gnd: Add shell completions command

Add a `completions` subcommand that generates shell completion scripts
for bash, elvish, fish, powershell, and zsh. Users can install
completions by adding the output to their shell configuration.

Example usage:
  gnd completions bash >> ~/.bashrc
  gnd completions zsh > ~/.zfunc/_gnd
  gnd completions fish > ~/.config/fish/completions/gnd.fish

This uses the clap_complete crate which generates completions directly
from the clap CLI definition, ensuring they stay in sync with the
actual commands and options.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: lutter

Cargo.lock

@@ -16,6 +16,7 @@ graph-node = { path = "../node" }
 # Direct dependencies from current dev.rs
 anyhow = { workspace = true }
 clap = { workspace = true }
+clap_complete = "4"
 env_logger = "0.11.8"
 git-testament = "0.2"
 lazy_static = "1.5.0"

gnd/Cargo.toml

@@ -1,5 +1,8 @@
+use std::io;
+
 use anyhow::Result;
-use clap::{Parser, Subcommand};
+use clap::{CommandFactory, Parser, Subcommand, ValueEnum};
+use clap_complete::{generate, Shell};
 use git_testament::{git_testament, render_testament};
 use graph::log::logger;
 use lazy_static::lazy_static;
@@ -79,6 +82,27 @@ enum Commands {
 
     /// Remove build artifacts and generated files
     Clean(CleanOpt),
+
+    /// Generate shell completions
+    Completions(CompletionsOpt),
+}
+
+/// Options for shell completion generation.
+#[derive(Parser, Debug)]
+pub struct CompletionsOpt {
+    /// Shell to generate completions for
+    #[clap(value_enum)]
+    pub shell: CompletionShell,
+}
+
+/// Supported shells for completion generation.
+#[derive(Copy, Clone, Debug, ValueEnum)]
+pub enum CompletionShell {
+    Bash,
+    Elvish,
+    Fish,
+    PowerShell,
+    Zsh,
 }
 
 fn shutdown_token() -> CancellationToken {
@@ -197,6 +221,16 @@ async fn main() -> Result<()> {
                 std::process::exit(1);
             }
         }
+        Commands::Completions(completions_opt) => {
+            let shell = match completions_opt.shell {
+                CompletionShell::Bash => Shell::Bash,
+                CompletionShell::Elvish => Shell::Elvish,
+                CompletionShell::Fish => Shell::Fish,
+                CompletionShell::PowerShell => Shell::PowerShell,
+                CompletionShell::Zsh => Shell::Zsh,
+            };
+            generate(shell, &mut Cli::command(), "gnd", &mut io::stdout());
+        }
     }
 
     Ok(())