Disallow r# at the start of identifiers (kdl v2)

CHANGES.md

@@ -5,7 +5,8 @@
 - Updated to KDL v2.0:
 - - Added Line Tabulation U+000B to whitespace characters
 - - Removed `\/` from escape sequences
-- Dropped support for OCaml < 4.10.0.
+- - Identifiers cannot start with `r#` anymore
+- Dropped support for OCaml < 4.10.0
 
 ## 0.1.0 (2022-10-01)
 

src/lexer.ml

@@ -206,6 +206,7 @@ let rec main lexbuf =
     Buffer.reset string_buffer;
     set_string_start lexbuf;
     string lexbuf
+  | "r#", Star identchar -> error "An identifier cannot start with r#"
   | '-', startident, Star identchar -> IDENT (Sedlexing.Utf8.lexeme lexbuf)
   | '-' -> IDENT "-"
   | Sub (startident, '-'), Star identchar -> IDENT (Sedlexing.Utf8.lexeme lexbuf)

test/parse.ml

@@ -139,6 +139,23 @@ let%expect_test "(raw) string literals as a property name" =
   test {|- "key\n"="value" r##"key\t"##=true|};
   [%expect {| (- ("key\n" (string value)) ("key\\t" true)) |}]
 
+let%expect_test "identifiers cannot start with r#" =
+  test {|- r#=0|};
+  test {|- r#a=1|};
+  test {|- r#<=1|};
+  [%expect {|
+    Error: :1:3-1:5: An identifier cannot start with r#
+    Error: :1:3-1:6: An identifier cannot start with r#
+    Error: :1:3-1:5: An identifier cannot start with r# |}]
+
+let%expect_test "identifiers cannot contain special characters (<, etc.)" =
+  test {|- a<=1|};
+  [%expect {| Error: :1:4-1:5: Illegal character '<' |}]
+
+let%expect_test "-- as an identifier" =
+  test {|- --=0|};
+  [%expect {| (- (-- (int 0))) |}]
+
 let%expect_test "single-line comments" =
   test {|node // comment // commment
         // comment node|};