fix: cross-section substitution resolves to empty when no factors match#3810
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gaborbernat merged 7 commits intotox-dev:mainfrom Feb 23, 2026
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When {[section]key} references a value with factor-conditional lines and
no factors match, the substitution should resolve to empty string rather
than remaining unresolved as a literal reference.
The root cause: process_raw() raises KeyError when factor filtering empties
a value that originally had content (added in tox-dev#3751 to fix tox-dev#3189). For
same-section config values this is correct — it allows fallback to computed
defaults (e.g. base_python derived from env name). But for cross-section
references via SectionProxy, the KeyError propagated all the way up to
the replacer, which returned None (unresolved), leaving the literal
{[section]key} in the output.
The fix: when a SectionProxy lookup raises KeyError but the key exists in
the section, the factor filtering emptied the value — return empty string
instead of propagating the error. This preserves the tox-dev#3189 fix for
same-section config values while correctly handling cross-section references.
Fixes tox-dev#3809
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
for more information, see https://pre-commit.ci
Move SectionProxy resolution logic into a helper method to stay within ruff's branch count and nesting depth limits. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
for more information, see https://pre-commit.ci
gaborbernat
requested changes
Feb 23, 2026
Consistent with the multiline style requested in review. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
auto-merge was automatically disabled
February 23, 2026 14:51
Head branch was pushed to by a user without write access
gaborbernat
approved these changes
Feb 23, 2026
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Summary
Fixes #3809
Cross-section substitution
{[section]key}now correctly resolves to empty string when the referenced value contains only factor-conditional lines and no factors match the requesting environment.Before:
{[devpisettings]storagebackend}remained as a literal unresolved reference when no factors matched.After: Resolves to empty string, matching pre-4.39.0 behavior.
Root cause
PR #3751 (fixing #3189) added a
KeyErrorinprocess_raw()when factor filtering empties a value that originally had content. This correctly causes same-section config values (likebase_python) to fall through to their computed defaults. However, for cross-section references loaded viaSectionProxy, theKeyErrorpropagated to the replacer which returnedNone(unresolved), leaving the literal{[section]key}in output.Fix
In
ReplaceReferenceIni.__call__(), when aSectionProxylookup raisesKeyErrorbut the key exists in the section, return empty string instead of propagating the error. This preserves the #3189 fix while correctly handling cross-section references.Test plan
test_cross_section_factor_conditional_resolves_to_emptytest_factor_conditional_falls_back_to_default(base_pythonsettings may breakignore_base_python_conflict = falsebehaviour #3189 regression test) passes🤖 Generated with Claude Code