Write to Write trait

src/main.rs

@@ -1,26 +1,31 @@
-use std::{error::Error, fs::File};
+use std::{
+    error::Error,
+    fs::File,
+    io::{self, Write},
+};
 
 use pgxn_meta::Validator;
 use serde_json::Value;
 
 fn main() -> Result<(), Box<dyn Error>> {
-    let file = parse_args()?;
+    let mut stdout = io::stdout();
+    let file = parse_args(&mut stdout)?;
     validate(&file)?;
     Ok(())
 }
 
-fn parse_args() -> Result<String, lexopt::Error> {
+fn parse_args(out: &mut impl Write) -> Result<String, Box<dyn Error>> {
     use lexopt::prelude::*;
     let mut file = String::from("META.json");
     let mut parser = lexopt::Parser::from_env();
 
     while let Some(arg) = parser.next()? {
         match arg {
-            Short('h') | Long("help") => usage(),
-            Short('v') | Long("version") => version(),
-            Short('m') | Long("man") => docs(),
+            Short('h') | Long("help") => usage(out)?,
+            Short('v') | Long("version") => version(out)?,
+            Short('m') | Long("man") => docs(out)?,
             Value(val) => file = val.string()?,
-            _ => return Err(arg.unexpected()),
+            _ => return Err(Box::new(arg.unexpected())),
         }
     }
 
@@ -48,20 +53,25 @@ fn bin_name() -> String {
     String::from(env!("CARGO_BIN_NAME"))
 }
 
-fn usage() {
-    println!(
-        "Usage: {} [--help | h] [--version | -v] [<path>]",
+fn usage(out: &mut impl Write) -> Result<(), Box<dyn Error>> {
+    writeln!(
+        out,
+        "Usage: {} [--help | h] [--version | -v] [<path>]\n\n\
+        Options:\n\
+        \x20 -h --help     Print this usage statement and exit\n\
+        \x20 -v --version  Print the version number and exit",
         bin_name()
-    );
+    )?;
+
     std::process::exit(0);
 }
 
-fn version() {
-    println!("{} {}", bin_name(), env!("CARGO_PKG_VERSION"));
+fn version(out: &mut impl Write) -> Result<(), Box<dyn Error>> {
+    writeln!(out, "{} {}", bin_name(), env!("CARGO_PKG_VERSION"))?;
     std::process::exit(0);
 }
 
-fn docs() {
-    println!("Docs");
+fn docs(out: &mut impl Write) -> Result<(), Box<dyn Error>> {
+    writeln!(out, "Docs")?;
     std::process::exit(0);
 }