Generate Jujutsu change description using llm tool in Conventional Commit format

llm_conventional_desc.fish

#!/usr/bin/env fish
# Shebang for testing, Jujutsu config at the end of this file
# LLMs are useful for generating the first line of the CC (the What), but you
# should always review generated description to include the Why and the How.

set -l DIFF $(jj diff --git -r @)
if [ -z "$DIFF" ]
    echo "No changes found."
    return 1
end

# Generate commit message using LLM
set -l DESC_MSG $(echo "$DIFF" | llm -m claude-3.5-sonnet "\
Generate a concise commit message (first line), blank line and detailed
description based on these changes. Follow conventional commits format.
Your response will be passed directly into version control command. Diff:\
")

if [ -z "$DESC_MSG" ]
    echo "Failed to generate change description."
    return 1
end

# Describe changes
printf %s\n $DESC_MSG | jj desc --stdin

# Jujutsu config
# [aliases]
# cdesc = ["util", "exec", "--", "llm_conventional_desc.fish"]

Inspired by https://gist.github.com/RafalWilinski/f0167ae404c7623ffb54c1429394323a, adapted for Jujutsu and Fish.