fix: Stop issuing unused variable warnings for variables in trait def…

…initions (#3797)

# Description

## Problem\*

Previously we'd issue a warning for each trait function parameter that
it is unused. This seemed to only trigger when the trait was in another
crate.

## Summary\*

Stop checking for unused variables in trait function declarations since
there is no body to use the variable in anyway.

## 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.

Co-authored-by: kevaundray <kevtheappdev@gmail.com>

compiler/noirc_frontend/src/hir/resolution/resolver.rs

@@ -239,9 +239,8 @@ impl<'a> Resolver<'a> {
         };
 
         let (hir_func, func_meta) = self.intern_function(NoirFunction { kind, def }, func_id);
-        let func_scope_tree = self.scopes.end_function();
-        self.check_for_unused_variables_in_scope_tree(func_scope_tree);
-
+        let _ = self.scopes.end_function();
+        // Don't check the scope tree for unused variables, they can't be used in a declaration anyway.
         self.trait_bounds.clear();
         (hir_func, func_meta)
     }

compiler/noirc_frontend/src/tests.rs

@@ -48,15 +48,6 @@ mod test {
         });
     }
 
-    /// Many of the tests in this file have odd unused variable warnings which do not occur
-    /// when running an identical program using `nargo execute`. They're filtered out of the
-    /// errors returned by `get_errors` for now.
-    pub(crate) fn remove_unused_variable_warnings(errors: &mut Vec<(CompilationError, FileId)>) {
-        errors.retain(|(error, _)| {
-            !matches!(error, CompilationError::ResolverError(ResolverError::UnusedVariable { .. }))
-        });
-    }
-
     pub(crate) fn get_program(
         src: &str,
     ) -> (ParsedModule, Context, Vec<(CompilationError, FileId)>) {
@@ -97,9 +88,7 @@ mod test {
     }
 
     pub(crate) fn get_program_errors(src: &str) -> Vec<(CompilationError, FileId)> {
-        let (_program, _context, mut errors) = get_program(src);
-        remove_unused_variable_warnings(&mut errors);
-        errors
+        get_program(src).2
     }
 
     #[test]
@@ -797,7 +786,7 @@ mod test {
             }
         "#;
 
-        let (_, _, errors) = get_program(src);
+        let errors = get_program_errors(src);
         assert!(errors.len() == 1, "Expected 1 error, got: {:?}", errors);
         // It should be regarding the unused variable
         match &errors[0].0 {
@@ -874,7 +863,7 @@ mod test {
             }
         "#;
 
-        let (_, _, errors) = get_program(src);
+        let errors = get_program_errors(src);
         assert!(errors.len() == 3, "Expected 3 errors, got: {:?}", errors);
 
         // Errors are: