fix(cli): add fish shell completion support

[limjonathan]

Description

Fixes issue #41232 where opencode completion fish incorrectly emitted bash/zsh completion scripts instead of proper fish syntax.

Changes

• Added new packages/opencode/src/cli/completion.ts with completion templates for bash, zsh, and fish
• Modified packages/opencode/src/index.ts to add a custom completion command that:
  • Accepts a positional shell argument (bash, zsh, fish)
  • Supports flags --bash/-b, --zsh/-z, --fish/-f
  • Falls back to $SHELL environment variable for auto-detection

Verification

• opencode completion fish → outputs fish completion script ✅
• opencode completion bash → outputs bash completion script ✅
• opencode completion zsh → outputs zsh completion script ✅
• opencode completion --fish → outputs fish completion script ✅
• SHELL=/bin/fish opencode completion → auto-detects fish ✅
• SHELL=/bin/zsh opencode completion → auto-detects zsh ✅
• SHELL=/bin/bash opencode completion → auto-detects bash ✅
• TypeScript typecheck passes ✅

Plugins

N/A

OpenCode version

Current dev branch

Steps to reproduce

1. Run opencode completion fish and look at the output. It is now a proper fish completion script.
2. In fish, run opencode completion fish | source.
3. fish no longer reports "Unsupported use of '='".

Screenshot and/or share link

N/A

Operating System

Linux (tested on Arch Linux)

Terminal

Any terminal supporting fish shell

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

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[github-actions]

Hey! Your PR title fix(#41232): add fish shell completion support doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential duplicate found:

• PR fix(cli): honor shell argument in completion command #41235: fix(cli): honor shell argument in completion command - fix(cli): honor shell argument in completion command #41235

This PR appears to be directly related to the current PR #41336. Both are addressing the same issue (#41232) and both involve adding/fixing shell completion support with multiple shell types (bash, zsh, fish). PR #41235 also adds shell argument handling to the completion command, which overlaps with the functionality in the current PR. You should check if #41235 is still open and whether it needs to be merged first or if this PR should be rebased on it.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[limjonathan]

Thanks for the heads-up! I see PR #41235 already addresses this issue with a more complete implementation including tests. I'll close this PR in favor of that one since it's more complete and already has test coverage.

[limjonathan]

Closing in favor of PR #41235 which has a more complete implementation with tests.