Support informal delimiter literals

README.md

@@ -136,11 +136,8 @@ Regexp::Scanner.scan( /(cat?([bhm]at)){3,5}/ ).map {|token| token[2]}
     to the lexer.
 
   * The MRI implementation may accept expressions that either conflict with
-    the documentation or are undocumented. The scanner does not support such
-    implementation quirks.
-    _(See issues [#3](https://github.com/ammar/regexp_parser/issues/3) and
-    [#15](https://github.com/ammar/regexp_parser/issues/15) for examples)_
-
+    the documentation or are undocumented, like `{}` and `]` _(unescaped)_.
+    The scanner will try to support as many of these cases as possible.
 
 ---
 ### Syntax

lib/regexp_parser/scanner/scanner.rl

@@ -62,9 +62,15 @@
   quantifier_possessive = '?+' | '*+' | '++';
   quantifier_mode       = '?'  | '+';
 
-  quantifier_interval   = range_open . (digit+)? . ','? . (digit+)? .
+  quantifier_exact      = range_open . (digit+) . range_close . quantifier_mode?;
+  quantifier_minimum    = range_open . (digit+) . ',' . range_close . quantifier_mode?;
+  quantifier_maximum    = range_open . ',' . (digit+) . range_close . quantifier_mode?;
+  quantifier_range      = range_open . (digit+) . ',' . (digit+) .
                           range_close . quantifier_mode?;
 
+  quantifier_interval   = quantifier_exact | quantifier_minimum |
+                          quantifier_maximum | quantifier_range;
+
   quantifiers           = quantifier_greedy | quantifier_reluctant |
                           quantifier_possessive | quantifier_interval;
 
@@ -114,6 +120,8 @@
                           curlies | parantheses | brackets |
                           line_anchor | quantifier_greedy;
 
+  literal_delimiters    = ']' | '}' | '{}';
+
   ascii_print           = ((0x20..0x7e) - meta_char);
   ascii_nonprint        = (0x01..0x1f | 0x7f);
 
@@ -417,6 +425,10 @@
       end
     };
 
+    literal_delimiters {
+      append_literal(data, ts, te)
+    };
+
     # Character sets
     # ------------------------------------------------------------------------
     set_open >set_opened {
@@ -620,10 +632,15 @@
       end
     };
 
-    quantifier_interval  @err(premature_end_error) {
+    quantifier_interval  {
       emit(:quantifier, :interval, *text(data, ts, te))
     };
 
+    # Catch unmatched curly braces as literals
+    range_open {
+      append_literal(data, ts, te)
+    };
+
     # Escaped sequences
     # ------------------------------------------------------------------------
     backslash > (backslashed, 1) {

spec/lexer/delimiters_spec.rb

@@ -0,0 +1,65 @@
+require 'spec_helper'
+
+RSpec.describe('Literal delimiter lexing') do
+  include_examples 'lex', '}',
+    0 => [:literal,     :literal,       '}',       0,  1,  0, 0, 0]
+
+  include_examples 'lex', '}}',
+    0 => [:literal,     :literal,       '}}',      0,  2,  0, 0, 0]
+
+  include_examples 'lex', '{',
+    0 => [:literal,     :literal,       '{',       0,  1,  0, 0, 0]
+
+  include_examples 'lex', '{{',
+    0 => [:literal,     :literal,       '{{',      0,  2,  0, 0, 0]
+
+  include_examples 'lex', '{}',
+    0 => [:literal,     :literal,       '{}',      0,  2,  0, 0, 0]
+
+  include_examples 'lex', '}{',
+    0 => [:literal,     :literal,       '}{',      0,  2,  0, 0, 0]
+
+  include_examples 'lex', '}{+',
+    0 => [:literal,     :literal,       '}',       0,  1,  0, 0, 0],
+    1 => [:literal,     :literal,       '{',       1,  2,  0, 0, 0],
+    2 => [:quantifier,  :one_or_more,   '+',       2,  3,  0, 0, 0]
+
+  include_examples 'lex', '{{var}}',
+    0 => [:literal,     :literal,       '{{var}}',  0,  7,  0, 0, 0]
+
+  include_examples 'lex', 'a{b}c',
+    0 => [:literal,     :literal,       'a{b}c',    0,  5,  0, 0, 0]
+
+  include_examples 'lex', '({.+})',
+    0 => [:group,       :capture,       '(',    0,  1,  0, 0, 0],
+    1 => [:literal,     :literal,       '{',    1,  2,  1, 0, 0],
+    2 => [:meta,        :dot,           '.',    2,  3,  1, 0, 0],
+    3 => [:quantifier,  :one_or_more,   '+',    3,  4,  1, 0, 0],
+    4 => [:literal,     :literal,       '}',    4,  5,  1, 0, 0],
+    5 => [:group,       :close,         ')',    5,  6,  0, 0, 0]
+
+  include_examples 'lex', ']',
+    0 => [:literal,     :literal,       ']',        0,  1,  0, 0, 0]
+
+  include_examples 'lex', ']]',
+    0 => [:literal,     :literal,       ']]',       0,  2,  0, 0, 0]
+
+  include_examples 'lex', ']\[',
+    0 => [:literal,     :literal,       ']',        0,  1,  0, 0, 0],
+    1 => [:escape,      :set_open,      '\[',       1,  3,  0, 0, 0]
+
+  include_examples 'lex', '()',
+    0 => [:group,       :capture,       '(',        0,  1,  0, 0, 0],
+    1 => [:group,       :close,         ')',        1,  2,  0, 0, 0]
+
+  include_examples 'lex', '{abc:.+}}}[^}]]}',
+    0 => [:literal,     :literal,       '{abc:',    0,  5,  0, 0, 0],
+    1 => [:meta,        :dot,           '.',        5,  6,  0, 0, 0],
+    2 => [:quantifier,  :one_or_more,   '+',        6,  7,  0, 0, 0],
+    3 => [:literal,     :literal,       '}}}',      7,  10, 0, 0, 0],
+    4 => [:set,         :open,          '[',        10, 11, 0, 0, 0],
+    5 => [:set,         :negate,        '^',        11, 12, 0, 1, 0],
+    6 => [:literal,     :literal,       '}',        12, 13, 0, 1, 0],
+    7 => [:set,         :close,         ']',        13, 14, 0, 0, 0],
+    8 => [:literal,     :literal,       ']}',       14, 16, 0, 0, 0]
+end

