rule to suggest using of const declaration for variables that are never reassigned after declared.
3 * @author Toru Nagashima
4 */
5
6"use strict";
7
8//------------------------------------------------------------------------------
9// Requirements
10//------------------------------------------------------------------------------
11
12const FixTracker = require("./utils/fix-tracker");
13const astUtils = require("./utils/ast-utils");
14
15//------------------------------------------------------------------------------
16// Helpers
17//------------------------------------------------------------------------------
18
19const PATTERN_TYPE = /^(?:.+?Pattern|RestElement|SpreadProperty|ExperimentalRestProperty|Property)$/u;
20const DECLARATION_HOST_TYPE = /^(?:Program|BlockStatement|StaticBlock|SwitchCase)$/u;
21const DESTRUCTURING_HOST_TYPE = /^(?:VariableDeclarator|AssignmentExpression)$/u;
22
23/**
24 * Checks whether a given node is located at `ForStatement.init` or not.
25 * @param {ASTNode} node A node to check.
26 * @returns {boolean} `true` if the node is located at `ForStatement.init`.
27 */
28function isInitOfForStatement(node) {
29 return node.parent.type === "ForStatement" && node.parent.init === node;
30}
31
32/**
33 * Checks whether a given Identifier node becomes a VariableDeclaration or not.
34 * @param {ASTNode} identifier An Identifier node to check.
35 * @returns {boolean} `true` if the node can become a VariableDeclaration.
36 */
37function canBecomeVariableDeclaration(identifier) {
38 let node = identifier.parent;
39
40 while (PATTERN_TYPE.test(node.type)) {
41 node = node.parent;
42 }
43
44 return (
45 node.type === "VariableDeclarator" ||
46 (
47 node.type === "AssignmentExpression" &&
48 node.parent.type === "ExpressionStatement" &&
49 DECLARATION_HOST_TYPE.test(node.parent.parent.type)
50 )
51 );
52}
53
54/**
55 * Checks if an property or element is from outer scope or function parameters
56 * in destructing pattern.
57 * @param {string} name A variable name to be checked.
58 * @param {eslint-scope.Scope} initScope A scope to start find.
59 * @returns {boolean} Indicates if the variable is from outer scope or function parameters.
60 */
61function isOuterVariableInDestructing(name, initScope) {
62
63 if (initScope.through.some(ref => ref.resolved && ref.resolved.name === name)) {
64 return true;
65 }
66
67 const variable = astUtils.getVariableByName(initScope, name);
68
69 if (variable !== null) {
70 return variable.defs.some(def => def.type === "Parameter");
71 }
72
73 return false;
74}
75
76/**
77 * Gets the VariableDeclarator/AssignmentExpression node that a given reference
78 * belongs to.
79 * This is used to detect a mix of reassigned and never reassigned in a
80 * destructuring.
81 * @param {eslint-scope.Reference} reference A reference to get.
82 * @returns {ASTNode|null} A VariableDeclarator/AssignmentExpression node or
83 * null.
84 */
85function getDestructuringHost(reference) {
86 if (!reference.isWrite()) {
87 return null;
88 }
89 let node = reference.identifier.parent;
90
91 while (PATTERN_TYPE.test(node.type)) {
92 node = node.parent;
93 }
94
95 if (!DESTRUCTURING_HOST_TYPE.test(node.type)) {
96 return null;
97 }
98 return node;
99}
100
101/**
102 * Determines if a destructuring assignment node contains
103 * any MemberExpression nodes. This is used to determine if a
104 * variable that is only written once using destructuring can be
105 * safely converted into a const declaration.
106 * @param {ASTNode} node The ObjectPattern or ArrayPattern node to check.
107 * @returns {boolean} True if the destructuring pattern contains
108 * a MemberExpression, false if not.
109 */
110function hasMemberExpressionAssignment(node) {
111 switch (node.type) {
112 case "ObjectPattern":
113 return node.properties.some(prop => {
114 if (prop) {
115
116 /*
117 * Spread elements have an argument property while
118 * others have a value property. Because different
119 * parsers use different node types for spread elements,
120 * we just check if there is an argument property.
