5 files changed, 92 insertions, 0 deletions
diff --git a/lib/prism/polyfill/append_as_bytes.rb b/lib/prism/polyfill/append_as_bytes.rb
new file mode 100644
index 0000000000..24218bd171
--- /dev/null
+++ b/lib/prism/polyfill/append_as_bytes.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+# Polyfill for String#append_as_bytes, which didn't exist until Ruby 3.4.
+if !("".respond_to?(:append_as_bytes))
+  String.include(
+    Module.new {
+      def append_as_bytes(*args)
+        args.each do |arg|
+          arg = Integer === arg ? [arg].pack("C") : arg.b
+          self.<<(arg) # steep:ignore
+        end
+      end
+    }
+  )
+end
diff --git a/lib/prism/polyfill/byteindex.rb b/lib/prism/polyfill/byteindex.rb
new file mode 100644
index 0000000000..98c6089f14
--- /dev/null
+++ b/lib/prism/polyfill/byteindex.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+# Polyfill for String#byteindex, which didn't exist until Ruby 3.2.
+if !("".respond_to?(:byteindex))
+  String.include(
+    Module.new {
+      def byteindex(needle, offset = 0)
+        charindex = index(needle, offset)
+        slice(0...charindex).bytesize if charindex
+      end
+    }
+  )
+end
diff --git a/lib/prism/polyfill/scan_byte.rb b/lib/prism/polyfill/scan_byte.rb
new file mode 100644
index 0000000000..9276e509fc
--- /dev/null
+++ b/lib/prism/polyfill/scan_byte.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require "strscan"
+
+# Polyfill for StringScanner#scan_byte, which didn't exist until Ruby 3.4.
+if !(StringScanner.method_defined?(:scan_byte))
+  StringScanner.include(
+    Module.new {
+      def scan_byte # :nodoc:
+        get_byte&.b&.ord
+      end
+    }
+  )
+end
diff --git a/lib/prism/polyfill/unpack1.rb b/lib/prism/polyfill/unpack1.rb
new file mode 100644
index 0000000000..3fa9b5a0c5
--- /dev/null
+++ b/lib/prism/polyfill/unpack1.rb
@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+# Polyfill for String#unpack1 with the offset parameter. Not all Ruby engines
+# have Method#parameters implemented, so we check the arity instead if
+# necessary.
+if (unpack1 = String.instance_method(:unpack1)).respond_to?(:parameters) ? unpack1.parameters.none? { |_, name| name == :offset } : (unpack1.arity == 1)
+  String.prepend(
+    Module.new {
+      def unpack1(format, offset: 0) # :nodoc:
+        offset == 0 ? super(format) : self[offset..].unpack1(format) # steep:ignore
+      end
+    }
+  )
+end
diff --git a/lib/prism/polyfill/warn.rb b/lib/prism/polyfill/warn.rb
new file mode 100644
index 0000000000..76a4264623
--- /dev/null
+++ b/lib/prism/polyfill/warn.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+# Polyfill for Kernel#warn with the category parameter. Not all Ruby engines
+# have Method#parameters implemented, so we check the arity instead if
+# necessary.
+if (method = Kernel.instance_method(:warn)).respond_to?(:parameters) ? method.parameters.none? { |_, name| name == :category } : (method.arity == -1)
+  Kernel.prepend(
+    Module.new {
+      def warn(*msgs, uplevel: nil, category: nil) # :nodoc:
+        case uplevel
+        when nil
+          super(*msgs)
+        when Integer
+          super(*msgs, uplevel: uplevel + 1)
+        else
+          super(*msgs, uplevel: uplevel.to_int + 1)
+        end
+      end
+    }
+  )
+
+  Object.prepend(
+    Module.new {
+      def warn(*msgs, uplevel: nil, category: nil) # :nodoc:
+        case uplevel
+        when nil
+          super(*msgs)
+        when Integer
+          super(*msgs, uplevel: uplevel + 1)
+        else
+          super(*msgs, uplevel: uplevel.to_int + 1)
+        end
+      end
+    }
+  )
+end