Hi,

the chain.org/elv code looks like a good starting point to write a personal theme so a open licence would be helpful.

Starship now can visualise the exit code, and it would be nice (not essential) to have this in Chain too, thank you!

https://github.com/starship/starship/releases/tag/v1.2.0

Using commit 5cd2d7c with Elvish v0.13 and the default prompts (both left and right). Example below where I originally launch the shell without the theme then call use to try to load it:

/usr/home/vendion> use github.com/zzamboni/elvish-themes/chain
/usr/home/vendion> read: Illegal option -d
prompt function error: sh exited with 2
(prompt here but not rendered)
read: Illegal option -d                                                                                                                                                                                                                        
prompt function error: sh exited with 2
(prompt here but not rendered)

I have even tried to manually define the segmants for the left and right prompts with the following and still get the same error:

chain:prompt-segments = [ su dir git-branch git-combined arrow ]
chain:rprompt-segments = [ (constantly (styled (whoami)✸(hostname) inverse)) timestamp ]

but I still get the same error as above.

Note that the left and right prompts are rendered in parallel in separate goroutines. This causes two data races in the chain theme.

The first is in the gitstatus:query function which starts gitstatusd if it isn't already running. Since gitstatus:query is always run in both prompts via the chain:-parse-git function both prompts can decide that the daemon isn't running and start it. One of those daemons will die almost immediately resulting in this error appearing in the terminal:

job (external $binary) \                                                                                                            WTF
        --num-threads=(thread-count) \
        --max-num-staged=$E:GITSTATUS_MAX_NUM_STAGED\
        --max-num-unstaged=$E:GITSTATUS_MAX_NUM_UNSTAGED\
        --max-num-untracked=$E:GITSTATUS_MAX_NUM_UNTRACKED\
        --max-num-conflicted=$E:GITSTATUS_MAX_NUM_CONFLICTED\
        < $state[stdin] \
        > $state[stdout] \
        2> /dev/null & finished

The fix is to call gitstatus:start right after the use github.com/href/elvish-gitstatus/gitstatus statement.

The second race is due to always calling chain:-git-parse even if the prompt does not contain any git segments. That can cause the left and right prompts to read from the gitstatusd pipe at the same time. Resulting in stochastic exceptions. Properly fixing this will require an Elvish mutex that can be used to protect critical sections. Or a major redesign of the chain module to ensure -git-parse is only run once whenever prompts are rendered. A partial fix is to call -git-parse only if the prompt contains at least one git segment. That is probably "good enough" since people won't normally put git information in both prompts. This is what my copy of chain:-build-chain looks like:

fn -build-chain [segments]{
  if (eq $segments []) {
    return
  }
  for seg $segments {
    if (str:has-prefix (to-string $seg) "git-") {
      -parse-git
      break
    }
  }
  first = $true
  output = ""

By default the timestamp segment is set to be colored as "grey" as per this line https://github.com/zzamboni/elvish-themes/blob/master/chain.elv#L45 but with Elvish 0.13 (and presumably going forward) "grey" is no longer a valid color for styled command:

[/u/h/v/ports]─[⎇ master]─> styled "this message should be red" red
▶ (styled (styled-segment this message should be red &fg-color=<unknown red> &bg-color=$nil))
[/u/h/v/ports]─[⎇ master]─> styled "this message should be grey" grey
Exception: grey is not a valid style transformer

The default color for this segment should be updated to be one of the other valid colors, probably "bright-black" instead as that is the closest parallel per the release notes https://elv.sh/blog/0.13-release-notes.html

I implemented support for my Anaconda virtual environment management functions. That involved modifying my prompt to insert a lambda into chain:prompt-segments:

# This is the default prompt definition but with the addition of a segment to
# report whether I have activated an Anaconda environment.
fn conda-segment []{
  if (not (eq "" $E:CONDA_DEFAULT_ENV)) {
    chain:prompt-segment conda-env $E:CONDA_DEFAULT_ENV
  }
}
chain:prompt-segments = [
  su $conda-segment~ dir git-branch git-combined arrow
]

I added agit-branch key to my definition of the chain:segment-style map. However, that results in an exception because that segment-style isn't defined by chain:default-segment-style. The bug is that this line should use $segment-style rather than $default-segment-style and $glyph rather than $default-glyph:

I find a prompt with spaces around the segments (imagine the segments being colored differently), ~/p/3/elvish ⎇ min-max-functions >, easier to read compared to brackets, [~/p/3/elvish][⎇ min-max-functions]>. Any chance you would entertain adding a var, such as chain:segment-brackets = $true, that fn prompt-segment can check for whether to use brackets or spaces. I don't think there is much value in making each char individually configurable as there is really only one other sensible option, {segment}, if you ignore non-ASCII characters.

https://github.com/zzamboni/elvish-themes/blob/master/chain.elv#L196

tmp is now a reserved keyword: elves/elvish@973fe39

Following the instructions to load the chain theme fails in a clean elvish shell:

~> use github.com/zzamboni/elvish-themes/chain
Exception: Compilation error: variable $nil not found
/Users/daniel/.elvish/lib/github.com/zzamboni/elvish-themes/chain.elv, line 125:   if (not-eq $branch $nil) {
[tty], line 1: use github.com/zzamboni/elvish-themes/chain

This is in Elvish version 0.12 installed from Homebrew on macOS. The shell has not been initialized beyond the instructions found in this repo.

To reproduce:

~> ls -la ~/.elvish
total 0
drwx------   2 daniel  staff    64 Aug 24 02:42 .
drwxr-xr-x+ 68 daniel  staff  2176 Aug 24 02:42 ..
~> use epm
~> epm:install github.com/zzamboni/elvish-themes
=> Installing github.com/zzamboni/elvish-themes
Cloning into '/Users/daniel/.elvish/lib/github.com/zzamboni/elvish-themes'...
remote: Enumerating objects: 202, done.
remote: Total 202 (delta 0), reused 0 (delta 0), pack-reused 202
Receiving objects: 100% (202/202), 63.68 KiB | 749.00 KiB/s, done.
Resolving deltas: 100% (98/98), done.
=> Installing dependencies: github.com/href/elvish-gitstatus
=> Installing github.com/href/elvish-gitstatus
Cloning into '/Users/daniel/.elvish/lib/github.com/href/elvish-gitstatus'...
remote: Enumerating objects: 30, done.
remote: Counting objects: 100% (30/30), done.
remote: Compressing objects: 100% (24/24), done.
remote: Total 30 (delta 10), reused 26 (delta 6), pack-reused 0
Unpacking objects: 100% (30/30), done.
~> use github.com/zzamboni/elvish-themes/chain
Exception: Compilation error: variable $nil not found
/Users/daniel/.elvish/lib/github.com/zzamboni/elvish-themes/chain.elv, line 125:   if (not-eq $branch $nil) {
[tty], line 1: use github.com/zzamboni/elvish-themes/chain