ssh: fix token expansion for ProxyCommand

refs: https://github.com/wez/wezterm/issues/3437

docs/changelog.md

@@ -81,6 +81,8 @@ As features stabilize some brief notes about them will accumulate here.
 * `wezterm connect --workspace WS DOM` didn't use the provided workspace when
   starting up the mux server. #2734
 * mux: `ClearScrollback` was not forwarded to remote server. #2624
+* ssh: `%r` `%h` and `%p` tokens were implicitly supported by libssh but stopped
+  working in `ProxyCommand` when we took over running the proxy command. #3437
 
 ### 20230326-111934-3666303c
 

wezterm-ssh/src/config.rs

@@ -533,6 +533,15 @@ impl Config {
 
         let mut token_map = self.tokens.clone();
         token_map.insert("%h".to_string(), host.to_string());
+        token_map.insert("%n".to_string(), host.to_string());
+        token_map.insert("%r".to_string(), target_user.to_string());
+        token_map.insert(
+            "%p".to_string(),
+            result
+                .get("port")
+                .map(|p| p.to_string())
+                .unwrap_or_else(|| "22".to_string()),
+        );
 
         for (k, v) in &mut result {
             if let Some(tokens) = self.should_expand_tokens(k) {
@@ -736,6 +745,37 @@ mod test {
     use super::*;
     use k9::snapshot;
 
+    #[test]
+    fn parse_proxy_command_tokens() {
+        let mut config = Config::new();
+        config.add_config_string(
+            r#"
+        Host foo
+            ProxyCommand /usr/bin/corp-ssh-helper -dst_username=%r %h %p
+            Port 2222
+            "#,
+        );
+        let mut fake_env = ConfigMap::new();
+        fake_env.insert("HOME".to_string(), "/home/me".to_string());
+        fake_env.insert("USER".to_string(), "me".to_string());
+        config.assign_environment(fake_env);
+
+        let opts = config.for_host("foo");
+        snapshot!(
+            opts,
+            r#"
+{
+    "hostname": "foo",
+    "identityfile": "/home/me/.ssh/id_dsa /home/me/.ssh/id_ecdsa /home/me/.ssh/id_ed25519 /home/me/.ssh/id_rsa",
+    "port": "2222",
+    "proxycommand": "/usr/bin/corp-ssh-helper -dst_username=me foo 2222",
+    "user": "me",
+    "userknownhostsfile": "/home/me/.ssh/known_hosts /home/me/.ssh/known_hosts2",
+}
+"#
+        );
+    }
+
     #[test]
     fn parse_proxy_command() {
         let mut config = Config::new();