bunch of write stuff

bitbuffer_derive/src/discriminant.rs

@@ -0,0 +1,36 @@
+use syn::{Expr, Lit, Variant};
+use syn_util::get_attribute_value;
+
+pub enum Discriminant {
+    Int(usize),
+    Default,
+    Wildcard,
+}
+
+impl From<Lit> for Discriminant {
+    fn from(lit: Lit) -> Self {
+        match lit {
+            Lit::Int(lit) => Discriminant::Int(lit.base10_parse::<usize>().unwrap()),
+            Lit::Str(lit) => match lit.value().as_str() {
+                "_" => Discriminant::Wildcard,
+                _ => panic!("discriminant is required to be an integer literal or \"_\""),
+            },
+            _ => panic!("discriminant is required to be an integer literal or \"_\""),
+        }
+    }
+}
+
+impl From<&Variant> for Discriminant {
+    fn from(variant: &Variant) -> Self {
+        variant
+            .discriminant
+            .as_ref()
+            .map(|(_, expr)| match expr {
+                Expr::Lit(expr_lit) => expr_lit.lit.clone(),
+                _ => panic!("discriminant is required to be an integer literal"),
+            })
+            .or_else(|| get_attribute_value(&variant.attrs, &["discriminant"]))
+            .map(Discriminant::from)
+            .unwrap_or(Discriminant::Default)
+    }
+}