be explicit in darling support

miniconf/tests/ui/internal_no_leaf.rs

@@ -9,6 +9,9 @@ pub enum EnumEmpty {#[tree(skip)] V}
 #[derive(Tree)]
 pub struct StructUnit;
 
+#[derive(Tree)]
+pub struct StructUnitTuple ();
+
 #[derive(Tree)]
 pub struct StructEmptyTuple (#[tree(skip)] ());
 

miniconf/tests/ui/internal_no_leaf.stderr

@@ -10,20 +10,28 @@ error: Internal nodes must have at least one leaf
 7 | pub enum EnumEmpty {#[tree(skip)] V}
   |          ^^^^^^^^^
 
+error: Unsupported shape `no fields`. Expected named fields or unnamed fields.
+ --> tests/ui/internal_no_leaf.rs:9:10
+  |
+9 | #[derive(Tree)]
+  |          ^^^^
+  |
+  = note: this error originates in the derive macro `Tree` (in Nightly builds, run with -Z macro-backtrace for more info)
+
 error: Internal nodes must have at least one leaf
-  --> tests/ui/internal_no_leaf.rs:10:12
+  --> tests/ui/internal_no_leaf.rs:13:12
    |
-10 | pub struct StructUnit;
-   |            ^^^^^^^^^^
+13 | pub struct StructUnitTuple ();
+   |            ^^^^^^^^^^^^^^^
 
 error: Internal nodes must have at least one leaf
-  --> tests/ui/internal_no_leaf.rs:13:12
+  --> tests/ui/internal_no_leaf.rs:16:12
    |
-13 | pub struct StructEmptyTuple (#[tree(skip)] ());
+16 | pub struct StructEmptyTuple (#[tree(skip)] ());
    |            ^^^^^^^^^^^^^^^^
 
 error: Internal nodes must have at least one leaf
-  --> tests/ui/internal_no_leaf.rs:16:12
+  --> tests/ui/internal_no_leaf.rs:19:12
    |
-16 | pub struct StructEmpty {#[tree(skip)] _f: ()}
+19 | pub struct StructEmpty {#[tree(skip)] _f: ()}
    |            ^^^^^^^^^^^

miniconf_derive/src/tree.rs

@@ -53,7 +53,7 @@ impl TreeVariant {
 }
 
 #[derive(Debug, FromDeriveInput, Clone)]
-#[darling(attributes(tree), supports(any), and_then=Self::parse)]
+#[darling(attributes(tree), supports(struct_named, struct_newtype, struct_tuple, enum_newtype, enum_tuple, enum_unit), and_then=Self::parse)]
 #[darling()]
 pub struct Tree {
     ident: syn::Ident,