Simplify parsing number of threads.

src/cli.rs

@@ -498,8 +498,8 @@ pub struct Opts {
 
     /// Set number of threads to use for searching & executing (default: number
     /// of available CPU cores)
-    #[arg(long, short = 'j', value_name = "num", hide_short_help = true, value_parser = clap::value_parser!(u32).range(1..))]
-    pub threads: Option<u32>,
+    #[arg(long, short = 'j', value_name = "num", hide_short_help = true, value_parser = str::parse::<NonZeroUsize>)]
+    pub threads: Option<NonZeroUsize>,
 
     /// Milliseconds to buffer before streaming search results to console
     ///
@@ -688,15 +688,8 @@ impl Opts {
         self.min_depth.or(self.exact_depth)
     }
 
-    pub fn threads(&self) -> usize {
-        // This will panic if the number of threads passed in is more than usize::MAX in an environment
-        // where usize is less than 32 bits (for example 16-bit architectures). It's pretty
-        // unlikely fd will be running in such an environment, and even more unlikely someone would
-        // be trying to use that many threads on such an environment, so I think panicing is an
-        // appropriate way to handle that.
-        self.threads.map_or_else(default_num_threads, |n| {
-            std::cmp::max(n.try_into().expect("too many threads"), 1)
-        })
+    pub fn threads(&self) -> NonZeroUsize {
+        self.threads.unwrap_or_else(default_num_threads)
     }
 
     pub fn max_results(&self) -> Option<usize> {
@@ -719,13 +712,14 @@ impl Opts {
 }
 
 /// Get the default number of threads to use, if not explicitly specified.
-fn default_num_threads() -> usize {
+fn default_num_threads() -> NonZeroUsize {
     // If we can't get the amount of parallelism for some reason, then
     // default to a single thread, because that is safe.
+    // Note that the minimum value for a NonZeroUsize is 1.
+    // Unfortunately, we can't do `NonZeroUsize::new(1).unwrap()`
+    // in a const context.
     const FALLBACK_PARALLELISM: NonZeroUsize = NonZeroUsize::MIN;
-    std::thread::available_parallelism()
-        .unwrap_or(FALLBACK_PARALLELISM)
-        .get()
+    std::thread::available_parallelism().unwrap_or(FALLBACK_PARALLELISM)
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, ValueEnum)]

src/main.rs

@@ -252,7 +252,7 @@ fn construct_config(mut opts: Opts, pattern_regexps: &[String]) -> Result<Config
         max_depth: opts.max_depth(),
         min_depth: opts.min_depth(),
         prune: opts.prune,
-        threads: opts.threads(),
+        threads: opts.threads().get(),
         max_buffer_time: opts.max_buffer_time,
         ls_colors,
         interactive_terminal,