Function ensureDockerfileHasFinalStageName

src/spec-node/dockerfileUtils.ts:226–261

(dockerfile: string, defaultLastStageName: string)

// not expected to be called externally (exposed for testing)
export function ensureDockerfileHasFinalStageName(dockerfile: string, defaultLastStageName: string): { lastStageName: string; modifiedDockerfile: string | undefined } {

	// Find the last line that starts with "FROM" (possibly preceeded by white-space)
	const fromLines = [...dockerfile.matchAll(findFromLines)];
	if (fromLines.length === 0) {
		throw new Error('Error parsing Dockerfile: Dockerfile contains no FROM instructions');
	}

	const lastFromLineMatch = fromLines[fromLines.length - 1];
	const lastFromLine = lastFromLineMatch.groups?.line as string;

	// Test for "FROM [--platform=someplat] base [as label]"
	// That is, match against optional platform and label
	const fromMatch = lastFromLine.match(parseFromLine);
	if (!fromMatch) {
		throw new Error('Error parsing Dockerfile: failed to parse final FROM line');
	}
	if (fromMatch.groups?.label) {
		return {
			lastStageName: fromMatch.groups.label,
			modifiedDockerfile: undefined,
		};
	}

	// Last stage doesn't have a name, so modify the Dockerfile to set the name to defaultLastStageName
	const lastLineStartIndex = (lastFromLineMatch.index as number) + (fromMatch.index as number);
	const lastLineEndIndex = lastLineStartIndex + lastFromLine.length;
	const matchedFromText = fromMatch[0];
	let modifiedDockerfile = dockerfile.slice(0, lastLineStartIndex + matchedFromText.length);

	modifiedDockerfile += ` AS ${defaultLastStageName}`;
	const remainingFromLineLength = lastFromLine.length - matchedFromText.length;
	modifiedDockerfile += dockerfile.slice(lastLineEndIndex - remainingFromLineLength);

	return { lastStageName: defaultLastStageName, modifiedDockerfile: modifiedDockerfile };
}

export function supportsBuildContexts(dockerfile: Dockerfile) {
	const version = dockerfile.preamble.version;