From c02a6f64b1920ec5a1a05e20df34227cc95d7b0a Mon Sep 17 00:00:00 2001
From: Ary Borenszweig <asterite@gmail.com>
Date: Thu, 25 Jul 2024 10:43:43 -0300
Subject: [PATCH] fix: let trait calls work in globals (#5602)

# Description

## Problem

Resolves #5029

## Summary

Trait constraints weren't checked after elaborating a global.

## Additional Context

I couldn't just call `check_and_pop_function_context()` because that
also defaults type variables... and if we do that the usage of a global
will not have an effect on its type. I guess this is one scenario:

```rust
global x = 1; // What's the type of x?
```

We don't know. I guess it ends up being `Field` later on (where?) But if
we have this:

```rust
global x = 1;

fn main() {
  let y: i32 = 0;
  assert_eq(x, y);
}
```

now x's type will be `i32` because of that comparison. So if we eagerly
bind `1` to its default type, this will break.

All of this to say: in Rust a global's type (well, for a `const`) must
be explicitly specified. I guess that if we also did that in Noir then
this wouldn't be a problem. And given that globals are, well, global, it
might be strange to have `global x = 1` expecting that to be a Field,
used as a Field in many places, but you accidentally compare it to an
`i32` and the type changes under the hood. But that's a bigger
discussion, so maybe the fix in this PR is good for now?

## 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_frontend/src/elaborator/mod.rs               | 1 +
 .../compile_success_empty/trait_call_in_global/Nargo.toml   | 6 ++++++
 .../compile_success_empty/trait_call_in_global/src/main.nr  | 5 +++++
 3 files changed, 12 insertions(+)
 create mode 100644 test_programs/compile_success_empty/trait_call_in_global/Nargo.toml
 create mode 100644 test_programs/compile_success_empty/trait_call_in_global/src/main.nr

diff --git a/compiler/noirc_frontend/src/elaborator/mod.rs b/compiler/noirc_frontend/src/elaborator/mod.rs
index e0affad1fbf..1c5f791ac38 100644
--- a/compiler/noirc_frontend/src/elaborator/mod.rs
+++ b/compiler/noirc_frontend/src/elaborator/mod.rs
@@ -248,6 +248,7 @@ impl<'context> Elaborator<'context> {
         let (comptime_items, runtime_items) = Self::filter_comptime_items(items);
         this.elaborate_items(comptime_items);
         this.elaborate_items(runtime_items);
+        this.check_and_pop_function_context();
         this
     }
 
diff --git a/test_programs/compile_success_empty/trait_call_in_global/Nargo.toml b/test_programs/compile_success_empty/trait_call_in_global/Nargo.toml
new file mode 100644
index 00000000000..005fec5bf36
--- /dev/null
+++ b/test_programs/compile_success_empty/trait_call_in_global/Nargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "trait_call_in_global"
+type = "bin"
+authors = [""]
+
+[dependencies]
diff --git a/test_programs/compile_success_empty/trait_call_in_global/src/main.nr b/test_programs/compile_success_empty/trait_call_in_global/src/main.nr
new file mode 100644
index 00000000000..775cb5f3b7d
--- /dev/null
+++ b/test_programs/compile_success_empty/trait_call_in_global/src/main.nr
@@ -0,0 +1,5 @@
+global s: BoundedVec<Field, 2> = From::from([0]);
+
+fn main() {
+    let _ = s;
+}