feat: Add literal command completion type

README.md

@@ -269,9 +269,22 @@ fi
 
 To enable completions for positional arguments in the `Usage` comment, add an
 `Options:` comment with a list of arguments. An option must have the format:
-`name (completion_type): description`. Completion type is optional. Currently,
-the only supported completion type is `script`, which allows for dynamic
-completions like the following example:
+`name (completion_type): description`. Completion type is optional.
+The following completion types are supported:
+
+- ``command``: Runs a command to generate completions. The command should print
+  completions to stdout:
+
+```sh
+# Usage: {cmd} <file>
+# Options:
+#   file (`ls -1`): File or directory
+
+# script logic
+# ...
+```
+
+- `script`: allows for more complex, dynamic completions:
 
 ```sh
 # Usage: {cmd} <name>
@@ -284,7 +297,7 @@ if [[ "$_HAT_COMPLETE" == "true" ]]; then
     echo "Alice"
     echo "Bob"
     echo "Charlie"
-    # note that you can run any command here to generate completions
+    # note that you can have any logic here to generate completions
   fi
 
   # make sure to exit when generating completions to prevent the script from running

integration/completions.bats

@@ -40,6 +40,15 @@ comp2"
 comp4"
 }
 
+@test "completions: literal command: invokes command for completions" {
+  fixture "completions"
+
+  run main --completions literal
+
+  assert_success
+  assert_output "itworks"
+}
+
 @test "completions: lists nothing if command provides no completions" {
   fixture "completions"
 

integration/fixtures/completions/libexec/literal

@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+#
+# Usage: {cmd} <option>
+# Options:
+#   option (`echo itworks`): Description of option
+
+exit 202

src/commands/file.rs

@@ -84,6 +84,17 @@ impl<'a> Command for FileCommand<'a> {
                         None => Err(Error::SubCommandInterrupted),
                     };
                 },
+                Some(usage::CompletionType::LiteralCommand(cmd)) => {
+                    let mut command = process::Command::new("/bin/sh");
+                    command.arg("-c").arg(&cmd);
+
+                    let status = command.status().unwrap();
+
+                    return match status.code() {
+                        Some(code) => Ok(code),
+                        None => Err(Error::SubCommandInterrupted),
+                    };
+                },
                 None => {
                     // do nothing
                 },

src/usage.rs

@@ -35,6 +35,7 @@ struct UsageLang {
 #[derive(Debug, PartialEq, Clone)]
 pub enum CompletionType {
     Script,
+    LiteralCommand(String),
 }
 
 #[derive(Debug, PartialEq)]
@@ -50,8 +51,9 @@ fn option_parser() -> impl Parser<char, OptionSpec, Error = Simple<char>> {
         .collect();
 
     let completion_type_script = just("script").map(|_| CompletionType::Script);
+    let completion_type_literal_command = just('`').ignore_then(take_until(just('`')).padded()).map(|(s, _)| CompletionType::LiteralCommand(s.into_iter().collect()));
 
-    let completion_type = completion_type_script;
+    let completion_type = completion_type_script.or(completion_type_literal_command);
 
     let description = take_until(end()).padded().map(|(s, _)| s.into_iter().collect());