AGENTS.md

@@ -88,10 +88,11 @@ The emitted markdown and HTML are contracts. After 1.0: previously-emitted outpu
 differently, or not at all, is MAJOR; new syntax while old output still round-trips is MINOR.
 Pre-1.0, normal 0.x rules.
 
-The error surface is a contract too. `ConvertError` is `{ code, message, path }` — the code from a
-closed list a consumer may switch exhaustively, the message free text, the path the node's position
-from the document root. Adding, removing or renaming a code is breaking, so a milestone meeting a
-new failure cause reuses a code where one fits; the list is complete at `0.1.0`. A code names the
+The error surface is a contract too. `ConvertError` is `{ code, message, path, position? }` — the
+code from a closed list a consumer may switch exhaustively, the message free text, the path the
+node's place from the document root, the position where a parse read the refusal in its input.
+Adding, removing or renaming a code is breaking, so a milestone meeting a new failure cause
+reuses a code where one fits; the list is complete at `0.1.0`. A code names the
 cause; where one cause recurs across node types or across directions, one code covers them all and
 `path` and `message` say which — `unsupported-nesting-depth` is the 500-level guard whichever
 direction hits it. A claim code names the spelling claimed, never the node that spelling would have built:
@@ -102,11 +103,27 @@ apart from a typo is what a consumer switches on when a later MINOR gives the na
 the grammar itself refuses stays a claim code, key order among it; a well-formed directive the
 node tables refuse — an attribute a node does not hold or spells elsewhere, a value outside its
 kind or its canonical spelling, an argument or a body its content model does not take — is
-`unsupported-node-shape`, the emitter's code for the same mismatch read the other way. A
-refusal found before its position is known — the block walk's, a directive reader's — is a
-`ConvertFault`, the code and message without the path; the node walk attaches the path as it
+`unsupported-node-shape`, the emitter's code for the same mismatch read the other way — one code
+across both directions for good, since the call site knows which direction it called and parting
+them after `0.1.0` is MAJOR. `unmappable-html` names the version rather than the element: this one
+converts no raw HTML, so at `0.3.0` the mapped elements stop erroring and the code stays for what
+no ADF node carries. A refusal found before its path is known — the block walk's, a directive
+reader's — is a `ConvertFault`, the code and message alone; the node walk attaches the path as it
 descends, so a document reports its first error in document order.
 
+`position` is the parse side's alone: an emitter reads no source, so an emit error carries `path`
+and nothing more. It is `{ line, offset }` at the start of the line the block holding the refusal
+begins on — the offset indexing the string the caller passed, the line counted from 1 — minted by
+the block walk and attached as results return, so the innermost block wins, the emitter's own
+refusals the parser re-enters for the CommonMark spelling included.
+
+A parse names a position for every refusal it returns, so the type says so rather than the prose:
+`Result<T, E extends ConvertError = ConvertError>`, and a direction reading a source returns
+`Result<T, ParseError>` — `ConvertError` with `position` required. An optional field a direction
+always fills is a branch a consumer cannot take, and the `!` §11 bans is how they take it anyway.
+`htmlToAdf` inherits this at `0.3.0`; the composed `markdownToHtml` and `htmlToMarkdown` keep the
+wide `Result<T>`, since half their refusals come from an emit stage that read no source.
+
 ## 9. Release automation
 
 - `package.json` version on `main` is the source of truth. CI on `main`: tests green and version

README.md

@@ -24,17 +24,23 @@ Pure functions, no I/O, no configuration. ADF is the hub: markdown↔HTML compos
 
 ```ts
 adfToMarkdown(doc: AdfDocument): Result<string>
-markdownToAdf(markdown: string): Result<AdfDocument>
+markdownToAdf(markdown: string): Result<AdfDocument, ParseError>
 adfToHtml(doc: AdfDocument): Result<string>
-htmlToAdf(html: string): Result<AdfDocument>
+htmlToAdf(html: string): Result<AdfDocument, ParseError>
 markdownToHtml(markdown: string): Result<string>   // via ADF
 htmlToMarkdown(html: string): Result<string>       // via ADF
 isAdfDocument(v: unknown): v is AdfDocument
 ```
 
 `Result<T>` is `{ ok: true; value: T } | { ok: false; error: ConvertError }` — nothing throws.
-`ConvertError` is `{ code, message, path }`: a code from a closed set, and the path of the node it
-names, from the document root.
+`ConvertError` is `{ code, message, path, position? }`: a code from a closed set, the path of the
+node it names from the document root, and — parsing — a `{ line, offset }` into the string passed
+in, at the start of the line the refused block begins on, `line` counted from 1.
+
+Parsing a source always names where in it the refusal sits, so `markdownToAdf` and `htmlToAdf`
+return the narrowed `ParseError`, whose `position` is there to read without a guard. Every other
+direction emits, from a document with no source behind it, and carries `path` alone — including
+`markdownToHtml` and `htmlToMarkdown`, where half the refusals come from the emit half.
 
