[guile] The message body is duplicated for MIME messages

[bauermann]

Describe the item

When the mu:body message method is called on a MIME message after a call to mu:header, the body text is duplicated in the returned value.

To Reproduce

With the commits from PR #2801 applied, add the following test to the test-message function in test-mu-guile.scm:

(str-equal-or-exit (mu:body msg)
                   "Hello world, forwarding some RFC822 message\n")

If you add it before the call to mu:header, it will pass. If you add it after, you get:

not ok /guile/message - ERROR:../guile/tests/test-mu-guile.cc:89:void test_something(const char*): assertion failed: (0)
Bail out!
----------------------------------- stderr -----------------------------------
*ERROR*: Expected "Hello world, forwarding some RFC822 message
", got "Hello world, forwarding some RFC822 message
Hello world, forwarding some RFC822 message

Environment
This is on Guix with Guile 3.0.9.
mu is v1.12.8 with the commits from PR #2801 applied.

Checklist

• [✓] you are running either the latest 1.4.x release, or a 1.5.11+ development release (otherwise, please upgrade).

Analysis

I did some debugging, and I believe the problem happens because mu:c:get-parts and mu:c:get-header call Message::unload_mime_message() at the end.

Because of this, next time Message::load_mime_message() gets called, priv_->mime_msg will be empty and fill_document(*priv_) will add a new instance of the body text in accumulate_text().

[djcb]

The (current) guile bindings have been deprecated for quite some time, so i'm not planning to do much work on this. But perhaps we can quickly fix this,