diff --git a/NEWS.md b/NEWS.md
index 7157700816c3e8..7534539a21d2c9 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -63,7 +63,7 @@ Note: We're only listing outstanding class updates.
 
 * IO
 
-    * `IO.select` accepts +Float::INFINITY+ as a timeout argument.
+    * `IO.select` accepts `Float::INFINITY` as a timeout argument.
       [[Feature #20610]]
 
 * Math
diff --git a/dir.c b/dir.c
index b934f2795c90e0..25ed59c668fab6 100644
--- a/dir.c
+++ b/dir.c
@@ -1480,7 +1480,7 @@ rb_dir_getwd_ospath(void)
     VALUE cwd;
     VALUE path_guard;
 
-    path_guard = rb_imemo_tmpbuf_auto_free_pointer();
+    path_guard = rb_imemo_tmpbuf_new();
     path = ruby_getcwd();
     rb_imemo_tmpbuf_set_ptr(path_guard, path);
 #ifdef __APPLE__
diff --git a/imemo.c b/imemo.c
index 02cba387bd22be..7cec33bc1edf00 100644
--- a/imemo.c
+++ b/imemo.c
@@ -48,23 +48,23 @@ rb_imemo_new(enum imemo_type type, VALUE v0, size_t size)
     return (VALUE)obj;
 }
 
-static rb_imemo_tmpbuf_t *
+VALUE
 rb_imemo_tmpbuf_new(void)
 {
-    return IMEMO_NEW(rb_imemo_tmpbuf_t, imemo_tmpbuf, 0);
+    VALUE flags = T_IMEMO | (imemo_tmpbuf << FL_USHIFT);
+    NEWOBJ_OF(obj, rb_imemo_tmpbuf_t, 0, flags, sizeof(rb_imemo_tmpbuf_t), NULL);
+
+    return (VALUE)obj;
 }
 
 void *
 rb_alloc_tmp_buffer_with_count(volatile VALUE *store, size_t size, size_t cnt)
 {
-    void *ptr;
-    rb_imemo_tmpbuf_t *tmpbuf;
-
     /* Keep the order; allocate an empty imemo first then xmalloc, to
      * get rid of potential memory leak */
-    tmpbuf = rb_imemo_tmpbuf_new();
+    rb_imemo_tmpbuf_t *tmpbuf = (rb_imemo_tmpbuf_t *)rb_imemo_tmpbuf_new();
     *store = (VALUE)tmpbuf;
-    ptr = ruby_xmalloc(size);
+    void *ptr = ruby_xmalloc(size);
     tmpbuf->ptr = ptr;
     tmpbuf->cnt = cnt;
 
@@ -97,7 +97,7 @@ rb_free_tmp_buffer(volatile VALUE *store)
 rb_imemo_tmpbuf_t *
 rb_imemo_tmpbuf_parser_heap(void *buf, rb_imemo_tmpbuf_t *old_heap, size_t cnt)
 {
-    rb_imemo_tmpbuf_t *tmpbuf = rb_imemo_tmpbuf_new();
+    rb_imemo_tmpbuf_t *tmpbuf = (rb_imemo_tmpbuf_t *)rb_imemo_tmpbuf_new();
     tmpbuf->ptr = buf;
     tmpbuf->next = old_heap;
     tmpbuf->cnt = cnt;
diff --git a/internal/imemo.h b/internal/imemo.h
index de39102432ea84..de617d94c1bf5c 100644
--- a/internal/imemo.h
+++ b/internal/imemo.h
@@ -132,16 +132,15 @@ struct MEMO {
 #ifndef RUBY_RUBYPARSER_H
 typedef struct rb_imemo_tmpbuf_struct rb_imemo_tmpbuf_t;
 #endif
+VALUE rb_imemo_tmpbuf_new(void);
 rb_imemo_tmpbuf_t *rb_imemo_tmpbuf_parser_heap(void *buf, rb_imemo_tmpbuf_t *old_heap, size_t cnt);
 struct vm_ifunc *rb_vm_ifunc_new(rb_block_call_func_t func, const void *data, int min_argc, int max_argc);
 static inline enum imemo_type imemo_type(VALUE imemo);
 static inline int imemo_type_p(VALUE imemo, enum imemo_type imemo_type);
 static inline bool imemo_throw_data_p(VALUE imemo);
 static inline struct vm_ifunc *rb_vm_ifunc_proc_new(rb_block_call_func_t func, const void *data);
-static inline VALUE rb_imemo_tmpbuf_auto_free_pointer(void);
 static inline void *RB_IMEMO_TMPBUF_PTR(VALUE v);
 static inline void *rb_imemo_tmpbuf_set_ptr(VALUE v, void *ptr);
-static inline VALUE rb_imemo_tmpbuf_auto_free_pointer_new_from_an_RString(VALUE str);
 static inline void MEMO_V1_SET(struct MEMO *m, VALUE v);
 static inline void MEMO_V2_SET(struct MEMO *m, VALUE v);
 
