[Bug #19769] Fix range of size 1 in `String#tr`

spec/ruby/core/string/tr_s_spec.rb

@@ -17,6 +17,15 @@ describe "String#tr_s" do
     "hello ^--^".tr_s("---", "_").should == "hello ^_^"
   end
 
+  ruby_bug "#19769", ""..."3.3" do
+    it "accepts c1-c1 notation to denote range of one character" do
+      "hello".tr_s('e-e', 'x').should == "hxllo"
+      "123456789".tr_s("2-23","xy").should == "1xy456789"
+      "hello ^-^".tr_s("e-", "a-a_").should == "hallo ^_^"
+      "hello ^-^".tr_s("---o", "_a").should == "hella ^_^"
+    end
+  end
+
   it "pads to_str with its last char if it is shorter than from_string" do
     "this".tr_s("this", "x").should == "x"
   end

spec/ruby/core/string/tr_spec.rb

@@ -16,6 +16,15 @@ describe "String#tr" do
     "hello ^-^".tr("---", "_").should == "hello ^_^"
   end
 
+  ruby_bug "#19769", ""..."3.3" do
+    it "accepts c1-c1 notation to denote range of one character" do
+      "hello".tr('e-e', 'x').should == "hxllo"
+      "123456789".tr("2-23","xy").should == "1xy456789"
+      "hello ^-^".tr("e-", "a-a_").should == "hallo ^_^"
+      "hello ^-^".tr("---o", "_a").should == "hella ^_^"
+    end
+  end
+
   it "pads to_str with its last char if it is shorter than from_string" do
     "this".tr("this", "x").should == "xxxx"
     "hello".tr("a-z", "A-H.").should == "HE..."

string.c

@@ -7714,8 +7714,10 @@ trnext(struct tr *t, rb_encoding *enc)
                         }
                         continue; /* not reached */
                     }
-                    t->gen = 1;
-                    t->max = c;
+                    else if (t->now < c) {
+                        t->gen = 1;
+                        t->max = c;
+                    }
                 }
             }
             return t->now;

test/ruby/test_string.rb

@@ -2301,6 +2301,8 @@ CODE
     assert_not_predicate(str, :ascii_only?)
     assert_not_predicate(star, :ascii_only?)
     assert_not_predicate(result, :ascii_only?, bug13950)
+
+    assert_equal(S("XYC"), S("ABC").tr("A-AB", "XY"))
   end
 
   def test_tr!
@@ -2325,6 +2327,8 @@ CODE
     a = S("abc".force_encoding(Encoding::US_ASCII))
     assert_nil(a.tr!(S("z"), S("\u0101")), '[ruby-core:22326]')
     assert_equal(Encoding::US_ASCII, a.encoding, '[ruby-core:22326]')
+
+    assert_equal(S("XYC"), S("ABC").tr!("A-AB", "XY"))
   end
 
   def test_tr_s
@@ -2332,6 +2336,8 @@ CODE
     assert_equal(S("h*o"),  S("hello").tr_s(S("el"), S("*")))
     assert_equal("a".hash, S("\u0101\u0101").tr_s("\u0101", "a").hash)
     assert_equal(true, S("\u3041\u3041").tr("\u3041", "a").ascii_only?)
+
+    assert_equal(S("XYC"), S("ABC").tr_s("A-AB", "XY"))
   end
 
   def test_tr_s!
@@ -2344,6 +2350,8 @@ CODE
     a = S("hello")
     assert_equal(S("h*o"), a.tr_s!(S("el"), S("*")))
     assert_equal(S("h*o"), a)
+
+    assert_equal(S("XYC"), S("ABC").tr_s!("A-AB", "XY"))
   end
 
   def test_unpack