feat: Add Environment Variable module (#409)

README.md

@@ -66,6 +66,7 @@ The prompt shows information you need while you're working, while staying sleek
 - Current Python version (`🐍`)
 - Current Go version (`🐹`)
 - Nix-shell environment detection
+- Print an environment variable
 - Current version of package in current directory (`📦`)
   - npm (Node.js)
   - cargo (Rust)

docs/config/README.md

@@ -84,7 +84,6 @@ prompt_order = [
     "username",
     "hostname",
     "directory",
-    "aws",
     "git_branch",
     "git_state",
     "git_status",
@@ -96,6 +95,8 @@ prompt_order = [
     "golang",
     "java",
     "nix_shell",
+    "aws",
+    "env_var",
     "cmd_duration",
     "line_break",
     "jobs",
@@ -309,6 +310,36 @@ it would have been `nixpkgs/pkgs`.
 truncation_length = 8
 ```
 
+## Environment Variable
+
+The `env_var` module displays the current value of a selected environment variable.
+The module will be shown only if any of the following conditions are met:
+
+- The `variable` configuration option matches an existing environment variable
+- The `variable` configuration option is not defined, but the `default` configuration option is
+
+### Options
+
+| Variable   | Default          | Description                                                                  |
+| ---------- | ---------------- | ---------------------------------------------------------------------------- |
+| `symbol`   |                  | The symbol used before displaying the variable value.                        |
+| `variable` |                  | The environment variable to be displayed.                                    |
+| `default`  |                  | The default value to be displayed when the selected variable is not defined. |
+| `prefix`   | `""`             | Prefix to display immediately before the variable value.                     |
+| `suffix`   | `""`             | Suffix to display immediately after the variable value.                      |
+| `style`    | `"dimmed black"` | The style for the module.                                                    |
+| `disabled` | `false`          | Disables the `env_var` module.                                               |
+
+### Example
+
+```toml
+# ~/.config/starship.toml
+
+[env_var]
+variable = "SHELL"
+default = "unknown shell"
+```
+
 ## Git Branch
 
 The `git_branch` module shows the active branch of the repo in your current directory.

src/module.rs

@@ -12,6 +12,7 @@ pub const ALL_MODULES: &[&str] = &[
     "character",
     "cmd_duration",
     "directory",
+    "env_var",
     "git_branch",
     "git_state",
     "git_status",

src/modules/env_var.rs

@@ -0,0 +1,43 @@
+use ansi_term::Color;
+use std::env;
+
+use super::{Context, Module};
+
+/// Creates a module with the value of the chosen environment variable
+///
+/// Will display the environment variable's value if all of the following criteria are met:
+///     - env_var.disabled is absent or false
+///     - env_var.variable is defined
+///     - a variable named as the value of env_var.variable is defined
+pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
+    let mut module = context.new_module("env_var");
+    let module_style = module
+        .config_value_style("style")
+        .unwrap_or_else(|| Color::Black.bold().dimmed());
+
+    let env_name = module.config_value_str("variable")?;
+
+    let default_value = module.config_value_str("default");
+
+    let env_value = get_env_value(env_name, default_value)?;
+
+    let prefix = module.config_value_str("prefix").unwrap_or("").to_owned();
+    let suffix = module.config_value_str("suffix").unwrap_or("").to_owned();
+
+    module.set_style(module_style);
+    module.get_prefix().set_value("with ");
+    module.new_segment_if_config_exists("symbol");
+    module.new_segment("env_var", &format!("{}{}{}", prefix, env_value, suffix));
+
+    Some(module)
+}
+
+fn get_env_value(name: &str, default: Option<&str>) -> Option<String> {
+    match env::var_os(name) {
+        Some(os_value) => match os_value.into_string() {
+            Ok(value) => Some(value),
+            Err(_error) => None,
+        },
+        None => default.map(|value| value.to_owned()),
+    }
+}

src/modules/mod.rs

@@ -3,6 +3,7 @@ mod aws;
 mod character;
 mod cmd_duration;
 mod directory;
+mod env_var;
 mod git_branch;
 mod git_state;
 mod git_status;
@@ -30,6 +31,7 @@ pub fn handle<'a>(module: &str, context: &'a Context) -> Option<Module<'a>> {
