Function parseUpdateFileChunk

src/core/tools/apply-patch/parser.ts:107–195

* Parse a single UpdateFileChunk from lines. * Returns the parsed chunk and number of lines consumed.

(
	lines: string[],
	lineNumber: number,
	allowMissingContext: boolean,
)

 * Returns the parsed chunk and number of lines consumed.
 */
function parseUpdateFileChunk(
	lines: string[],
	lineNumber: number,
	allowMissingContext: boolean,
): { chunk: UpdateFileChunk; linesConsumed: number } {
	if (lines.length === 0) {
		throw new ParseError("Update hunk does not contain any lines", lineNumber)
	}

	let changeContext: string | null = null
	let startIndex = 0

	// Check for context marker
	if (lines[0] === EMPTY_CHANGE_CONTEXT_MARKER) {
		changeContext = null
		startIndex = 1
	} else if (lines[0]?.startsWith(CHANGE_CONTEXT_MARKER)) {
		changeContext = lines[0].substring(CHANGE_CONTEXT_MARKER.length)
		startIndex = 1
	} else if (!allowMissingContext) {
		throw new ParseError(`Expected update hunk to start with a @@ context marker, got: '${lines[0]}'`, lineNumber)
	}

	if (startIndex >= lines.length) {
		throw new ParseError("Update hunk does not contain any lines", lineNumber + 1)
	}

	const chunk: UpdateFileChunk = {
		changeContext,
		oldLines: [],
		newLines: [],
		isEndOfFile: false,
	}

	let parsedLines = 0
	for (let i = startIndex; i < lines.length; i++) {
		const line = lines[i]

		if (line === EOF_MARKER) {
			if (parsedLines === 0) {
				throw new ParseError("Update hunk does not contain any lines", lineNumber + 1)
			}
			chunk.isEndOfFile = true
			parsedLines++
			break
		}

		const firstChar = line.charAt(0)

		// Empty line is treated as context
		if (line === "") {
			chunk.oldLines.push("")
			chunk.newLines.push("")
			parsedLines++
			continue
		}

		switch (firstChar) {