Render maps with all null values as ? a\n? b\n or { a, b }

__tests__/corner-cases.js

@@ -195,7 +195,7 @@ describe('eemeli/yaml#l19', () => {
   test('seq', () => {
     const src = '- a: # 123'
     const doc = YAML.parseDocument(src)
-    expect(String(doc)).toBe('- a: # 123\n    null\n')
+    expect(String(doc)).toBe('- ? a # 123\n')
   })
 })
 
@@ -275,3 +275,23 @@ test('comment on single-line value in flow map', () => {
   const doc = YAML.parseDocument(src)
   expect(String(doc)).toBe('{\n  a: 1 #c\n}\n')
 })
+
+describe('maps with no values', () => {
+  test('block map', () => {
+    const src = `a: null\n? b #c`
+    const doc = YAML.parseDocument(src)
+    expect(String(doc)).toBe(`? a\n? b #c\n`)
+    doc.contents.items[1].value = 'x'
+    expect(String(doc)).toBe(`a: null\n? b #c\n: x\n`)
+  })
+
+  test('flow map', () => {
+    const src = `{\na: null,\n? b\n}`
+    const doc = YAML.parseDocument(src)
+    expect(String(doc)).toBe(`{ a, b }\n`)
+    doc.contents.items[1].comment = 'c'
+    expect(String(doc)).toBe(`{\n  a,\n  b #c\n}\n`)
+    doc.contents.items[1].value = 'x'
+    expect(String(doc)).toBe(`{\n  a: null,\n  b: #c\n    x\n}\n`)
+  })
+})

src/schema/Collection.js

@@ -1,42 +1,74 @@
 import addComment from '../addComment'
 import Node from './Node'
+import Pair from './Pair'
+import Scalar from './Scalar'
 
 export default class Collection extends Node {
   static maxFlowStringSingleLineLength = 60
 
   items = []
 
+  hasAllNullValues() {
+    return this.items.every(node => {
+      if (!(node instanceof Pair)) return false
+      const n = node.value
+      return (
+        n == null ||
+        (n instanceof Scalar &&
+          n.value == null &&
+          !n.commentBefore &&
+          !n.comment &&
+          !n.tag)
+      )
+    })
+  }
+
   // overridden in implementations
   toJSON() {
     return null
   }
 
-  toString(ctx, { blockItem, flowChars, itemIndent }, onComment, onChompKeep) {
+  toString(
+    ctx,
+    { blockItem, flowChars, isMap, itemIndent },
+    onComment,
+    onChompKeep
+  ) {
     const { doc, indent } = ctx
     const inFlow =
       (this.type && this.type.substr(0, 4) === 'FLOW') || ctx.inFlow
     if (inFlow) itemIndent += '  '
-    ctx = Object.assign({}, ctx, { indent: itemIndent, inFlow, type: null })
+    const allNullValues = isMap && this.hasAllNullValues()
+    ctx = Object.assign({}, ctx, {
+      allNullValues,
+      indent: itemIndent,
+      inFlow,
+      type: null
+    })
     let chompKeep = false
     let hasItemWithNewLine = false
     const nodes = this.items.reduce((nodes, item, i) => {
       let comment
       if (item) {
-        if (!chompKeep && item.spaceBefore) {
-          hasItemWithNewLine = true
+        if (!chompKeep && item.spaceBefore)
           nodes.push({ type: 'comment', str: '' })
-        }
-        if (item.commentBefore) {
-          hasItemWithNewLine = true
+
+        if (item.commentBefore)
           item.commentBefore.match(/^.*$/gm).forEach(line => {
             nodes.push({ type: 'comment', str: `#${line}` })
           })
-        }
-        if (item.comment) {
+
+        if (item.comment) comment = item.comment
+
+        if (
+          inFlow &&
+          ((!chompKeep && item.spaceBefore) ||
+            item.commentBefore ||
+            item.comment ||
+            (item.key && (item.key.commentBefore || item.key.comment)) ||
+            (item.value && (item.value.commentBefore || item.value.comment)))
+        )
           hasItemWithNewLine = true
-          comment = item.comment
-        }
-        if (item.value && item.value.comment) hasItemWithNewLine = true
       }
       chompKeep = false
       let str = doc.schema.stringify(
@@ -45,7 +77,7 @@ export default class Collection extends Node {
         () => (comment = null),
         () => (chompKeep = true)
       )
-      if (!hasItemWithNewLine && str.indexOf('\n') !== -1)
+      if (inFlow && !hasItemWithNewLine && str.includes('\n'))
         hasItemWithNewLine = true
       if (inFlow && i < this.items.length - 1) str += ','
       str = addComment(str, itemIndent, comment)

src/schema/Map.js

@@ -76,6 +76,7 @@ export default class YAMLMap extends Collection {
       {
         blockItem: n => n.str,
         flowChars: { start: '{', end: '}' },
+        isMap: true,
         itemIndent: ctx.indent || ''
       },
       onComment,

src/schema/Pair.js

@@ -52,11 +52,22 @@ export default class Pair extends Node {
       implicitKey: !explicitKey,
       indent: indent + '  '
     })
-    let str = doc.schema.stringify(key, ctx, () => {
-      keyComment = null
-    })
+    let chompKeep = false
+    let str = doc.schema.stringify(
+      key,
+      ctx,
+      () => (keyComment = null),
+      () => (chompKeep = true)
+    )
     str = addComment(str, ctx.indent, keyComment)
-    str = explicitKey ? `? ${str}\n${indent}:` : `${str}:` // FIXME: Allow for `? key` w/o value
+    if (ctx.allNullValues) {
+      if (this.comment) {
+        str = addComment(str, ctx.indent, this.comment)
+        if (onComment) onComment()
+      } else if (chompKeep && !keyComment && onChompKeep) onChompKeep()
+      return ctx.inFlow ? str : `? ${str}`
+    }
+    str = explicitKey ? `? ${str}\n${indent}:` : `${str}:`
     if (this.comment) {
       // expected (but not strictly required) to be a single-line comment
       str = addComment(str, ctx.indent, this.comment)
@@ -72,7 +83,7 @@ export default class Pair extends Node {
     }
     ctx.implicitKey = false
     let valueComment = value instanceof Node && value.comment
-    let chompKeep = false
+    chompKeep = false
     const valueStr = doc.schema.stringify(
       value,
       ctx,

src/schema/Seq.js

@@ -15,6 +15,7 @@ export default class YAMLSeq extends Collection {
       {
         blockItem: n => (n.type === 'comment' ? n.str : `- ${n.str}`),
         flowChars: { start: '[', end: ']' },
+        isMap: false,
         itemIndent: (ctx.indent || '') + '  '
       },
       onComment,