refac: use clap's builtin env reader

src/alejandra_cli/Cargo.toml

@@ -7,6 +7,7 @@ alejandra = { path = "../alejandra" }
 clap = { version = "*", default-features = false, features = [
   "color",
   "derive",
+  "env",
   "std",
   "strsim",
 ] }

src/alejandra_cli/src/cli.rs

@@ -1,4 +1,3 @@
-use std::env;
 use std::fs::read_to_string;
 use std::io::Read;
 
@@ -49,7 +48,11 @@ struct CLIArgs {
 
     /// Number of formatting threads to spawn. Defaults to the number of
     /// physical CPUs.
-    #[clap(long, short, value_parser = value_parser!(u8).range(1..))]
+    #[clap(
+        long, short,
+        env = "ALEJANDRA_THREADS",
+        value_parser = value_parser!(u8).range(1..),
+    )]
     threads: Option<u8>,
 
     /// Use once to hide informational messages,
@@ -146,15 +149,8 @@ pub fn main() -> ! {
     let include: Vec<&str> =
         args.include.iter().map(String::as_str).collect::<Vec<&str>>();
 
-    // Try CLI value, then env var, then fall back to number of physical CPUs.
-    let threads: usize = if let Some(cli_threads) = args.threads {
-        cli_threads.into() // convert u8 to usize
-    } else {
-        env::var("ALEJANDRA_THREADS")
-            .ok()
-            .and_then(|v| v.parse::<usize>().ok())
-            .unwrap_or_else(num_cpus::get_physical)
-    };
+    let threads =
+        args.threads.map_or_else(num_cpus::get_physical, Into::<usize>::into);
 
     let verbosity = match args.quiet {
         0 => Verbosity::Everything,

src/alejandra_cli/tests/cli.rs

@@ -128,7 +128,7 @@ fn cases() {
         output_got.push_str(&format!("args: {:?}\n", case.args));
 
         let mut child = Command::new("cargo")
-            .env("ALEJANDRA_THREADS", "4")
+            .env("ALEJANDRA_THREADS", "1")
             .args(["run", "--quiet", "--"])
             .args(case.args)
             .stdin(Stdio::piped())

src/alejandra_cli/tests/output.txt

@@ -33,7 +33,7 @@ stdout:
   
       -t, --threads <THREADS>
               Number of formatting threads to spawn. Defaults to the number of
-              physical CPUs
+              physical CPUs [env: ALEJANDRA_THREADS=1]
   
       -V, --version
               Print version information
@@ -184,7 +184,7 @@ exit code: Some(1)
 ===
 args: [".", "--exclude", "."]
 stderr:
-  Checking style in 0 files using 4 threads.
+  Checking style in 0 files using 1 thread.
   
   
   Congratulations! Your code complies with the Alejandra style.
@@ -203,7 +203,7 @@ stdout:
   Requires formatting: tests/inputs/changed.nix
 
 stderr:
-  Checking style in 1 file using 4 threads.
+  Checking style in 1 file using 1 thread.
   
   
   Alert! 1 file requires formatting.
@@ -218,7 +218,7 @@ stdout:
   Requires formatting: tests/inputs/changed.nix
 
 stderr:
-  Checking style in 1 file using 4 threads.
+  Checking style in 1 file using 1 thread.
   
   
   Alert! 1 file requires formatting.
@@ -233,7 +233,7 @@ exit code: Some(2)
 ===
 args: ["-c", "tests/inputs/unchanged.nix"]
 stderr:
-  Checking style in 1 file using 4 threads.
+  Checking style in 1 file using 1 thread.
   
   
   Congratulations! Your code complies with the Alejandra style.
@@ -249,7 +249,7 @@ exit code: Some(0)
 ===
 args: ["--check", "tests/inputs/error.nix"]
 stderr:
-  Checking style in 1 file using 4 threads.
+  Checking style in 1 file using 1 thread.
   
   
   Failed! 1 error found at: