Make derive_parser work with all optional arguments (#397)

The current implementation using `winnow`'s `opt` does not work for optional arguments that are in the middle of the command. For example, `bar{.cta}.red.op.pred   p, a{, b}, {!}c;`. This is because `opt` is greedy, and will always match `{, b}` instead of `,{!} c`. This change switches to using a custom combinator that handles this properly

ptx_parser/src/lib.rs

@@ -1492,6 +1492,46 @@ pub struct TokenError(std::ops::Range<usize>);
 
 impl std::error::Error for TokenError {}
 
+fn first_optional<
+    'a,
+    'input,
+    Input: Stream,
+    OptionalOutput,
+    RequiredOutput,
+    Error,
+    ParseOptional,
+    ParseRequired,
+>(
+    mut optional: ParseOptional,
+    mut required: ParseRequired,
+) -> impl Parser<Input, (Option<OptionalOutput>, RequiredOutput), Error>
+where
+    ParseOptional: Parser<Input, OptionalOutput, Error>,
+    ParseRequired: Parser<Input, RequiredOutput, Error>,
+    Error: ParserError<Input>,
+{
+    move |input: &mut Input| -> Result<(Option<OptionalOutput>, RequiredOutput), ErrMode<Error>> {
+        let start = input.checkpoint();
+
+        let parsed_optional = match optional.parse_next(input) {
+            Ok(v) => Some(v),
+            Err(ErrMode::Backtrack(_)) => {
+                input.reset(&start);
+                None
+            },
+            Err(e) => return Err(e)
+        };
+
+        match required.parse_next(input) {
+            Ok(v) => return Ok((parsed_optional, v)),
+            Err(ErrMode::Backtrack(_)) => input.reset(&start),
+            Err(e) => return Err(e)
+        };
+
+        Ok((None, required.parse_next(input)?))
+    }
+}
+
 // This macro is responsible for generating parser code for instruction parser.
 // Instruction parsing is by far the most complex part of parsing PTX code:
 // * There are tens of instruction kinds, each with slightly different parsing rules
@@ -3413,6 +3453,7 @@ derive_parser!(
 
 #[cfg(test)]
 mod tests {
+    use crate::first_optional;
     use crate::parse_module_checked;
     use crate::PtxError;
 
@@ -3423,6 +3464,55 @@ mod tests {
     use logos::Span;
     use winnow::prelude::*;
 
+    #[test]
+    fn first_optional_present() {
+        let text = "AB";
+        let result = first_optional::<_, _, _, (), _, _>('A', 'B').parse(text);
+        assert_eq!(result, Ok((Some('A'), 'B')));
+    }
+
+    #[test]
+    fn first_optional_absent() {
+        let text = "B";
+        let result = first_optional::<_, _, _, (), _, _>('A', 'B').parse(text);
+        assert_eq!(result, Ok((None, 'B')));
+    }
+
+    #[test]
+    fn first_optional_repeated_absent() {
+        let text = "A";
+        let result = first_optional::<_, _, _, (), _, _>('A', 'A').parse(text);
+        assert_eq!(result, Ok((None, 'A')));
+    }
+
+    #[test]
+    fn first_optional_repeated_present() {
+        let text = "AA";
+        let result = first_optional::<_, _, _, (), _, _>('A', 'A').parse(text);
+        assert_eq!(result, Ok((Some('A'), 'A')));
+    }
+
+    #[test]
+    fn first_optional_sequence_absent() {
+        let text = "AA";
+        let result = ('A', first_optional::<_, _, _, (), _, _>('A', 'A')).parse(text);
+        assert_eq!(result, Ok(('A', (None, 'A'))));
+    }
+
+    #[test]
+    fn first_optional_sequence_present() {
+        let text = "AAA";
+        let result = ('A', first_optional::<_, _, _, (), _, _>('A', 'A')).parse(text);
+        assert_eq!(result, Ok(('A', (Some('A'), 'A'))));
+    }
+
+    #[test]
+    fn first_optional_no_match() {
+        let text = "C";
+        let result = first_optional::<_, _, _, (), _, _>('A', 'B').parse(text);
+        assert!(result.is_err());
+    }
+
     #[test]
     fn sm_11() {
         let text = ".target sm_11";

ptx_parser_macros/src/lib.rs

@@ -757,12 +757,13 @@ fn emit_definition_parser(
                 DotModifierRef::Direct { optional: true, .. }
                 | DotModifierRef::Indirect { optional: true, .. } => TokenStream::new(),
             });
-    let arguments_parse = definition.arguments.0.iter().enumerate().map(|(idx, arg)| {
+    let (arguments_pattern, arguments_parser) = definition.arguments.0.iter().enumerate().rfold((quote! { () }, quote! { empty }), |(emitted_pattern, emitted_parser), (idx, arg)| {
         let comma = if idx == 0 || arg.pre_pipe {
             quote! { empty }
         } else {
             quote! { any.verify(|(t, _)| *t == #token_type::Comma).void() }
         };
+
         let pre_bracket = if arg.pre_bracket {
             quote! {
                 any.verify(|(t, _)| *t == #token_type::LBracket).void()
@@ -833,16 +834,20 @@ fn emit_definition_parser(
                 #pattern.map(|(_, _, _, _, name, _, _)| name)
             }
         };
-        if arg.optional {
-            quote! {
-                let #arg_name = opt(#inner_parser).parse_next(stream)?;
-            }
+
+        let parser = if arg.optional {
+            quote! { first_optional(#inner_parser, #emitted_parser) }
         } else {
-            quote! {
-                let #arg_name = #inner_parser.parse_next(stream)?;
-            }
-        }
+            quote! { (#inner_parser, #emitted_parser) }
+        };
+
+        let pattern = quote! { ( #arg_name, #emitted_pattern ) };
+
+        (pattern, parser)
     });
+
+    let arguments_parse = quote! { let #arguments_pattern = ( #arguments_parser ).parse_next(stream)?; };
+
     let fn_args = definition.function_arguments();
     let fn_name = format_ident!("{}_{}", opcode, fn_idx);
     let fn_call = quote! {
@@ -863,7 +868,7 @@ fn emit_definition_parser(
             }
         }
         #(#unordered_parse_validations)*
-        #(#arguments_parse)*
+        #arguments_parse
         #fn_call
     }
 }