chore: adds a new option only-acir (#3683)

# Description

## Problem\*

Resolves #3119

## Summary\*

Adds a new option only-acir which compiles acir bytecode into acir.gz
generates witness as .gz instead of .tr
use only-acir when generating the artifacts and remove the un-needed
steps from rebuild.sh

## Additional Context



## Documentation\*

Check one:
- [ ] No documentation needed.
- [X] Documentation included in this PR.
- [ ] **[Exceptional Case]** Documentation to be submitted in a separate
PR.

# PR Checklist\*

- [X] I have tested the changes locally.
- [X] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

---------

Co-authored-by: kevaundray <[email protected]>

compiler/noirc_driver/src/lib.rs

@@ -62,6 +62,10 @@ pub struct CompileOptions {
     #[arg(long, conflicts_with = "deny_warnings")]
     pub silence_warnings: bool,
 
+    /// Output ACIR gzipped bytecode instead of the JSON artefact
+    #[arg(long, hide = true)]
+    pub only_acir: bool,
+
     /// Disables the builtin macros being used in the compiler
     #[arg(long, hide = true)]
     pub disable_macros: bool,

test_programs/rebuild.sh

@@ -14,17 +14,7 @@ process_dir() {
     if [ -d ./target/ ]; then
       rm -r ./target/
     fi
-    nargo compile && nargo execute witness
-
-    if [ -f ./target/witness.tr ]; then
-      mv ./target/witness.tr ./target/witness.gz
-    fi
-
-    if [ -f ./target/${dir_name}.json ]; then
-        jq -r '.bytecode' ./target/${dir_name}.json | base64 -d > ./target/acir.gz
-    fi
-
-    rm ./target/${dir_name}.json
+    cargo run compile --only-acir && cargo run execute witness
 
     if [ -d "$current_dir/acir_artifacts/$dir_name/target" ]; then
       rm -r "$current_dir/acir_artifacts/$dir_name/target"

tooling/nargo/src/constants.rs

@@ -20,4 +20,4 @@ pub const PKG_FILE: &str = "Nargo.toml";
 /// The extension for files containing circuit proofs.
 pub const PROOF_EXT: &str = "proof";
 /// The extension for files containing proof witnesses.
-pub const WITNESS_EXT: &str = "tr";
+pub const WITNESS_EXT: &str = "gz";

tooling/nargo_cli/src/cli/compile_cmd.rs

@@ -23,6 +23,7 @@ use clap::Args;
 use crate::backends::Backend;
 use crate::errors::CliError;
 
+use super::fs::program::only_acir;
 use super::fs::program::{
     read_debug_artifact_from_file, read_program_from_file, save_contract_to_file,
     save_debug_artifact_to_file, save_program_to_file,
@@ -215,8 +216,8 @@ fn compile_program(
     // Apply backend specific optimizations.
     let optimized_program = nargo::ops::optimize_program(program, np_language, is_opcode_supported)
         .expect("Backend does not support an opcode that is in the IR");
-
-    save_program(optimized_program.clone(), package, &workspace.target_directory_path());
+    let only_acir = compile_options.only_acir;
+    save_program(optimized_program.clone(), package, &workspace.target_directory_path(), only_acir);
 
     (context.file_manager, Ok((optimized_program, warnings)))
 }
@@ -244,16 +245,24 @@ fn compile_contract(
     (context.file_manager, Ok((optimized_contract, warnings)))
 }
 
-fn save_program(program: CompiledProgram, package: &Package, circuit_dir: &Path) {
+fn save_program(
+    program: CompiledProgram,
+    package: &Package,
+    circuit_dir: &Path,
+    only_acir_opt: bool,
+) {
     let preprocessed_program = PreprocessedProgram {
         hash: program.hash,
         backend: String::from(BACKEND_IDENTIFIER),
         abi: program.abi,
         noir_version: program.noir_version,
         bytecode: program.circuit,
     };
-
-    save_program_to_file(&preprocessed_program, &package.name, circuit_dir);
+    if only_acir_opt {
+        only_acir(&preprocessed_program, circuit_dir);
+    } else {
+        save_program_to_file(&preprocessed_program, &package.name, circuit_dir);
+    }
 
     let debug_artifact = DebugArtifact {
         debug_symbols: vec![program.debug],

tooling/nargo_cli/src/cli/fs/program.rs

@@ -1,5 +1,6 @@
 use std::path::{Path, PathBuf};
 
+use acvm::acir::circuit::Circuit;
 use nargo::artifacts::{
     contract::PreprocessedContract, debug::DebugArtifact, program::PreprocessedProgram,
 };
@@ -18,6 +19,19 @@ pub(crate) fn save_program_to_file<P: AsRef<Path>>(
     save_build_artifact_to_file(compiled_program, &circuit_name, circuit_dir)
 }
 
+/// Writes the bytecode as acir.gz
+pub(crate) fn only_acir<P: AsRef<Path>>(
+    compiled_program: &PreprocessedProgram,
+    circuit_dir: P,
+) -> PathBuf {
+    create_named_dir(circuit_dir.as_ref(), "target");
+    let circuit_path = circuit_dir.as_ref().join("acir").with_extension("gz");
+    let bytes = Circuit::serialize_circuit(&compiled_program.bytecode);
+    write_to_file(&bytes, &circuit_path);
+
+    circuit_path
+}
+
 pub(crate) fn save_contract_to_file<P: AsRef<Path>>(
     compiled_contract: &PreprocessedContract,
     circuit_name: &str,