[Bug #18955] format single character for %c

Merged: https://github.com/ruby/ruby/pull/6258

spec/ruby/core/kernel/shared/sprintf.rb

@@ -289,6 +289,7 @@ describe :kernel_sprintf, shared: true do
         @method.call("%c", "a").should == "a"
       end
 
+      ruby_version_is ""..."3.2" do
         it "raises ArgumentError if argument is a string of several characters" do
           -> {
             @method.call("%c", "abc")
@@ -300,6 +301,17 @@ describe :kernel_sprintf, shared: true do
             @method.call("%c", "")
           }.should raise_error(ArgumentError)
         end
+      end
+
+      ruby_version_is "3.2" do
+        it "displays only the first character if argument is a string of several characters" do
+          @method.call("%c", "abc").should == "a"
+        end
+
+        it "displays no characters if argument is an empty string" do
+          @method.call("%c", "").should == ""
+        end
+      end
 
       it "supports Unicode characters" do
         @method.call("%c", 1286).should == "Ԇ"

spec/ruby/core/string/modulo_spec.rb

@@ -368,9 +368,17 @@ describe "String#%" do
     ("%c" % 'A').should == "A"
   end
 
+  ruby_version_is ""..."3.2" do
     it "raises an exception for multiple character strings as argument for %c" do
       -> { "%c" % 'AA' }.should raise_error(ArgumentError)
     end
+  end
+
+  ruby_version_is "3.2" do
+    it "supports only the first character as argument for %c" do
+      ("%c" % 'AA').should == "A"
+    end
+  end
 
   it "calls to_str on argument for %c formats" do
     obj = mock('A')

sprintf.c

@@ -441,12 +441,10 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
 
                 tmp = rb_check_string_type(val);
                 if (!NIL_P(tmp)) {
-                    rb_encoding *valenc = rb_enc_get(tmp);
-                    if (rb_enc_strlen(RSTRING_PTR(tmp), RSTRING_END(tmp), valenc) != 1) {
-                        rb_raise(rb_eArgError, "%%c requires a character");
-                    }
-                    c = rb_enc_codepoint_len(RSTRING_PTR(tmp), RSTRING_END(tmp), &n, valenc);
-                    RB_GC_GUARD(tmp);
+                    flags |= FPREC;
+                    prec = 1;
+                    str = tmp;
+                    goto format_s1;
                 }
                 else {
                     c = NUM2INT(val);
@@ -488,6 +486,7 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
                 else {
                     str = rb_obj_as_string(arg);
                 }
+              format_s1:
                 len = RSTRING_LEN(str);
                 rb_str_set_len(result, blen);
                 if (coderange != ENC_CODERANGE_BROKEN && scanned < blen) {

test/ruby/test_m17n.rb

@@ -893,7 +893,7 @@ class TestM17N < Test::Unit::TestCase
       "%s%s" % [s("\xc2\xa1"), e("\xc2\xa1")]
     }
 
-    "%c" % "\u3042".encode('Windows-31J')
+    assert_equal("\u3042".encode('Windows-31J'), "%c" % "\u3042\u3044".encode('Windows-31J'))
   end
 
   def test_sprintf_p

test/ruby/test_sprintf.rb

@@ -362,7 +362,8 @@ class TestSprintf < Test::Unit::TestCase
   def test_char
     assert_equal("a", sprintf("%c", 97))
     assert_equal("a", sprintf("%c", ?a))
-    assert_raise(ArgumentError) { sprintf("%c", sprintf("%c%c", ?a, ?a)) }
+    assert_equal("a", sprintf("%c", "a"))
+    assert_equal("a", sprintf("%c", sprintf("%c%c", ?a, ?a)))
     assert_equal(" " * (BSIZ - 1) + "a", sprintf(" " * (BSIZ - 1) + "%c", ?a))
     assert_equal(" " * (BSIZ - 1) + "a", sprintf(" " * (BSIZ - 1) + "%-1c", ?a))
     assert_equal(" " * BSIZ + "a", sprintf("%#{ BSIZ + 1 }c", ?a))