Upgrade clap to v4

src/main.rs

@@ -2,7 +2,7 @@ use std::fs::File;
 use std::io::{Read, Write};
 use std::process::exit;
 
-use clap::{crate_authors, crate_description, crate_name, crate_version, App, Arg};
+use clap::{crate_authors, crate_description, crate_name, crate_version, Command, Arg};
 
 use md2pdf::{markdown_to_latex, markdown_to_pdf};
 
@@ -20,30 +20,33 @@ macro_rules! unwrap {
 
 fn main() {
 
-    let matches = App::new(crate_name!())
+    let matches = Command::new(crate_name!())
         .bin_name(crate_name!())
         .version(crate_version!())
         .author(crate_authors!("\n"))
         .about(crate_description!())
-        .arg(Arg::with_name("INPUT")
+        .arg(Arg::new("INPUT")
              .long("input")
-             .short("i")
+             .short('i')
              .help("Input markdown files")
              .required(true)
-             .takes_value(true))
-        .arg(Arg::with_name("OUTPUT")
+             .value_parser(clap::value_parser!(std::path::PathBuf))
+            )
+        .arg(Arg::new("OUTPUT")
              .long("output")
-             .short("o")
+             .short('o')
              .help("Output tex or pdf file")
              .required(true)
-             .takes_value(true))
+             .value_parser(clap::value_parser!(std::path::PathBuf))
+            )
         .get_matches();
 
+    let input_path = matches.get_one::<std::path::PathBuf>("INPUT").unwrap();
     let mut content = String::new();
-    let mut input = unwrap!(File::open(matches.value_of("INPUT").unwrap()), "couldn't open input file");
+    let mut input = unwrap!(File::open(input_path), "couldn't open input file");
     unwrap!(input.read_to_string(&mut content), "couldn't read file content");
 
-    let output_path = matches.value_of("OUTPUT").unwrap();
+    let output_path = matches.get_one::<std::path::PathBuf>("OUTPUT").unwrap();
     let mut output = unwrap!(File::create(output_path), "couldn't open output file");
 
     if output_path.ends_with(".tex") {
@@ -53,7 +56,7 @@ fn main() {
         let data = unwrap!(markdown_to_pdf(content), "error while compiling latex, this is most likely a bug");
         unwrap!(output.write(&data), "coudln't write output file");
     } else {
-        eprintln!("unknown file format for output: {}", output_path);
+        eprintln!("unknown file format for output: {}", output_path.display());
         exit(1);
     }