121 */
122 return hasMemberExpressionAssignment(prop.argument || prop.value);
123 }
124
125 return false;
126 });
127
128 case "ArrayPattern":
129 return node.elements.some(element => {
130 if (element) {
131 return hasMemberExpressionAssignment(element);
132 }
133
134 return false;
135 });
136
137 case "AssignmentPattern":
138 return hasMemberExpressionAssignment(node.left);
139
140 case "MemberExpression":
141 return true;
142
143 // no default
144 }
145
146 return false;
147}
148
149/**
150 * Gets an identifier node of a given variable.
151 *
152 * If the initialization exists or one or more reading references exist before
153 * the first assignment, the identifier node is the node of the declaration.
154 * Otherwise, the identifier node is the node of the first assignment.
155 *
156 * If the variable should not change to const, this function returns null.
157 * - If the variable is reassigned.
158 * - If the variable is never initialized nor assigned.
159 * - If the variable is initialized in a different scope from the declaration.
160 * - If the unique assignment of the variable cannot change to a declaration.
161 * e.g. `if (a) b = 1` / `return (b = 1)`
162 * - If the variable is declared in the global scope and `eslintUsed` is `true`.
163 * `/*exported foo` directive comment makes such variables. This rule does not
164 * warn such variables because this rule cannot distinguish whether the
165 * exported variables are reassigned or not.
166 * @param {eslint-scope.Variable} variable A variable to get.
167 * @param {boolean} ignoreReadBeforeAssign
168 * The value of `ignoreReadBeforeAssign` option.
169 * @returns {ASTNode|null}
170 * An Identifier node if the variable should change to const.
171 * Otherwise, null.
172 */
173function getIdentifierIfShouldBeConst(variable, ignoreReadBeforeAssign) {
174 if (variable.eslintUsed && variable.scope.type === "global") {
175 return null;
176 }
177
178 // Finds the unique WriteReference.
179 let writer = null;
180 let isReadBeforeInit = false;
181 const references = variable.references;
182
183 for (let i = 0; i < references.length; ++i) {
184 const reference = references[i];
185
186 if (reference.isWrite()) {
187 const isReassigned = (
188 writer !== null &&
189 writer.identifier !== reference.identifier
190 );
191
192 if (isReassigned) {
193 return null;
194 }
195
196 const destructuringHost = getDestructuringHost(reference);
197
198 if (destructuringHost !== null && destructuringHost.left !== void 0) {
199 const leftNode = destructuringHost.left;
200 let hasOuterVariables = false,
201 hasNonIdentifiers = false;
202
203 if (leftNode.type === "ObjectPattern") {
204 const properties = leftNode.properties;
205
206 hasOuterVariables = properties
207 .filter(prop => prop.value)
208 .map(prop => prop.value.name)
209 .some(name => isOuterVariableInDestructing(name, variable.scope));
210
211 hasNonIdentifiers = hasMemberExpressionAssignment(leftNode);
212
213 } else if (leftNode.type === "ArrayPattern") {
214 const elements = leftNode.elements;
215
216 hasOuterVariables = elements
217 .map(element => element && element.name)
218 .some(name => isOuterVariableInDestructing(name, variable.scope));
219
220 hasNonIdentifiers = hasMemberExpressionAssignment(leftNode);
221 }
222
223 if (hasOuterVariables || hasNonIdentifiers) {
224 return null;
225 }
226
227 }
228
229 writer = reference;
230
231 } else if (reference.isRead() && writer === null) {
232 if (ignoreReadBeforeAssign) {
233 return null;
234 }
235 isReadBeforeInit = true;
236 }
237 }
238
239 /*
240 * If the assignment is from a different scope, ignore it.
241 * If the assignment cannot change to a declaration, ignore it.
242 */
243 const shouldBeConst = (
244 writer !== null &&
245 writer.from === variable.scope &&
246 canBecomeVariableDeclaration(writer.identifier)
247 );
248
249 if (!shouldBeConst) {
250 return null;
251 }
252
253 if (isReadBeforeInit) {
254 return variable.defs[0].name;
255 }
256
257 return writer.identifier;
258}
259
260/**
261 * Groups by the VariableDeclarator/AssignmentExpression node that each
262 * reference of given variables belongs to.
