🐛 fix(config): set_env override lost after load#3775
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gaborbernat merged 2 commits intotox-dev:mainfrom Feb 19, 2026
Merged
🐛 fix(config): set_env override lost after load#3775gaborbernat merged 2 commits intotox-dev:mainfrom
gaborbernat merged 2 commits intotox-dev:mainfrom
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When `set_env` inherits via cross-section substitution and explicitly overrides the same key, `load()` moves the key from `_raw` to `_materialized` during iteration. By the time `_iter_needs_replacement` runs, the `key not in self._raw` guard no longer protects the explicit value, so the inherited one silently wins. Track originally-defined keys in a separate `_defined_keys` set that persists across `load()` calls, so deferred substitutions never overwrite values the user explicitly configured in the same section. Fixes tox-dev#3773
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When
set_envboth inherits via cross-section substitution (e.g.,{[testenv]set_env}) and explicitly overrides the same variable in the same section, the explicit value is silently replaced by the inherited one. 🐛 This regression was introduced in v4.39.0 and breaks a common configuration pattern where users layer environment variables across sections.The root cause is a timing issue in
_iter_needs_replacement(). During iteration,load()moves explicitly-set keys from_rawto_materialized. By the time the deferred cross-section substitution expands, thekey not in self._rawguard no longer sees those keys, so inherited values overwrite explicit ones. The fix tracks originally-defined keys in a separate_defined_keysset that persists acrossload()calls, ensuring deferred substitutions never overwrite values the user explicitly configured.All existing precedence behaviors are preserved: defaults still get overridden by cross-section values (#2872), explicit values still win over cross-section values (#2831), and
file|ordering still respects later inline definitions (#3335).Fixes #3773