expandable-snip: snip has no snipclass

I want to create an expandable-snip in the REPL. I don't care about the ability to copy-and-paste it.

The following code results in an error: write-snips-to-file: snip has no snipclass.

#lang racket/gui

(require mrlib/expandable-snip)

(define term-snip%
  (class expandable-snip%
    (define summary-t (new text%))
    (define inner-t (new text%))
    (send summary-t insert "foo")
    (send inner-t insert "bar")

    (super-instantiate ()
      (closed-editor summary-t)
      (open-editor inner-t))))

(new term-snip%)

@alex-hhh told me to try overriding the copy method. I found that it's not enough. Instead, I need to follow the instructions at https://docs.racket-lang.org/gui/editor-overview.html#%28part._snip-example%29

To define a class of snips that can be saved or cut-and-pasted

• Create an instance of snip-class%, implementing the read method. Export the snip-class% instance as snip-class from a module, and use a classname of the form "(lib ...)" as described in Snip Classes.
• For each instance of the snip class, set the snip’s class object with set-snipclass.
• Override the copy method.
• Override the write method.

The minimal code that "works", though it doesn't quite follow every step in the above instructions, is:

#lang racket/gui

(require mrlib/expandable-snip)

(define snip-class (new snip-class%))

(define term-snip%
  (class expandable-snip%
    (define summary-t (new text%))
    (define inner-t (new text%))
    (send summary-t insert "foo")
    (send inner-t insert "bar")

    (super-instantiate ()
      (closed-editor summary-t)
      (open-editor inner-t))

    (define/override (copy) (new term-snip%))
    (define/override (write _) (void))
    (inherit set-snipclass)
    (set-snipclass snip-class)))

(new term-snip%)

But this doesn't make any sense to me. I don't care about its ability to copy-and-paste. Why do I need to deal with snipclass?

Incidentally, this made me realized that snips are copyable, but then when I tried on the syntax browser snip, it errors.

Steps to reproduce:

1. Type #'1 at the definition window and run
2. Copy the snip from the REPL to the definition window

Result:

An error

read-bytes: cannot load snip-class reader, snipclass name has only one library path, but text mode requested: #"(lib \"syntax-browser.ss\" \"mrlib\")"

occurs.

Start with the expandable-snip example and the snip example in the editor overview linked in the issue. Reproduce the write-snips-to-file error in the REPL, then investigate the syntax-browser copy failure using the reported steps. Done means expandable snips can be used without unwanted copy-and-paste support, and the reported copy operation no longer errors.