See [lix-project/lix#1156], but basically currently the `:st <n>`
debugger command doesn't allow any negative indices, and putting a plus
sign in front of the arg doesn't change anything; thus, we can exploit
that "design space" to allow users to move between different stack
frames easily, by simply prepending their arg with a +/- sign.
The actual behavior is little more nuanced when you account for errors:
as suggested by @pennae (thanks! :), when the user inputs an offset that
would result in an invalid frame index, the debugger instead clamps it
to the closest bound (i.e. 0 for negative offsets, $maxFrame for
positive ones) and just prints a warning.
Fixes#1156
[lix-project/lix#1156]: https://git.lix.systems/lix-project/lix/issues/1156
Change-Id: I02a0cdb6aaebbdb0515308880a3bf9c0d2fcd25e
currently, the `:st <n>` command in the debugger will simply silently
fail if the argument cannot be converted to an integer, or if it falls
outside the range of valid stack indices. this isn't too big of problem,
but it can be nicer to tell the user something went wrong, rather than
not give them any output and having them guess (esp. in the second case).
this commit adds two errors, one for each case:
1. the argument is not actually an integer, or is outside INT_MIN/MAX
-> "argument '%arg' is not a valid integer"
2. the argument is an integer outside the range of stack traces
-> "stack index must be between 0 and %max_frame, but was %arg"
Change-Id: I8109feeede79a9ad3db9ee7dc95d37e7dd19741a
blokyk