[gdb/testsuite] Fix error handling in _dap_read_json
In _dap_read_json we have a gdb_expect with clauses that generate errors:
...
timeout {
error "timeout reading json header"
}
eof {
error "eof reading json header"
}
...
Proc gdb_expect uses dejagnu's remote_expect, which has some peculiar
semantics related to errors:
...
# remote_expect works basically the same as standard expect, but it
# also takes care of getting the file descriptor from the specified
# host and also calling the timeout/eof/default section if there is an
# error on the expect call.
.....
When a timeout triggers, it generates a timeout error, which is reported by
gdb_expect, after which it runs the timeout/eof/default clauses, which
generates an eof error, which is reported by runtest.
I think the intention here is to generate just a one error, a timeout error.
Fix this by postponing generating the error until after gdb_expect.
Tested on x86_64-linux, by:
- running all the DAP test-cases and observing no regressions, and
- modifying the gdb.dap/eof.exp test-case to trigger a timeout error, and
observing only a timeout error.
PR testsuite/31382
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31382