Function pointers are now compile time constants.

const enum cannot be set to function pointer unless it's a lambda #2282.

releasenotes.md

@@ -37,6 +37,7 @@
 - Array indices are now using int64 internally.
 - Bit shift operation fails with inline uint enum despite matching underlying type #2279.
 - Fix to codegen when using a bitstruct constant defined using a cast with an operator #2248.
+- Function pointers are now compile time constants. 
 
 ### Stdlib changes
 - Improve contract for readline. #2280

src/compiler/sema_decls.c

@@ -1675,7 +1675,7 @@ bool sema_analyse_const_enum_constant_val(SemaContext *context, Decl *decl)
 {
 	Expr *value = decl->enum_constant.value;
 	if (!sema_analyse_inferred_expr(context, decl->type, value)) return decl_poison(decl);
-	if (!sema_cast_const(value))
+	if (!expr_is_runtime_const(value))
 	{
 		SEMA_ERROR(value, "Expected an constant enum value.");
 		return decl_poison(decl);

src/compiler/sema_expr.c

@@ -8366,9 +8366,11 @@ RESOLVED:
 	if (no_optional->type_kind == TYPE_FUNC_RAW)
 	{
 		expr->type = type_add_optional(type_get_func_ptr(no_optional), IS_OPTIONAL((inner)));
-		return true;
 	}
-	expr->type = type_get_ptr_recurse(inner->type);
+	else
+	{
+		expr->type = type_get_ptr_recurse(inner->type);
+	}
 	if (inner->expr_kind == EXPR_IDENTIFIER)
 	{
 		Decl *ident = inner->ident_expr;

test/test_suite/enumerations/const_enum_with_function_ptr.c3t

@@ -0,0 +1,35 @@
+// #target: macos-x64
+module test;
+import std;
+fn int foo() => 0;
+alias FooFn = fn int();
+
+enum Foo : (FooFn f)
+{
+  FOO = fn int() => 0, // allowed
+  BAR = &foo, // allowed
+}
+
+enum Bar : const FooFn
+{
+  FOO = fn int() => 0, // allowed
+  BAR = &foo, // Error: Expected an constant enum value.
+}
+fn int main()
+{
+	Bar b = FOO;
+	Bar b2 = BAR;
+	var $c = &foo == &foo;
+	return 0;
+}
+
+/* #expect: test.ll
+
+define i32 @main() #0 {
+entry:
+  %b = alloca ptr, align 8
+  %b2 = alloca ptr, align 8
+  store ptr @"test.$global$lambda2", ptr %b, align 8
+  store ptr @test.foo, ptr %b2, align 8
+  ret i32 0
+}