Saying "the fields are not available" was under-claiming. A condition is a
struct, and Tast.structs holds every struct's field names and types in the
daemon, which owns the build — no running program is involved in answering
what a Missing is made of. Only the values need the pointer the break loop
was handed, and break_loop currently discards that pointer, so they are two
different gaps with two different fixes on two different sides of the socket.
The buffer now draws a field named and typed with its value refused, which is
what tells you whether the field you were about to blame is even a field of
this condition.
Navigation backwards was not the same list walked the other way. Forward
wrapped and backward stopped, and from the middle of a line the two disagreed
about where a field begins — a field line carries the property on all of it,
so a property-change walk from mid-line finds the end of the field you are
already in. Both now go through one list of field starts. The mid-line case
went red on the first try and the expectation was the thing that was wrong:
landing on the current field's start is what CIDER does and is the less
surprising of the two.
C-c C-b is a completing-read over restart names, which is the whole UI for
the one moment the dev loop exists to make survivable. It shows the names and
nothing else, and it will let you pick one that cannot be taken.
That last part is a bug, not a gap. §4 says restart lookup takes the first
frame offering a name, and flan_find_restart does exactly that; so a second
frame offering "retry" is real, is on the list, and is unreachable — picking
it sends the string "retry" and the inner frame runs, silently. SBCL has
shown this since forever by numbering the restarts and omitting the bracket
on a name already used. Taken as is, and the shadowed row now refuses by name
and says what would fix it: an index verb, which does not exist.
SBCL also decides the order. invoke-debugger prints the condition, then
show-restarts, and stops; the backtrace is a command you type. The restarts
are the decision and the stack is the explanation for it, and a debugger that
opens with forty frames has buried one under the other.
What CIDER's stacktrace buffer gives is the behaviour — frames that fold in
place, everything on the keyboard. Not its cause chain: a JVM exception wraps
another one and a Flan condition wraps nothing.
The fields, the stack and the locals are drawn as sections that say why they
are empty and what each would take. A section left out cannot be told from
one that happened to have nothing in it, and only one of those is a fact
about the program.
