[word_eval] Implement 'shopt -s compat_array'.

[akinomyoga]

Ref #726

• Fix a problem that the scalar form cannot be used in arithmetic expressions (9fc20e7 Test c2365f5 Fix):

$ osh -c '$((BASH_LINENO))'
  $((BASH_LINENO))
     ^~~~~~~~~~~
[ -c flag ]:1: fatal: Expected a value convertible to integer, got value.MaybeStrArray

• Implement shopt -s compat_array to allow $array (Test bf9f332, Fix 6704770)

• Disallow ${#BASH_SOURCE}, ${BASH_SOURCE:1:1}, ${BASH_SOURCE#X}, ${BASH_SOURCE-X}, etc. by default (Fix b1a16c2). In this implementation, everything with additional suffix/prefix are disallowed.

[andychu]

Great thanks for doing this!

It doesn't look like too big a change which I'm happy about.

[andychu]

Would this part be made obsolete if we made BASH_LINENO etc. immutable?

I guess that would make Oil technically incompatible, but I've been thinking about that. Also it makes sense to tighten up things like PATH=(a b c) and HOME=(a b c) (they shouldn't be arrays)

This doesn't have to be done in this commit; I'm just curious / brainstorming the semantics

[akinomyoga]

As you have already written in another comment, this change also affects the other mutable variables when shopt -s compat_array is set.

[andychu]

I would name compat_introspect something more descriptive like is_plain_var or is_plain_var_sub

( The difference between SimpleVarSub and BracedVarSub is one thing I want to get rid of with #604 )

[akinomyoga]

I renamed it to is_plain_var_sub b311fb3.

[andychu]

Ah never mind about my lvalue comment. I think this works now?

$ a=(1 0 0); (( a++ )); echo ${a[@]}
2 0 0

If so then I think we should add things like that as test cases. I don't think the tests are hitting some code paths.

[akinomyoga]

I think this works now?

$ a=(1 0 0); (( a++ )); echo ${a[@]}

I added a test case 4662002 to find that it actually doesn't work. Currently, it mutates the array to a scalar. I'll fix it later.

[andychu]

OK I think the continuous build might fail but let's see what happens ... e.g. the test/spec.sh numbers should generally be adjusted to keep it green.

[andychu]

I think this should also test ${arr} since that's a different code path. (as mentioned I want to collapse those)

[akinomyoga]

I added the test for ${arr} in another PR #733.

[andychu]

Oh I also had that other comment about testing ${arr} too, maybe you can sneak it in the next commit if you're touching this...

In any case I'm interested to see what works in ble.sh is, so if there is something I can try let me know. Should I just switch to the osh branch and try to run it with osh from head?

We can put instructions here too:

https://github.com/oilshell/oil/wiki/Running-ble.sh-With-Oil

[akinomyoga]

Oh, you have already merged it. Thank you!

OK I think the continuous build might fail but let's see what happens ...

I have actually fixed it now. I'll submit it in another PR.

In any case I'm interested to see what works in ble.sh is, so if there is something I can try let me know.

Yes, now it is ready so I'm going to prepare something that can be tried out.

We can put instructions here too:

OK.

[akinomyoga]

We can put instructions here too:

I added a description in the Wiki page. You can follow the instructions Update ble.osh and Try read -e