     match module {
         "aws" => aws::module(context),
         "directory" => directory::module(context),
+        "env_var" => env_var::module(context),
         "character" => character::module(context),
         "nodejs" => nodejs::module(context),
         "rust" => rust::module(context),

src/print.rs

@@ -15,7 +15,6 @@ const DEFAULT_PROMPT_ORDER: &[&str] = &[
     "username",
     "hostname",
     "directory",
-    "aws",
     "git_branch",
     "git_state",
     "git_status",
@@ -27,6 +26,8 @@ const DEFAULT_PROMPT_ORDER: &[&str] = &[
     "golang",
     "java",
     "nix_shell",
+    "aws",
+    "env_var",
     "cmd_duration",
     "line_break",
     "jobs",

tests/testsuite/env_var.rs

@@ -0,0 +1,141 @@
+use ansi_term::{Color, Style};
+use std::io;
+
+use crate::common;
+use crate::common::TestCommand;
+
+const TEST_VAR_VALUE: &str = "astronauts";
+
+#[test]
+fn empty_config() -> io::Result<()> {
+    let output = common::render_module("env_var")
+        .env_clear()
+        .use_config(toml::toml! {
+            [env_var]
+        })
+        .output()?;
+    let expected = "";
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+#[test]
+fn defined_variable() -> io::Result<()> {
+    let output = common::render_module("env_var")
+        .env_clear()
+        .use_config(toml::toml! {
+            [env_var]
+            variable = "TEST_VAR"
+        })
+        .env("TEST_VAR", TEST_VAR_VALUE)
+        .output()?;
+    let expected = format!("with {} ", style().paint(TEST_VAR_VALUE));
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+#[test]
+fn undefined_variable() -> io::Result<()> {
+    let output = common::render_module("env_var")
+        .env_clear()
+        .use_config(toml::toml! {
+            [env_var]
+            variable = "TEST_VAR"
+        })
+        .output()?;
+    let expected = "";
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+#[test]
+fn default_has_no_effect() -> io::Result<()> {
+    let output = common::render_module("env_var")
+        .env_clear()
+        .use_config(toml::toml! {
+            [env_var]
+            variable = "TEST_VAR"
+            default = "N/A"
+        })
+        .env("TEST_VAR", TEST_VAR_VALUE)
+        .output()?;
+    let expected = format!("with {} ", style().paint(TEST_VAR_VALUE));
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+#[test]
+fn default_takes_effect() -> io::Result<()> {
+    let output = common::render_module("env_var")
+        .env_clear()
+        .use_config(toml::toml! {
+            [env_var]
+            variable = "UNDEFINED_TEST_VAR"
+            default = "N/A"
+        })
+        .output()?;
+    let expected = format!("with {} ", style().paint("N/A"));
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+#[test]
+fn symbol() -> io::Result<()> {
+    let output = common::render_module("env_var")
+        .env_clear()
+        .use_config(toml::toml! {
+            [env_var]
+            symbol = "■ "
+            variable = "TEST_VAR"
+        })
+        .env("TEST_VAR", TEST_VAR_VALUE)
+        .output()?;
+    let expected = format!("with {} ", style().paint(format!("■ {}", TEST_VAR_VALUE)));
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+#[test]
+fn prefix() -> io::Result<()> {
+    let output = common::render_module("env_var")
+        .env_clear()
+        .use_config(toml::toml! {
+            [env_var]
+            variable = "TEST_VAR"
+            prefix = "_"
+        })
+        .env("TEST_VAR", TEST_VAR_VALUE)
+        .output()?;
+    let expected = format!("with {} ", style().paint(format!("_{}", TEST_VAR_VALUE)));
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+#[test]
+fn suffix() -> io::Result<()> {
+    let output = common::render_module("env_var")
+        .env_clear()
+        .use_config(toml::toml! {
+            [env_var]
+            variable = "TEST_VAR"
+            suffix = "_"
+        })
+        .env("TEST_VAR", TEST_VAR_VALUE)
+        .output()?;
+    let expected = format!("with {} ", style().paint(format!("{}_", TEST_VAR_VALUE)));
+    let actual = String::from_utf8(output.stdout).unwrap();
+    assert_eq!(expected, actual);
+    Ok(())
+}
+
+fn style() -> Style {
+    // default style
+    Color::Black.bold().dimmed()
+}

tests/testsuite/main.rs

@@ -4,6 +4,7 @@ mod cmd_duration;
 mod common;
 mod configuration;
 mod directory;
+mod env_var;
 mod git_branch;
 mod git_state;
 mod git_status;