GALA-E0090 — Anonymous Go struct type would have to be written

When it fires. A Go API hands GALA a value whose type is, or holds, an anonymous Go struct type, such as the struct{} of a signal channel (<-chan struct{} from ctx.Done()), and the generated Go would have to write that type out. That happens wherever GALA spells a type:

a type argument, as in Some(ctx.Done()) (std.Some[<-chan struct{}]) or a collection of such values;
a type GALA infers for a generic call, a method such as Map, a lambda’s parameter or result, or a var it declares to hold a branching value (if/match as an expression).

GALA has no syntax for an anonymous struct type, so it cannot be written in GALA source either. A value of one that only passes through is accepted: val done = ctx.Done(), a Go call’s result passed straight to another Go call, a receive such as <-done, and reading a field of a returned struct.

Minimal repro.

package main

import "context"

func main() {
    val ctx = context.Background()
    val done = Some(ctx.Done())
    Println(done.IsDefined())
}

Error output.

error[GALA-E0090]: type `<-chan struct{}` holds an anonymous Go struct type, which GALA cannot write
  --> main.gala:7:21
  |
7 |     val done = Some(ctx.Done())
  |                     ^^^ give the type a name on the Go side
  |
  = hint: give the type a name on the Go side; for a signal channel use go_interop.Signal and go_interop.WaitClosed, IsClosed or WaitClosedTimeout; for ctx.Done() use go_interop.WaitDone, IsDone or WaitDoneTimeout

Fix. Keep the value out of positions that write its type, or give the type a name:

for ctx.Done(), use the context helpers go_interop.WaitDone(ctx), go_interop.IsDone(ctx) and go_interop.WaitDoneTimeout(ctx, d);
for any other signal channel, use go_interop.WaitClosed(ch), go_interop.IsClosed(ch) and go_interop.WaitClosedTimeout(ch, d), and make your own signal channels with go_interop.NewSignal(): a go_interop.Signal is a named type, so it fits in an Option or a collection, and Go APIs that take a chan struct{} or a <-chan struct{} accept it;
for a struct with fields that your own Go code returns, declare it as a named type on the Go side (type Result struct { ... }).

package main

import (
    "context"

    "martianoff/gala/go_interop"
)

func main() {
    val ctx = context.Background()
    Println(go_interop.IsDone(ctx))
}

Rationale. GALA generates concrete Go types and never erases one to any. An anonymous struct type has no GALA spelling to generate from, and one with an unexported field cannot be written outside the package that declares it at all, so GALA reports the use instead of writing a type the program never named.

GALA-E0090 — Anonymous Go struct type would have to be written

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