userland/git: git-compatible CLI on v2's gix code (T10)

Local workflow, smart-HTTP clone/fetch/push and public HTTPS clone/fetch match
native git in stdout and exit codes. Only WASI imports (wasi:http, exit-with-code).

userland/git/src/main.rs

@@ -0,0 +1,39 @@
+//! Parse Git CLI arguments and return Git-compatible usage and operation exit codes.
+use clap::{Parser, error::ErrorKind};
+fn main() {
+    let cli = match git::Cli::try_parse() {
+        Ok(cli) => cli,
+        Err(error) => {
+            let code = if !error.use_stderr() {
+                0
+            } else {
+                match error.kind() {
+                    ErrorKind::InvalidSubcommand | ErrorKind::MissingSubcommand => 1,
+                    _ => 129,
+                }
+            };
+            let _ = error.print();
+            exit(code);
+        }
+    };
+    let code = match git::run(cli) {
+        Ok(code) => code,
+        Err(error) => {
+            eprintln!("fatal: {error}");
+            128
+        }
+    };
+    exit(code);
+}
+fn exit(code: i32) -> ! {
+    #[cfg(target_os = "wasi")]
+    {
+        use std::io::Write;
+        let _ = std::io::stdout().flush();
+        let _ = std::io::stderr().flush();
+        wasi::cli::exit::exit_with_code(code as u8);
+        unreachable!("WASI exit returned");
+    }
+    #[cfg(not(target_os = "wasi"))]
+    std::process::exit(code)
+}