Support using subcommand as Docker CLI plugin for tighter integration

See docker/cli#1534 for CLI plugin design.

README.md

@@ -64,7 +64,14 @@ The built executable is installed into the folder `~/.cargo/bin` by default.
 
 ### Docker CLI plugin
 
-Coming soon for integration with the familiar Docker CLI.
+Optionally, Wheelsticks can be set up as a Docker CLI plugin. With that, calls
+to `wheelsticks deploy` can be replaced by `docker deploy`, which some people
+prefer. Example [setup](https://github.com/docker/cli/issues/1534):
+
+```bash
+mkdir --parents ~/.docker/cli-plugins
+ln --symbolic "$(which wheelsticks)" ~/.docker/cli-plugins/docker-deploy
+```
 
 ## Usage
 

src/docker_cli_plugin_metadata.rs

@@ -0,0 +1,46 @@
+pub fn go() -> anyhow::Result<String> {
+    let authors = env!("CARGO_PKG_AUTHORS");
+    let first_author_name = authors
+        .split_once(" <")
+        .ok_or(anyhow::anyhow!("{authors}"))?
+        .0;
+    Ok(serde_json::to_string_pretty(&Metadata {
+        schema_version: "0.1.0".into(),
+        short_description: env!("CARGO_PKG_DESCRIPTION").into(),
+        url: env!("CARGO_PKG_HOMEPAGE").into(),
+        vendor: first_author_name.into(),
+        version: env!("CARGO_PKG_VERSION").into(),
+    })?)
+}
+
+#[derive(serde::Serialize)]
+#[serde(rename_all = "PascalCase")]
+struct Metadata {
+    schema_version: String,
+    short_description: String,
+    #[serde(rename = "URL")]
+    url: String,
+    vendor: String,
+    version: String,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn handles() -> anyhow::Result<()> {
+        let metadata = go()?;
+        assert_eq!(
+            metadata,
+            r#"{
+  "SchemaVersion": "0.1.0",
+  "ShortDescription": "Zero-downtime deployments for Docker Compose",
+  "URL": "https://github.com/evolutics/wheelsticks",
+  "Vendor": "Benjamin Fischer",
+  "Version": "1.0.0"
+}"#,
+        );
+        Ok(())
+    }
+}

src/main.rs

@@ -1,6 +1,7 @@
 mod command;
 mod deploy;
 mod docker;
+mod docker_cli_plugin_metadata;
 mod log;
 
 use clap::Parser;
@@ -116,6 +117,12 @@ fn main() -> anyhow::Result<()> {
                 wait_timeout: wait_timeout.map(|wait_timeout| wait_timeout.to_string()),
             })
         }
+
+        Subcommand::DockerCliPluginMetadata => {
+            let metadata = docker_cli_plugin_metadata::go()?;
+            println!("{metadata}");
+            Ok(())
+        }
     }
 }
 
@@ -278,8 +285,7 @@ enum ComposeEngine {
 enum Subcommand {
     // Source for some arguments:
     // https://docs.docker.com/engine/reference/commandline/compose_up/
-
-    // TODO: Support use as plugin (https://github.com/docker/cli/issues/1534).
+    //
     /// Create or update services
     ///
     /// Builds, (re)creates, and starts containers for a service.
@@ -351,6 +357,9 @@ enum Subcommand {
 
         service_names: Vec<String>,
     },
+
+    #[command(hide = true)]
+    DockerCliPluginMetadata,
 }
 
 #[derive(Clone, ValueEnum)]