always use delta and check if it exists

src/diff.rs

@@ -4,7 +4,7 @@ use terminal_size::{terminal_size, Width};
 
 use crate::{config::Config, utils::get_tree_files};
 
-pub async fn diff(config: &Config, diff_command: String) -> anyhow::Result<()> {
+pub async fn diff(config: &Config) -> anyhow::Result<()> {
 	tokio::fs::create_dir_all(&config.install_dir).await?;
 	let built_files = get_tree_files(config, &config.build_dir).await?;
 	let installed_files = get_tree_files(config, &config.install_dir).await?;
@@ -39,7 +39,7 @@ pub async fn diff(config: &Config, diff_command: String) -> anyhow::Result<()> {
 			)
 		};
 
-		let output = tokio::process::Command::new(&diff_command)
+		let output = tokio::process::Command::new("delta")
 			.current_dir(workdir)
 			.arg(second_path)
 			.arg(first_path)

src/main.rs

@@ -10,6 +10,7 @@ use std::path::PathBuf;
 use clap::{IntoApp, Parser};
 use clap_complete::generate;
 use directories::{ProjectDirs, UserDirs};
+use utils::command_exists;
 
 use crate::{build::build, config::Config, diff::diff, install::install, opts::Opts};
 
@@ -51,7 +52,12 @@ async fn main() -> anyhow::Result<()> {
 	if opts.install {
 		install(&config).await?;
 	} else {
-		diff(&config, opts.diff_command).await?;
+		if !command_exists("delta").await {
+			println!("'delta' is not installed");
+			return Ok(());
+		}
+		
+		diff(&config).await?;
 	}
 
 	Ok(())

src/opts.rs

@@ -24,14 +24,6 @@ pub struct Opts {
 	)]
 	pub repo_path: PathBuf,
 
-	#[clap(
-		short,
-		long,
-		default_value = "delta",
-		help = "Command to execute to show diffs"
-	)]
-	pub diff_command: String,
-
 	#[clap(long, value_name = "SHELL", help = "Generate shell completions")]
 	pub generate: Option<Shell>,
 }

src/utils.rs

@@ -63,3 +63,8 @@ pub async fn remove_dir_if_empty(path: &Path) -> anyhow::Result<()> {
 
 	Ok(())
 }
+
+pub async fn command_exists(command: &str) -> bool {
+	tokio::process::Command::new("which")
+			.arg(&command).status().await.is_ok()
+}