fix: format env variable for fish shell (#264)

crates/rattler_shell/src/shell/mod.rs

@@ -394,6 +394,11 @@ impl Shell for Fish {
         writeln!(f, "set -gx {} \"{}\"", env_var, value)
     }
 
+    fn format_env_var(&self, var_name: &str) -> String {
+        // Fish doesnt want the extra brackets '{}'
+        format!("${var_name}")
+    }
+
     fn unset_env_var(&self, f: &mut impl Write, env_var: &str) -> std::fmt::Result {
         writeln!(f, "set -e {}", env_var)
     }
@@ -616,6 +621,18 @@ mod tests {
         insta::assert_snapshot!(script.contents);
     }
 
+    #[test]
+    fn test_fish() {
+        let mut script = ShellScript::new(Fish, Platform::Linux64);
+
+        script
+            .set_env_var("FOO", "bar")
+            .unset_env_var("FOO")
+            .run_script(&PathBuf::from_str("foo.sh").expect("blah"));
+
+        insta::assert_snapshot!(script.contents);
+    }
+
     #[cfg(feature = "sysinfo")]
     #[test]
     fn test_from_parent_process_doenst_crash() {

crates/rattler_shell/src/shell/snapshots/rattler_shell__shell__tests__fish.snap

@@ -0,0 +1,8 @@
+---
+source: crates/rattler_shell/src/shell/mod.rs
+expression: script.contents
+---
+set -gx FOO "bar"
+set -e FOO
+source "foo.sh"
+

crates/rattler_shell/src/snapshots/rattler_shell__activation__tests__activation_script_fish.snap

@@ -2,6 +2,6 @@
 source: crates/rattler_shell/src/activation.rs
 expression: script
 ---
-set -gx PATH "${PATH}:__PREFIX__/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin"
+set -gx PATH "$PATH:__PREFIX__/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin"
 set -gx CONDA_PREFIX "__PREFIX__"