fix: Parsing nested generics (#1319)

* Implement parsing for nested generics

* Add regression test

* Fix test

* Update crates/noirc_frontend/src/lexer/lexer.rs

Co-authored-by: kevaundray <[email protected]>

* Uncomment line - merge error spans

* Update crates/noirc_frontend/src/parser/parser.rs

Co-authored-by: kevaundray <[email protected]>

* fix test

---------

Co-authored-by: kevaundray <[email protected]>

crates/nargo_cli/tests/test_data/generics/src/main.nr

@@ -49,4 +49,9 @@ fn main(x: Field, y: Field) {
 
     // Expected type error
     // assert(bar2.get_other() == bar2.other);
+
+    let one = x;
+    let two = y;
+    let nested_generics: Bar<Bar<Field>> = Bar { one, two, other: Bar { one, two, other: 0 } };
+    assert(nested_generics.other.other == bar1.get_other());
 }

crates/noirc_frontend/src/lexer/lexer.rs

@@ -162,9 +162,8 @@ impl<'a> Lexer<'a> {
                 if self.peek_char_is('=') {
                     self.next_char();
                     Ok(Token::GreaterEqual.into_span(start, start + 1))
-                } else if self.peek_char_is('>') {
-                    self.next_char();
-                    Ok(Token::ShiftRight.into_span(start, start + 1))
+                    // Note: There is deliberately no case for RightShift. We always lex >> as
+                    // two separate Greater tokens to help the parser parse nested generic types.
                 } else {
                     Ok(prev_token.into_single_span(start))
                 }
@@ -387,7 +386,8 @@ fn test_single_double_char() {
         Token::Assign,
         Token::Equal,
         Token::ShiftLeft,
-        Token::ShiftRight,
+        Token::Greater,
+        Token::Greater,
         Token::EOF,
     ];
 

crates/noirc_frontend/src/parser/errors.rs

@@ -147,7 +147,7 @@ impl chumsky::Error<Token> for ParserError {
             self.reason = other.reason;
         }
 
-        assert_eq!(self.span, other.span);
+        self.span = self.span.merge(other.span);
         self
     }
 }

crates/noirc_frontend/src/parser/parser.rs

@@ -517,9 +517,22 @@ where
     )
 }
 
+/// Parse an assignment operator `=` optionally prefixed by a binary operator for a combined
+/// assign statement shorthand. Notably, this must handle a few corner cases with how `>>` is
+/// lexed as two separate greater-than operators rather than a single right-shift.
 fn assign_operator() -> impl NoirParser<Token> {
     let shorthand_operators = Token::assign_shorthand_operators();
-    let shorthand_syntax = one_of(shorthand_operators).then_ignore(just(Token::Assign));
+    // We need to explicitly check for right_shift here since it is actually
+    // two separate greater-than operators.
+    let shorthand_operators = right_shift_operator().or(one_of(shorthand_operators));
+    let shorthand_syntax = shorthand_operators.then_ignore(just(Token::Assign));
+
+    // Since >> is lexed as two separate greater-thans, >>= is lexed as > >=, so
+    // we need to account for that case here as well.
+    let right_shift_fix =
+        just(Token::Greater).then(just(Token::GreaterEqual)).map(|_| Token::ShiftRight);
+
+    let shorthand_syntax = shorthand_syntax.or(right_shift_fix);
     just(Token::Assign).or(shorthand_syntax)
 }
 
@@ -726,14 +739,23 @@ fn create_infix_expression(lhs: Expression, (operator, rhs): (BinaryOp, Expressi
     Expression { span, kind: ExpressionKind::Infix(infix) }
 }
 
+// Right-shift (>>) is issued as two separate > tokens by the lexer as this makes it easier
+// to parse nested generic types. For normal expressions however, it means we have to manually
+// parse two greater-than tokens as a single right-shift here.
+fn right_shift_operator() -> impl NoirParser<Token> {
+    just(Token::Greater).then(just(Token::Greater)).map(|_| Token::ShiftRight)
+}
+
 fn operator_with_precedence(precedence: Precedence) -> impl NoirParser<Spanned<BinaryOpKind>> {
-    filter_map(move |span, token: Token| {
-        if Precedence::token_precedence(&token) == Some(precedence) {
-            Ok(token.try_into_binary_op(span).unwrap())
-        } else {
-            Err(ParserError::expected_label("binary operator".to_string(), token, span))
-        }
-    })
+    right_shift_operator()
+        .or(any()) // Parse any single token, we're validating it as an operator next
+        .try_map(move |token, span| {
+            if Precedence::token_precedence(&token) == Some(precedence) {
+                Ok(token.try_into_binary_op(span).unwrap())
+            } else {
+                Err(ParserError::expected_label("binary operator".to_string(), token, span))
+            }
+        })
 }
 
 fn term<'a, P>(expr_parser: P) -> impl NoirParser<Expression> + 'a