[devin-ai-integration]

What and why

runtime.memberSymbol(scope, node) returned the symbol a scope registered for a declaration by collecting every member of the scope (Scope.AllMembers, which allocates the slice) and scanning it. Scope.MemberDeclaring already answers the same question — the first registration of the declaration, as the scan found — from the scope's lazily built declaration index without allocating, so memberSymbol now calls it. Twelve runtime call sites share the helper.

The cost became visible when a nested requirement's subject was bound to its enclosing part (#1312): roleRedefiningDefault asks memberSymbol for every member of every instantiated type, and the 0.11.0 performance measurement of develop against v0.10.1 has tests/perf Instantiate at 2.51 M → 6.34 M allocations, of which 4.94 M → 6.34 M is that merge; the profile puts 1.81 M of it in memberSymbol → Scope.AllMembers.

Six interleaved rounds on a quiet machine, develop (5db0f74) | #1368 | this branch | both (benchstat, allocations exact, p = 0.002 on every moved row):

benchmark	allocs/op	B/op	time
tests/perf Instantiate	6.338 M | 4.224 M | 5.012 M | 2.219 M	425 | 338 | 389 | 207 MiB	1.52 | 1.03 | 1.44 | 0.73 s
tests/perf BatchSatisfy	8.301 M | 5.672 M | 6.965 M | 4.336 M	602 | 492 | 565 | 456 MiB	2.18 | 1.53 | 2.02 | 1.42 s
tests/perf FeaturesOf	6.450 M | 3.683 M | 5.030 M | 2.263 M	413 | 298 | 376 | 261 MiB	1.29 | 0.70 | 1.22 | 0.67 s
tests/stressmodel Satisfy/32	42.03 k | 42.03 k | 40.04 k | 40.04 k	—	~
tests/stressmodel FleetSatisfy/32	11.50 k | 11.50 k | 11.00 k | 11.00 k	—	~
tests/stressmodel FleetInstantiate/32	15.45 k | 15.45 k | 15.29 k | 15.29 k	—	~

v0.10.1: Instantiate 2.509 M, BatchSatisfy 4.301 M, FeaturesOf 4.130 M, Satisfy/32 33.4 k — with both fixes the tests/perf rows are at or below the previous release; the stress rows' remainder (+20 %) is #1276/#1319's wider type set, carried in the record as the earlier candidate measured it.

How it was verified

• TestMemberSymbolReadsTheScopeWithoutCollectingIt (new): the lookup answers the member declared for each of a scope's declarations and allocates nothing; on develop it allocates 3 per lookup.
• go build ./..., go vet ./..., gofmt -l . clean; go test of internal/exec/..., internal/frontend/repl, internal/frontend/grpc, tests/model green (the two internal/exec/solve corpus tests that need the downloaded training corpus fail identically on bare develop in this checkout).

Checklist

• make test and make lint pass locally (the packages above; full suite in CI)
• Tests added or updated for the change
• Documentation extended where it already covers the surface (the 0.11.0 performance record names this fix in its correction)
• Changelog entry added as changes/unreleased/member-symbol-by-decl.fixed.md
• baselines regenerated and make docs-counts run if a gate count moved (none moved)
• No internal work-item labels in the body, docs, or changelog

Link to Devin session: https://nasa-jpl-demo.devinenterprise.com/sessions/cf22d7a746814d20b2f0eaf11682fef9
Open in Devin Desktop: https://nasa-jpl-demo.devinenterprise.com/desktop/session/cf22d7a746814d20b2f0eaf11682fef9?variant=devin
Requested by: @HuiJun

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[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.