refactor(cheddar): Switch to clap-rs for command line arguments r/1005

The complexity of the arg parsing is increasing somewhat because we're
adding more features to cheddar, so to set us up for that this
switches the arg parsing to the somewhat more flexible clap.

Change-Id: I187bc0c1b6c6bd596fa0f6bb494b04e335262ba9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/445
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: tazjin <mail@tazj.in>

3 files changed, 29 insertions, 30 deletions

diff --git a/tools/cheddar/Cargo.lock b/tools/cheddar/Cargo.lock
index be70e178ab..ab1225cc6b 100644
--- a/tools/cheddar/Cargo.lock
+++ b/tools/cheddar/Cargo.lock
@@ -98,6 +98,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "cheddar"
 version = "0.1.0"
 dependencies = [
+ "clap 2.33.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "comrak 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "syntect 4.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/tools/cheddar/Cargo.toml b/tools/cheddar/Cargo.toml
index ca9ed0dfe4..b7d9a77586 100644
--- a/tools/cheddar/Cargo.toml
+++ b/tools/cheddar/Cargo.toml
@@ -8,3 +8,4 @@ edition = "2018"
 comrak = "0.7"
 lazy_static = "1.4"
 syntect = "4.2.0"
+clap = "2.33"
diff --git a/tools/cheddar/src/main.rs b/tools/cheddar/src/main.rs
index 01e6c868f7..9e16b1de43 100644
--- a/tools/cheddar/src/main.rs
+++ b/tools/cheddar/src/main.rs
@@ -1,3 +1,4 @@
+use clap::{Arg, App};
 use comrak::arena_tree::Node;
 use comrak::nodes::{Ast, AstNode, NodeValue, NodeCodeBlock, NodeHtmlBlock};
 use comrak::{Arena, parse_document, format_html, ComrakOptions};
@@ -72,35 +73,6 @@ struct Args {
     lang_override: Option<&'static str>,
 }
 
-/// Parse the command-line flags passed to cheddar to determine
-/// whether it is running in about-filter mode (`--about-filter`) and
-/// what file extension has been supplied.
-fn parse_args() -> Args {
-    let mut args = Args::default();
-
-    for (i, arg) in env::args().enumerate() {
-        if i == 0 {
-            continue;
-        }
-
-        if arg == "--about-filter" {
-            args.about_filter = true;
-            continue;
-        }
-
-        if let Some(lang) = (*FILENAME_OVERRIDES).get(arg.as_str()) {
-            args.lang_override = Some(lang);
-        }
-
-        args.extension = Path::new(&arg)
-            .extension()
-            .and_then(OsStr::to_str)
-            .map(|s| s.to_string());
-    }
-
-    return args
-}
-
 fn should_continue(res: &io::Result<usize>) -> bool {
     match *res {
         Ok(n) => n > 0,
@@ -312,7 +284,32 @@ fn format_code(args: &Args) {
 }
 
 fn main() {
-    let args = parse_args();
+    // Parse the command-line flags passed to cheddar to determine
+    // whether it is running in about-filter mode (`--about-filter`)
+    // and what file extension has been supplied.
+    let matches = App::new("cheddar")
+        .about("TVL's syntax highlighter")
+        .arg(Arg::with_name("about-filter")
+             .help("Run as a cgit about-filter (renders Markdown)")
+             .long("about-filter")
+             .takes_value(false))
+        .arg(Arg::with_name("filename")
+             .help("File to render")
+             .index(1))
+        .get_matches();
+
+    let mut args = Args::default();
+    args.about_filter = matches.is_present("about-filter");
+
+    let filename = matches.value_of("filename").expect("filename is required");
+    if let Some(lang) = (*FILENAME_OVERRIDES).get(filename) {
+        args.lang_override = Some(lang);
+    }
+
+    args.extension = Path::new(&filename)
+        .extension()
+        .and_then(OsStr::to_str)
+        .map(|s| s.to_string());
 
     match args.extension.as_ref().map(String::as_str) {
         Some("md") if args.about_filter => format_markdown(),