feat(hostname): add detect_env_vars as option (#5196)

* Added hostname.detect_env_vars

based on the newly added context::detect_env_vars

- extended context::detect_env_vars to check for negated environment
  variables as well, analogous to the other detect modules
- made hostname.detect_env_vars only active if ssh_only is set to false
  for backwards compatibility

Co-authored-by: Dominik Sander <dsander@users.noreply.github.com>

* added clippy recommendations, removed unneeded comments

* Added new logic (suggested in https://github.com/starship/starship/pull/5196#issuecomment-1566228913)

The new `detect_env_vars` now requires either SSH_ONLY to be false or the
environment variable SSH_CONNECTION to be set, so that is will be used

* Fixed typo

* Refactored the detect_env_vars function for early returns and better readability

* Change boolean logic for better readability

Co-authored-by: David Knaack <davidkna@users.noreply.github.com>

* Apply suggestions from code review to `detect_env_vars` method.

Co-authored-by: David Knaack <davidkna@users.noreply.github.com>

* Fixed bracket error & updated comments

- fixed bracket error in hostname.rs, after changes
- updated comments for context.rs, for the suggested changes

* Removed obsolete warning from docs/config/README.md

Co-authored-by: David Knaack <davidkna@users.noreply.github.com>

---------

Co-authored-by: Dominik Sander <dsander@users.noreply.github.com>
Co-authored-by: David Knaack <davidkna@users.noreply.github.com>

.github/config-schema.json

@@ -798,6 +798,7 @@
     },
     "hostname": {
       "default": {
+        "detect_env_vars": [],
         "disabled": false,
         "format": "[$ssh_symbol$hostname]($style) in ",
         "ssh_only": true,
@@ -3740,6 +3741,13 @@
           "default": ".",
           "type": "string"
         },
+        "detect_env_vars": {
+          "default": [],
+          "type": "array",
+          "items": {
+            "type": "string"
+          }
+        },
         "format": {
           "default": "[$ssh_symbol$hostname]($style) in ",
           "type": "string"

docs/config/README.md

@@ -2239,10 +2239,11 @@ The `hostname` module shows the system hostname.
 ### Options
 
 | Option            | Default                                | Description                                                                                                                           |
-| ------------ | -------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------ |
+| ----------------- | -------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------- |
 | `ssh_only`        | `true`                                 | Only show hostname when connected to an SSH session.                                                                                  |
 | `ssh_symbol`      | `'🌐 '`                                | A format string representing the symbol when connected to SSH session.                                                                |
-| `trim_at`    | `'.'`                                  | String that the hostname is cut off at, after the first match. `'.'` will stop after the first dot. `''` will disable any truncation |
+| `trim_at`         | `'.'`                                  | String that the hostname is cut off at, after the first match. `'.'` will stop after the first dot. `''` will disable any truncation. |
+| `detect_env_vars` | `[]`                                   | Which environment variable(s) should trigger this module.                                                                             |
 | `format`          | `'[$ssh_symbol$hostname]($style) in '` | The format for the module.                                                                                                            |
 | `style`           | `'bold dimmed green'`                  | The style for the module.                                                                                                             |
 | `disabled`        | `false`                                | Disables the `hostname` module.                                                                                                       |
@@ -2257,7 +2258,9 @@ The `hostname` module shows the system hostname.
 
 *: This variable can only be used as a part of a style string
 
-### Example
+### Examples
+
+#### Always show the hostname
 
 ```toml
 # ~/.config/starship.toml
@@ -2269,6 +2272,17 @@ trim_at = '.companyname.com'
 disabled = false
 ```
 
+#### Hide the hostname in remote tmux sessions
+
+```toml
+# ~/.config/starship.toml
+
+[hostname]
+ssh_only = false
+detect_env_vars = ['!TMUX', 'SSH_CONNECTION']
+disabled = false
+```
+
 ## Java
 
 The `java` module shows the currently installed version of [Java](https://www.oracle.com/java/).

src/configs/hostname.rs

@@ -11,6 +11,7 @@ pub struct HostnameConfig<'a> {
     pub ssh_only: bool,
     pub ssh_symbol: &'a str,
     pub trim_at: &'a str,
+    pub detect_env_vars: Vec<&'a str>,
     pub format: &'a str,
     pub style: &'a str,
     pub disabled: bool,
@@ -22,6 +23,7 @@ impl<'a> Default for HostnameConfig<'a> {
             ssh_only: true,
             ssh_symbol: "🌐 ",
             trim_at: ".",
+            detect_env_vars: vec![],
             format: "[$ssh_symbol$hostname]($style) in ",
             style: "green dimmed bold",
             disabled: false,

src/context.rs

@@ -235,8 +235,32 @@ impl<'a> Context<'a> {
         disabled == Some(true)
     }
 
