docs: deduplicate paired code-block checks

scripts/paired-markdown-derivatives.spec.ts

@@ -0,0 +1,66 @@
+import { describe, expect, it } from 'vitest'
+import { partitionPairedMarkdownDerivatives } from './paired-markdown-derivatives.ts'
+
+interface Block {
+  doc: string
+  kind: string
+  code: string
+}
+
+const partition = (blocks: Block[]) => partitionPairedMarkdownDerivatives(
+  blocks,
+  block => block.doc,
+  block => `${block.kind}\0${block.code}`,
+)
+
+describe('partitionPairedMarkdownDerivatives', () => {
+  it('treats a complete byte-identical Chinese sequence as derivative', () => {
+    const english = [
+      { doc: 'docs/example.md', kind: 'ts', code: 'const one = 1' },
+      { doc: 'docs/example.md', kind: 'type-equiv', code: 'interface Example {}' },
+    ]
+    const chinese = english.map(block => ({ ...block, doc: 'docs/example.zh.md' }))
+    const unrelated = { doc: 'docs/other.md', kind: 'ts', code: 'const other = 2' }
+
+    expect(partition([...english, ...chinese, unrelated])).toEqual({
+      primary: [...english, unrelated],
+      derivatives: chinese,
+    })
+  })
+
+  it('keeps reordered, changed, partial, and orphan Chinese sequences primary', () => {
+    const sequence = (doc: string) => [
+      { doc, kind: 'ts', code: 'const one = 1' },
+      { doc, kind: 'ts', code: 'const two = 2' },
+    ]
+    const english = sequence('docs/example.md')
+    const changed = english.map((block, index) => ({
+      ...block,
+      doc: 'docs/example.zh.md',
+      code: index === 0 ? 'const one = 0' : block.code,
+    }))
+    const reorderedEnglish = sequence('docs/reordered.md')
+    const reordered = [...reorderedEnglish].reverse().map(block => ({ ...block, doc: 'docs/reordered.zh.md' }))
+    const partialEnglish = sequence('docs/partial.md')
+    const partial = [{ ...partialEnglish[0]!, doc: 'docs/partial.zh.md' }]
+    const orphan = [{ doc: 'docs/orphan.zh.md', kind: 'ts', code: 'const orphan = true' }]
+    const blocks = [
+      ...english,
+      ...changed,
+      ...reorderedEnglish,
+      ...reordered,
+      ...partialEnglish,
+      ...partial,
+      ...orphan,
+    ]
+
+    expect(partition(blocks)).toEqual({ primary: blocks, derivatives: [] })
+  })
+
+  it('requires the fence kind to match as well as the body', () => {
+    const english = { doc: 'docs/example.md', kind: 'type-equiv', code: 'interface Example {}' }
+    const chinese = { ...english, doc: 'docs/example.zh.md', kind: 'public-api' }
+
+    expect(partition([english, chinese])).toEqual({ primary: [english, chinese], derivatives: [] })
+  })
+})