Add splice method to Bytes (#6823)

## Description
Adds a splice method to bytes that lets you select start and end
indices, and returns the range of bytes, removing them from the original
bytes.

## Checklist

- [x] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [x] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [ ] If my change requires substantial documentation changes, I have
[requested support from the DevRel
team](https://github.com/FuelLabs/devrel-requests/issues/new/choose)
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [x] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

---------

Co-authored-by: K1-R1 <77465250+K1-R1@users.noreply.github.com>

Author: SwayStar123

sway-lib-std/src/bytes.sw

@@ -719,6 +719,103 @@ impl Bytes {
         // set capacity and length
         self.len = both_len;
     }
+
+    /// Removes and returns a range of elements from the `Bytes` (i.e. indices `[start, end)`),
+    /// then replaces that range with the contents of `replace_with`.
+    ///
+    /// # Arguments
+    ///
+    /// * `start`: [u64] - The starting index for the splice (inclusive).
+    /// * `end`: [u64] - The ending index for the splice (exclusive).
+    /// * `replace_with`: [Bytes] - The elements to insert in place of the removed range.
+    ///
+    /// # Returns
+    ///
+    /// * [Bytes] - A new `Bytes` containing all of the elements from `start` up to (but not including) `end`.
+    ///
+    /// # Reverts
+    ///
+    /// * When `start > end`.
+    /// * When `end > self.len`.
+    ///
+    /// # Examples
+    ///
+    /// ```sway
+    /// use std::bytes::Bytes;
+    ///
+    /// fn foo() {
+    ///     let mut bytes = Bytes::new();
+    ///     bytes.push(5u8);  // index 0
+    ///     bytes.push(7u8);  // index 1
+    ///     bytes.push(9u8);  // index 2
+    ///
+    ///     // Replace the middle item (index 1) with two new items
+    ///     let mut replacement = Bytes::new();
+    ///     replacement.push(42u8);
+    ///     replacement.push(100u8);
+    ///
+    ///     // Splice out range [1..2) => removes the single element 7u8,
+    ///     // then inserts [42, 100] there
+    ///     let spliced = bytes.splice(1, 2, replacement);
+    ///
+    ///     // `spliced` has the element [7u8]
+    ///     assert(spliced.len() == 1);
+    ///     assert(spliced.get(0).unwrap() == 7u8);
+    ///
+    ///     // `bytes` is now [5u8, 42u8, 100u8, 9u8]
+    ///     assert(bytes.len() == 4);
+    ///     assert(bytes.get(0).unwrap() == 5u8);
+    ///     assert(bytes.get(1).unwrap() == 42u8);
+    ///     assert(bytes.get(2).unwrap() == 100u8);
+    ///     assert(bytes.get(3).unwrap() == 9u8);
+    /// }
+    /// ```
+    pub fn splice(ref mut self, start: u64, end: u64, replace_with: Bytes) -> Bytes {
+        assert(start <= end);
+        assert(end <= self.len);
+
+        let splice_len = end - start;
+        let replace_len = replace_with.len();
+
+        // Build the Bytes to return
+        let mut spliced = Bytes::with_capacity(splice_len);
+        if splice_len > 0 {
+            let old_ptr = self.buf.ptr().add_uint_offset(start);
+            old_ptr.copy_bytes_to(spliced.buf.ptr(), splice_len);
+            spliced.len = splice_len;
+        }
+
+        // New self
+        let new_len = self.len - splice_len + replace_len;
+        let mut new_buf = Bytes::with_capacity(new_len);
+
+        // Move head
+        if start > 0 {
+            let old_ptr = self.buf.ptr();
+            old_ptr.copy_bytes_to(new_buf.buf.ptr(), start);
+        }
+
+        // Move middle
+        if replace_len > 0 {
+            replace_with
+                .buf
+                .ptr()
+                .copy_bytes_to(new_buf.buf.ptr().add_uint_offset(start), replace_len);
+        }
+
+        // Move tail
+        let tail_len = self.len - end;
+        if tail_len > 0 {
+            let old_tail = self.buf.ptr().add_uint_offset(end);
+            let new_tail = new_buf.buf.ptr().add_uint_offset(start + replace_len);
+            old_tail.copy_bytes_to(new_tail, tail_len);
+        }
+
+        self.buf = new_buf.buf;
+        self.len = new_len;
+
+        spliced
+    }
 }
 
 impl core::ops::Eq for Bytes {

test/src/in_language_tests/test_programs/bytes_inline_tests/src/main.sw

@@ -1,17 +1,10 @@
 library;
 
