perf: export reflectx types from reachable state roots

[MeteorsLiu]

No description provided.

[codecov]

Codecov Report

❌ Patch coverage is 68.42105% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/reflectxtype/method.go	0.00%	4 Missing ⚠️
internal/reflectxtype/reflectxtype.go	80.00%	1 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[fennoai]

Review: roots-based reflectxtype.Export

This is a clean, well-scoped refactor. It replaces the parameterless Export() (which enumerated global reflect/reflectx caches via //go:linkname) with an explicit Export(roots []reflect.Type) that walks only the given roots and their dependencies, scoping each snapshot to a single object graph.

Strengths

• Genuine isolation improvement. Types owned by unrelated interpreters that merely sit in the shared process-global reflect cache are no longer swept into a snapshot. Verified by the new reflectx_roots_linux_test.go (unrelated vs referenced_by_method cases).
• Reduced unsafe surface. Removing the //go:linkname handles to reflect.ptrMap / lookupCache / funcLookupCache / structLookupCache and the reflectx.Default struct-punning eliminates a class of layout fragility and lock-discipline hazards from this package.
• Correct method.go fix. The interface-entry detection now keeps an entry when either receiver has real method text (OR semantics) instead of letting the pointer-receiver pass clobber the value receiver — covered by the new assertion in method_missing_test.go.
• Doc comments were rewritten accurately, all call sites updated consistently, and the loop termination / roots-monotonicity invariants are backed by the new tests.

The inline notes below are optional, low-priority observations — no blocking issues.

Additional findings

• internal/state/encode.go:983: [P3] Nil-deref of extended rests on an unguarded invariant: extended.IDs[typ] is dereferenced here when a reflected type is absent from the reflecttype snapshot. extended can be nil when the export loop broke early at the len(roots) == 0 && extended == nil condition. This path is currently unreachable — when roots is empty, every reflected type is already present in snapshot.IDs, so !ok never fires — but the safety depends on a subtle invariant. A one-line comment noting that !ok implies extended != nil, or an explicit nil check, would guard against future changes to how roots is populated.
• internal/reflectxtype/reflectxtype.go:88: [P3] concreteMethodSet computed twice per retained concrete type: In the previous != nil path, the pre-pass here calls concreteMethodSet(typ) for every retained concrete type to populate e.sharedMethods, and then the second pass at lines 102-111 calls e.encode(typ), which calls concreteMethodSet(typ) again (reflectxtype.go:175). So each retained type with methods pays for concreteMethodSet twice per Export — it iterates both method sets, resolves name/pkg offsets via linkname, and allocates a reflect.FuncOf per method. Threading the computed method set into encode (or caching it per-type on the exporter) would halve this cost. Minor; only matters for large retained type sets.