@@ -200,12 +199,6 @@ rb_vm_ifunc_proc_new(rb_block_call_func_t func, const void *data)
     return rb_vm_ifunc_new(func, data, 0, UNLIMITED_ARGUMENTS);
 }
 
-static inline VALUE
-rb_imemo_tmpbuf_auto_free_pointer(void)
-{
-    return rb_imemo_new(imemo_tmpbuf, 0, sizeof(rb_imemo_tmpbuf_t));
-}
-
 static inline void *
 RB_IMEMO_TMPBUF_PTR(VALUE v)
 {
@@ -220,7 +213,7 @@ rb_imemo_tmpbuf_set_ptr(VALUE v, void *ptr)
 }
 
 static inline VALUE
-rb_imemo_tmpbuf_auto_free_pointer_new_from_an_RString(VALUE str)
+rb_imemo_tmpbuf_new_from_an_RString(VALUE str)
 {
     const void *src;
     VALUE imemo;
@@ -230,7 +223,7 @@ rb_imemo_tmpbuf_auto_free_pointer_new_from_an_RString(VALUE str)
 
     StringValue(str);
     /* create tmpbuf to keep the pointer before xmalloc */
-    imemo = rb_imemo_tmpbuf_auto_free_pointer();
+    imemo = rb_imemo_tmpbuf_new();
     tmpbuf = (rb_imemo_tmpbuf_t *)imemo;
     len = RSTRING_LEN(str);
     src = RSTRING_PTR(str);
diff --git a/lib/optparse.rb b/lib/optparse.rb
index 06e33db1f533c4..ea6844b9558e5c 100644
--- a/lib/optparse.rb
+++ b/lib/optparse.rb
@@ -1855,7 +1855,7 @@ def permute(*argv, **keywords)
   #
   def permute!(argv = default_argv, **keywords)
     nonopts = []
-    order!(argv, **keywords, &nonopts.method(:<<))
+    order!(argv, **keywords) {|nonopt| nonopts << nonopt}
     argv[0, 0] = nonopts
     argv
   end
@@ -1908,13 +1908,16 @@ def getopts(*args, symbolize_names: false, **keywords)
     single_options, *long_options = *args
 
     result = {}
+    setter = (symbolize_names ?
+                ->(name, val) {result[name.to_sym] = val}
+              : ->(name, val) {result[name] = val})
 
     single_options.scan(/(.)(:)?/) do |opt, val|
       if val
-        result[opt] = nil
+        setter[opt, nil]
         define("-#{opt} VAL")
       else
-        result[opt] = false
+        setter[opt, false]
         define("-#{opt}")
       end
     end if single_options
@@ -1923,16 +1926,16 @@ def getopts(*args, symbolize_names: false, **keywords)
       arg, desc = arg.split(';', 2)
       opt, val = arg.split(':', 2)
       if val
-        result[opt] = val.empty? ? nil : val
+        setter[opt, (val unless val.empty?)]
         define("--#{opt}=#{result[opt] || "VAL"}", *[desc].compact)
       else
-        result[opt] = false
+        setter[opt, false]
         define("--#{opt}", *[desc].compact)
       end
     end
 