 ## The guarantees
 

package.json

@@ -13,7 +13,7 @@
     "node": ">=18"
   },
   "scripts": {
-    "test": "node --test --experimental-test-coverage --test-coverage-exclude=\"src/**/*.test.ts\" --test-coverage-branches=97.9 --test-coverage-functions=100 --test-coverage-lines=100 \"src/**/*.test.ts\"",
+    "test": "node --test --experimental-test-coverage --test-coverage-exclude=\"src/**/*.test.ts\" --test-coverage-branches=97.95 --test-coverage-functions=100 --test-coverage-lines=100 \"src/**/*.test.ts\"",
     "typecheck": "tsc --noEmit && tsc --noEmit -p tsconfig.build.json"
   },
   "devDependencies": {

src/corpus.test.ts

@@ -192,11 +192,21 @@ for (const name of pairedNames(normalizationRoot, '.md', '.json')) {
   })
 }
 
+// The position the input itself gives an offset, recomputed rather than trusted from the parser.
+function lineStarting(markdown: string, offset: number): { line: number; offset: number } | undefined {
+  const before = markdown.slice(0, offset)
+  if (offset !== 0 && !/(?:\r\n|[\n\r])$/.test(before)) return undefined
+  return { line: before.split(/\r\n|[\n\r]/).length, offset }
+}
+
 for (const name of pairedNames(errorsRoot, '.md', '.error')) {
-  test(`errors/${name} is refused with the error it names`, () => {
-    const result = markdownToAdf(readFileSync(join(errorsRoot, `${name}.md`), 'utf8'))
+  test(`errors/${name} is refused with the error it names, at a line of its own input`, () => {
+    const markdown = readFileSync(join(errorsRoot, `${name}.md`), 'utf8')
+    const result = markdownToAdf(markdown)
     assert.ok(!result.ok, result.ok ? `built ${JSON.stringify(result.value)}` : '')
     assert.equal(result.error.code, readFileSync(join(errorsRoot, `${name}.error`), 'utf8').trimEnd())
+    const { position } = result.error
+    assert.deepEqual(position, lineStarting(markdown, position.offset))
   })
 }
 

src/index.ts

@@ -1,5 +1,5 @@
 export type { AdfAttributes, AdfDocument, AdfMark, AdfNode } from './adf/document.ts'
-export type { ConvertError, ConvertErrorCode, Result } from './result.ts'
+export type { ConvertError, ConvertErrorCode, ConvertErrorPath, ParseError, Result, SourcePosition } from './result.ts'
 export type { JsonValue } from './json-value.ts'
 export { adfToMarkdown } from './markdown/emit/adf-to-markdown.ts'
 export { isAdfDocument } from './adf/document.ts'

src/markdown/commonmark-grammar.ts

@@ -1,4 +1,4 @@
-import { readEntityReference } from './entity-references.ts'
+import { readEntityReference, replacementCharacter } from './entity-references.ts'
 
 export type LinePosition = 'first' | 'later'
 
@@ -27,6 +27,7 @@ const bracketedAutolink = new RegExp(`<(?:${autolinkSource})>`, 'y')
 const controlCharacter = new RegExp(`[${controlCharacterRange}]`)
 const htmlTag = new RegExp(htmlTagSource, 'y')
 const nullCharacter = new RegExp(nullCharacterSource)
+const nullCharacters = new RegExp(nullCharacterSource, 'g')
 const tagName = new RegExp(`^</?(${tagNameSource})[\\s\\S]*$`)
 // The opener's own match ends with the terminator where the construct is complete on its own (`<!-->`).
 const inlineHtmlConstructs = [
@@ -137,6 +138,10 @@ export function holdsNullCharacter(text: string): boolean {
   return nullCharacter.test(text)
 }
 
+export function replaceNullCharacters(text: string): string {
+  return text.replaceAll(nullCharacters, replacementCharacter)
+}
+
 function htmlTagName(text: string): string {
   return text.replace(tagName, '<$1>')
 }

src/markdown/emit/adf-to-markdown.test.ts

@@ -25,12 +25,17 @@ function path(result: Result<string>): readonly (number | string)[] {
   return result.ok ? ['emitted'] : result.error.path
 }
 
-test('names the node a refusal came from', () => {
+function position(result: Result<string>): unknown {
+  return result.ok ? 'emitted' : result.error.position
+}
+
+test('names the node a refusal came from, and no source the emitter never read', () => {
   const unspellable: AdfNode = { text: 'x', type: 'paragraph' }
   const list: AdfNode = { content: [{ content: [paragraph({ text: 'x', type: 'text' })], type: 'listItem' }, { content: [unspellable], type: 'listItem' }], type: 'bulletList' }
   assert.deepEqual(path(adfToMarkdown(document(paragraph({ text: 'x', type: 'text' }), list))), ['content', 1, 'content', 1, 'content', 0])
   assert.deepEqual(path(adfToMarkdown(document(paragraph({ text: 'x', type: 'text' }, { type: 'text' })))), ['content', 0, 'content', 1])
   assert.deepEqual(path(adfToMarkdown({ type: 'doc', version: 2 })), [])
+  assert.equal(position(adfToMarkdown(document(paragraph({ text: 'x', type: 'text' }), list))), undefined)
 })
 
 test('refuses a value that is not an ADF document', () => {

src/markdown/entity-references.ts

@@ -5,7 +5,7 @@ const anchoredEntityReference = new RegExp(`(?:${entityReferenceSource})`, 'y')
 const decimalReference = /^&#(\d+);/
 const hexadecimalReference = /^&#[Xx]([A-Fa-f0-9]+);/
 const largestCodePoint = 0x10ffff
-const replacementCharacter = '\ufffd'
+export const replacementCharacter = '\ufffd'
 const surrogates = { first: 0xd800, last: 0xdfff }
 
