mix manager: default erlang toolchain constraint is hardcoded to ^26 and can resolve an Elixir/OTP combination that's incompatible

[Flo0807]

How are you running Renovate?

A Mend.io-hosted app

Which platform you running Renovate on?

GitHub.com

Which version of Renovate are you using?

43.234.1

Please tell us more about your question or problem

When the mix manager updates a lockfile, it provisions an Erlang + Elixir toolchain via two independent toolConstraints. The Erlang constraint falls back to a hardcoded ^26:

https://github.com/renovatebot/renovate/blob/43.234.1/lib/modules/manager/mix/artifacts.ts#L160:

toolConstraints: [
  {
    toolName: 'erlang',
    // https://hexdocs.pm/elixir/1.14.5/compatibility-and-deprecations.html#compatibility-between-elixir-and-erlang-otp
    constraint: config.constraints?.erlang ?? '^26',
  },
  {
    toolName: 'elixir',
    constraint: config.constraints?.elixir,
  },
],

The ^26 default was introduced in #22537 (June 2023), when OTP 26 was the newest stable release. It hasn't been updated since.

Why it's a problem

erlang and elixir are resolved independently:

• elixir → floats to newest stable (no default)
• erlang → newest matching ^26 → OTP 26.x

For recent Elixir this still happens to work, but Elixir 1.20 requires OTP 27+. The defaults would then resolve newest-Elixir against OTP 26 (an incompatible toolchain) and mix deps.get / deps.update can fail before it ever resolves dependencies. The default silently drifts further out of date with every Elixir release.

Possible fixes

1. Minimal: bump the default to track the current OTP line (^27). Fixes today, breaks again later.
2. Derive it: Renovate already downloads https://builds.hex.pm/builds/elixir/builds.txt via the hexpm-bob datasource, and every Elixir build line carries its compatible OTP major as a -otp-N suffix (e.g. v1.18.3-otp-27). That suffix is currently parsed and discarded in cleanVersion. The resolved Elixir version's -otp-N could instead seed the Erlang floor, so the two stay compatible automatically with no hardcoded value.

Workaround (for anyone hitting this)

Set it explicitly:

{ "constraints": { "erlang": "^27" } }

Logs (if relevant)

Logs

DEBUG: rawExec err (branch="renovate/floki-0.x")
{
  "err": {
    "cmd": "install-tool elixir v1.20.1",
    "stderr": "",
    "stdout": "[02:53:58.739] INFO (918): Installing tool elixir@1.20.1...\nDownload failed: https://github.com/elixir-lang/elixir/releases/download/v1.20.1/elixir-otp-26.zip\nDownload failed, retrying\nDownload failed: https://github.com/elixir-lang/elixir/releases/download/v1.20.1/elixir-otp-26.zip\nDownload failed, retrying\nDownload failed: https://github.com/elixir-lang/elixir/releases/download/v1.20.1/elixir-otp-26.zip\nDownload failed: https://github.com/elixir-lang/elixir/releases/download/v1.20.1/elixir-otp-26.zip\n[02:54:00.277] INFO (976): Downloading file ...\n    url: \"https://github.com/elixir-lang/elixir/releases/download/v1.20.1/elixir-otp-26.zip\"\n    output: \"/runner/cache/containerbase/99c24c2becd3b889a413735a4ca75aacf0ba5d0d99df5c47d8f174ee591ac017/elixir-otp-26.zip\"\n[02:54:00.391] ERROR (976): Request failed with status code 404 (Not Found): GET https://github.com/elixir-lang/elixir/releases/download/v1.20.1/elixir-otp-26.zip\n[02:54:00.392] FATAL (976): Download failed in 114ms.\n[02:54:00.548] ERROR (918): Command failed with exit code 1: bash /usr/local/containerbase/bin/v2-install-tool.sh install elixir 1.20.1\n[02:54:00.549] FATAL (918): Install tool elixir failed in 1.8s.\n",
    "options": {
      "cwd": "/tmp/renovate/repos/github/Flo0807/farens.me",
      "env": [
        "MIX_ARCHIVES",
        "HOME",
        "PATH",
        "LC_ALL",
        "LANG",
        "CONTAINERBASE_CACHE_DIR"
      ],
      "maxBuffer": 10485760,
      "timeout": 900000,
      "stdin": "pipe",
      "stdout": "pipe",
      "stderr": "pipe"
    },
    "exitCode": 1,
    "name": "ExecError",
    "message": "Command failed: install-tool elixir v1.20.1\n",
    "stack": "ExecError: Command failed: install-tool elixir v1.20.1\n\n    at ChildProcess.<anonymous> (file:///usr/local/renovate/lib/util/exec/common.ts:169:13)\n    at ChildProcess.emit (node:events:521:24)\n    at ChildProcess.emit (node:domain:489:12)\n    at Process.ChildProcess._handle.onexit (node:internal/child_process:295:12)"
  },
  "durationMs": 2140
}

[jamietanna]

OK, I've got a PR ready for (2): #44180

However, I've noticed that Erlang now uses a 4-part version number, which may mean there's some work to do for

renovate/lib/util/exec/containerbase.ts

Lines 67 to 71 in 9d0ddbd

	erlang: {
	datasource: 'github-releases',
	packageName: 'containerbase/erlang-prebuild',
	versioning: 'semver-coerced',
	},

Edit: no, that's OK

[jamietanna]

We'll collect dependency updates as part of #44180 - unsure if we'll be safe to update the default major version in a non-major Renovate version, but will discuss with the maintainers when we get the first dependency update. Thanks for flagging!