From 6be0a9136dca077864782d1ad3b53a2cbb35748e Mon Sep 17 00:00:00 2001
From: Eemeli Aro <eemeli@gmail.com>
Date: Tue, 19 Nov 2024 12:41:54 +0200
Subject: [PATCH] fix: Default to literal block scalar if folded would overflow
 (fixes #585)

---
 src/stringify/stringifyString.ts | 42 +++++++++++++++++++-------------
 tests/doc/foldFlowLines.ts       | 10 ++++++++
 2 files changed, 35 insertions(+), 17 deletions(-)

diff --git a/src/stringify/stringifyString.ts b/src/stringify/stringifyString.ts
index 401143cd..b21dedd2 100644
--- a/src/stringify/stringifyString.ts
+++ b/src/stringify/stringifyString.ts
@@ -246,29 +246,37 @@ function blockString(
   }
 
   const indentSize = indent ? '2' : '1' // root is at -1
-  let header =
-    (literal ? '|' : '>') + (startWithSpace ? indentSize : '') + chomp
+  // Leading | or > is added later
+  let header = (startWithSpace ? indentSize : '') + chomp
   if (comment) {
     header += ' ' + commentString(comment.replace(/ ?[\r\n]+/g, ' '))
     if (onComment) onComment()
   }
 
-  if (literal) {
-    value = value.replace(/\n+/g, `$&${indent}`)
-    return `${header}\n${indent}${start}${value}${end}`
+  if (!literal) {
+    const foldedValue = value
+      .replace(/\n+/g, '\n$&')
+      .replace(/(?:^|\n)([\t ].*)(?:([\n\t ]*)\n(?![\n\t ]))?/g, '$1$2') // more-indented lines aren't folded
+      //                ^ more-ind. ^ empty     ^ capture next empty lines only at end of indent
+      .replace(/\n+/g, `$&${indent}`)
+    let literalFallback = false
+    const foldOptions = getFoldOptions(ctx, true)
+    if (blockQuote !== 'folded' && type !== Scalar.BLOCK_FOLDED) {
+      foldOptions.onOverflow = () => {
+        literalFallback = true
+      }
+    }
+    const body = foldFlowLines(
+      `${start}${foldedValue}${end}`,
+      indent,
+      FOLD_BLOCK,
+      foldOptions
+    )
+    if (!literalFallback) return `>${header}\n${indent}${body}`
   }
-  value = value
-    .replace(/\n+/g, '\n$&')
-    .replace(/(?:^|\n)([\t ].*)(?:([\n\t ]*)\n(?![\n\t ]))?/g, '$1$2') // more-indented lines aren't folded
-    //                ^ more-ind. ^ empty     ^ capture next empty lines only at end of indent
-    .replace(/\n+/g, `$&${indent}`)
-  const body = foldFlowLines(
-    `${start}${value}${end}`,
-    indent,
-    FOLD_BLOCK,
-    getFoldOptions(ctx, true)
-  )
-  return `${header}\n${indent}${body}`
+
+  value = value.replace(/\n+/g, `$&${indent}`)
+  return `|${header}\n${indent}${start}${value}${end}`
 }
 
 function plainString(
diff --git a/tests/doc/foldFlowLines.ts b/tests/doc/foldFlowLines.ts
index 7b4e4485..6c225dab 100644
--- a/tests/doc/foldFlowLines.ts
+++ b/tests/doc/foldFlowLines.ts
@@ -272,6 +272,16 @@ describe('block scalar', () => {
           }
       `)
   })
+
+  test('block scalar with very long lines (#585)', () => {
+    const str = ('a'.repeat(30) + '\n').repeat(3)
+    expect(YAML.stringify(str, { lineWidth: 20 })).toBe(source`
+      |
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+    `)
+  })
 })
 
 describe('end-to-end', () => {