ssh: use env when assume_shell=Posix

This allows us to send over COLORTERM and TERM_PROGRAM_XXX environment
that the SSH server would have denied via AcceptEnv rules.

Cargo.lock

@@ -2323,6 +2323,7 @@ dependencies = [
  "ratelim",
  "regex",
  "serde",
+ "shell-words",
  "smol",
  "terminfo",
  "termwiz",

docs/config/lua/SshDomain.md

@@ -76,9 +76,9 @@ panes and tabs.  The following values are recognized for `assume_shell`:
 
 * `"Unknown"` - this is the default. We can't make any assumptions about the
   remote shell.
-* `"Posix"` - the remote host uses a Bourne Shell compatible shell that allows
-  the syntax `cd DIR ; exec CMD` and `cd DIR ; exec $SHELL`.
-
+* `"Posix"` - the remote host uses a POSIX/Bourne Shell compatible environment
+  that allows the syntax `env -c DIR ENV1=VAL1 ENV2=VAL2 CMD` and
+  `env -c DIR ENV1=VAL1 ENV2=VAL2 $SHELL`.
 
 ```lua
 return {
@@ -96,7 +96,7 @@ return {
       default_prog = {"fish"},
 
       -- assume that we can use syntax like:
-      -- "cd /some/where ; exec $SHELL"
+      -- "env -C /some/where $SHELL"
       -- using whatever the default command shell is on this
       -- remote host, so that shell integration will respect
       -- the current directory on the remote host.

mux/Cargo.toml

@@ -32,6 +32,7 @@ rangeset = { path = "../rangeset" }
 ratelim= { path = "../ratelim" }
 regex = "1"
 serde = {version="1.0", features = ["rc", "derive"]}
+shell-words = "1.0"
 smol = "1.2"
 terminfo = "0.7"
 termwiz = { path = "../termwiz" }

mux/src/ssh.rs

@@ -213,13 +213,43 @@ impl RemoteSshDomain {
             .iter_extra_env_as_str()
             .map(|(k, v)| (k.to_string(), v.to_string()))
             .collect();
-        env.insert("WEZTERM_PANE".to_string(), pane_id.to_string());
+
+        // FIXME: this isn't useful without a way to talk to the remote mux.
+        // One option is to forward the mux via unix domain, another is to
+        // embed the mux protocol in an escape sequence and just use the
+        // existing terminal connection
+        env.insert("WEZTERM_REMOTE_PANE".to_string(), pane_id.to_string());
+
+        fn build_env_command(
+            dir: Option<String>,
+            cmd: &CommandBuilder,
+            env: &HashMap<String, String>,
+        ) -> anyhow::Result<String> {
+            let mut env_cmd = vec!["env".to_string()];
+            if let Some(dir) = dir {
+                env_cmd.push("-C".to_string());
+                env_cmd.push(dir.clone());
+            } else if let Some(dir) = cmd.get_cwd() {
+                let dir = dir.to_str().context("converting cwd to string")?;
+                env_cmd.push("-C".to_string());
+                env_cmd.push(dir.to_string());
+            }
+
+            for (k, v) in env {
+                env_cmd.push(format!("{}={}", k, v));
+            }
+
+            let cmd = if cmd.is_default_prog() {
+                "$SHELL".to_string()
+            } else {
+                cmd.as_unix_command_line()?
+            };
+
+            Ok(shell_words::join(env_cmd) + " " + &cmd)
+        }
 
         let command_line = match (cmd.is_default_prog(), self.dom.assume_shell, command_dir) {
-            (true, Shell::Posix, Some(dir)) => Some(format!("cd {} ; exec $SHELL", dir)),
-            (false, Shell::Posix, Some(dir)) => {
-                Some(format!("cd {} ; exec {}", dir, cmd.as_unix_command_line()?))
-            }
+            (_, Shell::Posix, dir) => Some(build_env_command(dir, &cmd, &env)?),
             (true, _, _) => None,
             (false, _, _) => Some(cmd.as_unix_command_line()?),
         };