Remove taint support

Ruby 2.7 deprecates taint and it no longer has an effect.
The lack of taint support should not cause a problem in
previous Ruby versions.

I'm not sure if the untaint calls in deduplicate are still needed
after the removal of tainting in the parser.  If they are not
needed, they should be removed.

ext/psych/psych_parser.c

@@ -256,7 +256,6 @@ static VALUE parse(int argc, VALUE *argv, VALUE self)
     yaml_parser_t * parser;
     yaml_event_t event;
     int done = 0;
-    int tainted = 0;
     int state = 0;
     int parser_encoding = YAML_ANY_ENCODING;
     int encoding = rb_utf8_encindex();
@@ -275,13 +274,10 @@ static VALUE parse(int argc, VALUE *argv, VALUE self)
     yaml_parser_delete(parser);
     yaml_parser_initialize(parser);
 
-    if (OBJ_TAINTED(yaml)) tainted = 1;
-
     if (rb_respond_to(yaml, id_read)) {
 	yaml = transcode_io(yaml, &parser_encoding);
 	yaml_parser_set_encoding(parser, parser_encoding);
 	yaml_parser_set_input(parser, io_reader, (void *)yaml);
-	if (RTEST(rb_obj_is_kind_of(yaml, rb_cIO))) tainted = 1;
     } else {
 	StringValue(yaml);
 	yaml = transcode_string(yaml, &parser_encoding);
@@ -352,13 +348,11 @@ static VALUE parse(int argc, VALUE *argv, VALUE self)
 			VALUE prefix = Qnil;
 			if(start->handle) {
 			    handle = rb_str_new2((const char *)start->handle);
-			    if (tainted) OBJ_TAINT(handle);
 			    PSYCH_TRANSCODE(handle, encoding, internal_enc);
 			}
 
 			if(start->prefix) {
 			    prefix = rb_str_new2((const char *)start->prefix);
-			    if (tainted) OBJ_TAINT(prefix);
 			    PSYCH_TRANSCODE(prefix, encoding, internal_enc);
 			}
 
@@ -387,7 +381,6 @@ static VALUE parse(int argc, VALUE *argv, VALUE self)
 		VALUE alias = Qnil;
 		if(event.data.alias.anchor) {
 		    alias = rb_str_new2((const char *)event.data.alias.anchor);
-		    if (tainted) OBJ_TAINT(alias);
 		    PSYCH_TRANSCODE(alias, encoding, internal_enc);
 		}
 
@@ -406,19 +399,16 @@ static VALUE parse(int argc, VALUE *argv, VALUE self)
 		    (const char *)event.data.scalar.value,
 		    (long)event.data.scalar.length
 		    );
-		if (tainted) OBJ_TAINT(val);
 
 		PSYCH_TRANSCODE(val, encoding, internal_enc);
 
 		if(event.data.scalar.anchor) {
 		    anchor = rb_str_new2((const char *)event.data.scalar.anchor);
-		    if (tainted) OBJ_TAINT(anchor);
 		    PSYCH_TRANSCODE(anchor, encoding, internal_enc);
 		}
 
 		if(event.data.scalar.tag) {
 		    tag = rb_str_new2((const char *)event.data.scalar.tag);
-		    if (tainted) OBJ_TAINT(tag);
 		    PSYCH_TRANSCODE(tag, encoding, internal_enc);
 		}
 
@@ -448,14 +438,12 @@ static VALUE parse(int argc, VALUE *argv, VALUE self)
 		VALUE implicit, style;
 		if(event.data.sequence_start.anchor) {
 		    anchor = rb_str_new2((const char *)event.data.sequence_start.anchor);
-		    if (tainted) OBJ_TAINT(anchor);
 		    PSYCH_TRANSCODE(anchor, encoding, internal_enc);
 		}
 
 		tag = Qnil;
 		if(event.data.sequence_start.tag) {
 		    tag = rb_str_new2((const char *)event.data.sequence_start.tag);
-		    if (tainted) OBJ_TAINT(tag);
 		    PSYCH_TRANSCODE(tag, encoding, internal_enc);
 		}
 
@@ -484,13 +472,11 @@ static VALUE parse(int argc, VALUE *argv, VALUE self)
 		VALUE implicit, style;
 		if(event.data.mapping_start.anchor) {
 		    anchor = rb_str_new2((const char *)event.data.mapping_start.anchor);
-		    if (tainted) OBJ_TAINT(anchor);
 		    PSYCH_TRANSCODE(anchor, encoding, internal_enc);
 		}
 
 		if(event.data.mapping_start.tag) {
 		    tag = rb_str_new2((const char *)event.data.mapping_start.tag);
-		    if (tainted) OBJ_TAINT(tag);
 		    PSYCH_TRANSCODE(tag, encoding, internal_enc);
 		}
 

lib/psych/visitors/to_ruby.rb

@@ -369,13 +369,21 @@ def revive_hash hash, o
       end
 
       if String.method_defined?(:-@)
-        def deduplicate key
-          if key.is_a?(String)
-            # It is important to untaint the string, otherwise it won't
-            # be deduplicated into and fstring, but simply frozen.
-            -(key.untaint)
-          else
-            key
+        if RUBY_VERSION < '2.7'
+          def deduplicate key
+            if key.is_a?(String)
+              -(key.untaint)
+            else
+              key
+            end
+          end
+        else
+          def deduplicate key
+            if key.is_a?(String)
+              -key
+            else
+              key
+            end
           end
         end
       else