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Option to add trailing comma to multiline flow for toString #670

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Merged
eemeli merged 8 commits into from
Mar 13, 2026
+202 −3
Merged

Option to add trailing comma to multiline flow for toString #670

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aec5f4f
Option to add trailing comma to multiline flow for `toString`
datho7561 Feb 27, 2026
1c7a6d4
Place new option in alphabetical order
datho7561 Mar 2, 2026
cdb6a39
Clean up tests
datho7561 Mar 2, 2026
535fccf
Add test for line length == 0
datho7561 Mar 2, 2026
d248db9
Fix for lineWidth == 0, don't recompute values
datho7561 Mar 5, 2026
c89a2ef
Further cleanup of logic thanks to Eemeli's comments
datho7561 Mar 10, 2026
6d64af6
Move newline check right after `str` declaration
datho7561 Mar 13, 2026
620e668
Run prettier
datho7561 Mar 13, 2026
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7 changes: 7 additions & 0 deletions src/options.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -371,6 +371,13 @@ export type ToStringOptions = {
*/
singleQuote?: boolean | null

/**
* Add a trailing comma after the last entry in a flow map or flow sequence that's split across multiple lines.
*
* Default: `'false'`
*/
trailingComma?: boolean

/**
* String representation for `true`.
* With the core schema, use `'true'`, `'True'`, or `'TRUE'`.
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1 change: 1 addition & 0 deletions src/stringify/stringify.ts
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Expand Up @@ -55,6 +55,7 @@ export function createStringifyContext(
nullStr: 'null',
simpleKeys: false,
singleQuote: null,
trailingComma: false,
trueStr: 'true',
verifyAliasOrder: true
},
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17 changes: 14 additions & 3 deletions src/stringify/stringifyCollection.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -134,10 +134,21 @@ function stringifyFlowCollection(

if (comment) reqNewline = true
let str = stringify(item, itemCtx, () => (comment = null))
if (i < items.length - 1) str += ','
reqNewline ||= lines.length > linesAtValue || str.includes('\n')
if (i < items.length - 1) {
str += ','
} else if (ctx.options.trailingComma) {
if (ctx.options.lineWidth > 0) {
reqNewline ||=
lines.reduce((sum, line) => sum + line.length + 2, 2) +
(str.length + 2) >
ctx.options.lineWidth
}
if (reqNewline) {
str += ','
}
}
if (comment) str += lineComment(str, itemIndent, commentString(comment))
if (!reqNewline && (lines.length > linesAtValue || str.includes('\n')))
reqNewline = true
lines.push(str)
linesAtValue = lines.length
}
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180 changes: 180 additions & 0 deletions tests/doc/stringify.ts
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@eemeli eemeli Feb 28, 2026

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The tests added here are pretty hard to read, and they seem pretty random with how they use the source template tag. Please use the lineWidth and minContentWidth options to get the behaviour you want without needing to rely on the default wrapping at 80 characters.

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@datho7561 datho7561 Mar 2, 2026

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I tried made them look more consistent and added a shorter line width for the tests that are testing that. Let me know if they look better now.

Original file line number Diff line number Diff line change
Expand Up @@ -543,6 +543,186 @@ z:
expect(String(doc)).toBe(src)
})
})

