nils-common

nils-common is the workspace shared helper crate for cross-CLI primitives.

Primary constraint: shared helpers must preserve behavioral parity for each consuming CLI. Moving logic into this crate must not change user-facing output text, warnings, color behavior, or exit-code contracts.

Shared helper policy

What belongs in nils-common

• Reusable helper logic used by multiple CLI crates.
• Domain-neutral primitives (process/env/shell/git/clipboard/fs internals).
• APIs that return structured results and let callers own final UX text.
• Behavior that can be covered by deterministic unit tests.

What stays crate-local

• User-facing warning/error text (including emoji/prefix wording).
• Exit-code mapping and command-level failure policy.
• CLI-specific command composition and UX defaults.
• Product/business/domain flows that only make sense in one crate.

Modules and purpose

• env: truthy parsing helpers and NO_COLOR presence checks.
• shell: POSIX single-quote escaping and ANSI stripping modes.
• process: command execution wrappers plus PATH lookup helpers.
• git: git command wrappers for repo probes and rev-parse helpers.
• clipboard: best-effort clipboard copy with explicit tool priority.
• fs: atomic write, timestamp write/remove, SHA-256 hashing, and cross-platform replace helpers with structured errors.
• greeting: tiny sample helper used by cli-template.

API examples

env:

use nils_common::env;

let starship_enabled = env::env_truthy_or("AGENTS_CLI_STARSHIP", false);
let no_color = env::no_color_enabled();
println!("starship={starship_enabled}, no_color={no_color}");

shell:

use nils_common::shell::{self, AnsiStripMode, SingleQuoteEscapeStyle};

let quoted = shell::quote_posix_single_with_style("a'b", SingleQuoteEscapeStyle::Backslash);
let plain = shell::strip_ansi("\x1b[31mred\x1b[0m", AnsiStripMode::CsiSgrOnly);
assert_eq!(quoted, "'a'\\''b'");
assert_eq!(plain, "red");

process:

use nils_common::process;

assert!(process::cmd_exists("git"));
let git_path = process::find_in_path("git").expect("git should be on PATH");
let out = process::run_stdout_trimmed(git_path.to_string_lossy().as_ref(), &["--version"])
    .expect("git --version should run");
println!("{out}");

git:

use nils_common::git;

let inside = git::is_inside_work_tree().expect("git check should run");
if inside {
    let root = git::repo_root().expect("repo root check");
    println!("repo root: {root:?}");
}

clipboard:

use nils_common::clipboard::{copy_best_effort, ClipboardOutcome, ClipboardPolicy, ClipboardTool};

let tool_order = [
    ClipboardTool::Pbcopy,
    ClipboardTool::WlCopy,
    ClipboardTool::Xclip,
    ClipboardTool::Xsel,
    ClipboardTool::Clip,
];
let outcome = copy_best_effort("hello", &ClipboardPolicy::new(&tool_order));

if matches!(
    outcome,
    ClipboardOutcome::SkippedNoTool | ClipboardOutcome::SkippedFailure
) {
    eprintln!("clipboard copy unavailable; keep crate-local fallback messaging");
}

fs:

use nils_common::fs::{self, AtomicWriteError, SECRET_FILE_MODE};
use std::path::Path;

fs::write_atomic(Path::new("cache/auth.json"), br#"{"ok":true}"#, SECRET_FILE_MODE)?;
fs::write_timestamp(
    Path::new("cache/auth.json.timestamp"),
    Some("2026-02-01T00:00:00Z\n"),
)?;
let digest = fs::sha256_file(Path::new("cache/auth.json"))?;

if let Err(AtomicWriteError::CreateParentDir { path, .. }) =
    fs::write_atomic(Path::new("/tmp/demo.json"), b"{}", SECRET_FILE_MODE)
{
    eprintln!("parent directory error: {path:?}");
}

println!("sha256={digest}");
# Ok::<(), Box<dyn std::error::Error>>(())

Migration conventions for parity

When introducing a shared helper at a call site:

1. Add or keep characterization tests in the caller crate first.
2. Move only primitive logic; keep a crate-local adapter for message formatting and exit-code mapping. For write_atomic / write_timestamp / sha256_file migrations, map structured errors back to existing crate-local UX text.
3. Preserve existing quote/ANSI mode choices and NO_COLOR behavior.
4. Keep tool/command fallback order identical (for example clipboard tool order, git probe fallback behavior).
5. Re-run crate tests that cover the touched command paths before merging.

Non-goals

• Defining CLI-specific UX copy, warning templates, or emoji policy.
• Owning command-level business logic for a single CLI.
• Hiding meaningful behavior differences that should remain explicit in local adapters.
• Replacing specialized shared crates such as api-testing-core, nils-term, or nils-test-support.

Docs

• Docs index