options: Implement --version manually and print clang version on --version --verbose

Fixes #2138

Author: emilio

src/options.rs

@@ -23,13 +23,13 @@ where
     );
 
     let matches = App::new("bindgen")
-        .version(option_env!("CARGO_PKG_VERSION").unwrap_or("unknown"))
         .about("Generates Rust bindings from C/C++ headers.")
+        .setting(clap::AppSettings::NoAutoVersion)
         .override_usage("bindgen [FLAGS] [OPTIONS] <header> -- <clang-args>...")
         .args(&[
             Arg::new("header")
                 .help("C or C++ header file")
-                .required(true),
+                .required_unless_present("V"),
             Arg::new("depfile")
                 .long("depfile")
                 .takes_value(true)
@@ -545,9 +545,24 @@ where
             Arg::new("vtable-generation")
                 .long("vtable-generation")
                 .help("Enables generation of vtable functions."),
+            Arg::new("V")
+                .long("version")
+                .help("Prints the version, and exits"),
         ]) // .args()
         .get_matches_from(args);
 
+    let verbose = matches.is_present("verbose");
+    if matches.is_present("V") {
+        println!(
+            "bindgen {}",
+            option_env!("CARGO_PKG_VERSION").unwrap_or("unknown")
+        );
+        if verbose {
+            println!("Clang: {}", crate::clang_version().full);
+        }
+        std::process::exit(0);
+    }
+
     let mut builder = builder();
 
     if let Some(header) = matches.value_of("header") {
@@ -1015,7 +1030,5 @@ where
         builder = builder.vtable_generation(true);
     }
 
-    let verbose = matches.is_present("verbose");
-
     Ok((builder, output, verbose))
 }