tygorgen: source provider ignores TypeMapping for custom-marshaler/external types (maps to unknown, emits duplicates)

[broady]

Summary

TypeMapping(...) is silently ignored for any type that implements a custom JSON marshaler. The source provider rewrites such types to unknown during the type walk, before the emit-layer mappings are applied — and the provider never receives the user's TypeMappings at all. This makes it impossible to generate TypeScript for Go APIs built on k8s.io/apimachinery (and similar libraries), where time types like metav1.MicroTime/metav1.Time marshal to RFC3339 strings.

This is the exact scenario tygo's type_mappings: handles by pruning the walk (e.g. metav1.MicroTime: "string"). tygorgen's TypeMapping does not prune.

Repro

package main

import (
	v1alpha1 "github.com/tilt-dev/tilt/pkg/apis/core/v1alpha1"
	"tygor.dev/tygorgen"
)

func main() {
	// v1alpha1.UIResourceStatus.lastDeployTime is metav1.MicroTime (custom marshaler → string)
	_, _ = tygorgen.FromTypes(v1alpha1.UIResource{}).
		Provider("source").
		SingleFile().
		TypeMapping("metav1.MicroTime", "string"). // <-- ignored
		TypeMapping("metav1.Time", "string").      // <-- ignored
		ToDir("./out")
}

Actual

warning: CUSTOM_MARSHALER: type MicroTime implements custom marshaler, mapped to 'unknown'

export interface UIResourceStatus {
  lastDeployTime?: unknown;   // expected: string
  pendingBuildSince?: unknown;
  // ...
}

Expected

The explicit TypeMapping("metav1.MicroTime", "string") should take precedence, yielding lastDeployTime?: string.

Root cause

tygorgen/provider/source_provider.go (convert named type):

// Check for custom marshalers on the named type itself
if b.hasCustomMarshaler(named) {
    // ...
    // Create an alias to PrimitiveAny
    aliasDesc := &ir.AliasDescriptor{
        Name:       ir.GoIdentifier{Name: tn.Name(), Package: pkgPath},
        Underlying: ir.Any(),
        // ...
    }
    b.schema.AddType(aliasDesc)
    return nil
}

SourceInputOptions only carries Packages and RootTypes — TypeMappings are passed to the emitter, not the provider — so the walk cannot consult them. Two related symptoms fall out of the same gap:

1. Custom-marshaler types → unknown even with an explicit mapping (above).
2. Mapped external structs are still fully walked and emitted. Mapping metav1.ObjectMeta → ObjectMeta (defined in frontmatter) still emits a second ObjectMeta from k8s source plus its transitive junk (ManagedFieldsEntry, OwnerReference, FieldsV1, …), producing duplicate-identifier output. tygo avoids this because type_mappings prune the walk.

Why tygo doesn't hit this

tygo is syntactic and per-package. It walks the AST of the configured package dirs and emits only types textually declared there. A field of type metav1.MicroTime is an *ast.SelectorExpr, and tygo simply substitutes the name (tygo/write.go):

case *ast.SelectorExpr: // e.g. `time.Time`
    longType := fmt.Sprintf("%s.%s", t.X, t.Sel) // "metav1.MicroTime"
    mappedTsType, ok := g.conf.TypeMappings[longType]
    if ok { s.WriteString(mappedTsType) }        // -> "string"
    else  { /* fallback `any /* metav1.MicroTime */` */ }

It never resolves metav1.MicroTime to its definition, never recurses into apimachinery, and never sees the custom marshaler. The mapping is a pruning boundary by construction.

tygorgen's source provider is semantic (go/types): it resolves and walks the full reachable type graph, introspects marshalers, and emits reachable types. Because mappings are emit-only, the walk reaches external types it should have treated as opaque.

Suggested fix

Thread TypeMappings into SourceInputOptions and consult them in convertNamedType (and the struct-field walk): if a named type matches a user mapping, emit a mapped reference and do not descend into or emit the type. This makes TypeMapping a true pruning boundary, matching tygo semantics.

Workaround

Vendor the upstream tygo-generated .d.ts (which already maps these correctly) until mappings prune the source walk.

Environment

• tygor v0.8.6
• metav1 types from k8s.io/apimachinery (via github.com/tilt-dev/tilt pkg/apis/core/v1alpha1)