describe('trailing comma (maps)', () => {
test('no trailing comma is added when the flow map is shorter than the word wrap length', () => {
const doc = YAML.parseDocument(source`
{
a: aaa,
b: bbb,
c: ccc
}
`)
expect(doc.toString({ trailingComma: true, lineWidth: 40 })).toBe(
'{ a: aaa, b: bbb, c: ccc }\n'
)
})
test('no trailing comma is added when the flow map is exactly the word wrap length', () => {
const doc = YAML.parseDocument(source`
{
a: aaa,
b: bbb,
c: ccc,
d: dddddd
}
`)
expect(doc.toString({ trailingComma: true, lineWidth: 40 })).toBe(
'{ a: aaa, b: bbb, c: ccc, d: dddddd }\n'
)
})
test('a trailing comma is added when the flow map is exactly one more than the word wrap length', () => {
const doc = YAML.parseDocument(source`
{
a: aaa,
b: bbb,
c: ccc,
d: ddddddd
}
`)
expect(doc.toString({ trailingComma: true, lineWidth: 40 })).toBe(
'{\n a: aaa,\n b: bbb,\n c: ccc,\n d: ddddddd,\n}\n'
)
})
test('no trailing comma is added when the word wrap length is 0', () => {
const doc = YAML.parseDocument(source`
{
a: aaa,
b: bbb,
c: ccc
}
`)
expect(doc.toString({ trailingComma: true, lineWidth: 0 })).toBe(
'{ a: aaa, b: bbb, c: ccc }\n'
)
})
test('a trailing comma is added when a comment is present in the flow map', () => {
const doc = YAML.parseDocument(source`
{
a: aaa, # my cool comment
b: bbb,
c: ccc
}
`)
expect(doc.toString({ trailingComma: true })).toBe(
'{\n a: aaa, # my cool comment\n b: bbb,\n c: ccc,\n}\n'
)
})
test('a trailing comma is added when a newline is present in the flow map', () => {
const doc = YAML.parseDocument(source`
{
a: aaa,

b: bbb
}
`)
expect(doc.toString({ trailingComma: true })).toBe(
'{\n a: aaa,\n\n b: bbb,\n}\n'
)
})
test('a trailing comma is added when one of the entries includes a newline', () => {
const doc = YAML.parseDocument(source`
{
a: {
a: a # a
},
b: bbb
}
`)
expect(doc.toString({ trailingComma: true })).toBe(
'{\n a:\n {\n a: a, # a\n },\n b: bbb,\n}\n'
)
})
})

describe('trailing comma (arrays)', () => {
test('no trailing comma is added when the flow array is shorter than the word wrap length', () => {
const doc = YAML.parseDocument(source`
[
aaa,
bbb,
ccc
]
`)
expect(doc.toString({ trailingComma: true, lineWidth: 40 })).toBe(
'[ aaa, bbb, ccc ]\n'
)
})
test('no trailing comma is added when the flow array is exactly the word wrap length', () => {
const doc = YAML.parseDocument(source`
[
aaaaaa,
bbbbbb,
cccccc,
ddddddddd
]
`)
expect(doc.toString({ trailingComma: true, lineWidth: 40 })).toBe(
'[ aaaaaa, bbbbbb, cccccc, ddddddddd ]\n'
)
})
test('a trailing comma is added when the flow array is exactly one more than the word wrap length', () => {
const doc = YAML.parseDocument(source`
[
aaaaaa,
bbbbbb,
cccccc,
dddddddddd
]
`)
expect(doc.toString({ trailingComma: true, lineWidth: 40 })).toBe(
'[\n aaaaaa,\n bbbbbb,\n cccccc,\n dddddddddd,\n]\n'
)
})
test('no trailing comma is added when the word wrap length is 0', () => {
const doc = YAML.parseDocument(source`
[
aaa,
bbb,
ccc
]
`)
expect(doc.toString({ trailingComma: true, lineWidth: 0 })).toBe(
'[ aaa, bbb, ccc ]\n'
)
})
test('a trailing comma is added when a comment is present in the flow array', () => {
const doc = YAML.parseDocument(source`
[
aaa, # my cool comment
bbb,
ccc
]
`)
expect(doc.toString({ trailingComma: true })).toBe(
'[\n aaa, # my cool comment\n bbb,\n ccc,\n]\n'
)
})
test('a trailing comma is added when a newline is present in the flow array', () => {
const doc = YAML.parseDocument(source`
[
aaa,

bbb
]
`)
expect(doc.toString({ trailingComma: true })).toBe(
'[\n aaa,\n\n bbb,\n]\n'
)
})
test('a trailing comma is added when one of the entries includes a newline', () => {
const doc = YAML.parseDocument(source`
[
{
a: a # a
},
bbb
]
`)
expect(doc.toString({ trailingComma: true })).toBe(
'[\n {\n a: a, # a\n },\n bbb,\n]\n'
)
})
})
})

test('Quoting colons (#43)', () => {
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