+    /// Returns true when a negated environment variable is defined in `env_vars` and is present
+    fn has_negated_env_var(&self, env_vars: &'a [&'a str]) -> bool {
+        env_vars
+            .iter()
+            .filter_map(|env_var| env_var.strip_prefix('!'))
+            .any(|env_var| self.get_env(env_var).is_some())
+    }
+
+    /// Returns true if 'detect_env_vars' is empty,
+    /// or if at least one environment variable is set and no negated environment variable is set
     pub fn detect_env_vars(&'a self, env_vars: &'a [&'a str]) -> bool {
-        env_vars.is_empty() || (env_vars.iter().any(|e| self.get_env(e).is_some()))
+        if env_vars.is_empty() {
+            return true;
+        }
+
+        if self.has_negated_env_var(env_vars) {
+            return false;
+        }
+
+        // Returns true if at least one environment variable is set
+        let mut iter = env_vars
+            .iter()
+            .filter(|env_var| !env_var.starts_with('!'))
+            .peekable();
+
+        iter.peek().is_none() || iter.any(|env_var| self.get_env(env_var).is_some())
     }
 
     // returns a new ScanDir struct with reference to current dir_files of context

src/modules/hostname.rs

@@ -8,14 +8,18 @@ use crate::formatter::StringFormatter;
 /// Creates a module with the system hostname
 ///
 /// Will display the hostname if all of the following criteria are met:
-///     - hostname.disabled is absent or false
+///     - `hostname.disabled` is absent or false
 ///     - `hostname.ssh_only` is false OR the user is currently connected as an SSH session (`$SSH_CONNECTION`)
+///     - `hostname.ssh_only` is false AND `hostname.detect_env_vars` is either empty or contains a defined environment variable
 pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
     let mut module = context.new_module("hostname");
     let config: HostnameConfig = HostnameConfig::try_load(module.config);
 
     let ssh_connection = context.get_env("SSH_CONNECTION");
-    if config.ssh_only && ssh_connection.is_none() {
+
+    if (config.ssh_only && ssh_connection.is_none())
+        || !context.detect_env_vars(&config.detect_env_vars)
+    {
         return None;
     }
 
@@ -96,17 +100,82 @@ mod tests {
     }
 
     #[test]
-    fn ssh_only_false_no_ssh() {
+    fn ssh_only_false_with_empty_detect_env_vars() {
         let hostname = get_hostname!();
         let actual = ModuleRenderer::new("hostname")
             .config(toml::toml! {
                 [hostname]
                 ssh_only = false
                 trim_at = ""
+                detect_env_vars = []
             })
             .collect();
+
         let expected = Some(format!("{} in ", style().paint(hostname)));
-        println!("{}", expected.as_ref().unwrap());
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn ssh_only_false_with_matching_negated_env_var() {
+        let actual = ModuleRenderer::new("hostname")
+            .config(toml::toml! {
+                [hostname]
+                ssh_only = false
+                trim_at = ""
+                detect_env_vars = ["!NEGATED"]
+            })
+            .env("NEGATED", "true")
+            .collect();
+        let expected = None;
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn ssh_only_false_with_only_negated_env_vars() {
+        let hostname = get_hostname!();
+        let actual = ModuleRenderer::new("hostname")
+            .config(toml::toml! {
+                [hostname]
+                ssh_only = false
+                trim_at = ""
+                detect_env_vars = ["!NEGATED_ONE", "!NEGATED_TWO", "!NEGATED_THREE"]
+            })
+            .collect();
+
+        let expected = Some(format!("{} in ", style().paint(hostname)));
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn ssh_only_false_with_matching_env_var() {
+        let hostname = get_hostname!();
+        let actual = ModuleRenderer::new("hostname")
+            .config(toml::toml! {
+                [hostname]
+                ssh_only = false
+                trim_at = ""
+                detect_env_vars = ["FORCE_HOSTNAME"]
+            })
+            .env("FORCE_HOSTNAME", "true")
+            .collect();
+
+        let expected = Some(format!("{} in ", style().paint(hostname)));
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn ssh_only_false_without_matching_env_vars() {
+        let actual = ModuleRenderer::new("hostname")
+            .config(toml::toml! {
+                [hostname]
+                ssh_only = false
+                trim_at = ""
+                detect_env_vars = ["FORCE_HOSTNAME", "!NEGATED"]
+            })
+            .collect();
+        let expected = None;
+
         assert_eq!(expected, actual);
     }
 
@@ -121,6 +190,7 @@ mod tests {
             })
             .collect();
         let expected = Some(format!("{} in ", style().paint(hostname)));
+
         assert_eq!(expected, actual);
     }