 // HTML5's named character references (https://html.spec.whatwg.org/entities.json), the semicolon-terminated half

src/markdown/parse/blocks.test.ts

@@ -91,12 +91,15 @@ test('holds a directive container open until the fence that closes it', () => {
     {
       argument: 'info',
       attributes: new Map([['panelColor', { decoded: '#ff0000', spelling: '"#ff0000"' }]]),
-      blocks: [{ kind: 'paragraph', text: 'Part.' }],
+      blocks: [{ kind: 'paragraph', position: { line: 2, offset: 37 }, text: 'Part.' }],
       kind: 'directive',
       name: 'panel',
+      position: { line: 1, offset: 0 },
     },
   ])
-  assert.deepEqual(parseBlocks('::rule\n').blocks, [{ argument: undefined, attributes: new Map(), blocks: undefined, kind: 'directive', name: 'rule' }])
+  assert.deepEqual(parseBlocks('::rule\n').blocks, [
+    { argument: undefined, attributes: new Map(), blocks: undefined, kind: 'directive', name: 'rule', position: { line: 1, offset: 0 } },
+  ])
 })
 
 test('names the directive fence a container does not sit longer than', () => {

src/markdown/parse/blocks.ts

@@ -1,4 +1,4 @@
-import type { ConvertFault } from '../../result.ts'
+import type { ConvertFault, SourcePosition } from '../../result.ts'
 import type { DirectiveAttributes, DirectiveLine } from '../directive-syntax.ts'
 import type { LinkDefinition } from '../link-syntax.ts'
 import {
@@ -12,13 +12,14 @@ import {
   markerInterruptsParagraph,
   openingCodeFence,
   openingHtmlBlock,
+  replaceNullCharacters,
   setextHeadingLevel,
 } from '../commonmark-grammar.ts'
 import { isPipeAlignment, isPipeDelimiter, malformedPipeTable, pipeCells } from '../pipe-table-syntax.ts'
 import { malformedDirective, readDirectiveLine } from '../directive-syntax.ts'
 import { readLinkDefinitions } from './link-reference-definitions.ts'
 
-export type Block =
+export type Block = { position: SourcePosition } & (
   | { argument: string | undefined; attributes: DirectiveAttributes; blocks: Block[] | undefined; kind: 'directive'; name: string }
   | { blocks: Block[]; kind: 'blockquote' }
   | { construct: string; kind: 'html' }
@@ -30,6 +31,7 @@ export type Block =
   | { kind: 'paragraph'; text: string }
   | { kind: 'rule' }
   | { kind: 'table'; rows: string[][] }
+)
 
 export type ParsedBlocks = { blocks: Block[]; definitions: Map<string, LinkDefinition> }
 
@@ -37,26 +39,27 @@ export type DirectiveBlock = Extract<Block, { kind: 'directive' }>
 
 type ListBlock = Extract<Block, { items: Block[][] }>
 
-type OpenDirective = { blocks: Block[]; colons: number; index: number; kind: 'directive'; parent: Block[] }
+type OpenDirective = { blocks: Block[]; colons: number; index: number; kind: 'directive'; parent: Block[]; position: SourcePosition }
 
 type OpenContainer =
   | Extract<Block, { kind: 'blockquote' }>
   | OpenDirective
   | { blocks: Block[]; indentation: number; kind: 'item'; list: ListBlock }
 
-type OpenLeaf =
+type OpenLeaf = { position: SourcePosition } & (
   | { closer: RegExp | undefined; construct: string; kind: 'html' }
   | { held: string[]; kind: 'indented-code'; lines: string[] }
   | { indentation: number; info: string; kind: 'fenced-code'; lines: string[]; marker: string }
-  | { kind: 'paragraph'; lines: string[] }
+  | { kind: 'paragraph'; lines: string[]; positions: SourcePosition[] }
   | { kind: 'pipe-table'; rows: [string[], ...string[][]] }
+)
 
 type ContainerStart = { kind: 'blockquote'; rest: Line } | { fresh: boolean; indentation: number; kind: 'item'; list: ListBlock; rest: Line }
 
 // The line from an absolute column on: a tab a cut splits keeps the stop it is measured against.
 type Line = { column: number; text: string }
 
-type Walk = ParsedBlocks & { leaf: OpenLeaf | undefined; stack: OpenContainer[] }
+type Walk = ParsedBlocks & { leaf: OpenLeaf | undefined; position: SourcePosition; stack: OpenContainer[] }
 
 const blankLine = /^[ \t]*$/
 const indentedCodeColumns = 4
@@ -65,8 +68,11 @@ const leafColons = 2
 const tabStop = 4
 
 export function parseBlocks(markdown: string): ParsedBlocks {
-  const walk: Walk = { blocks: [], definitions: new Map(), leaf: undefined, stack: [] }
-  for (const text of normalizeInput(markdown).split('\n')) readLine(walk, { column: 0, text })
+  const walk: Walk = { blocks: [], definitions: new Map(), leaf: undefined, position: { line: 1, offset: 0 }, stack: [] }
+  for (const line of sourceLines(markdown)) {
+    walk.position = line.position
+    readLine(walk, { column: 0, text: line.text })
+  }
   closeContainers(walk, 0)
   return { blocks: walk.blocks, definitions: walk.definitions }
 }
@@ -127,7 +133,7 @@ function openContainers(walk: Walk, line: Line, paragraphOpen: boolean, depth: n
   let opened = false
   let rest = line
   while (leadingColumns(rest) < indentedCodeColumns) {
-    const start = containerStart(rest, opened ? false : paragraphOpen, opened ? undefined : unmatched)
+    const start = containerStart(rest, opened ? false : paragraphOpen, opened ? undefined : unmatched, walk.position)
     if (start === undefined) break
     if (!opened) closeContainers(walk, depth)
     opened = true
@@ -137,15 +143,15 @@ function openContainers(walk: Walk, line: Line, paragraphOpen: boolean, depth: n
   return { opened, rest }
 }
 
