[ehigham]

Stack 3 of 7. Based on #15919.

Why

Part of a stack that writes IR scoping once, as functions of the bound values, so the
planned abstract interpretation driver can share it with every other pass. #15918 has
the full motivation.

Most passes don't call Bindings.get themselves. They get child envs from the walkers in
BaseIR. Moving the walkers moves TypeCheck, NormalizeNames, Parser.annotateTypes,
PruneDeadFields.rebuildIR and FreeVariables in one step. Each pass now binds its own
values through v, where before it got a record of types and mapped it.

Summary

The child walkers in BaseIR take any env with a Scopes instance, plus a v.

-def forEachChildWithEnv[E <: GenericBindingEnv[E, Type]](env: E)(f: (BaseIR, E) => Unit)
+def forEachChildWithEnv[E[_]: Scopes, A](env: E[A])(v: (Name, Type) => A)(
+  f: (BaseIR, E[A]) => Unit
+)
-  val childEnv = env.extend(Bindings.get(this, i))
+  val childEnv = ChildEnv.get(env, this, i)(v)

Same change for mapChildrenWithEnv, mapChildrenWithEnvStackSafe,
forEachChildWithEnvStackSafe and VisitIR.withEnv. Callers pass v:

TypeCheck, Parser.annotateTypes, PruneDeadFields.rebuildIR   (_, t) => t
NormalizeNames                                               rename or keep the name
FreeVariables                                                (_, _) => ()

FreeVariableBindingEnv gets a Scopes instance in place of extend, through a phantom
type E[_] = FreeVariableBindingEnv.

🤖 Generated with Claude Code

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Walkthrough

IR child traversal now uses higher-kinded environments constrained by Scopes and an explicit child-value mapping function. FreeVariableBindingEnv implements scope operations. IR visitors use the updated traversal methods.

Changes: Scoped IR traversal

Layer / File(s)	Summary
Scoped traversal API hail/hail/src/is/hail/expr/ir/BaseIR.scala, hail/hail/src/is/hail/expr/ir/MapIR.scala	Traversal methods use E[A] environments and a (Name, Type) => A function to derive child environments. VisitIR.withEnv passes that function through recursive traversal.
Free-variable scope operations hail/hail/src/is/hail/expr/ir/FreeVariables.scala	FreeVariableEnv stores bound names in a set. FreeVariableBindingEnv implements scope binding, creation, dropping, and promotion through Scopes.
IR visitor migrations hail/hail/src/is/hail/expr/ir/NormalizeNames.scala, hail/hail/src/is/hail/expr/ir/Parser.scala, hail/hail/src/is/hail/expr/ir/PruneDeadFields.scala, hail/hail/src/is/hail/expr/ir/TypeCheck.scala	NormalizeNames supplies a name-mapping function. The other visitors supply identity mappings to the updated traversal methods.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Refactor

Possibly related PRs

• hail-is/hail#15919: Adds ChildEnv.get and the Scopes-based binding model used by this traversal update.
• hail-is/hail#15921: Continues the FreeVariableBindingEnv and VisitIR.withEnv changes to the Scopes model.
• hail-is/hail#15927: Replaces the stack-safe child walkers introduced here and updates several callers.

Merge Risk: Minimal · up to 6f4dd

No actionable merge-blocking risk was identified in the traversal changes.

Pre-merge checks: 3 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Description check		The description explains the motivation, scope, affected walkers, and caller updates. However, it does not include the required Security Assessment, Impact Rating, Impact Description, or Appsec Review…	Add the required Security Assessment section. State whether the change can impact the Hail Batch instance. If it cannot, select the no-impact option and provide a brief justification; otherwise provide the required impact rating, impact des…

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title clearly identifies the primary change: updating child traversal to use ChildEnv. It is concise and specific.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description explains the motivation, scope, affected walkers, and caller updates. However, it does not include the required Security Assessment, Impact Rating, Impact Description, or Appsec Review sections.

Resolution

Add the required Security Assessment section. State whether the change can impact the Hail Batch instance. If it cannot, select the no-impact option and provide a brief justification; otherwise provide the required impact rating, impact description, and Appsec Review status. Rename or expand the existing sections to match the repository template if needed.

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Failed pre-merge checks:
- Description check:
Add the required Security Assessment section. State whether the change can
impact the Hail Batch instance. If it cannot, select the no-impact option and
provide a brief justification; otherwise provide the required impact rating,
impact description, and Appsec Review status. Rename or expand the existing
sections to match the repository template if needed.

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Files selected for processing: 1

• hail/hail/src/is/hail/expr/ir/Parser.scala

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