263 * This is used to detect a mix of reassigned and never reassigned in a
264 * destructuring.
265 * @param {eslint-scope.Variable[]} variables Variables to group by destructuring.
266 * @param {boolean} ignoreReadBeforeAssign
267 * The value of `ignoreReadBeforeAssign` option.
268 * @returns {Map<ASTNode, ASTNode[]>} Grouped identifier nodes.
269 */
270function groupByDestructuring(variables, ignoreReadBeforeAssign) {
271 const identifierMap = new Map();
272
273 for (let i = 0; i < variables.length; ++i) {
274 const variable = variables[i];
275 const references = variable.references;
276 const identifier = getIdentifierIfShouldBeConst(variable, ignoreReadBeforeAssign);
277 let prevId = null;
278
279 for (let j = 0; j < references.length; ++j) {
280 const reference = references[j];
281 const id = reference.identifier;
282
283 /*
284 * Avoid counting a reference twice or more for default values of
285 * destructuring.
286 */
287 if (id === prevId) {
288 continue;
289 }
290 prevId = id;
291
292 // Add the identifier node into the destructuring group.
293 const group = getDestructuringHost(reference);
294
295 if (group) {
296 if (identifierMap.has(group)) {
297 identifierMap.get(group).push(identifier);
298 } else {
299 identifierMap.set(group, [identifier]);
300 }
301 }
302 }
303 }
304
305 return identifierMap;
306}
307
308/**
309 * Finds the nearest parent of node with a given type.
310 * @param {ASTNode} node The node to search from.
311 * @param {string} type The type field of the parent node.
312 * @param {Function} shouldStop A predicate that returns true if the traversal should stop, and false otherwise.
313 * @returns {ASTNode} The closest ancestor with the specified type; null if no such ancestor exists.
314 */
315function findUp(node, type, shouldStop) {
316 if (!node || shouldStop(node)) {
317 return null;
318 }
319 if (node.type === type) {
320 return node;
321 }
322 return findUp(node.parent, type, shouldStop);
323}
324
325//------------------------------------------------------------------------------
326// Rule Definition
327//------------------------------------------------------------------------------
328
329/** @type {import('../shared/types').Rule} */
330module.exports = {
331 meta: {
332 type: "suggestion",
333
334 docs: {
335 description: "Require `const` declarations for variables that are never reassigned after declared",
336 recommended: false,
337 url: "https://eslint.org/docs/latest/rules/prefer-const"
338 },
339
340 fixable: "code",
341
342 schema: [
343 {
344 type: "object",
345 properties: {
346 destructuring: { enum: ["any", "all"], default: "any" },
347 ignoreReadBeforeAssign: { type: "boolean", default: false }
348 },
349 additionalProperties: false
350 }
351 ],
352 messages: {
353 useConst: "'{{name}}' is never reassigned. Use 'const' instead."
354 }
355 },
356
357 create(context) {
358 const options = context.options[0] || {};
359 const sourceCode = context.sourceCode;
360 const shouldMatchAnyDestructuredVariable = options.destructuring !== "all";
361 const ignoreReadBeforeAssign = options.ignoreReadBeforeAssign === true;
362 const variables = [];
363 let reportCount = 0;
364 let checkedId = null;
365 let checkedName = "";
366
367
368 /**
369 * Reports given identifier nodes if all of the nodes should be declared
370 * as const.
371 *
372 * The argument 'nodes' is an array of Identifier nodes.
373 * This node is the result of 'getIdentifierIfShouldBeConst()', so it's
374 * nullable. In simple declaration or assignment cases, the length of
375 * the array is 1. In destructuring cases, the length of the array can
376 * be 2 or more.
377 * @param {(eslint-scope.Reference|null)[]} nodes
378 * References which are grouped by destructuring to report.
