feat(nargo): Default expression width field in Nargo.toml

compiler/noirc_driver/src/lib.rs

@@ -52,9 +52,9 @@ pub const NOIR_ARTIFACT_VERSION_STRING: &str =
 
 #[derive(Args, Clone, Debug, Default)]
 pub struct CompileOptions {
-    /// Override the expression width requested by the backend.
-    #[arg(long, value_parser = parse_expression_width, default_value = "4")]
-    pub expression_width: ExpressionWidth,
+    /// Specify the backend expression width that should be targeted
+    #[arg(long, value_parser = parse_expression_width)]
+    pub expression_width: Option<ExpressionWidth>,
 
     /// Force a full recompilation.
     #[arg(long = "force")]
@@ -113,7 +113,7 @@ pub struct CompileOptions {
     pub show_artifact_paths: bool,
 }
 
-fn parse_expression_width(input: &str) -> Result<ExpressionWidth, std::io::Error> {
+pub fn parse_expression_width(input: &str) -> Result<ExpressionWidth, std::io::Error> {
     use std::io::{Error, ErrorKind};
     let width = input
         .parse::<usize>()

compiler/wasm/src/compile.rs

@@ -164,10 +164,9 @@ pub fn compile_program(
     console_error_panic_hook::set_once();
     let (crate_id, mut context) = prepare_context(entry_point, dependency_graph, file_source_map)?;
 
-    let compile_options = CompileOptions {
-        expression_width: ExpressionWidth::Bounded { width: 4 },
-        ..CompileOptions::default()
-    };
+    let expression_width = ExpressionWidth::Bounded { width: 4 };
+    let compile_options =
+        CompileOptions { expression_width: Some(expression_width), ..CompileOptions::default() };
 
     let compiled_program =
         noirc_driver::compile_main(&mut context, crate_id, &compile_options, None)
@@ -180,8 +179,7 @@ pub fn compile_program(
             })?
             .0;
 
-    let optimized_program =
-        nargo::ops::transform_program(compiled_program, compile_options.expression_width);
+    let optimized_program = nargo::ops::transform_program(compiled_program, expression_width);
     let warnings = optimized_program.warnings.clone();
 
     Ok(JsCompileProgramResult::new(optimized_program.into(), warnings))
@@ -196,10 +194,9 @@ pub fn compile_contract(
     console_error_panic_hook::set_once();
     let (crate_id, mut context) = prepare_context(entry_point, dependency_graph, file_source_map)?;
 
-    let compile_options = CompileOptions {
-        expression_width: ExpressionWidth::Bounded { width: 4 },
-        ..CompileOptions::default()
-    };
+    let expression_width = ExpressionWidth::Bounded { width: 4 };
+    let compile_options =
+        CompileOptions { expression_width: Some(expression_width), ..CompileOptions::default() };
 
     let compiled_contract =
         noirc_driver::compile_contract(&mut context, crate_id, &compile_options)
@@ -212,8 +209,7 @@ pub fn compile_contract(
             })?
             .0;
 
-    let optimized_contract =
-        nargo::ops::transform_contract(compiled_contract, compile_options.expression_width);
+    let optimized_contract = nargo::ops::transform_contract(compiled_contract, expression_width);
     let warnings = optimized_contract.warnings.clone();
 
     Ok(JsCompileContractResult::new(optimized_contract.into(), warnings))

compiler/wasm/src/compile_new.rs

@@ -100,7 +100,10 @@ impl CompilerContext {
         } else {
             ExpressionWidth::Bounded { width: 4 }
         };
-        let compile_options = CompileOptions { expression_width, ..CompileOptions::default() };
+        let compile_options = CompileOptions {
+            expression_width: Some(expression_width),
+            ..CompileOptions::default()
+        };
 
         let root_crate_id = *self.context.root_crate_id();
         let compiled_program =
@@ -114,8 +117,7 @@ impl CompilerContext {
                 })?
                 .0;
 
-        let optimized_program =
-            nargo::ops::transform_program(compiled_program, compile_options.expression_width);
+        let optimized_program = nargo::ops::transform_program(compiled_program, expression_width);
         let warnings = optimized_program.warnings.clone();
 
         Ok(JsCompileProgramResult::new(optimized_program.into(), warnings))
@@ -130,7 +132,10 @@ impl CompilerContext {
         } else {
             ExpressionWidth::Bounded { width: 4 }
         };
-        let compile_options = CompileOptions { expression_width, ..CompileOptions::default() };
+        let compile_options = CompileOptions {
+            expression_width: Some(expression_width),
+            ..CompileOptions::default()
+        };
 
         let root_crate_id = *self.context.root_crate_id();
         let compiled_contract =
@@ -145,7 +150,7 @@ impl CompilerContext {
                 .0;
 
         let optimized_contract =
-            nargo::ops::transform_contract(compiled_contract, compile_options.expression_width);
+            nargo::ops::transform_contract(compiled_contract, expression_width);
         let warnings = optimized_contract.warnings.clone();
 
         Ok(JsCompileContractResult::new(optimized_contract.into(), warnings))

docs/docs/getting_started/hello_noir/project_breakdown.md

@@ -67,6 +67,7 @@ The package section defines a number of fields including:
 - `entry` (optional) - a relative filepath to use as the entry point into your package (overrides the default of `src/lib.nr` or `src/main.nr`)
 - `backend` (optional)
 - `license` (optional)
+- `expression_width` (optional) - Sets the default backend expression width. This field will override the default backend expression width specified by the Noir compiler (currently set to width 4). 
 
