always-return.js
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function isFunctionWithBlockStatement (node) {
if (node.type === 'FunctionExpression') {
return true
}
if (node.type === 'ArrowFunctionExpression') {
return node.body.type === 'BlockStatement'
}
return false
}
function isThenCallExpression (node) {
return (
node.type === 'CallExpression' &&
node.callee.type === 'MemberExpression' &&
node.callee.property.name === 'then'
)
}
function isFirstArgument (node) {
return (
node.parent &&
node.parent.arguments &&
node.parent.arguments[0] === node
)
}
function isInlineThenFunctionExpression (node) {
return (
isFunctionWithBlockStatement(node) &&
isThenCallExpression(node.parent) &&
isFirstArgument(node)
)
}
function hasParentReturnStatement (node) {
if (node && node.parent && node.parent.type) {
// if the parent is a then, and we haven't returned anything, fail
if (isThenCallExpression(node.parent)) {
return false
}
if (node.parent.type === 'ReturnStatement') {
return true
}
return hasParentReturnStatement(node.parent)
}
return false
}
function peek (arr) {
return arr[arr.length - 1]
}
module.exports = {
create: function (context) {
// funcInfoStack is a stack representing the stack of currently executing
// functions
// funcInfoStack[i].branchIDStack is a stack representing the currently
// executing branches ("codePathSegment"s) within the given function
// funcInfoStack[i].branchInfoMap is an object representing information
// about all branches within the given function
// funcInfoStack[i].branchInfoMap[j].good is a boolean representing whether
// the given branch explictly `return`s or `throw`s. It starts as `false`
// for every branch and is updated to `true` if a `return` or `throw`
// statement is found
// funcInfoStack[i].branchInfoMap[j].loc is a eslint SourceLocation object
// for the given branch
// example:
// funcInfoStack = [ { branchIDStack: [ 's1_1' ],
// branchInfoMap:
// { s1_1:
// { good: false,
// loc: <loc> } } },
// { branchIDStack: ['s2_1', 's2_4'],
// branchInfoMap:
// { s2_1:
// { good: false,
// loc: <loc> },
// s2_2:
// { good: true,
// loc: <loc> },
// s2_4:
// { good: false,
// loc: <loc> } } } ]
var funcInfoStack = []
function markCurrentBranchAsGood () {
var funcInfo = peek(funcInfoStack)
var currentBranchID = peek(funcInfo.branchIDStack)
if (funcInfo.branchInfoMap[currentBranchID]) {
funcInfo.branchInfoMap[currentBranchID].good = true
}
// else unreachable code
}
return {
ReturnStatement: markCurrentBranchAsGood,
ThrowStatement: markCurrentBranchAsGood,
onCodePathSegmentStart: function (segment, node) {
var funcInfo = peek(funcInfoStack)
funcInfo.branchIDStack.push(segment.id)
funcInfo.branchInfoMap[segment.id] = {good: false, node: node}
},
onCodePathSegmentEnd: function (segment, node) {
var funcInfo = peek(funcInfoStack)
funcInfo.branchIDStack.pop()
},
onCodePathStart: function (path, node) {
funcInfoStack.push({
branchIDStack: [],
branchInfoMap: {}
})
},
onCodePathEnd: function (path, node) {
var funcInfo = funcInfoStack.pop()
if (!isInlineThenFunctionExpression(node)) {
return
}
path.finalSegments.forEach((segment) => {
var id = segment.id
var branch = funcInfo.branchInfoMap[id]
if (!branch.good) {
if (hasParentReturnStatement(branch.node)) {
return
}
// check shortcircuit syntax like `x && x()` and `y || x()``
var prevSegments = segment.prevSegments
for (var ii = prevSegments.length - 1; ii >= 0; --ii) {
var prevSegment = prevSegments[ii]
if (funcInfo.branchInfoMap[prevSegment.id].good) return
}
context.report({
message: 'Each then() should return a value or throw',
node: branch.node
})
}
})
}
}
}
}