add Int::(unsafe)_to_char

builtin/builtin.mbti

@@ -412,6 +412,7 @@ impl Int {
   #deprecated
   shr(Int, Int) -> Int
   to_byte(Int) -> Byte
+  to_char(Int) -> Char?
   to_double(Int) -> Double
   to_float(Int) -> Float
   to_int16(Int) -> Int16
@@ -421,6 +422,7 @@ impl Int {
   to_uint(Int) -> UInt
   to_uint16(Int) -> UInt16
   to_uint64(Int) -> UInt64
+  unsafe_to_char(Int) -> Char
   until(Int, Int, step~ : Int = .., inclusive~ : Bool = ..) -> Iter[Int]
   #deprecated
   upto(Int, Int, inclusive~ : Bool = ..) -> Iter[Int]

builtin/intrinsics.mbt

@@ -1471,6 +1471,18 @@ pub fn Bytes::new(len : Int) -> Bytes {
 /// ```
 pub fn Int::to_byte(self : Int) -> Byte = "%i32_to_byte"
 
+///|
+pub fn Int::unsafe_to_char(self : Int) -> Char = "%char_from_int"
+
+///|
+pub fn Int::to_char(self : Int) -> Char? {
+  if self is (0..=0xD7FF) || self is (0xE000..=0x10FFFF) {
+    Some(self.unsafe_to_char())
+  } else {
+    None
+  }
+}
+
 ///|
 /// Converts an unsigned 64-bit integer to a byte by truncating it to fit within
 /// the byte range (0 to 255).

builtin/intrinsics_test.mbt

@@ -465,3 +465,50 @@ test "convert byte to int64" {
   let result = b.to_int64()
   inspect!(result, content="255")
 }
+
+///|
+test "Int::to_char" {
+  inspect!(Int::to_char(97), content="Some('a')")
+  inspect!(Int::to_char(65), content="Some('A')")
+  inspect!(Int::to_char(49), content="Some('1')")
+  inspect!(Int::to_char(33), content="Some('!')")
+}
+
+///|
+test "Int::to_char - Invalid values" {
+  inspect!(Int::to_char(-1), content="None")
+  inspect!(Int::to_char(1114112), content="None")
+  inspect!(Int::to_char(1114113), content="None")
+}
+
+///|
+test "Int::to_char - Valid values" {
+  inspect!(Int::to_char(0), content="Some('\\x00')")
+  inspect!(Int::to_char(127), content="Some('')")
+  inspect!(Int::to_char(128), content="Some('€')")
+  inspect!(Int::to_char(0x7F), content="Some('')")
+  inspect!(Int::to_char(0x80), content="Some('€')")
+  inspect!(Int::to_char(0xFF), content="Some('ÿ')")
+  inspect!(Int::to_char(0x100), content="Some('Ā')")
+  inspect!(Int::to_char(0xFFFF), content="Some('￿')")
+  inspect!(Int::to_char(0x10000), content="Some('𐀀')")
+  inspect!(Int::to_char(0x10FFFF), content="Some('􏿿')")
+}
+
+///|
+test "Int::to_char - Invalid values" {
+  inspect!(Int::to_char(-1), content="None")
+  inspect!(Int::to_char(0x10FFFF + 1), content="None")
+  inspect!(Int::to_char(0xD800), content="None")
+  inspect!(Int::to_char(0xDFFF), content="None")
+  inspect!(Int::to_char(0xD900), content="None")
+  inspect!(Int::to_char(0xDF00), content="None")
+}
+
+///|
+test "Int::to_char - Boundary cases" {
+  inspect!(Int::to_char(0xD7FF), content="Some('퟿')")
+  inspect!(Int::to_char(0xE000), content="Some('')")
+  inspect!(Int::to_char(0x10FFFF), content="Some('􏿿')")
+  inspect!(Int::to_char(0x10FFFF + 1), content="None")
+}

builtin/iter_test.mbt

@@ -231,7 +231,7 @@ test "map" {
   let iter = test_from_array(['1', '2', '3', '4', '5'])
   let exb = StringBuilder::new(size_hint=0)
   iter
-  .map(fn { x => Char::from_int(x.to_int() + 1) })
+  .map(fn { x => (x.to_int() + 1).to_char().unwrap() })
   .each(fn { x => exb.write_char(x) })
   inspect!(exb, content="23456")
 }