-function containerStart(line: Line, paragraphOpen: boolean, enclosing: OpenContainer | undefined): ContainerStart | undefined {
+function containerStart(line: Line, paragraphOpen: boolean, enclosing: OpenContainer | undefined, position: SourcePosition): ContainerStart | undefined {
   const opener = removeColumns(line, largestOpenerIndentation)
   const blockquote = blockquoteRest(opener)
   if (blockquote !== undefined) return { kind: 'blockquote', rest: blockquote }
   if (isThematicBreak(opener.text)) return undefined
-  return itemStart(line, opener, paragraphOpen, enclosing)
+  return itemStart(line, opener, paragraphOpen, enclosing, position)
 }
 
-function itemStart(line: Line, opener: Line, paragraphOpen: boolean, enclosing: OpenContainer | undefined): ContainerStart | undefined {
+function itemStart(line: Line, opener: Line, paragraphOpen: boolean, enclosing: OpenContainer | undefined, position: SourcePosition): ContainerStart | undefined {
   const marker = listMarker(opener.text)
   if (marker === undefined) return undefined
   const after: Line = { column: opener.column + marker.width, text: opener.text.slice(marker.width) }
@@ -159,19 +165,19 @@ function itemStart(line: Line, opener: Line, paragraphOpen: boolean, enclosing:
     fresh: !continued,
     indentation: leadingColumns(line) + marker.width + padding,
     kind: 'item',
-    list: continued ? enclosing.list : openList(marker.start),
+    list: continued ? enclosing.list : openList(marker.start, position),
     rest: blank ? after : removeColumns(after, padding),
   }
 }
 
-function openList(start: number | undefined): ListBlock {
-  return start === undefined ? { items: [], kind: 'bulletList' } : { items: [], kind: 'orderedList', start }
+function openList(start: number | undefined, position: SourcePosition): ListBlock {
+  return start === undefined ? { items: [], kind: 'bulletList', position } : { items: [], kind: 'orderedList', position, start }
 }
 
 function openContainer(walk: Walk, start: ContainerStart): void {
   const blocks: Block[] = []
   if (start.kind === 'blockquote') {
-    const blockquote: OpenContainer = { blocks, kind: 'blockquote' }
+    const blockquote: OpenContainer = { blocks, kind: 'blockquote', position: walk.position }
     currentBlocks(walk).push(blockquote)
     walk.stack.push(blockquote)
     return
@@ -195,7 +201,11 @@ function closeContainers(walk: Walk, depth: number): void {
   closeLeaf(walk)
   for (const container of walk.stack.slice(depth)) {
     if (container.kind !== 'directive') continue
-    container.parent[container.index] = { fault: malformedDirective(`a container fenced with ${container.colons} colons is unclosed`), kind: 'fault' }
+    container.parent[container.index] = {
+      fault: malformedDirective(`a container fenced with ${container.colons} colons is unclosed`),
+      kind: 'fault',
+      position: container.position,
+    }
   }
   dropContainers(walk, depth)
 }
@@ -211,10 +221,12 @@ function openDirective(walk: Walk, directive: Extract<DirectiveLine, { kind: 'he
     blocks: directive.colons > leafColons ? [] : undefined,
     kind: 'directive',
     name: directive.name,
+    position: walk.position,
   }
   const parent = currentBlocks(walk)
   parent.push(block)
-  if (block.blocks !== undefined) walk.stack.push({ blocks: block.blocks, colons: directive.colons, index: parent.length - 1, kind: 'directive', parent })
+  const { position } = block
+  if (block.blocks !== undefined) walk.stack.push({ blocks: block.blocks, colons: directive.colons, index: parent.length - 1, kind: 'directive', parent, position })
 }
 
 function applyDirectiveLine(walk: Walk, directive: DirectiveLine): void {
@@ -251,7 +263,7 @@ function innermostDirective(walk: Walk): { container: OpenDirective; depth: numb
 }
 
 function pushFault(walk: Walk, fault: ConvertFault): void {
-  currentBlocks(walk).push({ fault, kind: 'fault' })
+  currentBlocks(walk).push({ fault, kind: 'fault', position: walk.position })
 }
 
