Add a hint of `ASCII-8BIT` being `BINARY`

[Feature #18576]

Since outright renaming `ASCII-8BIT` is deemed to backward incompatible,
the next best thing would be to only change its `#inspect`, particularly
in exception messages.

encoding.c

@@ -1015,13 +1015,22 @@ rb_enc_get(VALUE obj)
     return rb_enc_from_index(rb_enc_get_index(obj));
 }
 
+const char *
+rb_enc_inspect_name(rb_encoding *enc)
+{
+    if (enc == global_enc_ascii) {
+        return "BINARY (ASCII-8BIT)";
+    }
+    return enc->name;
+}
+
 static rb_encoding*
 rb_encoding_check(rb_encoding* enc, VALUE str1, VALUE str2)
 {
     if (!enc)
         rb_raise(rb_eEncCompatError, "incompatible character encodings: %s and %s",
-                 rb_enc_name(rb_enc_get(str1)),
-                 rb_enc_name(rb_enc_get(str2)));
+                 rb_enc_inspect_name(rb_enc_get(str1)),
+                 rb_enc_inspect_name(rb_enc_get(str2)));
     return enc;
 }
 
@@ -1263,9 +1272,10 @@ enc_inspect(VALUE self)
     if (!(enc = DATA_PTR(self)) || rb_enc_from_index(rb_enc_to_index(enc)) != enc) {
         rb_raise(rb_eTypeError, "broken Encoding");
     }
+
     return rb_enc_sprintf(rb_usascii_encoding(),
                           "#<%"PRIsVALUE":%s%s%s>", rb_obj_class(self),
-                          rb_enc_name(enc),
+                          rb_enc_inspect_name(enc),
                           (ENC_DUMMY_P(enc) ? " (dummy)" : ""),
                           rb_enc_autoload_p(enc) ? " (autoload)" : "");
 }

internal/encoding.h

@@ -18,6 +18,7 @@
 
 /* encoding.c */
 ID rb_id_encoding(void);
+const char * rb_enc_inspect_name(rb_encoding *enc);
 rb_encoding *rb_enc_get_from_index(int index);
 rb_encoding *rb_enc_check_str(VALUE str1, VALUE str2);
 int rb_encdb_replicate(const char *alias, const char *orig);

re.c

@@ -1530,8 +1530,8 @@ reg_enc_error(VALUE re, VALUE str)
 {
     rb_raise(rb_eEncCompatError,
              "incompatible encoding regexp match (%s regexp with %s string)",
-             rb_enc_name(rb_enc_get(re)),
-             rb_enc_name(rb_enc_get(str)));
+             rb_enc_inspect_name(rb_enc_get(re)),
+             rb_enc_inspect_name(rb_enc_get(str)));
 }
 
 static inline int

spec/ruby/core/encoding/inspect_spec.rb

@@ -5,9 +5,23 @@ describe "Encoding#inspect" do
     Encoding::UTF_8.inspect.should be_an_instance_of(String)
   end
 
-  it "returns #<Encoding:name> for a non-dummy encoding named 'name'" do
-    Encoding.list.to_a.reject {|e| e.dummy? }.each do |enc|
-      enc.inspect.should =~ /#<Encoding:#{enc.name}>/
+  ruby_version_is ""..."3.4" do
+    it "returns #<Encoding:name> for a non-dummy encoding named 'name'" do
+      Encoding.list.to_a.reject {|e| e.dummy? }.each do |enc|
+        enc.inspect.should =~ /#<Encoding:#{enc.name}>/
+      end
+    end
+  end
+
+  ruby_version_is "3.4" do
+    it "returns #<Encoding:name> for a non-dummy encoding named 'name'" do
+      Encoding.list.to_a.reject {|e| e.dummy? }.each do |enc|
+        if enc.name == "ASCII-8BIT"
+          enc.inspect.should == "#<Encoding:BINARY (ASCII-8BIT)>"
+        else
+          enc.inspect.should =~ /#<Encoding:#{enc.name}>/
+        end
+      end
     end
   end
 

string.c

@@ -3374,7 +3374,7 @@ rb_enc_cr_str_buf_cat(VALUE str, const char *ptr, long len,
 
   incompatible:
     rb_raise(rb_eEncCompatError, "incompatible character encodings: %s and %s",
-             rb_enc_name(str_enc), rb_enc_name(ptr_enc));
+             rb_enc_inspect_name(str_enc), rb_enc_inspect_name(ptr_enc));
     UNREACHABLE_RETURN(Qundef);
 }
 
@@ -5854,8 +5854,8 @@ rb_str_sub_bang(int argc, VALUE *argv, VALUE str)
             if (coderange_scan(p, beg0, str_enc) != ENC_CODERANGE_7BIT ||
                 coderange_scan(p+end0, len-end0, str_enc) != ENC_CODERANGE_7BIT) {
                 rb_raise(rb_eEncCompatError, "incompatible character encodings: %s and %s",
-                         rb_enc_name(str_enc),
-                         rb_enc_name(STR_ENC_GET(repl)));
+                         rb_enc_inspect_name(str_enc),
+                         rb_enc_inspect_name(STR_ENC_GET(repl)));
             }
             enc = STR_ENC_GET(repl);
         }
@@ -11120,7 +11120,7 @@ str_compat_and_valid(VALUE str, rb_encoding *enc)
         rb_encoding *e = STR_ENC_GET(str);
         if (cr == ENC_CODERANGE_7BIT ? rb_enc_mbminlen(enc) != 1 : enc != e) {
             rb_raise(rb_eEncCompatError, "incompatible character encodings: %s and %s",
-                     rb_enc_name(enc), rb_enc_name(e));
+                     rb_enc_inspect_name(enc), rb_enc_inspect_name(e));
         }
     }
     return str;

test/ruby/test_m17n.rb

@@ -1091,7 +1091,7 @@ class TestM17N < Test::Unit::TestCase
     assert_nil(e("\xa1\xa2\xa3\xa4").rindex(e("\xa3")))
     s = e("\xa3\xb0\xa3\xb1\xa3\xb2\xa3\xb3\xa3\xb4")
 
-    a_with_e = /EUC-JP and ASCII-8BIT/
+    a_with_e = /EUC-JP and BINARY \(ASCII-8BIT\)/
     assert_raise_with_message(Encoding::CompatibilityError, a_with_e) do
       s.index(a("\xb1\xa3"))
     end
@@ -1099,7 +1099,7 @@ class TestM17N < Test::Unit::TestCase
       s.rindex(a("\xb1\xa3"))
     end
 
-    a_with_e = /ASCII-8BIT regexp with EUC-JP string/
+    a_with_e = /BINARY \(ASCII-8BIT\) regexp with EUC-JP string/
     assert_raise_with_message(Encoding::CompatibilityError, a_with_e) do
       s.index(Regexp.new(a("\xb1\xa3")))
     end

test/ruby/test_yjit.rb

@@ -1458,7 +1458,7 @@ class TestYJIT < Test::Unit::TestCase
   end
 
   def test_str_concat_encoding_mismatch
-    assert_compiles(<<~'RUBY', result: "incompatible character encodings: ASCII-8BIT and EUC-JP")
+    assert_compiles(<<~'RUBY', result: "incompatible character encodings: BINARY (ASCII-8BIT) and EUC-JP")
       def bar(a, b)
         a << b
       rescue => e