fix(ACIR): check vector length is not zero before pop_front

compiler/noirc_evaluator/src/acir/call/intrinsics/vector_ops.rs

@@ -362,7 +362,7 @@ impl Context<'_> {
         let vector_typ = dfg.type_of_value(vector_contents);
         let block_id = self.ensure_array_is_initialized(vector_contents, dfg)?;
 
-        // Check if we're trying to pop from an empty vector
+        // Check if we're trying to pop from a known empty vector.
         if self.has_zero_length(vector_contents, dfg) {
             // Make sure this code is disabled, or fail with "Index out of bounds".
             let msg = "cannot pop from a vector with length 0".to_string();
@@ -388,6 +388,19 @@ impl Context<'_> {
             return Ok(results);
         }
 
+        // Check that the vector length is not zero.
+        // This is different from the previous check as this is a runtime check.
+        let zero = self.acir_context.add_constant(FieldElement::zero());
+        let assert_message = self.acir_context.generate_assertion_message_payload(
+            "Attempt to pop_front from an empty vector".to_string(),
+        );
+        self.acir_context.assert_neq_var(
+            vector_length,
+            zero,
+            self.current_side_effects_enabled_var,
+            Some(assert_message),
+        )?;
+
         let one = self.acir_context.add_constant(FieldElement::one());
         let new_vector_length = self.acir_context.sub_var(vector_length, one)?;
 

test_programs/execution_failure/conditional_pop_back_from_empty_vector/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "conditional_pop_back_from_empty_vector"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.23.0"
+
+[dependencies]

test_programs/execution_failure/conditional_pop_back_from_empty_vector/Prover.toml

@@ -0,0 +1,2 @@
+input = [1]
+b = true

test_programs/execution_failure/conditional_pop_back_from_empty_vector/src/main.nr

@@ -0,0 +1,14 @@
+pub fn main(input: [u32; 1], b: bool) -> pub u32 {
+    let mut s = input.as_vector();
+
+    if (b) {
+        let (new_slice, _) = s.pop_back();
+        s = new_slice;
+    } else {
+        s = s.push_front(5);
+    }
+
+    let (_, ret) = s.pop_back();
+
+    ret
+}

test_programs/execution_failure/conditional_pop_front_from_empty_vector/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "conditional_pop_front_from_empty_vector"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.23.0"
+
+[dependencies]

test_programs/execution_failure/conditional_pop_front_from_empty_vector/Prover.toml

@@ -0,0 +1,2 @@
+input = [1]
+b = true

test_programs/execution_failure/conditional_pop_front_from_empty_vector/src/main.nr

@@ -0,0 +1,14 @@
+pub fn main(input: [u32; 1], b: bool) -> pub u32 {
+    let mut s = input.as_vector();
+
+    if (b) {
+        let (_, new_slice) = s.pop_front();
+        s = new_slice;
+    } else {
+        s = s.push_front(5);
+    }
+
+    let (ret, _) = s.pop_front();
+
+    ret
+}

test_programs/execution_failure/conditional_remove_from_empty_vector/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "conditional_remove_from_empty_vector"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.23.0"
+
+[dependencies]

test_programs/execution_failure/conditional_remove_from_empty_vector/Prover.toml

@@ -0,0 +1,2 @@
+input = [1]
+b = true

test_programs/execution_failure/conditional_remove_from_empty_vector/src/main.nr

@@ -0,0 +1,14 @@
+pub fn main(input: [u32; 1], b: bool) -> pub u32 {
+    let mut s = input.as_vector();
+
+    if (b) {
+        let (new_slice, _) = s.remove(0);
+        s = new_slice;
+    } else {
+        s = s.push_front(5);
+    }
+
+    let (_, ret) = s.remove(0);
+
+    ret
+}