no-constant-condition.js
5.32 KB
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
141
142
143
144
145
146
147
148
149
150
151
152
153
154
/**
* @fileoverview Rule to flag use constant conditions
* @author Christian Schulz <http://rndm.de>
*/
"use strict";
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
meta: {
docs: {
description: "disallow constant expressions in conditions",
category: "Possible Errors",
recommended: true
},
schema: [
{
type: "object",
properties: {
checkLoops: {
type: "boolean"
}
},
additionalProperties: false
}
]
},
create(context) {
const options = context.options[0] || {},
checkLoops = options.checkLoops !== false;
//--------------------------------------------------------------------------
// Helpers
//--------------------------------------------------------------------------
/**
* Checks if a branch node of LogicalExpression short circuits the whole condition
* @param {ASTNode} node The branch of main condition which needs to be checked
* @param {string} operator The operator of the main LogicalExpression.
* @returns {boolean} true when condition short circuits whole condition
*/
function isLogicalIdentity(node, operator) {
switch (node.type) {
case "Literal":
return (operator === "||" && node.value === true) ||
(operator === "&&" && node.value === false);
case "UnaryExpression":
return (operator === "&&" && node.operator === "void");
case "LogicalExpression":
return isLogicalIdentity(node.left, node.operator) ||
isLogicalIdentity(node.right, node.operator);
// no default
}
return false;
}
/**
* Checks if a node has a constant truthiness value.
* @param {ASTNode} node The AST node to check.
* @param {boolean} inBooleanPosition `false` if checking branch of a condition.
* `true` in all other cases
* @returns {Bool} true when node's truthiness is constant
* @private
*/
function isConstant(node, inBooleanPosition) {
switch (node.type) {
case "Literal":
case "ArrowFunctionExpression":
case "FunctionExpression":
case "ObjectExpression":
case "ArrayExpression":
return true;
case "UnaryExpression":
if (node.operator === "void") {
return true;
}
return (node.operator === "typeof" && inBooleanPosition) ||
isConstant(node.argument, true);
case "BinaryExpression":
return isConstant(node.left, false) &&
isConstant(node.right, false) &&
node.operator !== "in";
case "LogicalExpression": {
const isLeftConstant = isConstant(node.left, inBooleanPosition);
const isRightConstant = isConstant(node.right, inBooleanPosition);
const isLeftShortCircuit = (isLeftConstant && isLogicalIdentity(node.left, node.operator));
const isRightShortCircuit = (isRightConstant && isLogicalIdentity(node.right, node.operator));
return (isLeftConstant && isRightConstant) || isLeftShortCircuit || isRightShortCircuit;
}
case "AssignmentExpression":
return (node.operator === "=") && isConstant(node.right, inBooleanPosition);
case "SequenceExpression":
return isConstant(node.expressions[node.expressions.length - 1], inBooleanPosition);
// no default
}
return false;
}
/**
* Reports when the given node contains a constant condition.
* @param {ASTNode} node The AST node to check.
* @returns {void}
* @private
*/
function checkConstantCondition(node) {
if (node.test && isConstant(node.test, true)) {
context.report({ node, message: "Unexpected constant condition." });
}
}
/**
* Checks node when checkLoops option is enabled
* @param {ASTNode} node The AST node to check.
* @returns {void}
* @private
*/
function checkLoop(node) {
if (checkLoops) {
checkConstantCondition(node);
}
}
//--------------------------------------------------------------------------
// Public
//--------------------------------------------------------------------------
return {
ConditionalExpression: checkConstantCondition,
IfStatement: checkConstantCondition,
WhileStatement: checkLoop,
DoWhileStatement: checkLoop,
ForStatement: checkLoop
};
}
};