Move most of ParserError#json_path building logic in Ruby

This isn't a performance sensitive path, and that logic can be shared
with the eventual JRuby implementation.

Author: byroot

ext/json/ext/parser/parser.c

@@ -651,60 +651,30 @@ static VALUE build_parse_error_message(const char *format, JSON_ParserState *sta
     return rb_enc_sprintf(enc_utf8, format, ptr);
 }
 
-static bool json_path_append_key(VALUE path, VALUE key)
-{
-    if (RB_SYMBOL_P(key)) {
-        key = rb_sym2str(key);
-    } else if (!RB_TYPE_P(key, T_STRING)) {
-        return false;
-    }
-
-    long len = RSTRING_LEN(key);
-    bool plain = len > 0;
-    for (long i = 0; plain && i < len; i++) {
-        char c = RSTRING_PTR(key)[i];
-        bool alpha = (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_';
-        plain = alpha || (i > 0 && c >= '0' && c <= '9');
-    }
-
-    if (plain) {
-        rb_str_cat_cstr(path, ".");
-        rb_str_cat(path, RSTRING_PTR(key), len);
-        return true;
-    }
-
-    rb_str_cat_cstr(path, "[\"");
-    for (long i = 0; i < RSTRING_LEN(key); i++) {
-        char c = RSTRING_PTR(key)[i];
-        if (c == '"' || c == '\\') {
-            rb_str_cat(path, "\\", 1);
-        }
-        rb_str_cat(path, &c, 1);
-    }
-    rb_str_cat_cstr(path, "\"]");
-    return true;
-}
-
 static VALUE json_path_new(JSON_ParserState *state, VALUE duplicate_key)
 {
-    VALUE path = rb_utf8_str_new("$", 1);
+    VALUE path = rb_ary_new_capa(state->current_nesting);
+
     json_frame_stack *frames = state->frames;
     rvalue_stack *values = state->value_stack;
 
     for (long depth = 1; depth < frames->head; depth++) {
         json_frame *frame = &frames->ptr[depth];
+
         bool innermost = depth == frames->head - 1;
         long child_head = innermost ? values->head : frames->ptr[depth + 1].value_stack_head;
         long count = child_head - frame->value_stack_head;
 
         if (frame->type == JSON_FRAME_ARRAY) {
-            rb_str_catf(path, "[%ld]", frame->phase == JSON_PHASE_ARRAY_COMMA ? count - 1 : count);
+            rb_ary_push(path, LONG2NUM(frame->phase == JSON_PHASE_ARRAY_COMMA ? count - 1 : count));
         } else if (innermost && !UNDEF_P(duplicate_key)) {
-            if (!json_path_append_key(path, duplicate_key)) break;
+            rb_ary_push(path, duplicate_key);
         } else if (count & 1) {
-            if (!json_path_append_key(path, values->ptr[child_head - 1])) break;
+            rb_ary_push(path, values->ptr[child_head - 1]);
         } else if (frame->phase == JSON_PHASE_OBJECT_COMMA && count >= 2) {
-            if (!json_path_append_key(path, values->ptr[child_head - 2])) break;
+            rb_ary_push(path, values->ptr[child_head - 2]);
+        } else {
+            break;
         }
     }
 

lib/json/common.rb

@@ -142,7 +142,42 @@ class JSONError < StandardError; end
 
   # This exception is raised if a parser error occurs.
   class ParserError < JSONError
-    attr_reader :line, :column, :json_path
+    attr_reader :line, :column
+
+    def json_path
+      return @json_path if String === @json_path
+
+      if Array === @json_path
+        path = build_json_path(@json_path)
+        @json_path = path unless frozen?
+        return path
+      end
+    end
+
+    private
+
+    def build_json_path(segments)
+      error = false
+      path = segments.filter_map do |segment|
+        next if error
+
+        case segment
+        when Integer
+          "[#{segment}]"
+        when String, Symbol
+          if segment.match?(/\A[a-zA-Z\$\_][a-zA-Z\$\_0-9]*\z/)
+            ".#{segment}"
+          else
+            segment = segment.to_s.gsub(/["\\]/, { '"' => '\\"', '\\' => '\\\\' })
+            %{["#{segment}"]}
+          end
+        else
+          error = true
+          nil
+        end
+      end.join
+      "$#{path}".freeze
+    end
   end
 
   # This exception is raised if the nesting of parsed data structures is too