Implement mismatched indentation warning

Author: kddnewton

config.yml

@@ -298,10 +298,11 @@ warnings:
   - DUPLICATED_WHEN_CLAUSE
   - FLOAT_OUT_OF_RANGE
   - IGNORED_FROZEN_STRING_LITERAL
+  - INDENTATION_MISMATCH
   - INTEGER_IN_FLIP_FLOP
   - INVALID_CHARACTER
+  - INVALID_MAGIC_COMMENT_VALUE
   - INVALID_NUMBERED_REFERENCE
-  - INVALID_SHAREABLE_CONSTANT_VALUE
   - KEYWORD_EOL
   - LITERAL_IN_CONDITION_DEFAULT
   - LITERAL_IN_CONDITION_VERBOSE

include/prism/parser.h

@@ -902,6 +902,12 @@ struct pm_parser {
      * characters.
      */
     bool current_regular_expression_ascii_only;
+
+    /**
+     * By default, Ruby always warns about mismatched indentation. This can be
+     * toggled with a magic comment.
+     */
+    bool warn_mismatched_indentation;
 };
 
 #endif