Compute transitions for regex pattern rules

spec/rules/pattern_spec.cpp

@@ -0,0 +1,63 @@
+#include "spec_helper.h"
+#include "rules.h"
+#include "transition_map.h"
+
+using namespace tree_sitter::rules;
+
+Describe(pattern_rules) {
+    It(parses_simple_strings) {
+        pattern_ptr rule = pattern("abc");
+        AssertThat(
+            rule->to_rule_tree()->to_string(),
+            Equals(seq({
+                character('a'),
+                character('b'),
+                character('c')
+            })->to_string()));
+    };
+    
+    It(parses_choices) {
+        pattern_ptr rule = pattern("ab|cd|ef");
+        AssertThat(
+            rule->to_rule_tree()->to_string(),
+            Equals(choice({
+                seq({
+                    character('a'),
+                    character('b'),
+                }),
+                seq({
+                    character('c'),
+                    character('d')
+                }),
+                seq({
+                    character('e'),
+                    character('f')
+                })
+            })->to_string()));
+    };
+    
+    It(parses_choices_in_sequences) {
+        pattern_ptr rule = pattern("(a|b)cd");
+        AssertThat(
+            rule->to_rule_tree()->to_string(),
+            Equals(seq({
+                choice({
+                    character('a'),
+                    character('b'),
+                }),
+                character('c'),
+                character('d')
+            })->to_string()));
+    };
+    
+    It(parses_special_characters_when_they_are_escaped) {
+        pattern_ptr rule = pattern("a\\(b");
+        AssertThat(
+            rule->to_rule_tree()->to_string(),
+            Equals(seq({
+                character('a'),
+                character('('),
+                character('b')
+            })->to_string()));
+    }
+};