 #### Dependencies section
 

test_programs/execution_success/poseidon_bn254_hash_width_3/Nargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "poseidon_bn254_hash_width_3"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.31.0"
+# Test usage of `expression_width` field
+expression_width = "3"
+
+[dependencies]

test_programs/execution_success/poseidon_bn254_hash_width_3/Prover.toml

@@ -0,0 +1,4 @@
+x1 = [1,2]
+y1 = "0x115cc0f5e7d690413df64c6b9662e9cf2a3617f2743245519e19607a4417189a"
+x2 = [1,2,3,4]
+y2 = "0x299c867db6c1fdd79dcefa40e4510b9837e60ebb1ce0663dbaa525df65250465"

test_programs/execution_success/poseidon_bn254_hash_width_3/src/main.nr

@@ -0,0 +1,9 @@
+use std::hash::poseidon;
+
+fn main(x1: [Field; 2], y1: pub Field, x2: [Field; 4], y2: pub Field) {
+    let hash1 = poseidon::bn254::hash_2(x1);
+    assert(hash1 == y1);
+
+    let hash2 = poseidon::bn254::hash_4(x2);
+    assert(hash2 == y2);
+}

tooling/lsp/src/lib.rs

@@ -283,6 +283,7 @@ pub(crate) fn resolve_workspace_for_source_path(
         name: CrateName::from_str(parent_folder)
             .map_err(|err| LspError::WorkspaceResolutionError(err.to_string()))?,
         dependencies: BTreeMap::new(),
+        expression_width: None,
     };
     let workspace = Workspace {
         root_dir: PathBuf::from(parent_folder),

tooling/nargo/src/package.rs

@@ -1,5 +1,6 @@
 use std::{collections::BTreeMap, fmt::Display, path::PathBuf};
 
+use acvm::acir::circuit::ExpressionWidth;
 use noirc_frontend::graph::CrateName;
 
 use crate::constants::PROVER_INPUT_FILE;
@@ -51,6 +52,7 @@ pub struct Package {
     pub entry_path: PathBuf,
     pub name: CrateName,
     pub dependencies: BTreeMap<CrateName, Dependency>,
+    pub expression_width: Option<ExpressionWidth>,
 }
 
 impl Package {

tooling/nargo_cli/src/cli/compile_cmd.rs

@@ -2,6 +2,7 @@ use std::io::Write;
 use std::path::Path;
 use std::time::Duration;
 
+use acvm::acir::circuit::ExpressionWidth;
 use fm::FileManager;
 use nargo::ops::{collect_errors, compile_contract, compile_program, report_errors};
 use nargo::package::Package;
@@ -190,7 +191,11 @@ fn compile_programs(
                 compile_options,
                 load_cached_program(package),
             )?;
-            let program = nargo::ops::transform_program(program, compile_options.expression_width);
+
+            let target_width =
+                get_target_width(package.expression_width, compile_options.expression_width);
+            let program = nargo::ops::transform_program(program, target_width);
+
             save_program_to_file(
                 &program.clone().into(),
                 &package.name,
@@ -216,8 +221,9 @@ fn compiled_contracts(
         .map(|package| {
             let (contract, warnings) =
                 compile_contract(file_manager, parsed_files, package, compile_options)?;
-            let contract =
-                nargo::ops::transform_contract(contract, compile_options.expression_width);
+            let target_width =
+                get_target_width(package.expression_width, compile_options.expression_width);
+            let contract = nargo::ops::transform_contract(contract, target_width);
             save_contract(contract, package, target_dir, compile_options.show_artifact_paths);
             Ok(((), warnings))
         })
@@ -243,3 +249,21 @@ fn save_contract(
         println!("Saved contract artifact to: {}", artifact_path.display());
     }
 }
+
+/// Default expression width used for Noir compilation.
+/// The ACVM native type `ExpressionWidth` has its own default which should always be unbounded,
+/// while we can sometimes expect the compilation target width to change.
+/// Thus, we set it separately here rather than trying to alter the default derivation of the type.
+const DEFAULT_EXPRESSION_WIDTH: ExpressionWidth = ExpressionWidth::Bounded { width: 4 };
+
+/// If a target width was not specified in the CLI we can safely override the default.
+pub(crate) fn get_target_width(
+    package_default_width: Option<ExpressionWidth>,
+    compile_options_width: Option<ExpressionWidth>,
+) -> ExpressionWidth {
+    if let (Some(manifest_default_width), None) = (package_default_width, compile_options_width) {
+        manifest_default_width
+    } else {
+        compile_options_width.unwrap_or(DEFAULT_EXPRESSION_WIDTH)
+    }
+}

tooling/nargo_cli/src/cli/debug_cmd.rs

@@ -22,6 +22,7 @@ use noirc_frontend::debug::DebugInstrumenter;
 use noirc_frontend::graph::CrateName;
 use noirc_frontend::hir::ParsedFiles;
 
