From 908899357a0c71163d5c8d8b8d8cee73aeb2dd6d Mon Sep 17 00:00:00 2001 From: Milos Djermanovic Date: Tue, 29 Oct 2019 03:11:14 +0100 Subject: [PATCH] New: Add no-dupe-else-if rule (fixes #12469) --- docs/rules/no-dupe-else-if.md | 130 ++++++++++++++++++++++ lib/rules/index.js | 1 + lib/rules/no-dupe-else-if.js | 54 +++++++++ tests/lib/rules/no-dupe-else-if.js | 172 +++++++++++++++++++++++++++++ tools/rule-types.json | 1 + 5 files changed, 358 insertions(+) create mode 100644 docs/rules/no-dupe-else-if.md create mode 100644 lib/rules/no-dupe-else-if.js create mode 100644 tests/lib/rules/no-dupe-else-if.js diff --git a/docs/rules/no-dupe-else-if.md b/docs/rules/no-dupe-else-if.md new file mode 100644 index 00000000000..2f568b3a672 --- /dev/null +++ b/docs/rules/no-dupe-else-if.md @@ -0,0 +1,130 @@ +# Disallow duplicate conditions in `if-else-if` chains (no-dupe-else-if) + +`if-else-if` chains are commonly used when there is a need to execute only one branch or at most one branch out of several possible branches, based on certain conditions. + +```js +if (a) { + foo(); +} else if (b) { + bar(); +} else if (c) { + baz(); +} +``` + +Two identical test conditions in the same chain are almost always a mistake in the code. Unless there are side effects in the expressions, a duplicate will evaluate to the same `true` or `false` value as the identical expression earlier in the chain, meaning that its branch can never execute. + +```js +if (a) { + foo(); +} else if (b) { + bar(); +} else if (b) { + baz(); +} +``` + +In the above example, `baz()` can never execute. Obviously, `baz()` could be executed only when `b` evaluates to `true`, but in that case `bar()` would be executed instead, since it's earlier in the chain. + +## Rule Details + +This rule disallows duplicate conditions in the same `if-else-if` chain. + +Examples of **incorrect** code for this rule: + +```js +/*eslint no-dupe-else-if: "error"*/ + +if (isSomething(x)) { + foo(); +} else if (isSomething(x)) { + bar(); +} + +if (a) { + foo(); +} else if (b) { + bar(); +} else if (c && d) { + baz(); +} else if (c && d) { + quux(); +} else { + quuux(); +} + +if (n === 1) { + foo(); +} else if (n === 2) { + bar(); +} else if (n === 3) { + baz(); +} else if (n === 2) { + quux(); +} else if (n === 5) { + quuux(); +} +``` + +Examples of **correct** code for this rule: + +```js +/*eslint no-dupe-else-if: "error"*/ + +if (isSomething(x)) { + foo(); +} else if (isSomethingElse(x)) { + bar(); +} + +if (a) { + foo(); +} else if (b) { + bar(); +} else if (c && d) { + baz(); +} else if (c && e) { + quux(); +} else { + quuux(); +} + +if (n === 1) { + foo(); +} else if (n === 2) { + bar(); +} else if (n === 3) { + baz(); +} else if (n === 4) { + quux(); +} else if (n === 5) { + quuux(); +} +``` + +Please note that this rule does not compare conditions from the chain with conditions inside statements, and will not warn in the cases such as follows: + +```js +if (a) { + if (a) { + foo(); + } +} + +if (a) { + foo(); +} else { + if (a) { + bar(); + } +} +``` + +## When Not To Use It + +In rare cases where you really need identical test conditions in the same chain, which necessarily means that the expressions in the chain are causing and relying on side effects, you will have to turn this rule off. + +## Related Rules + +* [no-duplicate-case](no-duplicate-case.md) +* [no-lonely-if](no-lonely-if.md) diff --git a/lib/rules/index.js b/lib/rules/index.js index 8b0abc4ee7a..196e466ab91 100644 --- a/lib/rules/index.js +++ b/lib/rules/index.js @@ -108,6 +108,7 @@ module.exports = new LazyLoadingRuleMap(Object.entries({ "no-div-regex": () => require("./no-div-regex"), "no-dupe-args": () => require("./no-dupe-args"), "no-dupe-class-members": () => require("./no-dupe-class-members"), + "no-dupe-else-if": () => require("./no-dupe-else-if"), "no-dupe-keys": () => require("./no-dupe-keys"), "no-duplicate-case": () => require("./no-duplicate-case"), "no-duplicate-imports": () => require("./no-duplicate-imports"), diff --git a/lib/rules/no-dupe-else-if.js b/lib/rules/no-dupe-else-if.js new file mode 100644 index 00000000000..e1c4688432f --- /dev/null +++ b/lib/rules/no-dupe-else-if.js @@ -0,0 +1,54 @@ +/** + * @fileoverview Rule to disallow duplicate conditions in if-else-if chains + * @author Milos Djermanovic + */ + +"use strict"; + +//------------------------------------------------------------------------------ +// Requirements +//------------------------------------------------------------------------------ + +const astUtils = require("./utils/ast-utils"); + +//------------------------------------------------------------------------------ +// Rule Definition +//------------------------------------------------------------------------------ + +module.exports = { + meta: { + type: "problem", + + docs: { + description: "disallow duplicate conditions in if-else-if chains", + category: "Possible Errors", + recommended: false, + url: "https://eslint.org/docs/rules/no-dupe-else-if" + }, + + schema: [], + + messages: { + unexpected: "Duplicate condition in if-else-if chain." + } + }, + + create(context) { + const sourceCode = context.getSourceCode(); + + return { + IfStatement(node) { + let current = node; + + while (current.parent && current.parent.type === "IfStatement" && current.parent.alternate === current) { + current = current.parent; + + if (astUtils.equalTokens(node.test, current.test, sourceCode)) { + context.report({ node: node.test, messageId: "unexpected" }); + break; + } + } + } + }; + } +}; diff --git a/tests/lib/rules/no-dupe-else-if.js b/tests/lib/rules/no-dupe-else-if.js new file mode 100644 index 00000000000..ee60dc32186 --- /dev/null +++ b/tests/lib/rules/no-dupe-else-if.js @@ -0,0 +1,172 @@ +/** + * @fileoverview Tests for the no-dupe-else-if rule + * @author Milos Djermanovic + */ + +"use strict"; + +//------------------------------------------------------------------------------ +// Requirements +//------------------------------------------------------------------------------ + +const rule = require("../../../lib/rules/no-dupe-else-if"); +const { RuleTester } = require("../../../lib/rule-tester"); + +//------------------------------------------------------------------------------ +// Tests +//------------------------------------------------------------------------------ + +const ruleTester = new RuleTester(); + +ruleTester.run("no-dupe-else-if", rule, { + valid: [ + + // different test conditions + "if (a) {} else if (b) {}", + "if (a); else if (b); else if (c);", + "if (true) {} else if (false) {} else {}", + "if (1) {} else if (2) {}", + "if (f) {} else if (f()) {}", + "if (f(a)) {} else if (g(a)) {}", + "if (f(a)) {} else if (f(b)) {}", + "if (a === 1) {} else if (a === 2) {}", + "if (a === 1) {} else if (b === 1) {}", + + // not an if-else-if chain + "if (a) {}", + "if (a);", + "if (a) {} else {}", + "if (a) if (a) {}", + "if (a) if (a);", + "if (a) { if (a) {} }", + "if (a) {} else { if (a) {} }", + "if (a) {} if (a) {}", + "if (a); if (a);", + "while (a) if (a);", + "if (a); else a ? a : a;", + + // not same conditions in the chain + "if (a) { if (b) {} } else if (b) {}", + "if (a) if (b); else if (a);", + + // not equal tokens + "if (a) {} else if (!!a) {}", + "if (a === 1) {} else if (a === (1)) {}" + ], + + invalid: [ + + // basic tests + { + code: "if (a) {} else if (a) {}", + errors: [{ messageId: "unexpected", type: "Identifier", column: 20 }] + }, + { + code: "if (a); else if (a);", + errors: [{ messageId: "unexpected", type: "Identifier", column: 18 }] + }, + { + code: "if (a) {} else if (a) {} else {}", + errors: [{ messageId: "unexpected", type: "Identifier", column: 20 }] + }, + { + code: "if (a) {} else if (b) {} else if (a) {} else if (c) {}", + errors: [{ messageId: "unexpected", type: "Identifier", column: 35 }] + }, + { + code: "if (a) {} else if (b) {} else if (a) {}", + errors: [{ messageId: "unexpected", type: "Identifier", column: 35 }] + }, + { + code: "if (a) {} else if (b) {} else if (c) {} else if (a) {}", + errors: [{ messageId: "unexpected", type: "Identifier", column: 50 }] + }, + { + code: "if (a) {} else if (b) {} else if (b) {}", + errors: [{ messageId: "unexpected", type: "Identifier", column: 35 }] + }, + { + code: "if (a) {} else if (b) {} else if (b) {} else {}", + errors: [{ messageId: "unexpected", type: "Identifier", column: 35 }] + }, + { + code: "if (a) {} else if (b) {} else if (c) {} else if (b) {}", + errors: [{ messageId: "unexpected", type: "Identifier", column: 50 }] + }, + { + code: "if (a); else if (b); else if (c); else if (b); else if (d); else;", + errors: [{ messageId: "unexpected", type: "Identifier", column: 44 }] + }, + { + code: "if (a); else if (b); else if (c); else if (d); else if (b); else if (e);", + errors: [{ messageId: "unexpected", type: "Identifier", column: 57 }] + }, + + // multiple duplicates of the same condition + { + code: "if (a) {} else if (a) {} else if (a) {}", + errors: [ + { messageId: "unexpected", type: "Identifier", column: 20 }, + { messageId: "unexpected", type: "Identifier", column: 35 } + ] + }, + + // multiple duplicates of different conditions + { + code: "if (a) {} else if (b) {} else if (a) {} else if (b) {} else if (a) {}", + errors: [ + { messageId: "unexpected", type: "Identifier", column: 35 }, + { messageId: "unexpected", type: "Identifier", column: 50 }, + { messageId: "unexpected", type: "Identifier", column: 65 } + ] + }, + + // inner if statements do not affect chain + { + code: "if (a) { if (b) {} } else if (a) {}", + errors: [{ messageId: "unexpected", type: "Identifier", column: 31 }] + }, + + // various kinds of test conditions + { + code: "if (a === 1) {} else if (a === 1) {}", + errors: [{ messageId: "unexpected", type: "BinaryExpression", column: 26 }] + }, + { + code: "if (1 < a) {} else if (1 < a) {}", + errors: [{ messageId: "unexpected", type: "BinaryExpression", column: 24 }] + }, + { + code: "if (true) {} else if (true) {}", + errors: [{ messageId: "unexpected", type: "Literal", column: 23 }] + }, + { + code: "if (a && b) {} else if (a && b) {}", + errors: [{ messageId: "unexpected", type: "LogicalExpression", column: 25 }] + }, + { + code: "if (a && b || c) {} else if (a && b || c) {}", + errors: [{ messageId: "unexpected", type: "LogicalExpression", column: 31 }] + }, + { + code: "if (f(a)) {} else if (f(a)) {}", + errors: [{ messageId: "unexpected", type: "CallExpression", column: 23 }] + }, + + // spaces and comments do not affect comparison + { + code: "if (a === 1) {} else if (a===1) {}", + errors: [{ messageId: "unexpected", type: "BinaryExpression", column: 26 }] + }, + { + code: "if (a === 1) {} else if (a === /* comment */ 1) {}", + errors: [{ messageId: "unexpected", type: "BinaryExpression", column: 26 }] + }, + + // extra parens around the whole test condition do not affect comparison + { + code: "if (a === 1) {} else if ((a === 1)) {}", + errors: [{ messageId: "unexpected", type: "BinaryExpression", column: 27 }] + } + ] +}); diff --git a/tools/rule-types.json b/tools/rule-types.json index 6c72abb6cb2..518b459d736 100644 --- a/tools/rule-types.json +++ b/tools/rule-types.json @@ -95,6 +95,7 @@ "no-div-regex": "suggestion", "no-dupe-args": "problem", "no-dupe-class-members": "problem", + "no-dupe-else-if": "problem", "no-dupe-keys": "problem", "no-duplicate-case": "problem", "no-duplicate-imports": "problem",