 // A claimed line ends the lazy continuation CommonMark would fold it into (spec/flavour.md).
@@ -291,7 +303,7 @@ function readBlockLine(walk: Walk, line: Line): void {
     return
   }
   if (walk.leaf === undefined && leadingColumns(line) >= indentedCodeColumns) {
-    walk.leaf = { held: [], kind: 'indented-code', lines: [removeColumns(line, indentedCodeColumns).text] }
+    walk.leaf = { held: [], kind: 'indented-code', lines: [removeColumns(line, indentedCodeColumns).text], position: walk.position }
     return
   }
   openLeaf(walk, line)
@@ -320,14 +332,14 @@ function openLeaf(walk: Walk, line: Line): void {
   const cells = pipeCells(opener)
   if (cells !== undefined) {
     closeLeaf(walk)
-    walk.leaf = { kind: 'pipe-table', rows: [cells] }
+    walk.leaf = { kind: 'pipe-table', position: walk.position, rows: [cells] }
     return
   }
   if (readLineBlock(walk, opener)) return
   const fence = openingCodeFence(opener)
   if (fence !== undefined) {
     closeLeaf(walk)
-    walk.leaf = { indentation: leadingColumns(line), info: fence.info, kind: 'fenced-code', lines: [], marker: fence.marker }
+    walk.leaf = { indentation: leadingColumns(line), info: fence.info, kind: 'fenced-code', lines: [], marker: fence.marker, position: walk.position }
     return
   }
   const html = openingHtmlBlock(opener, walk.leaf?.kind === 'paragraph')
@@ -336,7 +348,7 @@ function openLeaf(walk: Walk, line: Line): void {
     return
   }
   closeLeaf(walk)
-  walk.leaf = { closer: html.closer, construct: html.construct, kind: 'html' }
+  walk.leaf = { closer: html.closer, construct: html.construct, kind: 'html', position: walk.position }
   if (html.closer?.test(line.text) === true) closeLeaf(walk)
 }
 
@@ -344,79 +356,98 @@ function openLeaf(walk: Walk, line: Line): void {
 function readLineBlock(walk: Walk, opener: string): boolean {
   const level = walk.leaf?.kind === 'paragraph' ? setextHeadingLevel(opener) : undefined
   if (level !== undefined) {
-    const text = takeParagraph(walk)
-    if (text !== undefined) {
-      currentBlocks(walk).push({ kind: 'heading', level, text })
+    const paragraph = takeParagraph(walk)
+    if (paragraph !== undefined) {
+      currentBlocks(walk).push({ kind: 'heading', level, position: paragraph.position, text: paragraph.text })
       return true
     }
   }
   if (isThematicBreak(opener)) {
     closeLeaf(walk)
-    currentBlocks(walk).push({ kind: 'rule' })
+    currentBlocks(walk).push({ kind: 'rule', position: walk.position })
     return true
   }
   const heading = atxHeading(opener)
   if (heading === undefined) return false
   closeLeaf(walk)
-  currentBlocks(walk).push({ kind: 'heading', level: heading.level, text: heading.text })
+  currentBlocks(walk).push({ kind: 'heading', level: heading.level, position: walk.position, text: heading.text })
   return true
 }
 
 function appendParagraph(walk: Walk, line: string): void {
   const leaf = walk.leaf
   const text = line.replace(/^[ \t]+/, '')
-  if (leaf?.kind === 'paragraph') leaf.lines.push(text)
-  else walk.leaf = { kind: 'paragraph', lines: [text] }
+  if (leaf?.kind !== 'paragraph') {
+    walk.leaf = { kind: 'paragraph', lines: [text], position: walk.position, positions: [walk.position] }
+    return
+  }
+  leaf.lines.push(text)
+  leaf.positions.push(walk.position)
 }
 
 function closeLeaf(walk: Walk): void {
   const leaf = walk.leaf
   if (leaf === undefined) return
   if (leaf.kind === 'paragraph') {
-    const text = takeParagraph(walk)
-    if (text !== undefined) currentBlocks(walk).push({ kind: 'paragraph', text })
+    const paragraph = takeParagraph(walk)
+    if (paragraph !== undefined) currentBlocks(walk).push(paragraph)
     return
   }
   walk.leaf = undefined
-  if (leaf.kind === 'html') currentBlocks(walk).push({ construct: leaf.construct, kind: 'html' })
-  else if (leaf.kind === 'pipe-table') currentBlocks(walk).push(pipeTableBlock(leaf.rows))
-  else currentBlocks(walk).push({ kind: 'code', language: leaf.kind === 'fenced-code' ? decodeTextEscapes(leaf.info) : '', text: leaf.lines.join('\n') })
+  const { position } = leaf
+  if (leaf.kind === 'html') currentBlocks(walk).push({ construct: leaf.construct, kind: 'html', position })
+  else if (leaf.kind === 'pipe-table') currentBlocks(walk).push(pipeTableBlock(leaf.rows, position))
+  else currentBlocks(walk).push({ kind: 'code', language: leaf.kind === 'fenced-code' ? decodeTextEscapes(leaf.info) : '', position, text: leaf.lines.join('\n') })
 }
 
-function pipeTableBlock(rows: readonly [string[], ...string[][]]): Block {
+function pipeTableBlock(rows: readonly [string[], ...string[][]], position: SourcePosition): Block {
   const [header, delimiter, ...body] = rows
   if (delimiter !== undefined && delimiter.some(isPipeAlignment)) {
-    return faultedBlock('a pipe table carries no column alignment ADF could hold')
+    return faultedBlock('a pipe table carries no column alignment ADF could hold', position)
   }
   if (delimiter === undefined || !delimiter.every(isPipeDelimiter)) {
-    return faultedBlock('a pipe table underlines its header with a row of `-` runs')
+    return faultedBlock('a pipe table underlines its header with a row of `-` runs', position)
   }
   const ragged = [delimiter, ...body].find((row) => row.length !== header.length)
-  if (ragged !== undefined) return faultedBlock(`a pipe table row holds ${ragged.length} cells where its header holds ${header.length}`)
-  return { kind: 'table', rows: [header, ...body] }
+  if (ragged !== undefined) return faultedBlock(`a pipe table row holds ${ragged.length} cells where its header holds ${header.length}`, position)
+  return { kind: 'table', position, rows: [header, ...body] }
 }
 
