[spec/builtin-trap] Add test case for ignored traps in subshells

[rolfan-ish]

POSIX specifies that if the action of trap is null the shell shall ignore each specified condition. Currently oils doesn't adhere.

POSIX also says:

When a subshell is entered, traps that are not being ignored shall
be set to the default actions, except in the case of a command
substitution containing only a single trap command, when the traps
need not be altered.

However dash and bash don't fully follow this behavior, which I am pretty sure is a bug in both shells. I haven't tested other shells yet, including oils.

TODO: Add the spec tests for the exception of traps.

[andychu]

I would think of it in terms of what strace says each shell is doing, not necessarily what POSIX says

"ignored" is an ambiguous term

• does it mean it executes nothing?
• does it mean SIG_IGN ?

[rolfan-ish]

Is it good now?
Otherwise I would appreciate any pointers to resources/examples in order to catch on the guidelines.

Note: Detailed information on the commits can be found in the commit messages.

[rolfan-ish]

Looking at the source code the fix seems simple.
TODO: decide how much to adhere to POSIX (specially on case 0). As much as bash? As much as ash? Not at all like dash and mksh?

[andychu]

Ah let's look at the results - https://op.oilshell.org/uuu/github-jobs/10320/

https://op.oilshell.org/uuu/github-jobs/10320/ovm-tarball.wwz/_tmp/spec/osh-py/index.html

https://op.oilshell.org/uuu/github-jobs/10320/ovm-tarball.wwz/_tmp/spec/osh-py/builtin-trap.html

[andychu]

OK the general idea does look good ! Other shells pass and OSH fails

We need assertions for the other shells, like

## BUG mk STDOUT:
## END

See https://github.com/oils-for-unix/oils/wiki/Spec-Tests

---

And we are inhibited by

• 'trap -p | cat' does not work - doesn't write anything to pipe? #2466

this is a really bad bug ... seems like it may block this spec test, gah

[andychu]

I think we have to figure out what OSH does here first:

Most shells don't respect traps in subshells: pipelines etc.

I think these tests are a bit confused by this issue, especially because bash behaves differently

Let's discuss on Zulip about what we're trying to accomplish