feat: create shell module (#2329)

* Add the shell module

This module allows to quickly identify which shell is currently used, in case someone frequently switches between them.

* Updated documentation with shell module.

Co-authored-by: mro <mro@fedorabox.localdomain>

7 files changed, 316 insertions, 0 deletions

diff --git a/docs/config/README.md b/docs/config/README.md
index 8fe4a631e..f2438edd2 100644
--- a/docs/config/README.md
+++ b/docs/config/README.md
@@ -236,6 +236,7 @@ $jobs\
 $battery\
 $time\
 $status\
+$shell\
 $character"""
 ```
 
@@ -2217,6 +2218,46 @@ The module will be shown if any of the following conditions are met:
 format = "via [⚙️ $version](red bold)"
 ```
 
+## Shell
+
+The `shell` module shows an indicator for currently used shell.
+
+::: tip
+
+This module is disabled by default.
+To enable it, set `disabled` to `false` in your configuration file.
+
+:::
+
+### Options
+
+| Option                 | Default       | Description |
+| ---------------------- | ------------- | --------------------------------------------- |
+| `bash_indicator`       | `bsh`         | A format string used to represent bash.       |
+| `fish_indicator`       | `fsh`         | A format string used to represent fish.       |
+| `zsh_indicator`        | `zsh`         | A format string used to represent zsh.        |
+| `powershell_indicator` | `psh`         | A format string used to represent powershell. |
+| `ion_indicator`        | `ion`         | A format string used to represent ion.        |
+| `elvish_indicator`     | `esh`         | A format string used to represent elvish.     |
+| `format`               | `$indicator ` | The format for the module.                    |
+| `disabled`             | `true`        | Disables the `shell` module.                  |
+
+### Variables
+
+| Variable    | Default | Description                                                |
+| ----------- | ------- | ---------------------------------------------------------- |
+| indicator   |         | Mirrors the value of `indicator` for currently used shell. |
+
+### Examples
+```toml
+# ~/.config/starship.toml
+
+[shell]
+fish_indicator = ""
+powershell_indicator = "_"
+disabled = false
+```
+
 ## SHLVL
 
 The `shlvl` module shows the current SHLVL ("shell level") environment variable, if it is
diff --git a/src/configs/mod.rs b/src/configs/mod.rs
index 91d3b1061..1052a6736 100644
--- a/src/configs/mod.rs
+++ b/src/configs/mod.rs
@@ -42,6 +42,7 @@ pub mod purescript;
 pub mod python;
 pub mod ruby;
 pub mod rust;
+pub mod shell;
 pub mod shlvl;
 pub mod singularity;
 mod starship_root;
diff --git a/src/configs/shell.rs b/src/configs/shell.rs
new file mode 100644
index 000000000..24551df97
--- /dev/null
+++ b/src/configs/shell.rs
@@ -0,0 +1,30 @@
+use crate::config::{ModuleConfig, RootModuleConfig};
+
+use starship_module_config_derive::ModuleConfig;
+
+#[derive(Clone, ModuleConfig)]
+pub struct ShellConfig<'a> {
+    pub format: &'a str,
+    pub bash_indicator: &'a str,
+    pub fish_indicator: &'a str,
+    pub zsh_indicator: &'a str,
+    pub powershell_indicator: &'a str,
+    pub ion_indicator: &'a str,
+    pub elvish_indicator: &'a str,
+    pub disabled: bool,
+}
+
+impl<'a> RootModuleConfig<'a> for ShellConfig<'a> {
+    fn new() -> Self {
+        ShellConfig {
+            format: "$indicator ",
+            bash_indicator: "bsh",
+            fish_indicator: "fsh",
+            zsh_indicator: "zsh",
+            powershell_indicator: "psh",
+            ion_indicator: "ion",
+            elvish_indicator: "esh",
+            disabled: true,
+        }
+    }
+}
diff --git a/src/configs/starship_root.rs b/src/configs/starship_root.rs
index 0c9ccc8fe..a73f0229a 100644
--- a/src/configs/starship_root.rs
+++ b/src/configs/starship_root.rs
@@ -71,6 +71,7 @@ pub const PROMPT_ORDER: &[&str] = &[
     "battery",
     "time",
     "status",
+    "shell",
     "character",
 ];
 
