Add nix-shell support (#173)

src/modules/mod.rs

@@ -8,6 +8,7 @@ mod git_status;
 mod golang;
 mod jobs;
 mod line_break;
+mod nix_shell;
 mod nodejs;
 mod package;
 mod python;
@@ -35,6 +36,7 @@ pub fn handle<'a>(module: &str, context: &'a Context) -> Option<Module<'a>> {
         "battery" => battery::module(context),
         "cmd_duration" => cmd_duration::module(context),
         "jobs" => jobs::module(context),
+        "nix_shell" => nix_shell::module(context),
 
         _ => {
             eprintln!("Error: Unknown module {}. Use starship module --list to list out all supported modules.", module);

src/modules/nix_shell.rs

@@ -0,0 +1,54 @@
+use ansi_term::Color;
+use std::env;
+
+use super::{Context, Module};
+
+// IN_NIX_SHELL should be "pure" or "impure" but lorri uses "1" for "impure"
+// https://github.com/target/lorri/issues/140
+
+/// Creates a module showing if inside a nix-shell
+///
+/// The module will use the `$IN_NIX_SHELL` and `$name` environment variable to
+/// determine if it's inside a nix-shell and the name of it.
+///
+/// The following options are availables:
+///     - use_name   (bool)   // print the name of the nix-shell
+///     - impure_msg (string) // change the impure msg
+///     - pure_msg (string)   // change the pure msg
+///
+/// Will display the following:
+///     - name (pure)    // use_name == true in a pure nix-shell
+///     - name (impure)  // use_name == true in an impure nix-shell
+///     - pure           // use_name == false in a pure nix-shell
+///     - impure         // use_name == false in an impure nix-shell
+pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
+    let mut module = context.new_module("nix_shell")?;
+
+    env::var("IN_NIX_SHELL")
+        .ok()
+        .and_then(|shell_type| {
+            if shell_type == "1" || shell_type == "impure" {
+                Some(module.config_value_str("impure_msg").unwrap_or("impure"))
+            } else if shell_type == "pure" {
+                Some(module.config_value_str("pure_msg").unwrap_or("pure"))
+            } else {
+                None
+            }
+        })
+        .map(|shell_type| {
+            if module.config_value_bool("use_name").unwrap_or(false) {
+                match env::var("name").ok() {
+                    Some(name) => format!("{} ({})", name, shell_type),
+                    None => shell_type.to_string(),
+                }
+            } else {
+                shell_type.to_string()
+            }
+        })
+        .map(|segment| {
+            let module_color = Color::Red.bold();
+            module.set_style(module_color);
+            module.new_segment("nix_shell", &segment);
+            module
+        })
+}

src/print.rs

@@ -22,6 +22,7 @@ const DEFAULT_PROMPT_ORDER: &[&str] = &[
     "rust",
     "python",
     "golang",
+    "nix_shell",
     "cmd_duration",
     "line_break",
     "jobs",