Add line comments to chirp parser

It is now possible to add comments to a chirp file using the

    // until end of line

syntax

Fixes #63

chirp/src/interpret.rs

@@ -123,13 +123,18 @@ impl<'w, 's, 'a, 'l, 'll, 'r, D: ParseDsl> Interpreter<'w, 's, 'a, 'l, 'll, 'r,
     pub fn statements(&self, input: &mut &BStr) -> PResult<(), ()> {
         use winnow::{
             ascii,
-            combinator::{alt, delimited, opt, preceded, separated0, separated_pair, success},
+            combinator::{
+                alt, delimited, opt, preceded, repeat, separated0, separated_pair, success,
+            },
             token::{one_of, take_till1},
         };
         // Note: we use `void` to reduce the size of input/output types. It's
         // a major source of performance problems in winnow.
+        let line_comment = || preceded(b"//", take_till1(b'\n'));
+        let repeat = repeat::<_, _, (), _, _>;
+        let spc_trail = || repeat(.., (line_comment(), ascii::multispace0));
         let (spc, spc1, opt) = (
-            || ascii::multispace0.void(),
+            || (ascii::multispace0, spc_trail()).void(),
             || ascii::multispace1.void(),
             || opt(b' ').void(),
         );

chirp/src/parse.rs

@@ -181,14 +181,15 @@ pub mod quick {
     impl<'a> Iterator for ArgIter<'a> {
         type Item = Result<&'a str, ArgError>;
         fn next(&mut self) -> Option<Self::Item> {
-            if self.input.is_empty() {
-                return None;
-            }
-            self.count += 1;
             #[cold]
+            #[allow(clippy::missing_const_for_fn)] // false positive
             fn err<T>(_: T) -> ArgError {
                 ArgError::ArgParse
             }
+            if self.input.is_empty() {
+                return None;
+            }
+            self.count += 1;
             if self.count - 1 == 0 {
                 let text = balanced_text.parse_next(&mut self.input).map_err(err);
                 // SAFETY: `ArgIter.input` is always valid utf8 because of the

examples/parse_dsl_macro/main.rs

@@ -173,10 +173,15 @@ fn main() {
 
     let mut world1 = World::new();
     let chirp = r#"
-        row("first row", rules(px(10), pct(11))) {
-            spawn(rules(pct(20), px(21)), "first child", empty_px 30);
-            spawn(empty_px 31, "2");
+        // Some comments
+        row(
+            "first row", // demonstrating
+            rules(px(10), pct(11))
+        ) { // that it is possible
+            spawn(rules(pct(20), px(21)), "first child", empty_px 30); // to
+            spawn(empty_px 31, "2"); // add comments
         }
+        // To a chirp file
         column("second element", rules(px(40), pct(41))) {
             spawn(rules(pct(50), px(51)), empty_px 60, "child3");
             spawn(empty_px 61, "so called \"fourth\" child");
@@ -190,10 +195,15 @@ fn main() {
     let mut state = SystemState::<Commands>::new(&mut world2);
     let mut cmds = state.get_mut(&mut world2);
     dsl! { <LayoutDsl> cmds,
-        row("first row", rules(px(10), pct(11))) {
-            spawn(rules(pct(20), px(21)), "first child", empty_px 30);
-            spawn(empty_px 31, "2");
+        // Some comments
+        row(
+            "first row", // demonstrating
+            rules(px(10), pct(11))
+        ) { // that it is possible
+            spawn(rules(pct(20), px(21)), "first child", empty_px 30); // to
+            spawn(empty_px 31, "2"); // add comments
         }
+        // To a chirp file
         column("second element", rules(px(40), pct(41))) {
             spawn(rules(pct(50), px(51)), empty_px 60, "child3");
             spawn(empty_px 61, "so called \"fourth\" child");