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ADR 0003: Single repo with machine_type templating, not branches

  • Status: Accepted
  • Date: 2025-04-12

Context

Personal and work Macs need overlapping but not identical configuration. Personal machines get Steam, Tidal, crypto wallets; work machines skip them. Both share the bulk of CLI tools, dev apps, and macOS defaults.

Options:

  1. One repo, conditional templating on a machine_type variable.
  2. Separate personal and work git branches with cherry-picks between them.
  3. Separate repos.
  4. A personal/ subdirectory layered on top of a base/ directory.

Decision

Option 1: a single repo with a machine_type prompt at chezmoi init time, stored in chezmoi's persistent state. Templates branch on {{ if eq .machine_type "personal" }}…{{ end }} where they need to.

Rationale

  • One source of truth. A change to a shared file (most files) is made once and lands on every machine. No cherry-picking between branches.
  • Visible diff between modes. Conditional blocks are inline and grep-able. git grep 'eq .machine_type' enumerates every machine-type-specific decision.
  • No merge tax. Branches drift; merges become a chore. A single main with conditionals never accumulates the merge debt.
  • Init-time, prompt-once. promptChoiceOnce writes the answer into chezmoi's state file. Subsequent chezmoi apply runs don't re-prompt. New machines pick a value once; existing machines keep theirs.
  • Composable with .chezmoi.arch. The same conditional pattern handles Apple Silicon vs Intel for credential helpers and GPG paths — no separate mechanism needed.

Alternatives rejected

  • Branches — duplication, merge churn, divergence over time. Doesn't compose well with arch differences (would need 4 branches: personal-arm, personal-intel, work-arm, work-intel).
  • Separate repos — same downsides plus operational overhead (two CIs, two pre-commit setups, two README updates).
  • Layered directories — chezmoi has no native "layer" concept; would require custom apply scripts and bespoke conflict resolution.

Consequences

  • Templates have visible conditional blocks, which is more verbose than a flat file. Acceptable trade for the alternatives' costs.
  • A new machine type (e.g. client-laptop) means adding it to the prompt's allowed values and auditing every existing conditional. Today there are ~10 conditionals; this remains tractable.
  • Test/CI burden grows: every .tmpl is rendered for personal × work × arm64 × amd64 (4 cells) by make verify-templates and the CI matrix. This is the right cost — without it, a typo on one branch wouldn't be caught until that machine type was used.