🔧 chore(tox): migrate tox.ini to tox.toml#3050
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Using substitutions like `{env_site_packages_dir}` inside `set_env` in
TOML format causes a `RecursionError` because the TOML loader eagerly
resolves all string substitutions via `Unroll` before constructing
`SetEnv`. This creates a circular dependency: `set_env` →
`env_site_packages_dir` → `create_python_env()` → `system_site_packages`
→ `environment_variables` → `set_env`.
The INI loader already handles this correctly by detecting `SetEnv` type
and deferring string substitution — raw strings are stored as-is and
only resolved when individual env vars are accessed via `SetEnv.load()`.
🔧 This applies the same pattern to the TOML loader: structural TOML
constructs (`replace: ref`, `replace: posargs`, `replace: env`) are
still resolved during config loading, but string-level `{...}`
substitutions are deferred via a proper TOML-aware replacer passed to
`SetEnv.use_replacer()`.
Discovered via pypa/virtualenv#3050 when migrating virtualenv's config
from `tox.ini` to `tox.toml`. The same configuration that worked in INI
format caused infinite recursion in TOML because of the eager
substitution.
Closes #3758
The tox ecosystem has moved to native TOML configuration. Switch from the legacy INI format and update the pre-commit hook from tox-ini-fmt to tox-toml-fmt v1.7.0.
Fixes quoted env key handling — keys like "3.13t" are now correctly expanded into separate table sections.
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3.13t and 3.14t are Python version specifications, not custom environments. These sections only contained env var overrides and were conflicting with tox's version resolution. Removing them allows tox to treat them as plain version specs.
This was referenced Mar 12, 2026
This was referenced Mar 13, 2026
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The tox ecosystem has moved to native TOML configuration as the preferred format. This migrates
tox.initotox.tomland switches the pre-commit hook fromtox-ini-fmttotox-toml-fmtv1.7.0 to match. 🔧The generated
tox.tomlhas been formatted withtox-toml-fmtto ensure it follows the canonical style.