feat: Enable dynamic indices on slices (#2446)

Co-authored-by: Jake Fecher <jake@aztecprotocol.com>

Cargo.toml

@@ -61,4 +61,4 @@ tower = "0.4"
 url = "2.2.0"
 wasm-bindgen = { version = "=0.2.86", features = ["serde-serialize"] }
 wasm-bindgen-test = "0.3.33"
-base64 = "0.21.2"
+base64 = "0.21.2"

crates/nargo_cli/tests/execution_success/slice_dynamic_index/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "slice_dynamic_index"
+type = "bin"
+authors = [""]
+compiler_version = "0.10.3"
+
+[dependencies]

crates/nargo_cli/tests/execution_success/slice_dynamic_index/Prover.toml

@@ -0,0 +1 @@
+x = "5"

crates/nargo_cli/tests/execution_success/slice_dynamic_index/src/main.nr

@@ -0,0 +1,222 @@
+fn main(x : Field) {
+    // The parameters to this function must come directly from witness values (inputs to main).
+    regression_dynamic_slice_index(x - 1, x - 4);
+}
+
+fn regression_dynamic_slice_index(x: Field, y: Field) {
+    let mut slice = [];
+    for i in 0..5 {
+        slice = slice.push_back(i);
+    }
+    assert(slice.len() == 5);
+
+    dynamic_slice_index_set_if(slice, x, y);
+    dynamic_slice_index_set_else(slice, x, y);
+    dynamic_slice_index_set_nested_if_else_else(slice, x, y);
+    dynamic_slice_index_set_nested_if_else_if(slice, x, y + 1);
+    dynamic_slice_index_if(slice, x);
+    dynamic_array_index_if([0, 1, 2, 3, 4], x);
+    dynamic_slice_index_else(slice, x);
+
+    dynamic_slice_merge_if(slice, x);
+    dynamic_slice_merge_else(slice, x);
+}
+
+fn dynamic_slice_index_set_if(mut slice: [Field], x: Field, y: Field) {
+    assert(slice[x] == 4);
+    assert(slice[y] == 1);
+    slice[y] = 0;
+    assert(slice[x] == 4);
+    assert(slice[1] == 0);
+    if x as u32 < 10 {
+        assert(slice[x] == 4);
+        slice[x] = slice[x] - 2;
+        slice[x - 1] = slice[x];
+    } else {
+        slice[x] = 0;
+    }
+    assert(slice[3] == 2);
+    assert(slice[4] == 2);
+}
+
+fn dynamic_slice_index_set_else(mut slice: [Field], x: Field, y: Field) {
+    assert(slice[x] == 4);
+    assert(slice[y] == 1);
+    slice[y] = 0;
+    assert(slice[x] == 4);
+    assert(slice[1] == 0);
+    if x as u32 > 10 {
+        assert(slice[x] == 4);
+        slice[x] = slice[x] - 2;
+        slice[x - 1] = slice[x];
+    } else {
+        slice[x] = 0;
+    }
+    assert(slice[4] == 0);
+}
+
+// This tests the case of missing a store instruction in the else branch
+// of merging slices
+fn dynamic_slice_index_if(mut slice: [Field], x: Field) {
+    if x as u32 < 10 {
+        assert(slice[x] == 4);
+        slice[x] = slice[x] - 2;
+    } else {
+        assert(slice[x] == 0);
+    }
+    assert(slice[4] == 2);
+}
+
+fn dynamic_array_index_if(mut array: [Field; 5], x: Field) {
+    if x as u32 < 10 {
+        assert(array[x] == 4);
+        array[x] = array[x] - 2;
+    } else {
+        assert(array[x] == 0);
+    }
+    assert(array[4] == 2);
+}
+
+// This tests the case of missing a store instruction in the then branch
+// of merging slices
+fn dynamic_slice_index_else(mut slice: [Field], x: Field) {
+    if x as u32 > 10 {
+        assert(slice[x] == 0);
+    } else {
+        assert(slice[x] == 4);
+        slice[x] = slice[x] - 2;
+    }
+    assert(slice[4] == 2);
+}
+
+
+fn dynamic_slice_merge_if(mut slice: [Field], x: Field) {
+    if x as u32 < 10 {
+        assert(slice[x] == 4);
+        slice[x] = slice[x] - 2;
+
+        slice = slice.push_back(10);
+        // Having an array set here checks whether we appropriately
+        // handle a slice length that is not yet resolving to a constant
+        // during flattening
+        slice[x] = 10;
+        assert(slice[slice.len() - 1] == 10);
+        assert(slice.len() == 6);
+
+        slice[x] = 20;
+        slice[x] = slice[x] + 10;
+
+        slice = slice.push_front(11);
+        assert(slice[0] == 11);
+        assert(slice.len() == 7);
+        assert(slice[5] == 30);
+
+        slice = slice.push_front(12);
+        assert(slice[0] == 12);
+        assert(slice.len() == 8);
+        assert(slice[6] == 30);
+
+        let (popped_slice, last_elem) = slice.pop_back();
+        assert(last_elem == 10);
+        assert(popped_slice.len() == 7);
+
+        let (first_elem, rest_of_slice) = popped_slice.pop_front();
+        assert(first_elem == 12);
+        assert(rest_of_slice.len() == 6);
+
+        // TODO(#2462): SliceInsert and SliceRemove with a dynamic index are not yet implemented in ACIR gen
+        slice = rest_of_slice.insert(2, 20);
+        assert(slice[2] == 20);
+        assert(slice[6] == 30);
+        assert(slice.len() == 7);
+
+        // TODO(#2462): SliceInsert and SliceRemove with a dynamic index are not yet implemented in ACIR gen
+        let (removed_slice, removed_elem) = slice.remove(3);
+        // The deconstructed tuple assigns to the slice but is not seen outside of the if statement
+        // without a direct assignment
+        slice = removed_slice;
+
+        assert(removed_elem == 1);
+        assert(slice.len() == 6);
+    } else {
+        assert(slice[x] == 0);
+        slice = slice.push_back(20);
+    }
+
+    assert(slice.len() == 6);
+    assert(slice[slice.len() - 1] == 30);
+}
+
+fn dynamic_slice_merge_else(mut slice: [Field], x: Field) {
+    if x as u32 > 10 {
+        assert(slice[x] == 0);
+        slice[x] = 2;
+    } else {
+        assert(slice[x] == 4);
+        slice[x] = slice[x] - 2;
+        slice = slice.push_back(10);
+    }
+    assert(slice.len() == 6);
+    assert(slice[slice.len() - 1] == 10);
+
+    slice = slice.push_back(20);
+    assert(slice.len() == 7);
+    assert(slice[slice.len() - 1] == 20);
+}
+
+fn dynamic_slice_index_set_nested_if_else_else(mut slice: [Field], x: Field, y: Field) {
+    assert(slice[x] == 4);
+    assert(slice[y] == 1);
+    slice[y] = 0;
+    assert(slice[x] == 4);
+    assert(slice[1] == 0);
+    if x as u32 < 10 {
+        slice[x] = slice[x] - 2;
+        if y != 1 {
+            slice[x] = slice[x] + 20;
+        } else {
+            if x == 5 {
+                // We should not hit this case
+                assert(slice[x] == 22);
+            } else {
+                slice[x] = 10;
+                slice = slice.push_back(15);
+                assert(slice.len() == 6);
+            }
+            assert(slice[4] == 10);
+        }
+    } else {
+        slice[x] = 0;
+    }
+    assert(slice[4] == 10);
+    assert(slice.len() == 6);
+    assert(slice[slice.len() - 1] == 15);
+
+    slice = slice.push_back(20);
+    assert(slice.len() == 7);
+    assert(slice[slice.len() - 1] == 20);
+}
+
+fn dynamic_slice_index_set_nested_if_else_if(mut slice: [Field], x: Field, y: Field) {
+    assert(slice[x] == 4);
+    assert(slice[y] == 2);
+    slice[y] = 0;
+    assert(slice[x] == 4);
+    assert(slice[2] == 0);
+    if x as u32 < 10 {
+        slice[x] = slice[x] - 2;
+        // TODO: this panics as we have a load for the slice in flattening
+        if y == 1 {
+            slice[x] = slice[x] + 20;
+        } else {
+            if x == 4 {
+                slice[x] = 5;
+            }
+            assert(slice[4] == 5);
+        }
+    } else {
+        slice[x] = 0;
+    }
+    assert(slice[4] == 5);
+}
+

