From 2ea92926956658ea99d8fb97734831eba00d3a4b Mon Sep 17 00:00:00 2001
From: jfecher <jake@aztecprotocol.com>
Date: Fri, 12 Apr 2024 12:30:26 -0400
Subject: [PATCH] fix: Fix panic when returning a zeroed unit value (#4797)

# Description

## Problem\*

Resolves #4791

## Summary\*

Zeroed used boolean values since we didn't have true unit values before.
These were meant to be filtered out by the type but as shown in the
issue, they'd still be used if they were directly returned.

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** 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.
---
 compiler/noirc_evaluator/src/ssa/ssa_gen/mod.rs         | 1 +
 compiler/noirc_frontend/src/monomorphization/ast.rs     | 1 +
 compiler/noirc_frontend/src/monomorphization/mod.rs     | 4 +---
 compiler/noirc_frontend/src/monomorphization/printer.rs | 3 +++
 test_programs/execution_success/unit_value/Nargo.toml   | 7 +++++++
 test_programs/execution_success/unit_value/src/main.nr  | 7 +++++++
 6 files changed, 20 insertions(+), 3 deletions(-)
 create mode 100644 test_programs/execution_success/unit_value/Nargo.toml
 create mode 100644 test_programs/execution_success/unit_value/src/main.nr

diff --git a/compiler/noirc_evaluator/src/ssa/ssa_gen/mod.rs b/compiler/noirc_evaluator/src/ssa/ssa_gen/mod.rs
index 3fe52f7f0e5..fd1a029af26 100644
--- a/compiler/noirc_evaluator/src/ssa/ssa_gen/mod.rs
+++ b/compiler/noirc_evaluator/src/ssa/ssa_gen/mod.rs
@@ -241,6 +241,7 @@ impl<'a> FunctionContext<'a> {
 
                 Ok(Tree::Branch(vec![string, field_count.into(), fields]))
             }
+            ast::Literal::Unit => Ok(Self::unit_value()),
         }
     }
 
diff --git a/compiler/noirc_frontend/src/monomorphization/ast.rs b/compiler/noirc_frontend/src/monomorphization/ast.rs
index 7d20c2bcfee..d9c33d8604e 100644
--- a/compiler/noirc_frontend/src/monomorphization/ast.rs
+++ b/compiler/noirc_frontend/src/monomorphization/ast.rs
@@ -92,6 +92,7 @@ pub enum Literal {
     Slice(ArrayLiteral),
     Integer(FieldElement, Type, Location),
     Bool(bool),
+    Unit,
     Str(String),
     FmtStr(String, u64, Box<Expression>),
 }
diff --git a/compiler/noirc_frontend/src/monomorphization/mod.rs b/compiler/noirc_frontend/src/monomorphization/mod.rs
index 6aa0abce152..ed620c2da0d 100644
--- a/compiler/noirc_frontend/src/monomorphization/mod.rs
+++ b/compiler/noirc_frontend/src/monomorphization/mod.rs
@@ -1553,9 +1553,7 @@ impl<'interner> Monomorphizer<'interner> {
                 ast::Expression::Literal(ast::Literal::Integer(0_u128.into(), typ, location))
             }
             ast::Type::Bool => ast::Expression::Literal(ast::Literal::Bool(false)),
-            // There is no unit literal currently. Replace it with 'false' since it should be ignored
-            // anyway.
-            ast::Type::Unit => ast::Expression::Literal(ast::Literal::Bool(false)),
+            ast::Type::Unit => ast::Expression::Literal(ast::Literal::Unit),
             ast::Type::Array(length, element_type) => {
                 let element = self.zeroed_value_of_type(element_type.as_ref(), location);
                 ast::Expression::Literal(ast::Literal::Array(ast::ArrayLiteral {
diff --git a/compiler/noirc_frontend/src/monomorphization/printer.rs b/compiler/noirc_frontend/src/monomorphization/printer.rs
index c253bfe7930..ea8f079cc2f 100644
--- a/compiler/noirc_frontend/src/monomorphization/printer.rs
+++ b/compiler/noirc_frontend/src/monomorphization/printer.rs
@@ -110,6 +110,9 @@ impl AstPrinter {
                 s.fmt(f)?;
                 write!(f, "\"")
             }
+            super::ast::Literal::Unit => {
+                write!(f, "()")
+            }
         }
     }
 
diff --git a/test_programs/execution_success/unit_value/Nargo.toml b/test_programs/execution_success/unit_value/Nargo.toml
new file mode 100644
index 00000000000..f7e3697a7c1
--- /dev/null
+++ b/test_programs/execution_success/unit_value/Nargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "short"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.23.0"
+
+[dependencies]
\ No newline at end of file
diff --git a/test_programs/execution_success/unit_value/src/main.nr b/test_programs/execution_success/unit_value/src/main.nr
new file mode 100644
index 00000000000..f3844e03cf2
--- /dev/null
+++ b/test_programs/execution_success/unit_value/src/main.nr
@@ -0,0 +1,7 @@
+fn get_transaction() {
+    dep::std::unsafe::zeroed()
+}
+
+fn main() {
+    get_transaction();
+}