feat: add command to gen shell completions

migra-cli/src/main.rs

@@ -12,6 +12,7 @@ mod opts;
 use crate::error::StdResult;
 use config::Config;
 use opts::{AppOpt, Command, StructOpt};
+use std::io;
 
 fn main() -> StdResult<()> {
     let opt = AppOpt::from_args();
@@ -40,6 +41,13 @@ fn main() -> StdResult<()> {
             let config = Config::read(opt.config)?;
             commands::downgrade_applied_migrations(config)?;
         }
+        Command::Completions(opts) => {
+            AppOpt::clap().gen_completions_to(
+                env!("CARGO_BIN_NAME"),
+                opts.into(),
+                &mut io::stdout(),
+            );
+        }
     }
 
     Ok(())

migra-cli/src/opts.rs

@@ -1,4 +1,5 @@
 use std::path::PathBuf;
+use structopt::clap;
 pub use structopt::StructOpt;
 
 #[derive(Debug, StructOpt)]
@@ -27,6 +28,8 @@ pub(crate) enum Command {
 
     #[structopt(name = "downgrade", visible_alias = "down")]
     Downgrade,
+
+    Completions(CompletionsShell),
 }
 
 #[derive(Debug, StructOpt)]
@@ -40,3 +43,24 @@ pub(crate) struct MakeCommandOpt {
     #[structopt(parse(from_str))]
     pub migration_name: String,
 }
+
+#[derive(Debug, StructOpt)]
+pub(crate) enum CompletionsShell {
+    Bash,
+    Fish,
+    Zsh,
+    PowerShell,
+    Elvish,
+}
+
+impl From<CompletionsShell> for clap::Shell {
+    fn from(shell: CompletionsShell) -> Self {
+        match shell {
+            CompletionsShell::Bash => Self::Bash,
+            CompletionsShell::Fish => Self::Fish,
+            CompletionsShell::Zsh => Self::Zsh,
+            CompletionsShell::PowerShell => Self::PowerShell,
+            CompletionsShell::Elvish => Self::Elvish,
+        }
+    }
+}