Add support for Nushell in shell builder (#33806)

We also swap out env variables before sending them to shells now in the
task system. This fixed issues Fish and Nushell had where an empty
argument could be sent into a command when no argument should be sent.
This only happened from task's generated by Zed.

Closes #31297 #31240

Release Notes:

- Fix bug where spawning a Zed generated task or debug session with Fish
or Nushell failed

crates/task/src/shell_builder.rs

@@ -5,6 +5,7 @@ enum ShellKind {
     #[default]
     Posix,
     Powershell,
+    Nushell,
     Cmd,
 }
 
@@ -18,6 +19,8 @@ impl ShellKind {
             ShellKind::Powershell
         } else if program == "cmd" || program.ends_with("cmd.exe") {
             ShellKind::Cmd
+        } else if program == "nu" {
+            ShellKind::Nushell
         } else {
             // Someother shell detected, the user might install and use a
             // unix-like shell.
@@ -30,6 +33,7 @@ impl ShellKind {
             Self::Powershell => Self::to_powershell_variable(input),
             Self::Cmd => Self::to_cmd_variable(input),
             Self::Posix => input.to_owned(),
+            Self::Nushell => Self::to_nushell_variable(input),
         }
     }
 
@@ -70,11 +74,86 @@ impl ShellKind {
         }
     }
 
+    fn to_nushell_variable(input: &str) -> String {
+        let mut result = String::new();
+        let mut source = input;
+        let mut is_start = true;
+
+        loop {
+            match source.chars().next() {
+                None => return result,
+                Some('$') => {
+                    source = Self::parse_nushell_var(&source[1..], &mut result, is_start);
+                    is_start = false;
+                }
+                Some(_) => {
+                    is_start = false;
+                    let chunk_end = source.find('$').unwrap_or(source.len());
+                    let (chunk, rest) = source.split_at(chunk_end);
+                    result.push_str(chunk);
+                    source = rest;
+                }
+            }
+        }
+    }
+
+    fn parse_nushell_var<'a>(source: &'a str, text: &mut String, is_start: bool) -> &'a str {
+        if source.starts_with("env.") {
+            text.push('$');
+            return source;
+        }
+
+        match source.chars().next() {
+            Some('{') => {
+                let source = &source[1..];
+                if let Some(end) = source.find('}') {
+                    let var_name = &source[..end];
+                    if !var_name.is_empty() {
+                        if !is_start {
+                            text.push_str("(");
+                        }
+                        text.push_str("$env.");
+                        text.push_str(var_name);
+                        if !is_start {
+                            text.push_str(")");
+                        }
+                        &source[end + 1..]
+                    } else {
+                        text.push_str("${}");
+                        &source[end + 1..]
+                    }
+                } else {
+                    text.push_str("${");
+                    source
+                }
+            }
+            Some(c) if c.is_alphabetic() || c == '_' => {
+                let end = source
+                    .find(|c: char| !c.is_alphanumeric() && c != '_')
+                    .unwrap_or(source.len());
+                let var_name = &source[..end];
+                if !is_start {
+                    text.push_str("(");
+                }
+                text.push_str("$env.");
+                text.push_str(var_name);
+                if !is_start {
+                    text.push_str(")");
+                }
+                &source[end..]
+            }
+            _ => {
+                text.push('$');
+                source
+            }
+        }
+    }
+
     fn args_for_shell(&self, interactive: bool, combined_command: String) -> Vec<String> {
         match self {
             ShellKind::Powershell => vec!["-C".to_owned(), combined_command],
             ShellKind::Cmd => vec!["/C".to_owned(), combined_command],
-            ShellKind::Posix => interactive
+            ShellKind::Posix | ShellKind::Nushell => interactive
                 .then(|| "-i".to_owned())
                 .into_iter()
                 .chain(["-c".to_owned(), combined_command])
@@ -142,9 +221,12 @@ impl ShellBuilder {
             ShellKind::Cmd => {
                 format!("{} /C '{}'", self.program, command_label)
             }
-            ShellKind::Posix => {
+            ShellKind::Posix | ShellKind::Nushell => {
                 let interactivity = self.interactive.then_some("-i ").unwrap_or_default();
-                format!("{} {interactivity}-c '{}'", self.program, command_label)
+                format!(
+                    "{} {interactivity}-c '$\"{}\"'",
+                    self.program, command_label
+                )
             }
         }
     }
@@ -170,3 +252,36 @@ impl ShellBuilder {
         (self.program, self.args)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_nu_shell_variable_substitution() {
+        let shell = Shell::Program("nu".to_owned());
+        let shell_builder = ShellBuilder::new(true, &shell);
+
+        let (program, args) = shell_builder.build(
+            Some("echo".into()),
+            &vec![
+                "${hello}".to_string(),
+                "$world".to_string(),
+                "nothing".to_string(),
+                "--$something".to_string(),
+                "$".to_string(),
+                "${test".to_string(),
+            ],
+        );
+
+        assert_eq!(program, "nu");
+        assert_eq!(
+            args,
+            vec![
+                "-i",
+                "-c",
+                "echo $env.hello $env.world nothing --($env.something) $ ${test"
+            ]
+        );
+    }
+}

crates/task/src/task_template.rs

@@ -256,7 +256,7 @@ impl TaskTemplate {
                     },
                 ),
                 command: Some(command),
-                args: self.args.clone(),
+                args: args_with_substitutions,
                 env,
                 use_new_terminal: self.use_new_terminal,
                 allow_concurrent_runs: self.allow_concurrent_runs,
@@ -642,11 +642,11 @@ mod tests {
             assert_eq!(
                 spawn_in_terminal.args,
                 &[
-                    "arg1 $ZED_SELECTED_TEXT",
-                    "arg2 $ZED_COLUMN",
-                    "arg3 $ZED_SYMBOL",
+                    "arg1 test_selected_text",
+                    "arg2 5678",
+                    "arg3 010101010101010101010101010101010101010101010101010101010101",
                 ],
-                "Args should not be substituted with variables"
+                "Args should be substituted with variables"
             );
             assert_eq!(
                 spawn_in_terminal.command_label,