rewrite derive macro

bitbuffer_derive/src/discriminant.rs

@@ -1,36 +1,105 @@
-use syn::{Expr, Lit, Variant};
-use syn_util::get_attribute_value;
+use crate::err;
+use proc_macro2::{Span, TokenStream};
+use quote::{quote, quote_spanned};
+use std::convert::{TryFrom, TryInto};
+use syn::spanned::Spanned;
+use syn::{Error, Expr, ExprLit, Lit, LitInt};
 
+#[derive(Copy, Clone)]
 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 TryFrom<Expr> for Discriminant {
+    type Error = Error;
+
+    fn try_from(value: Expr) -> Result<Self, Self::Error> {
+        match value {
+            Expr::Lit(ExprLit { lit, .. }) => lit.try_into(),
+            _ => err("non literal discriminant", value.span())?,
         }
     }
 }
 
-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)
+impl TryFrom<Lit> for Discriminant {
+    type Error = Error;
+
+    fn try_from(value: Lit) -> Result<Self, Self::Error> {
+        let span = value.span();
+        match value {
+            Lit::Int(lit) => Ok(Discriminant::Int(lit.base10_parse()?)),
+            Lit::Str(lit) => match lit.value().as_str() {
+                "_" => Ok(Discriminant::Wildcard),
+                _ => err(
+                    "discriminant is required to be an integer literal or \"_\"",
+                    span,
+                ),
+            },
+            _ => err(
+                "discriminant is required to be an integer literal or \"_\"",
+                span,
+            ),
+        }
+    }
+}
+
+impl Discriminant {
+    pub fn read_token(&self, last_discriminant: &mut isize, span: Span) -> TokenStream {
+        match self {
+            Discriminant::Int(discriminant) => {
+                let lit = LitInt::new(&format!("{}", discriminant), span);
+                *last_discriminant = *discriminant as isize;
+                quote! { #lit }
+            }
+            Discriminant::Wildcard => quote! { _ },
+            Discriminant::Default => {
+                let new_discriminant = (*last_discriminant + 1) as usize;
+                let lit = LitInt::new(&format!("{}", new_discriminant), span);
+                *last_discriminant += 1;
+                quote! { #lit }
+            }
+        }
+    }
+    pub fn write_token(
+        &self,
+        last_discriminant: &mut isize,
+        max_discriminant: usize,
+        span: Span,
+    ) -> TokenStream {
+        match self {
+            Discriminant::Int(discriminant) => {
+                let lit = LitInt::new(&format!("{}", discriminant), span);
+                *last_discriminant = *discriminant as isize;
+                quote_spanned! { span => #lit }
+            }
+            Discriminant::Wildcard => {
+                let free_discriminant = max_discriminant + 1;
+                let lit = LitInt::new(&format!("{}", free_discriminant), span);
+                quote_spanned! { span => #lit }
+            }
+            Discriminant::Default => {
+                let new_discriminant = (*last_discriminant + 1) as usize;
+                let lit = LitInt::new(&format!("{}", new_discriminant), span);
+                *last_discriminant += 1;
+                quote_spanned! { span => #lit }
+            }
+        }
+    }
+
+    pub fn max_value(&self, last_discriminant: &mut isize) -> usize {
+        match self {
+            Discriminant::Int(discriminant) => {
+                *last_discriminant = *discriminant as isize;
+                *discriminant
+            }
+            Discriminant::Wildcard => 0,
+            Discriminant::Default => {
+                let new_discriminant = (*last_discriminant + 1) as usize;
+                *last_discriminant += 1;
+                new_discriminant
+            }
+        }
     }
 }