1 files changed, 66 insertions, 0 deletions
diff --git a/lib/prism/parse_result/errors.rb b/lib/prism/parse_result/errors.rb
new file mode 100644
index 0000000000..26c376b3ce
--- /dev/null
+++ b/lib/prism/parse_result/errors.rb
@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+# :markup: markdown
+
+require "stringio"
+
+module Prism
+  class ParseResult < Result
+    # An object to represent the set of errors on a parse result. This object
+    # can be used to format the errors in a human-readable way.
+    class Errors
+      # The parse result that contains the errors.
+      attr_reader :parse_result
+
+      # Initialize a new set of errors from the given parse result.
+      def initialize(parse_result)
+        @parse_result = parse_result
+      end
+
+      # Formats the errors in a human-readable way and return them as a string.
+      def format
+        error_lines = {} #: Hash[Integer, Array[ParseError]]
+        parse_result.errors.each do |error|
+          location = error.location
+          (location.start_line..location.end_line).each do |line|
+            error_lines[line] ||= []
+            error_lines[line] << error
+          end
+        end
+
+        source_lines = parse_result.source.source.lines
+        source_lines << "" if error_lines.key?(source_lines.size + 1)
+
+        io = StringIO.new
+        source_lines.each.with_index(1) do |line, line_number|
+          io.puts(line)
+
+          (error_lines.delete(line_number) || []).each do |error|
+            location = error.location
+
+            case line_number
+            when location.start_line
+              io.print(" " * location.start_column + "^")
+
+              if location.start_line == location.end_line
+                if location.start_column != location.end_column
+                  io.print("~" * (location.end_column - location.start_column - 1))
+                end
+
+                io.puts(" " + error.message)
+              else
+                io.puts("~" * (line.bytesize - location.start_column))
+              end
+            when location.end_line
+              io.puts("~" * location.end_column + " " + error.message)
+            else
+              io.puts("~" * line.bytesize)
+            end
+          end
+        end
+
+        io.puts
+        io.string
+      end
+    end
+  end
+end