feat(rewrite): introspect container[key] in failure messages - #14815
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visit_operand() only froze a bare name, so two other unhoisted operands
kept being evaluated after everything that follows them:
assert collect((x := 1), identity(x := 2)) == (1, 2)
assert collect(*items, identity(items := [9])) == (1, [9])
A walrus operator left in place assigns once the enclosing expression is
assembled, which is after the later arguments have run -- so the earlier
argument saw the later assignment. A starred argument hid its value
inside an ast.Starred, where the existing Name check could not see it.
Closes the order-starred-argument group and the remaining
order-call-argument entry in the coverage matrix.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
…eeds visit_operand freezes a walrus operand whenever anything follows it, and a comparison always has at least one comparator -- so by the time visit_Compare looks at its left operand, a NamedExpr has already been copied into a temporary. The special case that did it here can never run. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
The rewriter only ever visits expressions inside an assert condition, so an attribute always arrives in Load context and the fallback never runs. Removing it keeps the next visitor from copying a guard that cannot fire. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
A subscript was opaque: the message showed the value it produced with no indication of which container or key it came from. Decompose it the way attribute access already is. The container goes through visit_operand() because taking the expression away from generic_visit() takes away the hoisting that kept it ordered -- without that, `assert box[identity(box := other)] == 1` would start reading the post-walrus container. The order-axis guard in the coverage matrix fails if this is dropped. Slices keep the generic treatment; decomposing start/stop/step is rarely what a failure message needs. Closes the introspect-subscript group in the coverage matrix. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Stacked on #14814 → #14447 → #14921 → #14813. Its diff includes theirs.
A subscript was opaque: the message showed the value it produced with no indication of which container or key it came from. Decompose it the way attribute access already is.
Slices keep the generic treatment; decomposing start/stop/step is rarely what a failure message needs.
The container goes through
visit_operand(), because taking the expression away fromgeneric_visittakes away the hoisting that kept it ordered. Without that,assert box[identity(box := other)] == 1would start reading the post-walrus container — a bug this PR would have introduced. Theorder-subscript-containerguard in #14813 fails if the freeze is dropped; I checked by dropping it.This is what the guards in that matrix are for: they are passing tests on
mainprecisely so that a new visitor cannot quietly regress them.Lands the
introspect-subscriptcases of the coverage matrix in #14813, as passing tests (+3).Supersedes part of #14448.