crates/nargo_cli/tests/execution_success/slices/src/main.nr

@@ -1,5 +1,6 @@
 use dep::std::slice;
 use dep::std;
+
 fn main(x : Field, y : pub Field) {
     let mut slice = [0; 2];
     assert(slice[0] == 0);
@@ -155,4 +156,4 @@ fn merge_slices_mutate_in_loop(x: Field, y: Field) -> [Field] {
         slice = slice.push_back(x);
     }
     slice
-}
+}

crates/noirc_evaluator/src/brillig/brillig_gen/brillig_block.rs

@@ -492,7 +492,7 @@ impl<'block> BrilligBlock<'block> {
                     destination_variable,
                 );
             }
-            Instruction::ArraySet { array, index, value } => {
+            Instruction::ArraySet { array, index, value, .. } => {
                 let source_variable = self.convert_ssa_value(*array, dfg);
                 let index_register = self.convert_ssa_register_value(*index, dfg);
                 let value_variable = self.convert_ssa_value(*value, dfg);

crates/noirc_evaluator/src/errors.rs

@@ -116,7 +116,8 @@ impl RuntimeError {
             }
             _ => {
                 let message = self.to_string();
-                let location = self.call_stack().back().expect("Expected RuntimeError to have a location");
+                let location =
+                    self.call_stack().back().expect("Expected RuntimeError to have a location");
 
                 Diagnostic::simple_error(message, String::new(), location.span)
             }

crates/noirc_evaluator/src/ssa/acir_gen/acir_ir/acir_variable.rs

@@ -240,7 +240,7 @@ impl AcirContext {
     }
 
     /// Converts an [`AcirVar`] to an [`Expression`]
-    fn var_to_expression(&self, var: AcirVar) -> Result<Expression, InternalError> {
+    pub(crate) fn var_to_expression(&self, var: AcirVar) -> Result<Expression, InternalError> {
         let var_data = match self.vars.get(&var) {
             Some(var_data) => var_data,
             None => {