spec/scanner/delimiters_spec.rb

@@ -0,0 +1,49 @@
+require 'spec_helper'
+
+RSpec.describe('Literal delimiter scanning') do
+  include_examples 'scan', '}',
+    0 => [:literal,     :literal,       '}',        0,  1]
+
+  include_examples 'scan', '}}',
+    0 => [:literal,     :literal,       '}}',       0,  2]
+
+  include_examples 'scan', '{',
+    0 => [:literal,     :literal,       '{',        0,  1]
+
+  include_examples 'scan', '{{',
+    0 => [:literal,     :literal,       '{{',       0,  2]
+
+  include_examples 'scan', '{}',
+    0 => [:literal,     :literal,       '{}',       0,  2]
+
+  include_examples 'scan', '}{',
+    0 => [:literal,     :literal,       '}{',       0,  2]
+
+  include_examples 'scan', '}{+',
+    0 => [:literal,     :literal,       '}{',       0,  2]
+
+  include_examples 'scan', '{{var}}',
+    0 => [:literal,     :literal,       '{{var}}',  0,  7]
+
+  include_examples 'scan', '({.+})',
+    0 => [:group,       :capture,       '(',        0,  1],
+    1 => [:literal,     :literal,       '{',        1,  2],
+    2 => [:meta,        :dot,           '.',        2,  3],
+    3 => [:quantifier,  :one_or_more,   '+',        3,  4],
+    4 => [:literal,     :literal,       '}',        4,  5],
+    5 => [:group,       :close,         ')',        5,  6]
+
+  include_examples 'scan', ']',
+    0 => [:literal,     :literal,       ']',        0,  1]
+
+  include_examples 'scan', ']]',
+    0 => [:literal,     :literal,       ']]',       0,  2]
+
+  include_examples 'scan', ']\[',
+    0 => [:literal,     :literal,       ']',        0,  1],
+    1 => [:escape,      :set_open,      '\[',       1,  3]
+
+  include_examples 'scan', '()',
+    0 => [:group,       :capture,       '(',        0,  1],
+    1 => [:group,       :close,         ')',        1,  2]
+end

spec/scanner/errors_spec.rb

@@ -10,7 +10,6 @@
   include_examples 'scan error', RS::PrematureEndError, 'unbalanced set', '[a'
   include_examples 'scan error', RS::PrematureEndError, 'unbalanced set', '[[:alpha:]'
   include_examples 'scan error', RS::PrematureEndError, 'unbalanced group', '(abc'
-  include_examples 'scan error', RS::PrematureEndError, 'unbalanced interval', 'a{1,2'
   include_examples 'scan error', RS::PrematureEndError, 'eof in property', '\p{asci'
   include_examples 'scan error', RS::PrematureEndError, 'incomplete property', '\p{ascii abc'
   include_examples 'scan error', RS::PrematureEndError, 'eof options', '(?mix'