fix: Reject invalid expression with in CLI parser

acvm-repo/acvm/src/compiler/mod.rs

@@ -11,8 +11,8 @@ mod transformers;
 
 pub use optimizers::optimize;
 use optimizers::optimize_internal;
-pub use transformers::transform;
 use transformers::transform_internal;
+pub use transformers::{transform, MIN_EXPRESSION_WIDTH};
 
 /// This module moves and decomposes acir opcodes. The transformation map allows consumers of this module to map
 /// metadata they had about the opcodes to the new opcode structure generated after the transformation.

acvm-repo/acvm/src/compiler/transformers/csat.rs

@@ -6,6 +6,9 @@
 };
 use indexmap::IndexMap;
 
+/// Minimum width accepted by the `CSatTransformer`.
+pub const MIN_EXPRESSION_WIDTH: usize = 3;
+
 /// A transformer which processes any [`Expression`]s to break them up such that they
 /// fit within the [`ProofSystemCompiler`][crate::ProofSystemCompiler]'s width.
 ///
@@ -22,9 +25,11 @@
 }
 
 impl CSatTransformer {
-    // Configure the width for the optimizer
+    /// Create an optimizer with a given width.
+    ///
+    /// Panics if `width` is less than `MIN_EXPRESSION_WIDTH`.
     pub(crate) fn new(width: usize) -> CSatTransformer {
-        assert!(width > 2);
+        assert!(width >= MIN_EXPRESSION_WIDTH, "width has to be at least {MIN_EXPRESSION_WIDTH}");
 
         CSatTransformer { width, solvable_witness: HashSet::new() }
     }
@@ -87,7 +92,7 @@
     // This optimization will search for combinations of terms which can be represented in a single assert-zero opcode
     // Case 1 : qM * wL * wR + qL * wL + qR * wR + qO * wO + qC
     // This polynomial does not require any further optimizations, it can be safely represented in one opcode
     // ie a polynomial with 1 mul(bi-variate) term and 3 (univariate) terms where 2 of those terms match the bivariate term
     // wL and wR, we can represent it in one opcode
     // GENERALIZED for WIDTH: instead of the number 3, we use `WIDTH`
     //

acvm-repo/acvm/src/compiler/transformers/mod.rs

@@ -8,6 +8,7 @@ use indexmap::IndexMap;
 mod csat;
 
 pub(crate) use csat::CSatTransformer;
+pub use csat::MIN_EXPRESSION_WIDTH;
 
 use super::{transform_assert_messages, AcirTransformationMap};
 

compiler/noirc_driver/src/lib.rs

@@ -5,6 +5,7 @@
 
 use abi_gen::{abi_type_from_hir_type, value_from_hir_expression};
 use acvm::acir::circuit::ExpressionWidth;
+use acvm::compiler::MIN_EXPRESSION_WIDTH;
 use clap::Args;
 use fm::{FileId, FileManager};
 use iter_extended::vecmap;
@@ -134,7 +135,11 @@ pub fn parse_expression_width(input: &str) -> Result<ExpressionWidth, std::io::E
 
     match width {
         0 => Ok(ExpressionWidth::Unbounded),
-        _ => Ok(ExpressionWidth::Bounded { width }),
+        w if w >= MIN_EXPRESSION_WIDTH => Ok(ExpressionWidth::Bounded { width }),
+        _ => Err(Error::new(
+            ErrorKind::InvalidInput,
+            format!("has to be 0 or at least {MIN_EXPRESSION_WIDTH}"),
+        )),
     }
 }
 

tooling/nargo_cli/src/cli/mod.rs

@@ -112,3 +112,19 @@ pub(crate) fn start_cli() -> eyre::Result<()> {
     println!("{markdown}");
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use clap::Parser;
+    #[test]
+    fn test_parse_invalid_expression_width() {
+        let cmd = "nargo --program-dir . compile --expression-width 1";
+        let res = super::NargoCli::try_parse_from(cmd.split_ascii_whitespace());
+
+        let err = res.expect_err("should fail because of invalid width");
+        assert!(err.to_string().contains("expression-width"));
+        assert!(err
+            .to_string()
+            .contains(acvm::compiler::MIN_EXPRESSION_WIDTH.to_string().as_str()));
+    }
+}