-function faultedBlock(message: string): Block {
-  return { fault: malformedPipeTable(message), kind: 'fault' }
+function faultedBlock(message: string, position: SourcePosition): Block {
+  return { fault: malformedPipeTable(message), kind: 'fault', position }
 }
 
-function takeParagraph(walk: Walk): string | undefined {
+// The definitions a paragraph gives up are whole lines, so what is left starts at one this held.
+function takeParagraph(walk: Walk): Extract<Block, { kind: 'paragraph' }> | undefined {
   const leaf = walk.leaf
   if (leaf?.kind !== 'paragraph') return undefined
   walk.leaf = undefined
   const text = readLinkDefinitions(walk.definitions, leaf.lines.join('\n'))
-  return text === '' ? undefined : text
+  if (text === '') return undefined
+  const kept = leaf.positions[leaf.lines.length - text.split('\n').length]
+  return { kind: 'paragraph', position: kept ?? leaf.position, text }
 }
 
 function currentBlocks(walk: Walk): Block[] {
   return walk.stack.at(-1)?.blocks ?? walk.blocks
 }
 
-function normalizeInput(markdown: string): string {
-  return markdown
-    .replace(/\r\n?/g, '\n')
-    .replaceAll('\u0000', '\ufffd')
-    .replace(/\n$/, '')
+function* sourceLines(markdown: string): Generator<{ position: SourcePosition; text: string }> {
+  let line = 1
+  let start = 0
+  for (let index = 0; index < markdown.length; index += 1) {
+    const character = markdown.charAt(index)
+    if (character !== '\n' && character !== '\r') continue
+    yield sourceLine(markdown, line, start, index)
+    if (character === '\r' && markdown.charAt(index + 1) === '\n') index += 1
+    line += 1
+    start = index + 1
+  }
+  if (start < markdown.length) yield sourceLine(markdown, line, start, markdown.length)
+}
+
+function sourceLine(markdown: string, line: number, start: number, end: number): { position: SourcePosition; text: string } {
+  return { position: { line, offset: start }, text: replaceNullCharacters(markdown.slice(start, end)) }
 }
 
 function leadingColumns(line: Line): number {

src/markdown/parse/markdown-to-adf.test.ts

@@ -2,7 +2,7 @@ import assert from 'node:assert/strict'
 import test from 'node:test'
 
 import type { AdfAttributes, AdfDocument, AdfMark, AdfNode } from '../../adf/document.ts'
-import type { Result } from '../../result.ts'
+import type { ParseError, Result, SourcePosition } from '../../result.ts'
 import { largestNesting } from '../../nesting.ts'
 import { markdownToAdf } from './markdown-to-adf.ts'
 
@@ -23,6 +23,10 @@ function path(result: Result<AdfDocument>): readonly (number | string)[] {
   return result.ok ? ['built'] : result.error.path
 }
 
+function position(result: Result<AdfDocument, ParseError>): SourcePosition | string {
+  return result.ok ? 'built' : result.error.position
+}
+
 function text(value: string): AdfNode {
   return { text: value, type: 'text' }
 }
@@ -443,6 +447,30 @@ test('swallows an HTML block ahead of the claim a line inside it would make', ()
   assert.equal(code(markdownToAdf('<div>\n| x |\n</div>\n')), 'unmappable-html')
 })
 
+test('names the line and the offset in the input a refusal sits at, the innermost block winning', () => {
+  assert.deepEqual(position(markdownToAdf('<div>\n')), { line: 1, offset: 0 })
+  assert.deepEqual(position(markdownToAdf('Part.\n\n<div>\n')), { line: 3, offset: 7 })
+  assert.deepEqual(position(markdownToAdf('> Part.\n>\n> a <span>b</span>\n')), { line: 3, offset: 10 })
+  assert.deepEqual(position(markdownToAdf('- Part.\n- a <span>b</span>\n')), { line: 2, offset: 8 })
+  assert.deepEqual(position(markdownToAdf('Part.\n\n:::panel info\nMore.\n')), { line: 3, offset: 7 })
+  assert.deepEqual(position(markdownToAdf('x\n\na <span>b</span>\n===\n')), { line: 3, offset: 3 })
+  assert.deepEqual(position(markdownToAdf('x\n\n```adf\n{\n```\n')), { line: 3, offset: 3 })
+  assert.deepEqual(position(markdownToAdf('x\n\n| a |\n')), { line: 3, offset: 3 })
+  assert.deepEqual(position(markdownToAdf('a\nb <span>c</span>\n')), { line: 1, offset: 0 })
+  assert.deepEqual(position(markdownToAdf('Part.\r\n\r\n<div>\r\n')), { line: 3, offset: 9 })
+  assert.deepEqual(position(markdownToAdf('a\u0000b\n\n<div>\n')), { line: 3, offset: 5 })
+  assert.deepEqual(position(markdownToAdf(':::caption\na <span>b</span>\n:::\n')), { line: 2, offset: 11 })
+  assert.deepEqual(position(markdownToAdf('x\n\n:::caption\n- a\n:::\n')), { line: 3, offset: 3 })
+})
+
+test('names the line the text a paragraph keeps starts on, never a definition line it gave up', () => {
+  assert.deepEqual(position(markdownToAdf('[a]: /url\n<span>b</span>\n')), { line: 2, offset: 10 })
+  assert.deepEqual(position(markdownToAdf('[a]: /a\n[b]: /b\n[c]: /c\n[d]: /d\n<span>x</span>\n')), { line: 5, offset: 32 })
+  assert.deepEqual(position(markdownToAdf('[a]:\n<the url>\n"Title"\n<span>b</span>\n')), { line: 4, offset: 23 })
+  assert.deepEqual(position(markdownToAdf('> [a]: /url\n> <span>b</span>\n')), { line: 2, offset: 12 })
+  assert.deepEqual(position(markdownToAdf(':::caption\n[a]: /url\n<span>b</span>\n:::\n')), { line: 3, offset: 21 })
+})
+
 test('gives up the link reference definitions a paragraph opens with', () => {
   assert.deepEqual(content(markdownToAdf('[a]: /url\n')), [])
   assert.deepEqual(content(markdownToAdf('[a]: /url\n[b]: /other\nPart.\n')), [paragraph('Part.')])

