minor grammar fixes/improvements, better error messages

src/lexer.ml

@@ -15,7 +15,8 @@ let achar =
   [%sedlex.regexp? Sub (any, (ctl | '"' | '\\' | '\'' | '{' | '}' | wsp))]
 
 let newline =
-  [%sedlex.regexp? Star wsp, '\n', Star wsp, Opt ('#', Sub (any, '\n'))]
+  [%sedlex.regexp?
+    Plus (Star wsp, '\n', Star wsp, Opt ('#', Star (Sub (any, '\n'))))]
 
 let esc_pair = [%sedlex.regexp? '\\', vchar]
 
@@ -76,14 +77,17 @@ let string_of_dqword s =
 
 exception Error of string
 
+let error msg = raise @@ Error msg
+
 let rec token buf =
   match%sedlex buf with
   (* 1 *)
-  | "{" -> LBRACE
-  | "}" -> RBRACE
+  | "{", newline -> LBRACE
+  | newline, "}" -> RBRACE
   (* other *)
   | wsp -> token buf
-  | Plus newline -> NEWLINE
+  | Opt newline, eof -> EOF
+  | newline -> NEWLINE
   | atom ->
     let word = Utf8.lexeme buf in
     let word = string_of_atom word in
@@ -97,8 +101,12 @@ let rec token buf =
     let word = Utf8.lexeme buf in
     let word = String.sub word 1 (String.length word - 2) in
     WORD word
-  | eof -> EOF
   | any ->
     let invalid = Utf8.lexeme buf in
-    raise @@ Error invalid
+    let start, _stop = Sedlexing.lexing_positions buf in
+    Format.ksprintf error
+      "File %s, line %i, character %i: unexpected lexeme `%s`" start.pos_fname
+      start.pos_lnum
+      (start.pos_cnum - start.pos_bol)
+      invalid
   | _ -> assert false

src/menhir_parser.mly

@@ -1,5 +1,8 @@
 %token<String.t> WORD
-%token LBRACE RBRACE NEWLINE EOF
+%token LBRACE
+%token RBRACE
+%token NEWLINE
+%token EOF
 
 %{ open Types %}
 
@@ -10,14 +13,14 @@
 let params ==
 | ~ = list(WORD); <>
 
-let children ==
-| LBRACE; NEWLINE; ~ = list(directive); RBRACE; <>
+let children :=
+| LBRACE; ~ = separated_list(NEWLINE, directive); RBRACE; <>
 | { [] }
 
 let directive :=
-| name = WORD; ~ = params; ~ = children; NEWLINE; {
+| name = WORD; ~ = params; ~ = children; {
   { name; params; children }
 }
 
 let config :=
-| option(NEWLINE); ~ = list(directive); EOF; <>
+| option(NEWLINE); ~ = separated_list(NEWLINE, directive); EOF; <>

src/parse.ml

@@ -1,24 +1,36 @@
 (** Module providing functions to parse a config from various kind of inputs. *)
 
+(** Pretty print a token *)
+let pp_token fmt = function
+  | Menhir_parser.WORD s -> Format.fprintf fmt "WORD %s" s
+  | LBRACE -> Format.pp_print_string fmt "LBRACE"
+  | RBRACE -> Format.pp_print_string fmt "RBRACE"
+  | NEWLINE -> Format.pp_print_string fmt "NEWLINE"
+  | EOF -> Format.pp_print_string fmt "EOF"
+
 (** Parse a config from a lexing buffer. *)
 let from_lexbuf =
   let parser =
     MenhirLib.Convert.Simplified.traditional2revised Menhir_parser.config
   in
   fun buf ->
+    let last_token = ref None in
     let provider () =
       let tok = Lexer.token buf in
       let start, stop = Sedlexing.lexing_positions buf in
+      last_token := Some tok;
       (tok, start, stop)
     in
     try Ok (parser provider) with
     | Menhir_parser.Error ->
       let start, _stop = Sedlexing.lexing_positions buf in
-      Format.ksprintf Result.error
-        "File %s, line %i, character %i: unexpected token" start.pos_fname
+      Format.kasprintf Result.error
+        "File %s, line %i, character %i: unexpected token %a" start.pos_fname
         start.pos_lnum
         (start.pos_cnum - start.pos_bol)
-    | Lexer.Error msg -> Error (Format.sprintf "lexer error: %S" msg)
+        (Format.pp_print_option pp_token)
+        !last_token
+    | Lexer.Error msg -> Error msg
 
 (** Parse a config from a string. *)
 let from_string s = from_lexbuf (Sedlexing.Utf8.from_string s)
@@ -37,6 +49,8 @@ let from_channel c = from_lexbuf (Sedlexing.Utf8.from_channel c)
 (** Parse a config from a file. *)
 let from_file f =
   let chan = open_in f in
-  let result = from_lexbuf (Sedlexing.Utf8.from_channel chan) in
+  let lexbuf = Sedlexing.Utf8.from_channel chan in
+  Sedlexing.set_filename lexbuf f;
+  let result = from_lexbuf lexbuf in
   close_in chan;
   result

test/cram/test.t

@@ -25,23 +25,23 @@ test 2:
   }
 lex error 1:
   $ dune exec -- scfg lex_error.scfg
-  error: lexer error: "\""
+  error: File lex_error.scfg, line 1, character 2: unexpected lexeme `"`
   [1]
 parse error 1:
   $ dune exec -- scfg parse_error1.scfg
-  error: File , line 1, character 4: unexpected token
+  error: File parse_error1.scfg, line 1, character 2: unexpected lexeme `{`
   [1]
 parse error 2:
   $ dune exec -- scfg parse_error2.scfg
-  error: File , line 2, character 0: unexpected token
+  error: File parse_error2.scfg, line 2, character 0: unexpected token EOF
   [1]
 parse error 3:
   $ dune exec -- scfg parse_error3.scfg
-  error: File , line 1, character 2: unexpected token
+  error: File parse_error3.scfg, line 1, character 2: unexpected lexeme `}`
   [1]
 parse error 4:
   $ dune exec -- scfg parse_error4.scfg
-  error: File , line 1, character 3: unexpected token
+  error: File parse_error4.scfg, line 1, character 2: unexpected lexeme `{`
   [1]
 bug 1:
   $ dune exec -- scfg bug1.scfg