[ruby/strscan] Deprecate undocumented toplevel constant ScanError

ruby/strscan@b4ddc3a2a6

Author: nobu

ext/strscan/extconf.rb

@@ -4,6 +4,7 @@
   $INCFLAGS << " -I$(top_srcdir)" if $extmk
   have_func("onig_region_memsize(NULL)")
   have_func("rb_reg_onig_match", "ruby/re.h")
+  have_func("rb_deprecate_constant")
   create_makefile 'strscan'
 else
   File.write('Makefile', dummy_makefile("").join)

ext/strscan/strscan.c

@@ -24,6 +24,14 @@ extern size_t onig_region_memsize(const struct re_registers *regs);
 
 #define STRSCAN_VERSION "3.1.6.dev"
 
+
+#ifdef HAVE_RB_DEPRECATE_CONSTANT
+/* In ruby 3.0, defined but exposed in external headers */
+extern void rb_deprecate_constant(VALUE mod, const char *name);
+#else
+# define rb_deprecate_constant(mod, name) ((void)0)
+#endif
+
 /* =======================================================================
                          Data Type Definitions
    ======================================================================= */
@@ -1604,7 +1612,7 @@ name_to_backref_number(struct re_registers *regs, VALUE regexp, const char* name
                                               (const unsigned char* )name_end,
                                               regs);
         if (num >= 1) {
-	        return num;
+	    return num;
         }
     }
     rb_enc_raise(enc, rb_eIndexError, "undefined group name reference: %.*s",
@@ -2210,6 +2218,7 @@ Init_strscan(void)
     ScanError = rb_define_class_under(StringScanner, "Error", rb_eStandardError);
     if (!rb_const_defined(rb_cObject, id_scanerr)) {
 	rb_const_set(rb_cObject, id_scanerr, ScanError);
+	rb_deprecate_constant(rb_cObject, "ScanError");
     }
     tmp = rb_str_new2(STRSCAN_VERSION);
     rb_obj_freeze(tmp);

test/strscan/test_stringscanner.rb

@@ -875,7 +875,7 @@ def test_unscan
     assert_equal({}, s.named_captures)
     assert_equal("te", s.scan(/../))
     assert_equal(nil, s.scan(/\d/))
-    assert_raise(ScanError) { s.unscan }
+    assert_raise(StringScanner::Error) { s.unscan }
   end
 
   def test_rest