-use std::bytes::Bytes;
+pub mod utils;
+pub mod splice;
 
-fn setup() -> (Bytes, u8, u8, u8) {
-    let mut bytes = Bytes::new();
-    let a = 5u8;
-    let b = 7u8;
-    let c = 9u8;
-    bytes.push(a);
-    bytes.push(b);
-    bytes.push(c);
-    (bytes, a, b, c)
-}
+use utils::setup;
+use std::bytes::Bytes;
 
 #[test()]
 fn bytes_new() {

test/src/in_language_tests/test_programs/bytes_inline_tests/src/splice.sw

@@ -0,0 +1,208 @@
+library;
+
+use std::bytes::Bytes;
+use ::utils::setup;
+
+#[test()]
+fn bytes_splice() {
+    let (mut bytes, a, b, c) = setup();
+    bytes.push(11u8);
+    bytes.push(13u8);
+    // bytes = [5, 7, 9, 11, 13]
+
+    // Remove [1..4), replace with nothing
+    let spliced = bytes.splice(1, 4, Bytes::new());
+
+    // bytes => [5, 13]
+    assert(bytes.len() == 2);
+    assert(bytes.get(0).unwrap() == a);
+    assert(bytes.get(1).unwrap() == 13u8);
+
+    // spliced => [7, 9, 11]
+    assert(spliced.len() == 3);
+    assert(spliced.get(0).unwrap() == b);
+    assert(spliced.get(1).unwrap() == c);
+    assert(spliced.get(2).unwrap() == 11u8);
+}
+
+#[test()]
+fn bytes_splice_front() {
+    let (mut bytes, a, b, c) = setup();
+    // Remove [0..2) => [5, 7], replace with nothing
+    let spliced = bytes.splice(0, 2, Bytes::new());
+
+    // bytes => [9]
+    assert(bytes.len() == 1);
+    assert(bytes.get(0).unwrap() == c);
+
+    // spliced => [5, 7]
+    assert(spliced.len() == 2);
+    assert(spliced.get(0).unwrap() == a);
+    assert(spliced.get(1).unwrap() == b);
+}
+
+#[test()]
+fn bytes_splice_end() {
+    let (mut bytes, a, b, c) = setup();
+    // Remove [1..3) => [7, 9], replace with nothing
+    let spliced = bytes.splice(1, bytes.len(), Bytes::new());
+
+    // bytes => [5]
+    assert(bytes.len() == 1);
+    assert(bytes.get(0).unwrap() == a);
+
+    // spliced => [7, 9]
+    assert(spliced.len() == 2);
+    assert(spliced.get(0).unwrap() == b);
+    assert(spliced.get(1).unwrap() == c);
+}
+
+#[test()]
+fn bytes_splice_empty_range() {
+    let (mut bytes, a, b, c) = setup();
+    // Remove [1..1) => nothing, replace with nothing
+    let spliced = bytes.splice(1, 1, Bytes::new());
+
+    assert(bytes.len() == 3);
+    assert(bytes.get(0).unwrap() == a);
+    assert(bytes.get(1).unwrap() == b);
+    assert(bytes.get(2).unwrap() == c);
+    assert(spliced.len() == 0);
+}
+
+#[test()]
+fn bytes_splice_entire_range() {
+    let (mut bytes, a, b, c) = setup();
+    // Remove [0..3) => [5, 7, 9], replace with nothing
+    let spliced = bytes.splice(0, bytes.len(), Bytes::new());
+
+    assert(bytes.len() == 0);
+    assert(bytes.is_empty());
+    assert(spliced.len() == 3);
+    assert(spliced.get(0).unwrap() == a);
+    assert(spliced.get(1).unwrap() == b);
+    assert(spliced.get(2).unwrap() == c);
+}
+
+#[test(should_revert)]
+fn revert_bytes_splice_start_greater_than_end() {
+    let (mut bytes, _, _, _) = setup();
+    let _spliced = bytes.splice(2, 1, Bytes::new());
+}
+
+#[test(should_revert)]
+fn revert_bytes_splice_end_out_of_bounds() {
+    let (mut bytes, _, _, _) = setup();
+    let _spliced = bytes.splice(0, bytes.len() + 1, Bytes::new());
+}
+
+/// Additional tests for replacing a spliced range with different Byte lengths.
+#[test()]
+fn bytes_splice_replace_smaller() {
+    let (mut bytes, a, b, c) = setup();
+    bytes.push(11u8);
+    bytes.push(13u8);
+    // bytes = [5, 7, 9, 11, 13]
+    let mut replacement = Bytes::new();
+    replacement.push(42u8);
+    // Remove [1..4) => [7, 9, 11], replace with [42]
+    let spliced = bytes.splice(1, 4, replacement);
+
+    // bytes => [5, 42, 13]
+    assert(bytes.len() == 3);
+    assert(bytes.get(0).unwrap() == a);
+    assert(bytes.get(1).unwrap() == 42u8);
+    assert(bytes.get(2).unwrap() == 13u8);
+
+    // spliced => [7, 9, 11]
+    assert(spliced.len() == 3);
+    assert(spliced.get(0).unwrap() == b);
+    assert(spliced.get(1).unwrap() == c);
+    assert(spliced.get(2).unwrap() == 11u8);
+}
+
+#[test()]
+fn bytes_splice_replace_larger() {
+    let (mut bytes, a, b, c) = setup();
+    // bytes = [5, 7, 9]
+    let mut replacement = Bytes::new();
+    replacement.push(42u8);
+    replacement.push(50u8);
+    replacement.push(60u8);
+    // Remove [1..2) => [7], replace with [42, 50, 60]
+    let spliced = bytes.splice(1, 2, replacement);
+
+    // bytes => [5, 42, 50, 60, 9]
+    assert(bytes.len() == 5);
+    assert(bytes.get(0).unwrap() == a);
+    assert(bytes.get(1).unwrap() == 42u8);
+    assert(bytes.get(2).unwrap() == 50u8);
+    assert(bytes.get(3).unwrap() == 60u8);
+    assert(bytes.get(4).unwrap() == c);
+
+    // spliced => [7]
+    assert(spliced.len() == 1);
+    assert(spliced.get(0).unwrap() == b);
+}
+
+#[test()]
+fn bytes_splice_replace_same_length() {
+    let (mut bytes, a, b, c) = setup();
+    // bytes = [5, 7, 9]
+    let mut replacement = Bytes::new();
+    replacement.push(42u8);
+    replacement.push(50u8);
+    // Remove [1..3) => [7, 9], replace with [42, 50] (same length = 2)
+    let spliced = bytes.splice(1, 3, replacement);
+
+    // bytes => [5, 42, 50]
+    assert(bytes.len() == 3);
+    assert(bytes.get(0).unwrap() == a);
+    assert(bytes.get(1).unwrap() == 42u8);
+    assert(bytes.get(2).unwrap() == 50u8);
+
+    // spliced => [7, 9]
+    assert(spliced.len() == 2);
+    assert(spliced.get(0).unwrap() == b);
+    assert(spliced.get(1).unwrap() == c);
+}
+
+#[test()]
+fn bytes_splice_replace_empty_bytes() {
+    let (mut bytes, a, b, c) = setup();
+    // bytes = [5, 7, 9]
+    let replacement = Bytes::new();
+    // Remove [0..1) => [5], replace with []
+    let spliced = bytes.splice(0, 1, replacement);
+
+    // bytes => [7, 9]
+    assert(bytes.len() == 2);
+    assert(bytes.get(0).unwrap() == b);
+    assert(bytes.get(1).unwrap() == c);
+
+    // spliced => [5]
+    assert(spliced.len() == 1);
+    assert(spliced.get(0).unwrap() == a);
+}
+
+#[test()]
+fn bytes_splice_replace_overlap() {
+    let (mut bytes, a, b, c) = setup();
+    // bytes = [5, 7, 9]
+    let mut replacement = Bytes::new();
+    replacement.push(10u8);
+    replacement.push(12u8);
+    // Remove [0..1) => [5], replace with [10, 12]
+    let spliced = bytes.splice(0, 1, replacement);
+
+    // Expect spliced to contain the removed element [5]
+    assert(spliced.len() == 1);
+    assert(spliced.get(0).unwrap() == a);
+
+    // After replacement, bytes should now be [10, 12, 7, 9]
+    assert(bytes.len() == 4);
+    assert(bytes.get(0).unwrap() == 10u8);
+    assert(bytes.get(1).unwrap() == 12u8);
+    assert(bytes.get(2).unwrap() == b);
+    assert(bytes.get(3).unwrap() == c);
+}

test/src/in_language_tests/test_programs/bytes_inline_tests/src/utils.sw

@@ -0,0 +1,14 @@
+library;
+
+use std::bytes::Bytes;
+
+pub fn setup() -> (Bytes, u8, u8, u8) {
+    let mut bytes = Bytes::new();
+    let a = 5u8;
+    let b = 7u8;
+    let c = 9u8;
+    bytes.push(a);
+    bytes.push(b);
+    bytes.push(c);
+    (bytes, a, b, c)
+}