diff --git a/src/module.rs b/src/module.rs
index 431a37907..e222ef2e0 100644
--- a/src/module.rs
+++ b/src/module.rs
@@ -56,6 +56,7 @@ pub const ALL_MODULES: &[&str] = &[
     "php",
     "swift",
     "terraform",
+    "shell",
     "shlvl",
     "singularity",
     "status",
diff --git a/src/modules/mod.rs b/src/modules/mod.rs
index 91872b360..207d4e66b 100644
--- a/src/modules/mod.rs
+++ b/src/modules/mod.rs
@@ -43,6 +43,7 @@ mod purescript;
 mod python;
 mod ruby;
 mod rust;
+mod shell;
 mod shlvl;
 mod singularity;
 mod status;
@@ -113,6 +114,7 @@ pub fn handle<'a>(module: &str, context: &'a Context) -> Option<Module<'a>> {
             "python" => python::module(context),
             "ruby" => ruby::module(context),
             "rust" => rust::module(context),
+            "shell" => shell::module(context),
             "shlvl" => shlvl::module(context),
             "singularity" => singularity::module(context),
             "swift" => swift::module(context),
@@ -191,6 +193,7 @@ pub fn description(module: &str) -> &'static str {
         "ruby" => "The currently installed version of Ruby",
         "rust" => "The currently installed version of Rust",
         "swift" => "The currently installed version of Swift",
+        "shell" => "The currently used shell indicator",
         "shlvl" => "The current value of SHLVL",
         "status" => "The status of the last command",
         "terraform" => "The currently selected terraform workspace and version",
diff --git a/src/modules/shell.rs b/src/modules/shell.rs
new file mode 100644
index 000000000..fe90b2e89
--- /dev/null
+++ b/src/modules/shell.rs
@@ -0,0 +1,239 @@
+use super::{Context, Module, RootModuleConfig, Shell};
+
+use crate::configs::shell::ShellConfig;
+use crate::formatter::StringFormatter;
+
+pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
+    let mut module = context.new_module("shell");
+    let config: ShellConfig = ShellConfig::try_load(module.config);
+
+    if config.disabled {
+        return None;
+    }
+
+    let shell = context.shell;
+
+    let parsed = StringFormatter::new(config.format).and_then(|formatter| {
+        formatter
+            .map_meta(|variable, _| match variable {
+                "indicator" => match shell {
+                    Shell::Bash => Some(config.bash_indicator),
+                    Shell::Fish => Some(config.fish_indicator),
+                    Shell::Zsh => Some(config.zsh_indicator),
+                    Shell::PowerShell => Some(config.powershell_indicator),
+                    Shell::Ion => Some(config.ion_indicator),
+                    Shell::Elvish => Some(config.elvish_indicator),
+                    Shell::Unknown => None,
+                },
+                _ => None,
+            })
+            .parse(None)
+    });
+
+    module.set_segments(match parsed {
+        Ok(segments) => segments,
+        Err(error) => {
+            log::warn!("Error in module `shell`: \n{}", error);
+            return None;
+        }
+    });
+
+    Some(module)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::context::Shell;
+    use crate::test::ModuleRenderer;
+    use ansi_term::Color;
+
+    #[test]
+    fn test_none_if_disabled() {
+        let expected = None;
+        let actual = ModuleRenderer::new("shell").shell(Shell::Bash).collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_none_if_unknown_shell() {
+        let expected = None;
+        let actual = ModuleRenderer::new("shell").shell(Shell::Unknown).collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_bash_default_format() {
+        let expected = Some(format!("{} ", "bsh"));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Bash)
+            .config(toml::toml! {
+                [shell]
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_bash_custom_format() {
+        let expected = Some(format!("{} ", Color::Cyan.bold().paint("bash")));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Bash)
+            .config(toml::toml! {
+                [shell]
+                bash_indicator = "[bash](bold cyan)"
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_fish_default_format() {
+        let expected = Some(format!("{} ", "fsh"));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Fish)
+            .config(toml::toml! {
+                [shell]
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_fish_custom_format() {
+        let expected = Some(format!("{} ", Color::Cyan.bold().paint("fish")));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Fish)
+            .config(toml::toml! {
+                [shell]
+                fish_indicator = "[fish](cyan bold)"
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_zsh_default_format() {
+        let expected = Some(format!("{} ", "zsh"));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Zsh)
+            .config(toml::toml! {
+                [shell]
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_zsh_custom_format() {
+        let expected = Some(format!("{} ", Color::Cyan.bold().paint("zsh")));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Bash)
+            .config(toml::toml! {
+                [shell]
+                bash_indicator = "[zsh](bold cyan)"
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_powershell_default_format() {
+        let expected = Some(format!("{} ", "psh"));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::PowerShell)
+            .config(toml::toml! {
+                [shell]
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_powershell_custom_format() {
+        let expected = Some(format!("{} ", Color::Cyan.bold().paint("powershell")));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::PowerShell)
+            .config(toml::toml! {
+                [shell]
+                powershell_indicator = "[powershell](bold cyan)"
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_ion_default_format() {
+        let expected = Some(format!("{} ", "ion"));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Ion)
+            .config(toml::toml! {
+                [shell]
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_ion_custom_format() {
+        let expected = Some(format!("{} ", Color::Cyan.bold().paint("ion")));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Ion)
+            .config(toml::toml! {
+                [shell]
+                ion_indicator = "[ion](bold cyan)"
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_elvish_default_format() {
+        let expected = Some(format!("{} ", "esh"));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Elvish)
+            .config(toml::toml! {
+                [shell]
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+
+    #[test]
+    fn test_elvish_custom_format() {
+        let expected = Some(format!("{} ", Color::Cyan.bold().paint("elvish")));
+        let actual = ModuleRenderer::new("shell")
+            .shell(Shell::Elvish)
+            .config(toml::toml! {
+                [shell]
+                elvish_indicator = "[elvish](bold cyan)"
+                disabled = false
+            })
+            .collect();
+
+        assert_eq!(expected, actual);
+    }
+}