Handle invalid indexes in ByteArray.copy_from

ByteArray.copy_from didn't check if the `at` argument was out of bounds
or not, resulting in a Rust/runtime panic when using such an index.

Changelog: fixed

Author: yorickpeterse

std/src/std/byte_array.inko

@@ -451,6 +451,10 @@ type builtin ByteArray {
   # The return value is the number of bytes copied. This value may be less than
   # `size` if there are fewer bytes in `bytes`.
   #
+  # # Panics
+  #
+  # This method panics if `at` is out of bounds.
+  #
   # # Examples
   #
   # ```inko
@@ -462,6 +466,7 @@ type builtin ByteArray {
   # b # => ByteArray.from_array([1, 2])
   # ```
   fn pub mut copy_from(bytes: ref ByteArray, at: Int, size: Int) -> Int {
+    bounds_check(at, bytes.size)
     inko_byte_array_copy_from(self, bytes.to_pointer, bytes.size, at, size)
   }
 

std/test/std/test_byte_array.inko

@@ -349,13 +349,31 @@ fn pub tests(t: mut Tests) {
   t.test('ByteArray.copy_from', fn (t) {
     let a = ByteArray.from_array([1, 2, 3, 4])
     let b = ByteArray.new
+    let c = ByteArray.new
 
     t.equal(b.copy_from(a, at: 0, size: 2), 2)
     t.equal(a, ByteArray.from_array([1, 2, 3, 4]))
     t.equal(b, ByteArray.from_array([1, 2]))
 
     t.equal(b.copy_from(b, at: 0, size: 2), 2)
     t.equal(b, ByteArray.from_array([1, 2, 1, 2]))
+
+    t.equal(c.copy_from(a, at: 3, size: 1), 1)
+    t.equal(c, ByteArray.from_array([4]))
+  })
+
+  t.panic('ByteArray.copy_from with an index that is too great', fn {
+    let a = ByteArray.from_array([1, 2, 3, 4])
+    let b = ByteArray.new
+
+    b.copy_from(a, at: 10, size: 2)
+  })
+
+  t.panic('ByteArray.copy_from with an index that is too small', fn {
+    let a = ByteArray.from_array([1, 2, 3, 4])
+    let b = ByteArray.new
+
+    b.copy_from(a, at: -3, size: 2)
   })
 
   t.test('ByteArray.resize', fn (t) {