+use super::compile_cmd::get_target_width;
 use super::fs::{inputs::read_inputs_from_file, witness::save_witness_to_dir};
 use super::NargoConfig;
 use crate::errors::CliError;
@@ -80,8 +81,10 @@ pub(crate) fn run(args: DebugCommand, config: NargoConfig) -> Result<(), CliErro
         args.compile_options.clone(),
     )?;
 
-    let compiled_program =
-        nargo::ops::transform_program(compiled_program, args.compile_options.expression_width);
+    let target_width =
+        get_target_width(package.expression_width, args.compile_options.expression_width);
+
+    let compiled_program = nargo::ops::transform_program(compiled_program, target_width);
 
     run_async(package, compiled_program, &args.prover_name, &args.witness_name, target_dir)
 }

tooling/nargo_cli/src/cli/info_cmd.rs

@@ -16,7 +16,9 @@ use serde::Serialize;
 use crate::errors::CliError;
 
 use super::{
-    compile_cmd::compile_workspace_full, fs::program::read_program_from_file, NargoConfig,
+    compile_cmd::{compile_workspace_full, get_target_width},
+    fs::program::read_program_from_file,
+    NargoConfig,
 };
 
 /// Provides detailed information on each of a program's function (represented by a single circuit)
@@ -84,11 +86,9 @@ pub(crate) fn run(args: InfoCommand, config: NargoConfig) -> Result<(), CliError
         .into_iter()
         .par_bridge()
         .map(|(package, program)| {
-            count_opcodes_and_gates_in_program(
-                program,
-                &package,
-                args.compile_options.expression_width,
-            )
+            let target_width =
+                get_target_width(package.expression_width, args.compile_options.expression_width);
+            count_opcodes_and_gates_in_program(program, &package, target_width)
         })
         .collect();
 

tooling/nargo_cli/tests/stdlib-tests.rs

@@ -27,6 +27,7 @@ fn run_stdlib_tests() {
         entry_path: PathBuf::from("main.nr"),
         name: "stdlib".parse().unwrap(),
         dependencies: BTreeMap::new(),
+        expression_width: None,
     };
 
     let (mut context, dummy_crate_id) =

tooling/nargo_toml/Cargo.toml

@@ -18,6 +18,7 @@ serde.workspace = true
 thiserror.workspace = true
 toml.workspace = true
 url.workspace = true
+noirc_driver.workspace = true
 semver = "1.0.20"
 
 [dev-dependencies]

tooling/nargo_toml/src/errors.rs

@@ -72,6 +72,9 @@ pub enum ManifestError {
 
     #[error("Cyclic package dependency found when processing {cycle}")]
     CyclicDependency { cycle: String },
+
+    #[error("Failed to parse expression width with the following error: {0}")]
+    ParseExpressionWidth(String),
 }
 
 #[allow(clippy::enum_variant_names)]

tooling/nargo_toml/src/lib.rs

@@ -14,6 +14,7 @@ use nargo::{
     package::{Dependency, Package, PackageType},
     workspace::Workspace,
 };
+use noirc_driver::parse_expression_width;
 use noirc_frontend::graph::CrateName;
 use serde::Deserialize;
 
@@ -199,6 +200,16 @@ impl PackageConfig {
             })?;
         }
 
+        let expression_width = self
+            .package
+            .expression_width
+            .as_ref()
+            .map(|expression_width| {
+                parse_expression_width(expression_width)
+                    .map_err(|err| ManifestError::ParseExpressionWidth(err.to_string()))
+            })
+            .map_or(Ok(None), |res| res.map(Some))?;
+
         Ok(Package {
             version: self.package.version.clone(),
             compiler_required_version: self.package.compiler_version.clone(),
@@ -207,6 +218,7 @@ impl PackageConfig {
             package_type,
             name,
             dependencies,
+            expression_width,
         })
     }
 }
@@ -275,6 +287,7 @@ struct PackageMetadata {
     // so you will not need to supply an ACIR and compiler version
     compiler_version: Option<String>,
     license: Option<String>,
+    expression_width: Option<String>,
 }
 
 #[derive(Debug, Deserialize, Clone)]
@@ -531,3 +544,18 @@ fn parse_workspace_default_member_toml() {
     assert!(Config::try_from(String::from(src)).is_ok());
     assert!(Config::try_from(src).is_ok());
 }
+
+#[test]
+fn parse_package_expression_width_toml() {
+    let src = r#"
+    [package]
+    name = "test"
+    version = "0.1.0"
+    type = "bin"
+    authors = [""]
+    expression_width = "3"
+    "#;
+
+    assert!(Config::try_from(String::from(src)).is_ok());
+    assert!(Config::try_from(src).is_ok());
+}