From b3ddf10a2cbb80e88821baf7d76c478c3b98b3ea Mon Sep 17 00:00:00 2001
From: Tom French <15848336+TomAFrench@users.noreply.github.com>
Date: Fri, 2 Feb 2024 16:31:23 +0000
Subject: [PATCH] fix: allow performing bitwise NOT on unsigned integers
 (#4229)
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# Description

## Problem\*

Resolves <!-- Link to GitHub Issue -->

## Summary\*

Currently running `bit_not` results in the output

```
$ nargo info --show-ssa
error: u8 cannot be used in a unary operation
  ┌─ /home/tom/Programming/aztec/noir/test_programs/execution_success/bit_not/src/main.nr:3:30
  │
3 │     let not_four_as_u8: u8 = !four_as_u8;
  │                              -----------
  │

error: u32 cannot be used in a unary operation
  ┌─ /home/tom/Programming/aztec/noir/test_programs/execution_success/bit_not/src/main.nr:6:32
  │
6 │     let not_four_as_u32: u32 = !four_as_u32;
  │                                ------------
  │
```

We're unable to perform bitwise nots for unsigned integers (signed is
fine). This PR loosens the check being applied in
`lint_overflowing_uint` so that it only errors for using an unary `-`.

## Additional Context



## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] 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.
---
 compiler/noirc_frontend/src/hir/type_check/stmt.rs  | 13 ++++++++++---
 test_programs/execution_success/bit_not/Nargo.toml  |  7 +++++++
 test_programs/execution_success/bit_not/Prover.toml |  1 +
 test_programs/execution_success/bit_not/src/main.nr |  8 ++++++++
 4 files changed, 26 insertions(+), 3 deletions(-)
 create mode 100644 test_programs/execution_success/bit_not/Nargo.toml
 create mode 100644 test_programs/execution_success/bit_not/Prover.toml
 create mode 100644 test_programs/execution_success/bit_not/src/main.nr

diff --git a/compiler/noirc_frontend/src/hir/type_check/stmt.rs b/compiler/noirc_frontend/src/hir/type_check/stmt.rs
index a38a16a6580..76bd064bf83 100644
--- a/compiler/noirc_frontend/src/hir/type_check/stmt.rs
+++ b/compiler/noirc_frontend/src/hir/type_check/stmt.rs
@@ -8,6 +8,7 @@ use crate::hir_def::stmt::{
 };
 use crate::hir_def::types::Type;
 use crate::node_interner::{DefinitionId, ExprId, StmtId};
+use crate::UnaryOp;
 
 use super::errors::{Source, TypeCheckError};
 use super::TypeChecker;
@@ -361,9 +362,15 @@ impl<'interner> TypeChecker<'interner> {
                     };
                 };
             }
-            HirExpression::Prefix(_) => self
-                .errors
-                .push(TypeCheckError::InvalidUnaryOp { kind: annotated_type.to_string(), span }),
+            HirExpression::Prefix(expr) => {
+                self.lint_overflowing_uint(&expr.rhs, annotated_type);
+                if matches!(expr.operator, UnaryOp::Minus) {
+                    self.errors.push(TypeCheckError::InvalidUnaryOp {
+                        kind: "annotated_type".to_string(),
+                        span,
+                    });
+                }
+            }
             HirExpression::Infix(expr) => {
                 self.lint_overflowing_uint(&expr.lhs, annotated_type);
                 self.lint_overflowing_uint(&expr.rhs, annotated_type);
diff --git a/test_programs/execution_success/bit_not/Nargo.toml b/test_programs/execution_success/bit_not/Nargo.toml
new file mode 100644
index 00000000000..e89a338595b
--- /dev/null
+++ b/test_programs/execution_success/bit_not/Nargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "bit_not"
+type = "bin"
+authors = [""]
+compiler_version = ">=0.23.0"
+
+[dependencies]
diff --git a/test_programs/execution_success/bit_not/Prover.toml b/test_programs/execution_success/bit_not/Prover.toml
new file mode 100644
index 00000000000..b4bcbcec177
--- /dev/null
+++ b/test_programs/execution_success/bit_not/Prover.toml
@@ -0,0 +1 @@
+four_as_u32 = 4
diff --git a/test_programs/execution_success/bit_not/src/main.nr b/test_programs/execution_success/bit_not/src/main.nr
new file mode 100644
index 00000000000..30b78d330ce
--- /dev/null
+++ b/test_programs/execution_success/bit_not/src/main.nr
@@ -0,0 +1,8 @@
+fn main(four_as_u32: u32) {
+    let four_as_u8: u8 = 4;
+    let not_four_as_u8: u8 = !four_as_u8;
+    assert_eq(not_four_as_u8, 251);
+
+    let not_four_as_u32: u32 = !four_as_u32;
+    assert_eq(not_four_as_u32, 4294967291);
+}