add ability to explicitly cast enum with no payload to int

src/all_types.hpp

@@ -404,6 +404,7 @@ enum CastOp {
     CastOpBoolToInt,
     CastOpResizeSlice,
     CastOpIntToEnum,
+    CastOpEnumToInt,
     CastOpBytesToSlice,
 };
 

src/analyze.cpp

@@ -2641,7 +2641,12 @@ static TypeTableEntry *analyze_container_init_expr(CodeGen *g, ImportTableEntry
         codegen->type_entry = fixed_size_array_type;
         codegen->source_node = node;
         if (!const_val->ok) {
-            context->fn_entry->struct_val_expr_alloca_list.append(codegen);
+            if (!context->fn_entry) {
+                add_node_error(g, node,
+                    buf_sprintf("unable to evaluate constant expression"));
+            } else {
+                context->fn_entry->struct_val_expr_alloca_list.append(codegen);
+            }
         }
 
         return fixed_size_array_type;
@@ -4601,6 +4606,14 @@ static TypeTableEntry *analyze_cast_expr(CodeGen *g, ImportTableEntry *import, B
         return resolve_cast(g, context, node, expr_node, wanted_type, CastOpIntToEnum, false);
     }
 
+    // explicit cast from enum type with no payload to integer
+    if (wanted_type->id == TypeTableEntryIdInt &&
+        actual_type->id == TypeTableEntryIdEnum &&
+        actual_type->data.enumeration.gen_field_count == 0)
+    {
+        return resolve_cast(g, context, node, expr_node, wanted_type, CastOpEnumToInt, false);
+    }
+
     add_node_error(g, node,
         buf_sprintf("invalid cast from type '%s' to '%s'",
             buf_ptr(&actual_type->name),

src/codegen.cpp

@@ -1062,6 +1062,8 @@ static LLVMValueRef gen_cast_expr(CodeGen *g, AstNode *node) {
 
         case CastOpIntToEnum:
             return gen_widen_or_shorten(g, node, actual_type, wanted_type->data.enumeration.tag_type, expr_val);
+        case CastOpEnumToInt:
+            return gen_widen_or_shorten(g, node, actual_type->data.enumeration.tag_type, wanted_type, expr_val);
     }
     zig_unreachable();
 }

src/eval.cpp

@@ -694,6 +694,9 @@ void eval_const_expr_implicit_cast(CastOp cast_op,
                 const_val->ok = true;
                 break;
             }
+        case CastOpEnumToInt:
+            bignum_init_unsigned(&const_val->data.x_bignum, other_val->data.x_enum.tag);
+            const_val->ok = true;
     }
 }
 

test/cases/enum_to_int.zig

@@ -0,0 +1,24 @@
+const assert = @import("std").debug.assert;
+
+enum Number {
+    Zero,
+    One,
+    Two,
+    Three,
+    Four,
+}
+
+#attribute("test")
+fn enumToInt() {
+    shouldEqual(Number.Zero, 0);
+    shouldEqual(Number.One, 1);
+    shouldEqual(Number.Two, 2);
+    shouldEqual(Number.Three, 3);
+    shouldEqual(Number.Four, 4);
+}
+
+// TODO add test with this disabled
+#static_eval_enable(false)
+fn shouldEqual(n: Number, expected: usize) {
+    assert(usize(n) == expected);
+}