fix(data): convert constructor arguments to declared field types

[Roger-luo]

Summary

Fixes #32 — TypeError in getproperty on container-typed fields.

Root cause

Variant storage structs use Any for a field whenever its declared type "collapses" in guess_self_as_any (src/data/scan.jl):

• A genuine Any type parameter — e.g. Vector{Any} becomes an Any storage field.
• A self-referential container — e.g. Vector{Self} must use Any because the wrapper Type isn't defined yet when the storage struct is emitted (removing the collapse, as suggested in the issue thread, breaks these).

Because the storage field is Any, Julia's inner constructor performs no conversion, so the stored value keeps its original type (Vector{Int}). But getproperty/variant_getfield type-assert against the declared annotation (Vector{Any}), producing:

ERROR: TypeError: in typeassert, expected Vector{Any}, got a value of type Vector{Int64}

Fix

Convert each argument to its declared annotation type in the positional (emit_each_variant_cons) and keyword (emit_each_variant_kw_cons) constructors, restoring the normal Julia struct-construction semantics that were lost to the Any storage. The conversion is a no-op when the value already matches, so construction stays type stable (verified via Base.return_types).

This resolves all three failure modes from the issue:

• OptionVec.Some{String}("hi", [1, 2]) (the report)
• M.V([5]) (anonymous variant with Vector{Any})
• Pattern.Row([]) (self-referential Vector{Self})

It also fixes a latent bug in the explicit-brace form of self-referential constructors: Tree.Node{Int}(5, Tree.Leaf(3), Tree.Empty()) now promotes the parametric singleton bottom correctly.

Not changed

The strict type-inferring constructor (Some("hi", [1,2]) without {String}) still requires exact argument types — this is pre-existing behavior shared by all concrete field types (it also rejects Int for a Float64 field), not the reported bug, and that path is deliberately delicate for type-parameter inference (see #34).

Tests

Adds test/data/emit/container.jl covering generic/anonymous/named/keyword Vector{Any} fields, self-referential Vector{Self} conversion, and explicit-brace self-ref promotion. Full suite passes (data 285 → 304).

🤖 Generated with Claude Code

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
moshi-jl	Ignored		Jul 12, 2026 6:01pm

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.70%. Comparing base (a74db69) to head (8da1b32).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #83   +/-   ##
=======================================
  Coverage   91.69%   91.70%           
=======================================
  Files          43       43           
  Lines        1661     1663    +2     
=======================================
+ Hits         1523     1525    +2     
  Misses        138      138           

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Benchmark Results (Julia v1)

Time benchmarks

	main	8da1b32...	main / 8da1b32...
adt_transform/transform n=100	2.67 ± 0.19 μs	6.67 ± 0.15 μs	0.399 ± 0.03
adt_transform/transform n=1000	29 ± 0.69 μs	0.0648 ± 0.00091 ms	0.448 ± 0.012
linked_list/sum n=100	0.471 ± 0 μs	0.501 ± 0.01 μs	0.94 ± 0.019
linked_list/sum n=1000	5.14 ± 0.04 μs	5.44 ± 0.06 μs	0.945 ± 0.013
time_to_load	0.0779 ± 0.00096 s	0.0784 ± 0.00073 s	0.994 ± 0.015

Memory benchmarks

	main	8da1b32...	main / 8da1b32...
adt_transform/transform n=100	0.178 k allocs: 5.94 kB	0.204 k allocs: 6.34 kB	0.936
adt_transform/transform n=1000	1.79 k allocs: 0.0583 MB	2.02 k allocs: 0.0619 MB	0.943
linked_list/sum n=100	0 allocs: 0 B	0 allocs: 0 B
linked_list/sum n=1000	0 allocs: 0 B	0 allocs: 0 B
time_to_load	0.145 k allocs: 11 kB	0.145 k allocs: 11 kB	1