src/markdown/parse/markdown-to-adf.ts

@@ -4,16 +4,18 @@ import type { BlockDirectiveNode } from './directive-nodes.ts'
 import type { LinkDefinitions } from './inline-content.ts'
 import { carryName, readCarriedBlock } from '../opaque-carry.ts'
 import { commonMarkSpelling } from '../emit/adf-to-markdown.ts'
-import { failure, faulted, success, type ConvertErrorPath, type Result } from '../../result.ts'
+import { failure, faulted, positioned, success, type ConvertErrorPath, type ParseError, type Result, type SourcePosition } from '../../result.ts'
 import { languageSlot } from '../code-language.ts'
 import { largestNesting } from '../../nesting.ts'
 import { parseBlocks } from './blocks.ts'
 import { parseInlineContent } from './inline-content.ts'
 import { readBlockDirectiveNode } from './directive-nodes.ts'
 
-export function markdownToAdf(markdown: string): Result<AdfDocument> {
+const documentStart: SourcePosition = { line: 1, offset: 0 }
+
+export function markdownToAdf(markdown: string): Result<AdfDocument, ParseError> {
   const parsed = parseBlocks(markdown)
-  const content = blockNodes(parsed.blocks, parsed.definitions, [], 0)
+  const content = positioned(blockNodes(parsed.blocks, parsed.definitions, [], 0), documentStart)
   if (!content.ok) return content
   return success(content.value.length === 0 ? { type: 'doc', version: 1 } : { content: content.value, type: 'doc', version: 1 })
 }
@@ -22,7 +24,7 @@ function blockNodes(blocks: readonly Block[], definitions: LinkDefinitions, path
   if (depth > largestNesting) return failure('unsupported-nesting-depth', `the input nests deeper than the ${largestNesting} levels the parser carries`, path)
   const content: AdfNode[] = []
   for (const [index, block] of blocks.entries()) {
-    const node = blockNode(block, definitions, [...path, 'content', index], depth)
+    const node = positioned(blockNode(block, definitions, [...path, 'content', index], depth), block.position)
     if (!node.ok) return node
     content.push(node.value)
   }
@@ -111,7 +113,7 @@ function inlineBodyNode(node: AdfNode, blocks: readonly Block[], definitions: Li
   if (blocks.length === 0) return failure('unsupported-node-shape', `an empty ${node.type} takes the leaf form, ::`, path)
   const only = blocks.length === 1 ? blocks[0] : undefined
   if (only?.kind !== 'paragraph') return failure('unsupported-node-shape', `${node.type} takes one paragraph as its body`, path)
-  return contentNode(node, only.text, definitions, path)
+  return positioned(contentNode(node, only.text, definitions, path), only.position)
 }
 
 function containerNode(node: AdfNode, blocks: readonly Block[], definitions: LinkDefinitions, path: ConvertErrorPath, depth: number): Result<AdfNode> {

src/result.ts

@@ -17,15 +17,18 @@ export type ConvertErrorCode =
 
 export type ConvertErrorPath = readonly (number | string)[]
 
-export type ConvertError = {
+export type SourcePosition = { line: number; offset: number }
+
+export type ConvertFault = {
   code: ConvertErrorCode
   message: string
-  path: ConvertErrorPath
 }
 
-export type ConvertFault = Omit<ConvertError, 'path'>
+export type ConvertError = ConvertFault & { path: ConvertErrorPath; position?: SourcePosition }
 
-export type Result<T> = { error: ConvertError; ok: false } | { ok: true; value: T }
+export type ParseError = ConvertError & { position: SourcePosition }
+
+export type Result<T, E extends ConvertError = ConvertError> = { error: E; ok: false } | { ok: true; value: T }
 
 export function failure<T>(code: ConvertErrorCode, message: string, path: ConvertErrorPath): Result<T> {
   return { error: { code, message, path }, ok: false }
@@ -35,6 +38,11 @@ export function faulted<T>(fault: ConvertFault, path: ConvertErrorPath): Result<
   return failure(fault.code, fault.message, path)
 }
 
