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feat(spawn-usage): throw error if spawn-usage is used with xstate > 4
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Using the rule no longer makes sense in XState v5 since the new API makes it impossible to call it
outside of an assign function.
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@rlaffers
rlaffers committed Aug 17, 2023
1 parent d461b42 commit 02976f2
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Showing 5 changed files with 105 additions and 61 deletions.
2 changes: 1 addition & 1 deletion README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -96,7 +96,7 @@ The default shareable configurations are for XState v5. If you use the older XSt

| Rule | Description | Recommended |
| ---------------------------------------------------------------------------------- | ------------------------------------------------------------------ | ------------------ |
| [spawn-usage](docs/rules/spawn-usage.md) | Enforce correct usage of `spawn` | :heavy_check_mark: |
| [spawn-usage](docs/rules/spawn-usage.md) | Enforce correct usage of `spawn`. **Only for XState v4!** | :heavy_check_mark: |
| [no-infinite-loop](docs/rules/no-infinite-loop.md) | Detect infinite loops with eventless transitions | :heavy_check_mark: |
| [no-imperative-action](docs/rules/no-imperative-action.md) | Forbid using action creators imperatively | :heavy_check_mark: |
| [no-ondone-outside-compound-state](docs/rules/no-ondone-outside-compound-state.md) | Forbid onDone transitions on `atomic`, `history` and `final` nodes | :heavy_check_mark: |
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6 changes: 6 additions & 0 deletions docs/rules/spawn-usage.md
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Expand Up @@ -2,10 +2,16 @@

Ensure that the `spawn` function imported from xstate is used correctly.

** This rule is compatible with XState v4 only! **

## Rule Details

The `spawn` function has to be used in the context of an assignment function. Failing to do so creates an orphaned actor which has no effect.

### XState v5

XState v5 changed the way the `spawn` function is accessed. This effectively eliminated the possibility of using the `spawn` function outside of the `assign` function. Therefore, this rule becomes obsolete in XState v5. Do not use it with XState v5.

