Renovate doesn't handle single-quoted empty value for Dockerfile's ARG

[RahulGautamSingh]

Discussed in #43631

^{Originally posted by gavvvr May 27, 2026}

Description

Renovate's Dockerfile manager strips double quotes from ARG default values but not single quotes.

Docker treats ARG FOO='' and ARG FOO="" identically (both = empty string), but Renovate keeps the literal '', so a variable reference like FROM ${FOO}node:... resolves to ''node and the lookup fails.

Steps to reproduce

ARG DOCKER_HUB_MIRROR=''
ARG NODE_VERSION=21
FROM ${DOCKER_HUB_MIRROR}node:${NODE_VERSION}-alpine

Expected : '' treated as empty, image resolves to node:21-alpine
Actual : Failed to look up docker package ''node: no-result

Cause

This code block only unquotes double quotes but it should also handle single-quoted values

renovate/lib/modules/manager/dockerfile/extract.ts

Lines 326 to 328 in e77f3d1

	if (argMatchValue.startsWith('"') && argMatchValue.endsWith('"')) {
	argMatchValue = argMatchValue.slice(1, -1);
	}

Fix

One-line fix plus a test case

Here is the repo: https://github.com/gavvvr/repros/tree/renovate-43631
and CI logs: https://github.com/gavvvr/repros/actions/runs/26522833187/job/78118379664#step:3:118