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[ty] More type-variable default validation by AlexWaygood · Pull Request #23639 · astral-sh/ruff · GitHub
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[ty] More type-variable default validation - #23639

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AlexWaygood merged 3 commits into
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claude/fix-type-param-scope-oe7ea
Mar 5, 2026
Merged

[ty] More type-variable default validation#23639
AlexWaygood merged 3 commits into
mainfrom
claude/fix-type-param-scope-oe7ea

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@AlexWaygood

@AlexWaygood AlexWaygood commented Feb 28, 2026 •
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Summary

We have several checks at the moment which fire on legacy type variables with invalid defaults in a class context, but which fail to check for legacy type variables with invalid defaults in a function context. This PR adds those missing checks.

The typing spec states that both legacy and PEP-695 type variables are not allowed to have defaults that:

  • reference type variables bound in outer scopes, or
  • reference type variables that are put into scope later on in the type parameter list or function signature

The typing spec also states that a type variable with a default is not allowed to come before any type variables without defaults.

Test Plan

mdtests and snapshots

@AlexWaygood AlexWaygood added ty The ty type checker ecosystem-analyzer labels Feb 28, 2026
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astral-sh-bot Bot commented Feb 28, 2026 •
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Typing conformance results

No changes detected ✅

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astral-sh-bot Bot commented Feb 28, 2026 •
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mypy_primer results

No ecosystem changes detected ✅

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astral-sh-bot Bot commented Feb 28, 2026 •
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Memory usage report

Memory usage unchanged ✅

@AlexWaygood

AlexWaygood commented Feb 28, 2026

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Following #23623, I guess we now pass all the conformance tests regarding typevar default scoping. But I still think this PR improves semantics -- it matches pyright's behaviour. The upstream tests seem like they're missing some coverage.

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ecosystem-analyzer results

No diagnostic changes detected ✅

Full report with detailed diff (timing results)

@AlexWaygood
AlexWaygood force-pushed the claude/fix-type-param-scope-oe7ea branch 2 times, most recently from af5547b to c1a2615 Compare February 28, 2026 23:31
@AlexWaygood AlexWaygood changed the title [ty] Detect type variables with invalid defaults [ty] More type-variable default validation Feb 28, 2026
@AlexWaygood
AlexWaygood marked this pull request as ready for review February 28, 2026 23:37
@AlexWaygood
AlexWaygood force-pushed the claude/fix-type-param-scope-oe7ea branch 2 times, most recently from 8e099a8 to 2920f62 Compare March 2, 2026 13:15
@carljm
carljm removed their request for review March 2, 2026 17:44
oconnor663
oconnor663 reviewed Mar 3, 2026
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LGTM with some nits.

Comment thread crates/ty_python_semantic/resources/mdtest/generics/scoping.md Resolved
Comment thread crates/ty_python_semantic/src/types/infer/builder.rs Resolved
Comment thread crates/ty_python_semantic/src/types/infer/builder.rs Resolved
oconnor663
oconnor663 approved these changes Mar 3, 2026
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Meant to put the green checkmark on the last comment.

@oconnor663 oconnor663 removed their assignment Mar 3, 2026
@AlexWaygood
AlexWaygood force-pushed the claude/fix-type-param-scope-oe7ea branch from 2920f62 to 6408c53 Compare March 5, 2026 13:02
AlexWaygood
AlexWaygood commented Mar 5, 2026
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Comment thread crates/ty_python_semantic/src/types/infer/builder.rs

@AlexWaygood AlexWaygood Mar 5, 2026

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I know, I know... 400+ lines being added to infer/builder.rs... I'll rip it out into a submodule as a followup.

@AlexWaygood
AlexWaygood enabled auto-merge (squash) March 5, 2026 13:04
@AlexWaygood
AlexWaygood merged commit 5f0fd91 into main Mar 5, 2026
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@AlexWaygood
AlexWaygood deleted the claude/fix-type-param-scope-oe7ea branch March 5, 2026 13:06
carljm added a commit that referenced this pull request Mar 5, 2026
@carljm
Merge branch 'main' into cjm/remove-container-literal-unknown
461f4c9 
* main:
  Update conformance suite commit hash (#23746)
  conformance.py: Collapse the summary paragraph when nothing changed (#23745)
  [ty] Make inferred specializations line up with source types more better (#23715)
  Bump 0.15.5 (#23743)
  [ty] Render all changed diagnostics in conformance.py (#23613)
  [ty] Split deferred checks out of `types/infer/builder.rs` (#23740)
  Discover markdown files by default in preview mode (#23434)
  [ty] Use `HasOptionalDefinition` for `except` handlers (#23739)
  [ty] Fix precedence of `all` selector in TOML configurations (#23723)
  [ty] Make `all` selector case sensitive (#23713)
  [ty] Add a diagnostic if a `TypeVar` is used to specialize a `ParamSpec`, or vice versa (#23738)
  [ty] Override home directory in ty tests (#23724)
  [ty] More type-variable default validation (#23639)
  [ty] Validate bare ParamSpec usage in type annotations, and support stringified ParamSpecs as the first argument to `Callable` (#23625)
  [ty] Add `all` selector to ty.json's `schema` (#23721)
  [ty] Add quotes to related issues links (#23720)
  [ty] Fix panic on incomplete except handlers (#23708)
carljm added a commit that referenced this pull request Mar 16, 2026
@carljm
Merge branch 'main' into charlie/metaclass
c0f4ee5 
* main:
  Update conformance suite commit hash (#23746)
  conformance.py: Collapse the summary paragraph when nothing changed (#23745)
  [ty] Make inferred specializations line up with source types more better (#23715)
  Bump 0.15.5 (#23743)
  [ty] Render all changed diagnostics in conformance.py (#23613)
  [ty] Split deferred checks out of `types/infer/builder.rs` (#23740)
  Discover markdown files by default in preview mode (#23434)
  [ty] Use `HasOptionalDefinition` for `except` handlers (#23739)
  [ty] Fix precedence of `all` selector in TOML configurations (#23723)
  [ty] Make `all` selector case sensitive (#23713)
  [ty] Add a diagnostic if a `TypeVar` is used to specialize a `ParamSpec`, or vice versa (#23738)
  [ty] Override home directory in ty tests (#23724)
  [ty] More type-variable default validation (#23639)
  [ty] Validate bare ParamSpec usage in type annotations, and support stringified ParamSpecs as the first argument to `Callable` (#23625)
  [ty] Add `all` selector to ty.json's `schema` (#23721)
  [ty] Add quotes to related issues links (#23720)
  [ty] Fix panic on incomplete except handlers (#23708)
  Update conformance suite commit hash (#23719)
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@sharkdp sharkdp Awaiting requested review from sharkdp
@dcreager dcreager Awaiting requested review from dcreager
@ibraheemdev ibraheemdev Awaiting requested review from ibraheemdev
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@oconnor663 oconnor663 oconnor663 approved these changes
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@AlexWaygood @oconnor663