-    parse_in_order(argv, result.method(:[]=), **keywords)
-    symbolize_names ? result.transform_keys(&:to_sym) : result
+    parse_in_order(argv, setter, **keywords)
+    result
   end
 
   #
@@ -1982,7 +1985,7 @@ def complete(typ, opt, icase = false, *pat) # :nodoc:
       visit(:complete, typ, opt, icase, *pat) {|o, *sw| return sw}
     }
     exc = ambiguous ? AmbiguousOption : InvalidOption
-    raise exc.new(opt, additional: self.method(:additional_message).curry[typ])
+    raise exc.new(opt, additional: proc {|o| additional_message(typ, o)})
   end
   private :complete
 
@@ -2273,9 +2276,10 @@ def recover(argv)
       argv
     end
 
+    DIR = File.join(__dir__, '')
     def self.filter_backtrace(array)
       unless $DEBUG
-        array.delete_if(&%r"\A#{Regexp.quote(__FILE__)}:"o.method(:=~))
+        array.delete_if {|bt| bt.start_with?(DIR)}
       end
       array
     end
diff --git a/lib/prism/translation/ruby_parser.rb b/lib/prism/translation/ruby_parser.rb
index ac538a2e97ae43..2ca7da0bf2a5d5 100644
--- a/lib/prism/translation/ruby_parser.rb
+++ b/lib/prism/translation/ruby_parser.rb
@@ -152,7 +152,7 @@ def visit_assoc_splat_node(node)
         # ^^
         # ```
         def visit_back_reference_read_node(node)
-          s(node, :back_ref, node.name.name.delete_prefix("$").to_sym)
+          s(node, :back_ref, node.name.to_s.delete_prefix("$").to_sym)
         end
 
         # ```
diff --git a/numeric.c b/numeric.c
index 89cff8a730fc9c..de5b02aaf9eb41 100644
--- a/numeric.c
+++ b/numeric.c
@@ -6455,7 +6455,7 @@ Init_Numeric(void)
      *
      *	If the platform supports denormalized numbers,
      *	there are numbers between zero and Float::MIN.
-     *	0.0.next_float returns the smallest positive floating point number
+     *	+0.0.next_float+ returns the smallest positive floating point number
      *	including denormalized numbers.
      */
     rb_define_const(rb_cFloat, "MIN", DBL2NUM(DBL_MIN));
diff --git a/prism/prism.c b/prism/prism.c
index 06419d13789e45..2e202c37456ea5 100644
--- a/prism/prism.c
+++ b/prism/prism.c
@@ -18491,20 +18491,28 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, b
             return (pm_node_t *) node;
         }
         case PM_TOKEN_CHARACTER_LITERAL: {
-            parser_lex(parser);
-
-            pm_token_t opening = parser->previous;
-            opening.type = PM_TOKEN_STRING_BEGIN;
-            opening.end = opening.start + 1;
-
-            pm_token_t content = parser->previous;
-            content.type = PM_TOKEN_STRING_CONTENT;
-            content.start = content.start + 1;
-
             pm_token_t closing = not_provided(parser);
-            pm_node_t *node = (pm_node_t *) pm_string_node_create_current_string(parser, &opening, &content, &closing);
+            pm_node_t *node = (pm_node_t *) pm_string_node_create_current_string(
+                parser,
+                &(pm_token_t) {
+                    .type = PM_TOKEN_STRING_BEGIN,
+                    .start = parser->current.start,
+                    .end = parser->current.start + 1
+                },
+                &(pm_token_t) {
+                    .type = PM_TOKEN_STRING_CONTENT,
+                    .start = parser->current.start + 1,
+                    .end = parser->current.end
+                },
+                &closing
+            );
+
             pm_node_flag_set(node, parse_unescaped_encoding(parser));
 
