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

# Use existing revset description to provide CC description
set -l DESC_DETAIL $(jj log --no-graph -T description -r @)
if [ -z "$DESC_DETAIL" ]
    set -l DESC_DETAIL ""
end

# Generate commit message using LLM
if [ -n "$DESC_DETAIL" ]
    # Use handwritten description
    set -f DESC_MSG $(printf '\
Generate a conventional commit message following this exact format:
- First line: type(scope): brief description (50 chars max)
- Blank line
- This detailed explanation: %s

Use conventional commit types: feat, fix, docs, style, refactor, test, chore, build, ci, perf.
Only output the commit message - no code blocks, explanations, or extra formatting.

Code changes:
%s' $DESC_DETAIL $(echo "$DIFF") | llm --log)
else
    # Generate simple conventional commit message
    set -f DESC_MSG $(printf '\
Generate a conventional commit message from this diff:
- First line only: type(scope): brief description (50 chars max)
- Use conventional commit types: feat, fix, docs, style, refactor, test, chore, build, ci, perf
- Only output the commit message - no code blocks, explanations, or extra formatting

Code changes:
%s' $(echo "$DIFF") | llm --log)
end

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

set -l FIRST_LINE $(echo "$DESC_MSG" | head -1)
if ! echo "$FIRST_LINE" | grep -q "^[a-z][a-z]*\(.*\)*:"
    echo "Warning: Generated message may not follow conventional commits format:"
    echo "  First line: $FIRST_LINE"
    echo "  Expected: type(scope): description"
    echo ""
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.