Remove unnecessary cast in generated code

The cast seems to have been added as a precaution, but upon further
inspection we can see that it's not necessary in any situation.

Add a test to make sure this allow-by-default lint isn't triggered.
Also test enums with exactly one variant, as the generated code is
subtly different.

Author: meithecatte

enumflags_derive/src/lib.rs

@@ -224,7 +224,7 @@ fn gen_enumflags(ident: &Ident, item: &DeriveInput, data: &DataEnum)
 
                 fn all() -> Self::Type {
                     // make sure it's evaluated at compile time
-                    const VALUE: #ty = #all as #ty;
+                    const VALUE: #ty = #all;
                     VALUE
                 }
 

test_suite/tests/not_literal.rs

@@ -1,3 +1,5 @@
+#![forbid(trivial_numeric_casts)]
+
 const FOO_BAR: u8 = 1;
 const FOO_BAZ: u8 = 2;
 
@@ -7,3 +9,9 @@ enum Foo {
     Bar = FOO_BAR,
     Baz = FOO_BAZ,
 }
+
+#[derive(Clone, Copy, enumflags2::BitFlags)]
+#[repr(u8)]
+enum SingleTest {
+    Hello = FOO_BAR,
+}