feat: Add `deno serve` subcommand (#23511)

By default, `deno serve` will assign port 8000 (like `Deno.serve`).
Users may choose a different port using `--port`.

`deno serve /tmp/file.ts`

`server.ts`:
```ts
export default {
  fetch(req) {
    return new Response("hello world!\n");
  },
};
```

1 files changed, 21 insertions, 0 deletions

diff --git a/cli/args/mod.rs b/cli/args/mod.rs
index aa3622d09..bb0ef1aba 100644
--- a/cli/args/mod.rs
+++ b/cli/args/mod.rs
@@ -61,6 +61,7 @@ use std::env;
 use std::io::BufReader;
 use std::io::Cursor;
 use std::net::SocketAddr;
+use std::num::NonZeroU16;
 use std::num::NonZeroUsize;
 use std::path::Path;
 use std::path::PathBuf;
@@ -1022,6 +1023,22 @@ impl CliOptions {
     }
   }
 
+  pub fn serve_port(&self) -> Option<NonZeroU16> {
+    if let DenoSubcommand::Serve(flags) = self.sub_command() {
+      Some(flags.port)
+    } else {
+      None
+    }
+  }
+
+  pub fn serve_host(&self) -> Option<String> {
+    if let DenoSubcommand::Serve(flags) = self.sub_command() {
+      Some(flags.host.clone())
+    } else {
+      None
+    }
+  }
+
   pub fn enable_future_features(&self) -> bool {
     *DENO_FUTURE
   }
@@ -1062,6 +1079,10 @@ impl CliOptions {
             .map_err(AnyError::from)
         }
       }
+      DenoSubcommand::Serve(run_flags) => {
+        resolve_url_or_path(&run_flags.script, self.initial_cwd())
+          .map_err(AnyError::from)
+      }
       _ => {
         bail!("No main module.")
       }