fix: complete executables in fish for benchmark commands

build.rs

@@ -1,9 +1,23 @@
 use std::fs;
+use std::path::{Path, PathBuf};
 
 use clap_complete::{generate_to, Shell};
 
 include!("src/cli.rs");
 
+const FISH_COMMAND_COMPLETION: &str = "\
+# Complete executables from $PATH for benchmark command arguments (see #872)
+complete -c hyperfine -n \"__fish_use_subcommand\" -x -a \"(__fish_complete_command)\"
+";
+
+fn patch_fish_completions(path: &Path) {
+    let mut content = fs::read_to_string(path).expect("read fish completions");
+    if !content.contains("__fish_use_subcommand") {
+        content.push_str(FISH_COMMAND_COMPLETION);
+        fs::write(path, content).expect("write fish completions");
+    }
+}
+
 fn main() {
     let var = std::env::var_os("SHELL_COMPLETIONS_DIR").or_else(|| std::env::var_os("OUT_DIR"));
     let outdir = match var {
@@ -21,5 +35,19 @@ fn main() {
         Shell::Elvish,
     ] {
         generate_to(shell, &mut command, "hyperfine", &outdir).unwrap();
+        if shell == Shell::Fish {
+            patch_fish_completions(&PathBuf::from(&outdir).join("hyperfine.fish"));
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::FISH_COMMAND_COMPLETION;
+
+    #[test]
+    fn fish_command_completion_snippet_uses_path_executable_helper() {
+        assert!(FISH_COMMAND_COMPLETION.contains("__fish_use_subcommand"));
+        assert!(FISH_COMMAND_COMPLETION.contains("__fish_complete_command"));
     }
 }

src/cli.rs

@@ -91,6 +91,7 @@ fn build_command() -> Command {
                 .long("reference")
                 .action(ArgAction::Set)
                 .value_name("CMD")
+                .value_hint(ValueHint::CommandString)
                 .help(
                     "The reference command for the relative comparison of results. \
                     If this is unset, results are compared with the fastest command as reference."