feat: adds set_len to boundedVec

docs/docs/noir/standard_library/containers/boundedvec.md

@@ -186,6 +186,19 @@ Example:
 
 #include_code bounded-vec-max-len-example test_programs/noir_test_success/bounded_vec/src/main.nr rust
 
+### set_len
+
+```rust
+pub fn set_len(&mut self, len: u32) {
+```
+
+Sets the length of the BoundedVec manually. This is useful to update the length after
+updating the content of the vector using `set_unchecked`.
+
+Example:
+
+#include_code bounded-vec-set-len-example test_programs/noir_test_success/bounded_vec/src/main.nr rust
+
 ### storage
 
 ```rust

noir_stdlib/src/collections/bounded_vec.nr

@@ -213,6 +213,26 @@ impl<T, let MaxLen: u32> BoundedVec<T, MaxLen> {
         self.len
     }
 
+    /// Allows user to update the length of the vector once
+    /// after doing multiple pushes.
+    /// Example:
+    ///
+    /// ```noir
+    /// let mut v: BoundedVec<Field, 10> = BoundedVec::from([1, 2, 3, 4, 5]);
+    ///
+    /// assert(v.len() == 5);
+    /// v.set_unchecked(5, 6);
+    /// v.set_unchecked(6, 7);
+    /// v.set_unchecked(7, 8);
+    /// v.set_len(8);
+    /// assert(v.len() == 8);
+    /// ```
+    pub fn set_len(&mut self, len: u32) {
+        assert(len <= MaxLen, "set_len out of bounds");
+        assert(len >= self.len(), "can not set_len to a length shorter than the current length");
+        self.len = len;
+    }
+
     /// Returns the maximum length of this vector. This is always
     /// equal to the `MaxLen` parameter this vector was initialized with.
     ///
@@ -713,6 +733,35 @@ mod bounded_vec_tests {
         }
     }
 
+    mod set_len {
+        use crate::collections::bounded_vec::BoundedVec;
+
+        #[test]
+        fn set_len_works_after_multiple_unchecked_sets() {
+            let mut vec: BoundedVec<u8, 10> = BoundedVec::from_array([1, 2, 3]);
+            vec.set_unchecked(3, 44);
+            vec.set_unchecked(4, 55);
+            vec.set_unchecked(5, 66);
+            vec.set_unchecked(6, 77);
+            vec.set_len(8);
+            assert_eq(vec.len(), 8);
+            vec.extend_from_array([88, 99]);
+            assert_eq(vec.len(), 10);
+        }
+
+        #[test(should_fail_with = "can not set_len to a length shorter than the current length")]
+        fn panics_when_set_len_to_shorter_length() {
+            let mut vec: BoundedVec<u32, 5> = BoundedVec::from_array([1, 2, 3]);
+            vec.set_len(2);
+        }
+
+        #[test(should_fail_with = "set_len out of bounds")]
+        fn panics_when_set_len_beyond_max_len() {
+            let mut vec: BoundedVec<u32, 5> = BoundedVec::from_array([1, 2, 3]);
+            vec.set_len(6);
+        }
+    }
+
     mod any {
         use crate::collections::bounded_vec::BoundedVec;
 

test_programs/noir_test_success/bounded_vec/src/main.nr

@@ -139,6 +139,20 @@ fn max_len_docs_example() {
     // docs:end:bounded-vec-max-len-example
 }
 
+#[test]
+fn set_len_docs_example() {
+    // docs:start:bounded-vec-set-len-example
+    let mut v: BoundedVec<Field, 10> = BoundedVec::from_array([1, 2, 3, 4, 5]);
+
+    v.set_unchecked(5, 6);
+    v.set_unchecked(6, 7);
+    v.set_unchecked(7, 8);
+    assert(v.len() == 5);
+    v.set_len(9);
+    assert(v.len() == 9);
+    // docs:end:bounded-vec-set-len-example
+}
+
 #[test]
 fn storage_docs_example() {
     // docs:start:bounded-vec-storage-example