+            // Skip past the character literal here, since now we have handled
+            // parser->explicit_encoding correctly.
+            parser_lex(parser);
+
             // Characters can be followed by strings in which case they are
             // automatically concatenated.
             if (match1(parser, PM_TOKEN_STRING_BEGIN)) {
diff --git a/process.c b/process.c
index da9ce74027ce3c..0fb727db8af9f8 100644
--- a/process.c
+++ b/process.c
@@ -2635,7 +2635,7 @@ rb_exec_fillarg(VALUE prog, int argc, VALUE *argv, VALUE env, VALUE opthash, VAL
         }
         rb_str_buf_cat(argv_str, (char *)&null, sizeof(null)); /* terminator for execve.  */
         eargp->invoke.cmd.argv_str =
-            rb_imemo_tmpbuf_auto_free_pointer_new_from_an_RString(argv_str);
+            rb_imemo_tmpbuf_new_from_an_RString(argv_str);
     }
     RB_GC_GUARD(execarg_obj);
 }
@@ -2726,7 +2726,7 @@ open_func(void *ptr)
 static void
 rb_execarg_allocate_dup2_tmpbuf(struct rb_execarg *eargp, long len)
 {
-    VALUE tmpbuf = rb_imemo_tmpbuf_auto_free_pointer();
+    VALUE tmpbuf = rb_imemo_tmpbuf_new();
     rb_imemo_tmpbuf_set_ptr(tmpbuf, ruby_xmalloc(run_exec_dup2_tmpbuf_size(len)));
     eargp->dup2_tmpbuf = tmpbuf;
 }
@@ -2830,7 +2830,7 @@ rb_execarg_parent_start1(VALUE execarg_obj)
         p = NULL;
         rb_str_buf_cat(envp_str, (char *)&p, sizeof(p));
         eargp->envp_str =
-            rb_imemo_tmpbuf_auto_free_pointer_new_from_an_RString(envp_str);
+            rb_imemo_tmpbuf_new_from_an_RString(envp_str);
         eargp->envp_buf = envp_buf;
 
