Port builtin count to rust (#9963)

* Port builtin count to rust

* Explicitly use wstring

fish-rust/src/builtins/count.rs

@@ -0,0 +1,33 @@
+use super::prelude::*;
+
+// How many bytes we read() at once.
+// Since this is just for counting, it can be massive.
+const COUNT_CHUNK_SIZE: usize = 512 * 256;
+
+/// Implementation of the builtin count command, used to count the number of arguments sent to it.
+pub fn count(
+    _parser: &mut parser_t,
+    streams: &mut io_streams_t,
+    argv: &mut [&wstr],
+) -> Option<c_int> {
+    // Always add the size of argv (minus 0, which is "count").
+    // That means if you call `something | count a b c`, you'll get the count of something _plus 3_.
+    let mut numargs = argv.len() - 1;
+
+    // (silly variable for Arguments to do nothing with)
+    let mut zero = 0;
+
+    // Count the newlines coming in via stdin like `wc -l`.
+    // This means excluding lines that don't end in a newline!
+    numargs += Arguments::new(&[] as _, &mut zero, streams, COUNT_CHUNK_SIZE)
+        // second is "want_newline" - whether the line ended in a newline
+        .filter(|x| x.1)
+        .count();
+
+    streams.out.appendln(numargs.to_wstring());
+
+    if numargs == 0 {
+        return STATUS_CMD_ERROR;
+    }
+    STATUS_CMD_OK
+}

fish-rust/src/builtins/mod.rs

@@ -8,6 +8,7 @@
 pub mod cd;
 pub mod command;
 pub mod contains;
+pub mod count;
 pub mod echo;
 pub mod emit;
 pub mod exit;

fish-rust/src/builtins/shared.rs

@@ -240,6 +240,7 @@ pub fn run_builtin(
         RustBuiltin::Cd => super::cd::cd(parser, streams, args),
         RustBuiltin::Contains => super::contains::contains(parser, streams, args),
         RustBuiltin::Command => super::command::command(parser, streams, args),
+        RustBuiltin::Count => super::count::count(parser, streams, args),
         RustBuiltin::Echo => super::echo::echo(parser, streams, args),
         RustBuiltin::Emit => super::emit::emit(parser, streams, args),
         RustBuiltin::Exit => super::exit::exit(parser, streams, args),