feat: add docker context module (#996)

* feat: add docker context module

Adds a simple module that checks for a Docker config file and if present, reads the `currentContext` value out and displays on the prompt with a whale.

* feat: add `only_with_compose_yml` option to docker_context

When enabled, will only show the docker context name if there's a docker-compose.yml file in the current directory.

* Update src/modules/docker_context.rs

Co-Authored-By: Thomas O'Donnell <andytom@users.noreply.github.com>

* Update src/modules/docker_context.rs

Co-Authored-By: Thomas O'Donnell <andytom@users.noreply.github.com>

* rename `only_with_compose_yml` configuration key to a more generic `only_with_files`

* Update src/modules/docker_context.rs

Co-Authored-By: Thomas O'Donnell <andytom@users.noreply.github.com>

* re-order configuration table

* Update docs/config/README.md

Co-Authored-By: Thomas O'Donnell <andytom@users.noreply.github.com>

* Update src/configs/docker_context.rs

Co-Authored-By: Thomas O'Donnell <andytom@users.noreply.github.com>

Co-authored-by: Thomas O'Donnell <andytom@users.noreply.github.com>

7 files changed, 104 insertions, 0 deletions

diff --git a/docs/config/README.md b/docs/config/README.md
index 3de40b5ee..8c0131fb0 100644
--- a/docs/config/README.md
+++ b/docs/config/README.md
@@ -100,6 +100,7 @@ prompt_order = [
     "git_state",
     "git_status",
     "hg_branch",
+    "docker_context",
     "package",
     "dotnet",
     "elixir",
@@ -405,6 +406,30 @@ a single character. For `fish_style_pwd_dir_length = 2`, it would be `/bu/th/ci/
 truncation_length = 8
 ```
 
+## Docker Context
+
+The `docker_context` module shows the currently active
+[Docker context](https://docs.docker.com/engine/context/working-with-contexts/) if it's not set to
+`default`.
+
+### Options
+
+| Variable          | Default       | Description                                                                  |
+| ----------------- | ------------- | ---------------------------------------------------------------------------- |
+| `symbol`          | `"🐳 "`       | The symbol used before displaying the Docker context .                       |
+| `only_with_files` | `false`       | Only show when there's a `docker-compose.yml` or `Dockerfile` in the current directory. |
+| `style`           | `"bold blue"` | The style for the module.                                                    |
+| `disabled`        | `true`        | Disables the `docker_context` module.                                        |
+
+### Example
+
+```toml
+# ~/.config/starship.toml
+
+[docker_context]
+symbol = "🐋 "
+```
+
 ## Dotnet
 
 The `dotnet` module shows the relevant version of the .NET Core SDK for the current directory. If
diff --git a/src/configs/docker_context.rs b/src/configs/docker_context.rs
new file mode 100644
index 000000000..79be04294
--- /dev/null
+++ b/src/configs/docker_context.rs
@@ -0,0 +1,25 @@
+use crate::config::{ModuleConfig, RootModuleConfig, SegmentConfig};
+
+use ansi_term::{Color, Style};
+use starship_module_config_derive::ModuleConfig;
+
+#[derive(Clone, ModuleConfig)]
+pub struct DockerContextConfig<'a> {
+    pub symbol: SegmentConfig<'a>,
+    pub context: SegmentConfig<'a>,
+    pub style: Style,
+    pub only_with_files: bool,
+    pub disabled: bool,
+}
+
+impl<'a> RootModuleConfig<'a> for DockerContextConfig<'a> {
+    fn new() -> Self {
+        DockerContextConfig {
+            symbol: SegmentConfig::new("🐳 "),
+            context: SegmentConfig::default(),
+            style: Color::Blue.bold(),
+            only_with_files: true,
+            disabled: false,
+        }
+    }
+}
diff --git a/src/configs/mod.rs b/src/configs/mod.rs
index d6110bca4..54f1455a5 100644
--- a/src/configs/mod.rs
+++ b/src/configs/mod.rs
@@ -5,6 +5,7 @@ pub mod cmd_duration;
 pub mod conda;
 pub mod crystal;
 pub mod directory;
+pub mod docker_context;
 pub mod dotnet;
 pub mod elixir;
 pub mod elm;
