This repository has been archived by the owner on Mar 25, 2021. It is now read-only.
/
noBooleanLiteralCompareRule.ts
140 lines (127 loc) · 4.56 KB
/
noBooleanLiteralCompareRule.ts
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
/**
* @license
* Copyright 2017 Palantir Technologies, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import * as utils from "tsutils";
import * as ts from "typescript";
import * as Lint from "../index";
export class Rule extends Lint.Rules.TypedRule {
/* tslint:disable:object-literal-sort-keys */
public static metadata: Lint.IRuleMetadata = {
ruleName: "no-boolean-literal-compare",
description: "Warns on comparison to a boolean literal, as in `x === true`.",
hasFix: true,
optionsDescription: "Not configurable.",
options: null,
optionExamples: [true],
rationale: Lint.Utils.dedent`
Comparing boolean values to boolean literals is unnecessary, as those expressions will result in booleans too.
Just use the boolean values directly or negate them.
`,
type: "style",
typescriptOnly: true,
requiresTypeInfo: true,
};
/* tslint:enable:object-literal-sort-keys */
public static FAILURE_STRING(negate: boolean) {
return `This expression is unnecessarily compared to a boolean. Just ${
negate ? "negate it" : "use it directly"
}.`;
}
public applyWithProgram(sourceFile: ts.SourceFile, program: ts.Program): Lint.RuleFailure[] {
return this.applyWithFunction(sourceFile, walk, undefined, program.getTypeChecker());
}
}
function walk(ctx: Lint.WalkContext<void>, checker: ts.TypeChecker): void {
return ts.forEachChild(ctx.sourceFile, function cb(node: ts.Node): void {
if (utils.isBinaryExpression(node)) {
const cmp = getBooleanComparison(node, checker);
if (cmp !== undefined) {
ctx.addFailureAtNode(
cmp.expression,
Rule.FAILURE_STRING(cmp.negate),
fix(node, cmp),
);
}
}
return ts.forEachChild(node, cb);
});
}
interface Compare {
negate: boolean;
expression: ts.Expression;
}
function getBooleanComparison(
node: ts.BinaryExpression,
checker: ts.TypeChecker,
): Compare | undefined {
const cmp = deconstructComparison(node);
return cmp === undefined ||
!utils.isTypeFlagSet(checker.getTypeAtLocation(cmp.expression), ts.TypeFlags.Boolean)
? undefined
: cmp;
}
function fix(node: ts.BinaryExpression, { negate, expression }: Compare): Lint.Fix {
const deleted =
node.left === expression
? Lint.Replacement.deleteFromTo(node.left.end, node.end)
: Lint.Replacement.deleteFromTo(node.getStart(), node.right.getStart());
if (!negate) {
return deleted;
}
if (needsParenthesesForNegate(expression)) {
return [
deleted,
Lint.Replacement.appendText(node.getStart(), "!("),
Lint.Replacement.appendText(node.getEnd(), ")"),
];
}
return [deleted, Lint.Replacement.appendText(node.getStart(), "!")];
}
function needsParenthesesForNegate(node: ts.Expression): boolean {
switch (node.kind) {
case ts.SyntaxKind.AsExpression:
case ts.SyntaxKind.BinaryExpression:
return true;
default:
return false;
}
}
function deconstructComparison(node: ts.BinaryExpression): Compare | undefined {
const { left, operatorToken, right } = node;
const eq = Lint.getEqualsKind(operatorToken);
if (eq === undefined) {
return undefined;
}
const leftValue = booleanFromExpression(left);
if (leftValue !== undefined) {
return { negate: leftValue !== eq.isPositive, expression: right };
}
const rightValue = booleanFromExpression(right);
if (rightValue !== undefined) {
return { negate: rightValue !== eq.isPositive, expression: left };
}
return undefined;
}
function booleanFromExpression(node: ts.Expression): boolean | undefined {
switch (node.kind) {
case ts.SyntaxKind.TrueKeyword:
return true;
case ts.SyntaxKind.FalseKeyword:
return false;
default:
return undefined;
}
}