Generate CLI completions

Cargo.toml

@@ -43,6 +43,7 @@ backoff = { version = "0.4.0", default-features = false }
 camino = "1.1.4"
 # Clap 4.4 is the last version supporting Rust 1.72.
 clap = { version = "~4.4", features = ["derive", "wrap_help", "env", "string"] }
+clap_complete = "~4.4"
 clearscreen = "2.0.1"
 command-group = { version = "2.1.0", features = ["tokio", "with-tokio"] }
 crossterm = { version = "0.27.0", features = ["event-stream"] }

nix/packages/ghciwatch.nix

@@ -3,6 +3,7 @@
   stdenv,
   libiconv,
   darwin,
+  buildPackages,
   haskell,
   haskellPackages,
   ghc,
@@ -12,6 +13,7 @@
   rustPlatform,
   rust-analyzer,
   mdbook,
+  installShellFiles,
   # Versions of GHC to include in the environment for integration tests.
   # These should be attributes of `haskell.compiler`.
   ghcVersions ? null,
@@ -103,6 +105,9 @@
       inherit cargoArtifacts;
     };
 
+  can-run-ghciwatch = stdenv.hostPlatform.emulatorAvailable buildPackages;
+  run-ghciwatch = "${stdenv.hostPlatform.emulator buildPackages} $out/bin/ghciwatch";
+
   releaseArgs =
     commonArgs
     // {
@@ -114,6 +119,17 @@
       # Only build `ghciwatch`, not the test macros.
       cargoBuildCommand = "cargoWithProfile build";
 
+      nativeBuildInputs = (commonArgs.nativeBuildInputs or []) ++ [installShellFiles];
+
+      postInstall =
+        (commonArgs.postInstall or "")
+        + lib.optionalString can-run-ghciwatch ''
+          installShellCompletion --cmd ghciwatch \
+            --bash <(${run-ghciwatch} --completions bash) \
+            --fish <(${run-ghciwatch} --completions fish) \
+            --zsh <(${run-ghciwatch} --completions zsh)
+        '';
+
       passthru = {
         inherit GHC_VERSIONS checks devShell user-manual user-manual-tar-xz;
       };

src/cli.rs

@@ -4,6 +4,7 @@ use std::time::Duration;
 use camino::Utf8PathBuf;
 use clap::builder::ValueParserFactory;
 use clap::Parser;
+use clap_complete::Shell;
 use tracing_subscriber::fmt::format::FmtSpan;
 
 use crate::clap::FmtSpanParserFactory;
@@ -100,6 +101,10 @@ pub struct Opts {
     #[arg(long, hide = true)]
     pub generate_markdown_help: bool,
 
+    /// Generate shell completions for the given shell.
+    #[arg(long)]
+    pub completions: Option<Shell>,
+
     /// Lifecycle hooks and commands to run at various points.
     #[command(flatten)]
     pub hooks: crate::hooks::HookOpts,

src/main.rs

@@ -6,6 +6,7 @@
 
 use std::time::Duration;
 
+use clap::CommandFactory;
 use clap::Parser;
 use ghciwatch::cli;
 use ghciwatch::run_ghci;
@@ -30,6 +31,12 @@ async fn main() -> miette::Result<()> {
         return Ok(());
     }
 
+    if let Some(shell) = opts.completions {
+        let mut command = cli::Opts::command();
+        clap_complete::generate(shell, &mut command, "ghciwatch", &mut std::io::stdout());
+        return Ok(());
+    }
+
     std::env::set_var("IN_GHCIWATCH", "1");
 
     let (ghci_sender, ghci_receiver) = mpsc::channel(32);