From e5825de7c9f07e4f7bd2b83ce8973e19a4652916 Mon Sep 17 00:00:00 2001
From: alexandre184 <110398901+alexandre184@users.noreply.github.com>
Date: Sat, 15 Jul 2023 09:36:53 +0200
Subject: [PATCH] [Bug #19769] Fix range of size 1 in `String#tr`

---
 spec/ruby/core/string/tr_s_spec.rb | 9 +++++++++
 spec/ruby/core/string/tr_spec.rb   | 9 +++++++++
 string.c                           | 6 ++++--
 test/ruby/test_string.rb           | 8 ++++++++
 4 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/spec/ruby/core/string/tr_s_spec.rb b/spec/ruby/core/string/tr_s_spec.rb
index b5c87d4e4e..3c31473044 100644
--- a/spec/ruby/core/string/tr_s_spec.rb
+++ b/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
diff --git a/spec/ruby/core/string/tr_spec.rb b/spec/ruby/core/string/tr_spec.rb
index cf485d32a3..d60480dc7e 100644
--- a/spec/ruby/core/string/tr_spec.rb
+++ b/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..."
diff --git a/string.c b/string.c
index af0668e4b2..9cc4dfd3ce 100644
--- a/string.c
+++ b/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;
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index 06df67de38..6cc958332f 100644
--- a/test/ruby/test_string.rb
+++ b/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