diff --git a/src/configs/starship_root.rs b/src/configs/starship_root.rs
index c15642544..113f96551 100644
--- a/src/configs/starship_root.rs
+++ b/src/configs/starship_root.rs
@@ -27,6 +27,7 @@ impl<'a> RootModuleConfig<'a> for StarshipRootConfig<'a> {
                 "git_state",
                 "git_status",
                 "hg_branch",
+                "docker_context",
                 "package",
                 // ↓ Toolchain version modules ↓
                 // (Let's keep these sorted alphabetically)
diff --git a/src/module.rs b/src/module.rs
index 90bca641f..7fc2c72e5 100644
--- a/src/module.rs
+++ b/src/module.rs
@@ -17,6 +17,7 @@ pub const ALL_MODULES: &[&str] = &[
     "cmd_duration",
     "conda",
     "directory",
+    "docker_context",
     "dotnet",
     "elixir",
     "elm",
diff --git a/src/modules/docker_context.rs b/src/modules/docker_context.rs
new file mode 100644
index 000000000..6cf0e2d94
--- /dev/null
+++ b/src/modules/docker_context.rs
@@ -0,0 +1,48 @@
+use dirs::home_dir;
+
+use super::{Context, Module, RootModuleConfig};
+
+use crate::configs::docker_context::DockerContextConfig;
+use crate::utils;
+
+const DOCKER_CONFIG_FILE: &str = ".docker/config.json";
+
+/// Creates a module with the currently active Docker context
+///
+/// Will display the Docker context if the following criteria are met:
+///     - There is a file named `$HOME/.docker/config.json`
+///     - The file is JSON and contains a field named `currentContext`
+///     - The value of `currentContext` is not `default`
+pub fn module<'a>(context: &'a Context) -> Option<Module<'a>> {
+    let mut module = context.new_module("docker_context");
+    let config: DockerContextConfig = DockerContextConfig::try_load(module.config);
+
+    if config.only_with_files
+        && !context
+            .try_begin_scan()?
+            .set_files(&["docker-compose.yml", "Dockerfile"])
+            .is_match()
+    {
+        return None;
+    }
+
+    let config_path = home_dir()?.join(DOCKER_CONFIG_FILE);
+    let json = utils::read_file(config_path).ok()?;
+    let parsed_json = serde_json::from_str(&json).ok()?;
+
+    match parsed_json {
+        serde_json::Value::Object(root) => {
+            let current_context = root.get("currentContext")?;
+            match current_context {
+                serde_json::Value::String(ctx) => {
+                    module.set_style(config.style);
+                    module.create_segment("symbol", &config.symbol);
+                    module.create_segment("context", &config.context.with_value(&ctx));
+                    Some(module)
+                }
+                _ => None,
+            }
+        }
+        _ => None,
+    }
+}
diff --git a/src/modules/mod.rs b/src/modules/mod.rs
index 167f7b639..fba3ded50 100644
--- a/src/modules/mod.rs
+++ b/src/modules/mod.rs
@@ -5,6 +5,7 @@ mod cmd_duration;
 mod conda;
 mod crystal;
 mod directory;
+mod docker_context;
 mod dotnet;
 mod elixir;
 mod elm;
@@ -54,6 +55,7 @@ pub fn handle<'a>(module: &str, context: &'a Context) -> Option<Module<'a>> {
         "cmd_duration" => cmd_duration::module(context),
         "conda" => conda::module(context),
         "directory" => directory::module(context),
+        "docker_context" => docker_context::module(context),
         "dotnet" => dotnet::module(context),
         "elixir" => elixir::module(context),
         "elm" => elm::module(context),
@@ -101,6 +103,7 @@ pub fn description(module: &str) -> &'static str {
         "cmd_duration" => "How long the last command took to execute",
         "conda" => "The current conda environment, if $CONDA_DEFAULT_ENV is set",
         "directory" => "The current working directory",
+        "docker_context" => "The current docker context",
         "dotnet" => "The relevant version of the .NET Core SDK for the current directory",
         "env_var" => "Displays the current value of a selected environment variable",
         "git_branch" => "The active branch of the repo in your current directory",