net/http: `t.roundTrip undefined` on js+wasm build (TinyGo 0.41.0 / 0.41.1)

[yuta-yoshinaga]

Summary

When building any program that imports net/http for TinyGo's wasm target (i.e. js && wasm build constraints), compilation fails because http/roundtrip_js.go calls t.roundTrip(req) on *Transport, but http/transport.go declares Transport as an empty stub (type Transport struct{}) with no roundTrip method.

Affected versions

• TinyGo 0.41.0 (released 2026-04-21)
• TinyGo 0.41.1 (released 2026-04-22)

TinyGo 0.40.1 is unaffected.

Reproduction

// main.go
package main

import _ "net/http"

func main() {}

go mod init repro
tinygo build -target wasm -o app.wasm .

Actual output

# net/http
$TINYGO_ROOT/src/net/http/roundtrip_js.go:73:12: t.roundTrip undefined (type *Transport has no field or method roundTrip, but does have method RoundTrip)

Root cause

PR #42 ("Add Transporter for wasm js target", commit b2d3a2b, merged 2026-04-17) backported roundtrip_js.go from upstream Go. In upstream Go 1.26.x, *Transport has a private roundTrip method declared in transport.go, and roundtrip_js.go falls back to it when jsFetchMissing || jsFetchDisabled:

https://github.com/tinygo-org/net/blob/master/http/roundtrip_js.go#L72-L74

if jsFetchMissing || jsFetchDisabled {
    return t.roundTrip(req)
}

But TinyGo intentionally keeps transport.go as a minimal stub:

https://github.com/tinygo-org/net/blob/master/http/transport.go#L25

type Transport struct{}

The private roundTrip method was not backported, so the fallback call at roundtrip_js.go:73 does not type-check.

Suggested fixes

Either:

1. Add a stub roundTrip method on *Transport in transport.go (or a new _js.go variant) that returns an error like the unsupported-target wrappers elsewhere in TinyGo, or
2. Remove the jsFetchMissing || jsFetchDisabled fallback path from roundtrip_js.go since the empty Transport cannot perform a real round-trip anyway, and simply return an error in that branch.

Impact

This blocks the entire wasm target for any program that depends on net/http (directly or transitively, e.g. via github.com/syumai/workers for Cloudflare Workers).