$_ incorrectly highlighted red

[mxmilkiib]

$_ (dollar underscore) is the last parameter from the previous line. I often (with autocd on) enter "$_" directly after a command to jump into the destination directory. However it's always highlighted red. Apologies if this is covered by another issue, I went through a number but couldn't find anything directly related. Thanks.

[danielshahaf]

Are literal directory names highlighted in green at command position when AUTO_CD is set? AFAICS they aren't [can't test this myself right now], so you're essentially asking for AUTO_CD support to be added. (Once literal directory names are handled, simple parameter expansions will DTRT too.)

Would you be interested in contributing this feature?

[danielshahaf]

By the way, M-. (Alt+.) is equivalent and has fewer keystrokes.

[mxmilkiib]

Whoops, AUTO_CD paths are made purple (on my system) not green.

I'm afraid I don't have the understanding, time or energy to implement this.

Alt-. doesn't work for me, I guess either conflict with another zsh script or bad key binds. Thank you for the tip though.

[phy1729]

It's a bit more complicated than just supporting AUTO_CD. Currently _ is not recognized as a parameter name

zsh-syntax-highlighting/highlighters/main/main-highlighter.zsh

Line 393 in d766243

readonly parameter_name_pattern='([A-Za-z_][A-Za-z0-9_]*|[0-9]+)'

. The hard part is expanding _ properly. We'd need to save the value of _ and then special case the expansion code because _ will have changed many times over once we've gotten to here

zsh-syntax-highlighting/highlighters/main/main-highlighter.zsh

Line 607 in d766243

# Set $arg.

[danielshahaf]

That pattern would match $_ 's name, but if we are able unable to compute the correct expansion, we might have another use-case for the envisioned indeterminate style — not just for $_ but for any [[ ${(t)foo} == *special* ]] parameter at command position, unless whitelisted as an exception?

[danielshahaf]

See #617 for indeterminate (although that term isn't used there).

[danielshahaf]

My reading is two separate issues:

• Support AUTO_CD.
• Don't expand special parameters at command position.

[phy1729]

Indeed it does match $_ oops. I agree in general special parameters should use a indererminate style; however, I think $_ is useful enough to special case. There may be a cleaner way, but worst case we could save ${${(z)BUFFER}[-1]} on zle-line-finish.

[danielshahaf]

Indeed it does match `$_` oops. I agree in general special parameters should use a `indererminate` style; however, I think `$_` is useful enough to special case. There may be a cleaner way, but worst case we could save `${${(z)BUFFER}[-1]}` on `zle-line-finish`.

And what guarantees us that value would be equal to the actual value of $_ that will be used when zsh executes the line? What if there is another plugin after z-sy-h in the set of plugins and it writes to ${BUFFER} before the line is executed?

[phy1729]

Nothing. However, highlighting on the modified line would already be incorrect for those users (and we do document that we should be sourced last).

[danielshahaf]

Fair enough. Re 'cleaner way', I thought we could have zle expose the REPL-level value of $_ through a new preset variable (akin to BUFFER, WIDGET, &c). WDYT?

[danielshahaf]

For the record, AUTO_CD support is in #669 (PR for 0.8.0) and parameters in command position are #674 (has WIP PR). Support for $_ specifically would require further work, as discussed in this issue.