test and document var x = $(false)

[andychu]

• do var, const, setvar have exit codes?
  • maybe you should document it as not the LAST one, but as the GREATEST exit code?
• should it temporarily turn on command_sub_errexit so it fails early?

[andychu]

Yeah var fails with bin/oil, but not bin/osh, which is not desirable.

$ bin/osh -c 'var x = $(false); echo $?'
0

I think it should exit with the last one/?

var x = "$(false)-$(exit 42)"

[andychu]

Idea: what happens when myfunc(x) returns an error? The only way you can catch it is like this?

if ! var result = myfunc(x) {
  echo 'error'
}

This is invalid syntax!

$ bin/oil -c 'if var x = 42 { echo $x }'
  if var x = 42 { echo $x }
                ^
[ -c flag ]:1: Syntax error in expression (near Id.Op_LBrace)

[andychu]

Another syntactic issue with error handling: Checking the return value of procs that take blocks

I think you have to use

try --assign :status myproc {
  echo $x
}
echo $status

[andychu]

This is part of #477 , but it's worth having our own issue

[andychu]

Note on the design problem

$ bin/oil -c 'if { var x = 42 }; then echo hi; fi
 '
  if { var x = 42 }; then echo hi; fi
                   ^
[ -c flag ]:1: fatal: strict_errexit only allows simple commands (got command.Sentence). Hint: use 'run'.

TODO: also fix run, which was renamed to try

[andychu]

Crazy idea:

if try (var x = 42) {

Except this means that () has statements

if try { var x = f(x) } { echo ok }

hm this is weird, I think it runs into a parsing issue

[andychu]

Maybe, some kind of RHS assignment operator

_ f(42) => var status

var x = f(42) => var status  # feels a little weird

Or simply use $?

shopt --unset errexit {
  var x = f(42)
}
echo "status = $?"

Doesn't work with try --assign but that might be OK

[andychu]

try --assign :st {
  var x = f(42)
  var y = f(0)
}
if (st != 0) {
  echo "failed"
}

Hm this is not horrible ...

It's long but we want to discourage this style I think ... functions should mostly be "pure".

However it may be a challenge to people who want to import Python/JS knowledge ...

try {
  var x = f(42)
  var y = f(0)
}

This really isn't any different than

var x = f(42)
var y = f(0)

[andychu]

Related: https://news.ycombinator.com/item?id=27163494

[andychu]

https://oilshell.zulipchat.com/#narrow/stream/121540-oil-discuss/topic/errexit.20issue.20and.20docs

I suggest

trycatch {
  var x = 1 / 0
}
echo "status = $?"

Not sure how common it will be ?

[andychu]

I defined expression errors to be status 3.

var x = $(false) respects command_sub_errexit, so it won't fail if it's off. This is perhaps not ideal but it's consistent.

[andychu]

Released http://www.oilshell.org/blog/2022/05/release-0.10.0.html