From 8ecd728f14da6ce1376822557fd63d3002a380de Mon Sep 17 00:00:00 2001
From: HampusM <hampus@hampusmat.com>
Date: Wed, 16 Oct 2024 23:44:30 +0200
Subject: feat(util-macros): add macro FromRepr

---
 util-macros/src/lib.rs | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

(limited to 'util-macros/src/lib.rs')

diff --git a/util-macros/src/lib.rs b/util-macros/src/lib.rs
index 26f1936..83b5f58 100644
--- a/util-macros/src/lib.rs
+++ b/util-macros/src/lib.rs
@@ -1,5 +1,6 @@
 use proc_macro::{TokenStream, TokenTree};
 use quote::quote;
+use syn::{parse, Ident, ItemEnum};
 
 /// Subtracts two numbers and calls a given callback macro with the result. Optionally, a
 /// additional argument (delimeted) can be given which will also be passed to the
@@ -139,3 +140,62 @@ pub fn sub(input: TokenStream) -> TokenStream
     }
     .into()
 }
+
+#[proc_macro_derive(FromRepr)]
+pub fn from_repr(input: TokenStream) -> TokenStream
+{
+    let enum_item = parse::<ItemEnum>(input).unwrap();
+
+    let repr_attr = enum_item
+        .attrs
+        .iter()
+        .find(|attr| {
+            attr.path()
+                .get_ident()
+                .is_some_and(|attr_ident| attr_ident == "repr")
+        })
+        .unwrap();
+
+    let repr = repr_attr.parse_args::<Ident>().unwrap();
+
+    let repr_str = repr.to_string();
+
+    if !((repr_str.starts_with('u') || repr_str.starts_with('i'))
+        && repr_str
+            .chars()
+            .skip(1)
+            .all(|character| character.is_ascii_digit()))
+    {
+        panic!("Invalid repr. Must be u* or i* where * is a number");
+    }
+
+    let variants = enum_item.variants.iter().map(|variant| {
+        let Some((_, discriminant)) = &variant.discriminant else {
+            panic!("All variants must have discriminants");
+        };
+
+        (variant.ident.clone(), discriminant.clone())
+    });
+
+    let match_arms = variants.map(|(variant, discriminant)| {
+        quote! {
+            #discriminant => Some(Self::#variant),
+        }
+    });
+
+    let enum_ident = enum_item.ident.clone();
+
+    quote! {
+        impl #enum_ident
+        {
+            pub fn from_repr(repr: #repr) -> Option<Self>
+            {
+                match repr {
+                    #(#match_arms)*
+                    _ => None
+                }
+            }
+        }
+    }
+    .into()
+}
-- 
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