Examples of **incorrect** code for this rule:

```javascript
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2 changes: 0 additions & 2 deletions lib/index.js
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Original file line number Diff line number Diff line change
Expand Up @@ -38,7 +38,6 @@ module.exports = {
},
plugins: ['xstate'],
rules: {
'xstate/spawn-usage': 'error',
'xstate/no-infinite-loop': 'error',
'xstate/no-imperative-action': 'error',
'xstate/no-ondone-outside-compound-state': 'error',
Expand All @@ -62,7 +61,6 @@ module.exports = {
},
plugins: ['xstate'],
rules: {
'xstate/spawn-usage': 'error',
'xstate/no-infinite-loop': 'error',
'xstate/no-imperative-action': 'error',
'xstate/no-ondone-outside-compound-state': 'error',
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23 changes: 21 additions & 2 deletions lib/rules/spawn-usage.js
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@@ -1,8 +1,17 @@
'use strict'
/**
* This rule is relevant only for XState v4.
*
*/

const getDocsUrl = require('../utils/getDocsUrl')
const { isFunctionExpression, isIIFE } = require('../utils/predicates')
const XStateDetector = require('../utils/XStateDetector')
const getSettings = require('../utils/getSettings')

// TODO instead of the detector, consider using:
// context.getDeclaredVariables(node)
// context.sourceCode.getScope(node).variables

function isAssignCall(node) {
return node.type === 'CallExpression' && node.callee.name === 'assign'
Expand Down Expand Up @@ -30,8 +39,6 @@ function isInsideAssignerFunction(node) {
if (isAssignCall(parent)) {
return false
}
// TODO it's possible that a function expression inside assigner function
// does not get called, so nothing is ever spawned
parent = parent.parent
}
return false
Expand All @@ -55,6 +62,18 @@ module.exports = {

create: function (context) {
const xstateDetector = new XStateDetector()
const { version } = getSettings(context)
if (version !== 4) {
throw new Error(`Rule "spawn-usage" should be used with XState v4 only! Your XState version: ${version}. Either remove this rule from your ESLint config or set the correct version of XState in the config:
{
"settings": {
"xstate": {
"version": 4
}
}
}
`)
}

return {
...xstateDetector.visitors,
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133 changes: 77 additions & 56 deletions tests/lib/rules/spawn-usage.js
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@@ -1,84 +1,120 @@
const RuleTester = require('eslint').RuleTester
const rule = require('../../../lib/rules/spawn-usage')
const { withVersion } = require('../utils/settings')

const tests = {
valid: [
// not imported from xstate - ignore the rule
`
withVersion(
4,
`
spawn(x)
`,
`
),
withVersion(
4,
`
import { spawn } from 'xstate'
assign({
ref: () => spawn(x)
})
`,
`
),
withVersion(
4,
`
import { spawn } from 'xstate'
assign({
ref: () => spawn(x)
})
`,
`
),
withVersion(
4,
`
import { spawn } from 'xstate'
assign({
ref: () => spawn(x)
})
`,
`
),
withVersion(
4,
`
import { spawn } from 'xstate'
assign(() => ({
ref: spawn(x, 'id')
}))
`,
`
),
withVersion(
4,
`
import { spawn } from 'xstate'
assign(() => {
return {
ref: spawn(x)
}
})
`,
`
),
withVersion(
4,
`
import { spawn } from 'xstate'
assign(() => {
const ref = spawn(x)
return {
ref,
}
})
`,
`
),
withVersion(
4,
`
import { spawn } from 'xstate'
assign(() => {
const start = () => spawn(x)
return {
ref: start()
}
})
`,
`
),
withVersion(
4,
`
import { spawn } from 'xstate'
assign({
ref: function() { return spawn(x) }
})
`,
`
),
withVersion(
4,
`
import { spawn } from 'xstate'
assign(function() {
return {
ref: spawn(x, 'id')
}
})
`,
// other import types
`
),
// other import types
withVersion(
4,
`
import { spawn as foo } from 'xstate'
assign({
ref: () => foo(x)
})
`,
`
),
withVersion(
4,
`
import xs from 'xstate'
const { spawn } = xs
const foo = xs.spawn
Expand All @@ -89,8 +125,11 @@ const tests = {
ref3: () => xs.spawn(x),
ref4: () => xs['spawn'](x),
})
`,
`
),
withVersion(
4,
`
import * as xs from 'xstate'
const { spawn } = xs
const foo = xs.spawn
Expand All @@ -101,50 +140,51 @@ const tests = {
ref3: () => xs.spawn(x),
ref4: () => xs['spawn'](x),
})
`,
`
),
],
invalid: [
{
withVersion(4, {
code: `
import { spawn } from 'xstate'
spawn(x)
`,
errors: [{ messageId: 'invalidCallContext' }],
},
{
}),
withVersion(4, {
code: `
import { spawn } from 'xstate'
assign(spawn(x))
`,
errors: [{ messageId: 'invalidCallContext' }],
},
{
}),
withVersion(4, {
code: `
import { spawn } from 'xstate'
assign({
ref: spawn(x)
})
`,
errors: [{ messageId: 'invalidCallContext' }],
},
{
}),
withVersion(4, {
code: `
import { spawn } from 'xstate'
assign((() => ({
ref: spawn(x)
}))())
`,
errors: [{ messageId: 'invalidCallContext' }],
},
}),
// test other import types with a single invalid call
{
withVersion(4, {
code: `
import { spawn as foo } from 'xstate'
foo(x)
`,
errors: [{ messageId: 'invalidCallContext' }],
},
{
}),
withVersion(4, {
code: `
import xs from 'xstate'
const { spawn } = xs
Expand All @@ -162,8 +202,8 @@ const tests = {
{ messageId: 'invalidCallContext' },
{ messageId: 'invalidCallContext' },
],
},
{
}),
withVersion(4, {
code: `
import * as xs from 'xstate'
const { spawn } = xs
Expand All @@ -181,54 +221,35 @@ const tests = {
{ messageId: 'invalidCallContext' },
{ messageId: 'invalidCallContext' },
],
},
{
}),
withVersion(4, {
code: `
const { spawn } = require('xstate')
spawn(x)
`,
errors: [{ messageId: 'invalidCallContext' }],
},
{
}),
withVersion(4, {
code: `
const spawn = require('xstate').spawn
spawn(x)
`,
errors: [{ messageId: 'invalidCallContext' }],
},
{
}),
withVersion(4, {
code: `
const spawn = require('xstate')['spawn']
spawn(x)
`,
errors: [{ messageId: 'invalidCallContext' }],
},
{
}),
withVersion(4, {
code: `
const xs = require('xstate')
xs.spawn(x)
`,
errors: [{ messageId: 'invalidCallContext' }],
},
// {
// code: `
// import xs from 'xstate'
// xs.spawn(x)
// `,
// errors: [{ messageId: 'invalidCallContext' }],
// },
// TODO extend the rule to catch this use case
// {
// code: `
// assign(() => {
// const start = () => spawn(x)
// return {
// ref: start
// }
// })
// `,
// errors: [{ messageId: 'spawnNeverCalled' }],
// },
}),
],
}

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