[core] codegen/types: Add check_struct_type_matches_fields

Shorthand for checking if a type is representable by a StructFields
instance.

nac3core/src/codegen/types/structure.rs

@@ -2,7 +2,7 @@ use std::marker::PhantomData;
 
 use inkwell::{
     context::AsContextRef,
-    types::{BasicTypeEnum, IntType},
+    types::{BasicTypeEnum, IntType, StructType},
     values::{BasicValue, BasicValueEnum, IntValue, PointerValue, StructValue},
 };
 
@@ -201,3 +201,49 @@ impl FieldIndexCounter {
         v
     }
 }
+
+type FieldTypeVerifier<'ctx> = dyn Fn(BasicTypeEnum<'ctx>) -> Result<(), String>;
+
+/// Checks whether [`llvm_ty`][StructType] contains the fields described by the given
+/// [`StructFields`] instance.
+///
+/// By default, this function will compare the type of each field in `expected_fields` against
+/// `llvm_ty`. To override this behavior for individual fields, pass in overrides to
+/// `custom_verifiers`, which will use the specified verifier when a field with the matching field
+/// name is being checked.
+pub(super) fn check_struct_type_matches_fields<'ctx>(
+    expected_fields: impl StructFields<'ctx>,
+    llvm_ty: StructType<'ctx>,
+    ty_name: &'static str,
+    custom_verifiers: &[(&str, &FieldTypeVerifier<'ctx>)],
+) -> Result<(), String> {
+    let expected_fields = expected_fields.to_vec();
+
+    if llvm_ty.count_fields() != u32::try_from(expected_fields.len()).unwrap() {
+        return Err(format!(
+            "Expected {} fields in `{ty_name}`, got {}",
+            expected_fields.len(),
+            llvm_ty.count_fields(),
+        ));
+    }
+
+    expected_fields
+        .into_iter()
+        .enumerate()
+        .map(|(i, (field_name, expected_ty))| {
+            (field_name, expected_ty, llvm_ty.get_field_type_at_index(i as u32).unwrap())
+        })
+        .try_for_each(|(field_name, expected_ty, actual_ty)| {
+            if let Some((_, verifier)) =
+                custom_verifiers.iter().find(|verifier| verifier.0 == field_name)
+            {
+                verifier(actual_ty)
+            } else if expected_ty == actual_ty {
+                Ok(())
+            } else {
+                Err(format!("Expected {expected_ty} for `{ty_name}.{field_name}`, got {actual_ty}"))
+            }
+        })?;
+
+    Ok(())
+}