Support old-style shell for rebar3 shell #995
Conversation
This is quite the hack.
This requires to detect the current shell running; if it's the new
shell, business as usual.
However, if it's the old shell, we have to find a way to take over it
and drive IO. This requires a few steps because:
- the old shell does not let you be supervised intelligently (it uses
supervisor_bridge, so killing the child is not a supported operation
from the supervisor)
- the old shell ignores all trappable exit signals except those coming
from the Port in charge of stdio ({fd, 0, 1})
- the old shell shuts down on all exit signals from the stdio Port
except for badsig, and replicates the shutdown reason otherwise
- An escript does not tolerate the `user` process dying (old shell) for
any non-normal reason without also taking the whole escript down
- Booting in an escript has an implicit 'noshell' argument interpreted
by the old shell as a way to boot the stdio Port with only stdout
taken care of
Because of all these points, we have to kill the old `user` process by
sending it a message pretending to be the Stdio port dying of reason
`normal`, which lets it die without triggering the ire of its
supervision tree and keeping the escript alive. This, in turn, kills the
old stdio port since its parent (user.erl) has died.
Then we have to boot our copy of user.erl (rebar_user.erl) which
conveniently ignores the possibility of running the stdio port on stdout
only -- always using stdin *and* stdout, giving us a bona fide old-style
shell.
A known issue introduced is that running r3:do(ct) seems to then kill
the shell, and r3:do(dialyzer) appears to have an odd failure, but
otherwise most other commands appear to work fine.
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This feels very dirty. |
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(this is gruesome 😀) |
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Do not merge yet. I just found out that the old style shell is always booted even in an escript, so the mechanism chosen to replace shells is wrong. Will have to fix this. |
This reuses the trick used within OTP to pick within old and new shell. The 'user' structure is the same for all cases (escript, escript + dumb TERM, unstable install, unstable install + dumb TERM), so we take it down first. Then we boot the TTY driver, which fails if TERM=dumb, in which case we boot the retro-style usr. If it worked, we shut down the driver again, and boot a modern shell structure. This avoids all warnings and seems to work in all cases.
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fixed. |
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So things appear to work, but I still get weird failures on |
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OK, I can confirm the problem with There's possible fixes there (move to a soft purge, subtract I think this is good to merge if it passes review -- I know this is one hell of a janky patch pulling big chunks of code from OTP itself, but yeaaah. |
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If it helps some users I'm fine with it. |
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At the very least it brings the feature to all of windows users. Otherwise I don't know about what has a dumb term. Maybe output to files or some remote consoles? |
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Ok, cool, +1 |
Support old-style shell for rebar3 shell
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speaking as erlang's only windows user, i support this patch even so, it's reaper level grim 😀 |
This is quite the hack.
This requires to detect the current shell running; if it's the new
shell, business as usual.
However, if it's the old shell, we have to find a way to take over it
and drive IO. This requires a few steps because:
supervisor_bridge, so killing the child is not a supported operation
from the supervisor)
from the Port in charge of stdio ({fd, 0, 1})
except for badsig, and replicates the shutdown reason otherwise
userprocess dying (old shell) forany non-normal reason without also taking the whole escript down
by the old shell as a way to boot the stdio Port with only stdout
taken care of
Because of all these points, we have to kill the old
userprocess bysending it a message pretending to be the Stdio port dying of reason
normal, which lets it die without triggering the ire of itssupervision tree and keeping the escript alive. This, in turn, kills the
old stdio port since its parent (user.erl) has died.
Then we have to boot our copy of user.erl (rebar_user.erl) which
conveniently ignores the possibility of running the stdio port on stdout
only -- always using stdin and stdout, giving us a bona fide old-style
shell.
A known issue introduced is that running r3:do(ct) seems to then kill
the shell, and r3:do(dialyzer) appears to have an odd failure, but
otherwise most other commands appear to work fine.
This should fix #946 and #563