379 * @returns {void}
380 */
381 function checkGroup(nodes) {
382 const nodesToReport = nodes.filter(Boolean);
383
384 if (nodes.length && (shouldMatchAnyDestructuredVariable || nodesToReport.length === nodes.length)) {
385 const varDeclParent = findUp(nodes[0], "VariableDeclaration", parentNode => parentNode.type.endsWith("Statement"));
386 const isVarDecParentNull = varDeclParent === null;
387
388 if (!isVarDecParentNull && varDeclParent.declarations.length > 0) {
389 const firstDeclaration = varDeclParent.declarations[0];
390
391 if (firstDeclaration.init) {
392 const firstDecParent = firstDeclaration.init.parent;
393
394 /*
395 * First we check the declaration type and then depending on
396 * if the type is a "VariableDeclarator" or its an "ObjectPattern"
397 * we compare the name and id from the first identifier, if the names are different
398 * we assign the new name, id and reset the count of reportCount and nodeCount in
399 * order to check each block for the number of reported errors and base our fix
400 * based on comparing nodes.length and nodesToReport.length.
401 */
402
403 if (firstDecParent.type === "VariableDeclarator") {
404
405 if (firstDecParent.id.name !== checkedName) {
406 checkedName = firstDecParent.id.name;
407 reportCount = 0;
408 }
409
410 if (firstDecParent.id.type === "ObjectPattern") {
411 if (firstDecParent.init.name !== checkedName) {
412 checkedName = firstDecParent.init.name;
413 reportCount = 0;
414 }
415 }
416
417 if (firstDecParent.id !== checkedId) {
418 checkedId = firstDecParent.id;
419 reportCount = 0;
420 }
421 }
422 }
423 }
424
425 let shouldFix = varDeclParent &&
426
427 // Don't do a fix unless all variables in the declarations are initialized (or it's in a for-in or for-of loop)
428 (varDeclParent.parent.type === "ForInStatement" || varDeclParent.parent.type === "ForOfStatement" ||
429 varDeclParent.declarations.every(declaration => declaration.init)) &&
430
431 /*
432 * If options.destructuring is "all", then this warning will not occur unless
433 * every assignment in the destructuring should be const. In that case, it's safe
434 * to apply the fix.
435 */
436 nodesToReport.length === nodes.length;
437
438 if (!isVarDecParentNull && varDeclParent.declarations && varDeclParent.declarations.length !== 1) {
439
440 if (varDeclParent && varDeclParent.declarations && varDeclParent.declarations.length >= 1) {
441
442 /*
443 * Add nodesToReport.length to a count, then comparing the count to the length
444 * of the declarations in the current block.
445 */
446
447 reportCount += nodesToReport.length;
448
449 let totalDeclarationsCount = 0;
450
451 varDeclParent.declarations.forEach(declaration => {
452 if (declaration.id.type === "ObjectPattern") {
453 totalDeclarationsCount += declaration.id.properties.length;
454 } else if (declaration.id.type === "ArrayPattern") {
455 totalDeclarationsCount += declaration.id.elements.length;
456 } else {
457 totalDeclarationsCount += 1;
458 }
459 });
460
461 shouldFix = shouldFix && (reportCount === totalDeclarationsCount);
462 }
463 }
464
465 nodesToReport.forEach(node => {
466 context.report({
467 node,
468 messageId: "useConst",
469 data: node,
470 fix: shouldFix
471 ? fixer => {
472 const letKeywordToken = sourceCode.getFirstToken(varDeclParent, t => t.value === varDeclParent.kind);
473
474 /**
475 * Extend the replacement range to the whole declaration,
476 * in order to prevent other fixes in the same pass
477 * https://github.com/eslint/eslint/issues/13899
478 */
479 return new FixTracker(fixer, sourceCode)
480 .retainRange(varDeclParent.range)
481 .replaceTextRange(letKeywordToken.range, "const");
482 }
483 : null
484 });
485 });
486 }
487 }
488
489 return {
490 "Program:exit"() {
491 groupByDestructuring(variables, ignoreReadBeforeAssign).forEach(checkGroup);
492 },
493
494 VariableDeclaration(node) {
495 if (node.kind === "let" && !isInitOfForStatement(node)) {
496 variables.push(...sourceCode.getDeclaredVariables(node));
497 }
498 }
499 };
500 }
501};
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