         /*
diff --git a/string.c b/string.c
index 8d27248020cded..834641cfdbf0c1 100644
--- a/string.c
+++ b/string.c
@@ -10744,20 +10744,79 @@ rb_str_hex(VALUE str)
  *  call-seq:
  *    oct -> integer
  *
- *  Interprets the leading substring of +self+ as a string of octal digits
- *  (with an optional sign) and returns the corresponding number;
- *  returns zero if there is no such leading substring:
+ *  Interprets the leading substring of +self+ as octal, binary, decimal, or hexadecimal, possibly signed;
+ *  returns their value as an integer.
  *
- *    '123'.oct             # => 83
- *    '-377'.oct            # => -255
- *    '0377non-numeric'.oct # => 255
- *    'non-numeric'.oct     # => 0
+ *  In brief:
  *
- *  If +self+ starts with <tt>0</tt>, radix indicators are honored;
- *  see Kernel#Integer.
+ *    # Interpreted as octal.
+ *    '777'.oct   # => 511
+ *    '777x'.oct  # => 511
+ *    '0777'.oct  # => 511
+ *    '0o777'.oct # => 511
+ *    '-777'.oct  # => -511
+ *    # Not interpreted as octal.
+ *    '0b111'.oct # => 7     # Interpreted as binary.
+ *    '0d999'.oct # => 999   # Interpreted as decimal.
+ *    '0xfff'.oct # => 4095  # Interpreted as hexadecimal.
  *
- *  Related: String#hex.
+ *  The leading substring is interpreted as octal when it begins with:
  *
+ *  - One or more character  representing octal digits
+ *    (each in the range <tt>'0'..'7'</tt>);
+ *    the string to be interpreted ends at the first character that does not represent an octal digit:
+ *
+ *      '7'.oct      @ => 7
+ *      '11'.oct     # => 9
+ *      '777'.oct    # => 511
+ *      '0777'.oct   # => 511
+ *      '7778'.oct   # => 511
+ *      '777x'.oct   # => 511
+ *
+ *  - <tt>'0o'</tt>, followed by one or more octal digits:
+ *
+ *      '0o777'.oct  # => 511
+ *      '0o7778'.oct # => 511
+ *
+ *  The leading substring is _not_ interpreted as octal when it begins with:
+ *
+ *  - <tt>'0b'</tt>, followed by one or more characters representing binary digits
+ *    (each in the range <tt>'0'..'1'</tt>);
+ *    the string to be interpreted ends at the first character that does not represent a binary digit.
+ *    the string is interpreted as binary digits (base 2):
+ *
+ *      '0b111'.oct  # => 7
+ *      '0b1112'.oct # => 7
+ *
+ *  - <tt>'0d'</tt>, followed by one or more characters representing decimal digits
+ *    (each in the range <tt>'0'..'9'</tt>);
+ *    the string to be interpreted ends at the first character that does not represent a decimal digit.
+ *    the string is interpreted as decimal digits (base 10):
+ *
+ *      '0d999'.oct  # => 999
+ *      '0d999x'.oct # => 999
+ *
+ *  - <tt>'0x'</tt>, followed by one or more characters representing hexadecimal digits
+ *    (each in one of the ranges <tt>'0'..'9'</tt>, <tt>'a'..'f'</tt>, or <tt>'A'..'F'</tt>);
+ *    the string to be interpreted ends at the first character that does not represent a hexadecimal digit.
+ *    the string is interpreted as hexadecimal digits (base 16):
+ *
+ *      '0xfff'.oct  # => 4095
+ *      '0xfffg'.oct # => 4095
+ *
+ *  Any of the above may prefixed with <tt>'-'</tt>, which negates the interpreted value:
+ *
+ *    '-777'.oct   # => -511
+ *    '-0777'.oct  # => -511
+ *    '-0b111'.oct # => -7
+ *    '-0xfff'.oct # => -4095
+ *
+ *  For any substring not described above, returns zero:
+ *
+ *    'foo'.oct      # => 0
+ *    ''.oct         # => 0
+ *
+ *  Related: see {Converting to Non-String}[rdoc-ref:String@Converting+to+Non--5CString].
  */
 
 static VALUE
diff --git a/test/prism/fixtures/character_literal.txt b/test/prism/fixtures/character_literal.txt
new file mode 100644
index 00000000000000..920332123f13ac
--- /dev/null
+++ b/test/prism/fixtures/character_literal.txt
@@ -0,0 +1,2 @@
+# encoding: Windows-31J
+p ?\u3042""
diff --git a/test/prism/ruby/ruby_parser_test.rb b/test/prism/ruby/ruby_parser_test.rb
index bcaed7979150bc..b21ad81391ed1e 100644
--- a/test/prism/ruby/ruby_parser_test.rb
+++ b/test/prism/ruby/ruby_parser_test.rb
@@ -16,6 +16,7 @@
 module Prism
   class RubyParserTest < TestCase
     todos = [
+      "character_literal.txt",
       "encoding_euc_jp.txt",
       "regex_char_width.txt",
       "seattlerb/masgn_colon3.txt",
diff --git a/util.c b/util.c
index 3e8ae590a8d54e..4caa324849af31 100644
--- a/util.c
+++ b/util.c
@@ -529,7 +529,7 @@ ruby_strdup(const char *str)
 char *
 ruby_getcwd(void)
 {
-    VALUE guard = rb_imemo_tmpbuf_auto_free_pointer();
+    VALUE guard = rb_imemo_tmpbuf_new();
     int size = 200;
     char *buf = xmalloc(size);