-export function success<T>(value: T): Result<T> {
+export function positioned<T>(result: Result<T>, position: SourcePosition): Result<T, ParseError> {
+  if (result.ok) return result
+  return { error: { ...result.error, position: result.error.position ?? position }, ok: false }
+}
+
+export function success<T>(value: T): { ok: true; value: T } {
   return { ok: true, value }
 }

todo-history.md

@@ -392,3 +392,23 @@ Under **3 — `markdownToAdf` (`0.1.0`)**:
       **Settled** (the maintainer, 2026-09-01): ADF's own `A` is "Atlassian", and "converter" is
       the one-way lossy tool §2 exists to replace, where a codec is both directions. It names the
       hub, not the formats around it.
+  - [x] **5b1 — The error's source position.** A parse error names an ADF path into a document the
+        caller does not hold yet — `unmappable-html` at `["content", 5]` for a `<span>` on line
+        12 — and no coordinate into the markdown string it passed in. `ConvertError` gains an
+        optional `position` the parser carries to every parse-side mint, and the README's published
+        shape gains it.
+        **Settled** (the maintainer, 2026-09-03): the position is the parse side's alone — an
+        emitter has no source string to point into, so emit-side errors keep `path` unchanged. The
+        representation and where the position is captured are implementation judgment.
+        The block walk mints it and the node walk attaches it as results return — at `blockNodes`,
+        and at the inline body a directive holds — so the innermost block wins and the emitter's
+        own refusals, which the parser re-enters for the CommonMark spelling, get an input
+        coordinate too. `markdownToAdf` wraps the walk once more, which is what turns the wide
+        `Result<T>` into the `Result<T, ParseError>` its signature promises rather than guarding
+        anything: the depth guard under it cannot fire at depth 0. A paragraph names the line its
+        kept text starts on, never a link reference definition it gave up. Line endings stay as
+        the input spells them, so an offset indexes the string the caller passed rather than a
+        normalized copy of it. §8 records the framings the review settled beside it:
+        `unsupported-node-shape` stays one code across the two directions, `unmappable-html` names
+        the version rather than the element, and a direction that reads a source returns the
+        narrowed error type.

todo.md

@@ -5,7 +5,8 @@ milestone. A done item shrinks to its title here; its full text moves to `todo-h
 
 ## Milestones
 
-Shipping order: 3h, 3i, 3j, 5a, 5 → `0.1.0`; 4b and 4c → `0.1.1`; 4, 3k → `0.2.0`; 6, 7 → `0.3.0`.
+Shipping order: 3h, 3i, 3j, 5a, 5b, 5 → `0.1.0`; 4b and 4c → `0.1.1`; 4, 3k → `0.2.0`; 6, 7 →
+`0.3.0`.
 The numbering is the order the work was planned in, not the order it ships.
 
 - [x] **0 — Scaffold.**
@@ -139,6 +140,37 @@ The numbering is the order the work was planned in, not the order it ships.
       `0.1.0` keeps — 3e names three shapes that parse and then refuse — so the release narrows
       that sentence or lists them.
 - [x] **5a — Rename to `@larvit/adf-codec`.**
+- [ ] **5b — The consumer's error surface (`0.1.0`).** A product-owner read of the public surface
+      found the error result legible to the library and opaque to the consumer holding it, and the
+      README documenting no part of it. The sub-items are that read's answers, and they land before
+      5 because §8 freezes the code list at `0.1.0` and 5b3's table is what reads the list before
+      the freeze closes it.
+  - [x] **5b1 — The error's source position.**
+  - [ ] **5b2 — The error messages.** Most state the rule and leave the violation to be inferred —
+        `a text node holds text` for a node holding none — so `rule: violation` becomes house style
+        across the sites that do. `not-an-adf-document` gives one sentence of eight words to `null`,
+        a string, a missing `version`, a `type` that is not `doc` and a REST envelope around the
+        document; naming the check that failed makes the highest-frequency integrator mistake
+        self-diagnosing without the library naming a REST shape (§7). The three carve-out claim
+        messages name the escape that unclaims the line — `\|`, `\~~`, `\:::` — which today only
+        `spec/flavour.md` holds. `unmappable-html` reads as §8 now frames it: this version converts
+        no raw HTML, never a permanent judgment on the element.
+  - [ ] **5b3 — The README's consumer surface.** §8 invites an exhaustive switch on `code` and no
+        code name appears in the README, so it gains a table — code, when it fires, what the
+        consumer does — grouped by direction; drafting it is the audit that reads the fifteen names
+        before 5 freezes them. Four things a reader who has not opened the code cannot know: raw
+        HTML is core CommonMark and every construct in input is an error until `0.3.0`, which the
+        guarantees' "three carve-outs and one gap" denies and which is the bot and LLM personas'
+        most common failure; `adfToHtml`, `htmlToAdf`, `markdownToHtml` and `htmlToMarkdown` sit
+        unmarked in the code block people copy from, as do the two HTML guarantee bullets, and take
+        a `0.3.0` mark or leave the block; `adfToMarkdown` is partial on valid ADF — two adjacent
+        `bulletList` nodes are an error result — which the viewer persona needs told along with
+        what to do about it; and GFM past tables and strikethrough is literal text, task lists
+        taking `:::taskList`. One sentence for the LLM persona: `code` is stable across minors,
+        `message` is free text. The type-level surface freezes at the same moment and gets the same
+        read: what `index.ts` exports and what it withholds, `ParseError` against `ConvertError`
+        where a direction reads a source, and `ConvertFault` staying internal — the README table
+        names the shapes a consumer switches on, so the two audits are one.
 - [ ] **6 — The HTML dialect spec (`0.3.0`).** Element-by-element mapping, the `data-*` fidelity
       scheme, the opaque-carry form, and the documented foreign-element set `htmlToAdf` accepts.
 - [ ] **7 — HTML, ship `0.3.0`.** `adfToHtml`, `htmlToAdf`, the composed `markdownToHtml` /