From 4c0f94bd48fb391ea5c0d2d9fe93c171d5fd07f7 Mon Sep 17 00:00:00 2001
From: Jessi <me@jessiep.me>
Date: Mon, 10 Jun 2024 14:28:36 -0400
Subject: [PATCH] from_repr

---
 proc_macro/src/from_repr.rs | 64 +++++++++++++++++++++++++++++++++++++
 proc_macro/src/lib.rs       |  6 ++++
 src/lib.rs                  | 13 +++++---
 3 files changed, 79 insertions(+), 4 deletions(-)
 create mode 100644 proc_macro/src/from_repr.rs

diff --git a/proc_macro/src/from_repr.rs b/proc_macro/src/from_repr.rs
new file mode 100644
index 0000000..a3b7a79
--- /dev/null
+++ b/proc_macro/src/from_repr.rs
@@ -0,0 +1,64 @@
+use proc_macro::{TokenStream};
+
+const VALID: &[&'static str] = &[
+    "u8", "u16", "u32", "u64", "u128",
+    "i8", "i16", "i32", "i64", "i128",
+];
+
+pub fn derive_from_repr(input: TokenStream) -> TokenStream {
+    let syn::DeriveInput { attrs, ident, data, .. } = syn::parse_macro_input!(input);
+    let edata = match data {
+        syn::Data::Enum(edata) => edata,
+        _invalid => return TokenStream::from(quote::quote! { compile_error!("The identifier should not be empty"); }),
+    };
+
+    let repr_type = attrs.iter()
+        .filter_map(|attribute| {
+            // verify it is a repr type
+            attribute.path().get_ident()?
+                .to_string().eq("repr")
+                .then_some(())?;
+            let mut repr_type: Option<syn::Path> = None;
+            let _ = attribute.parse_nested_meta(|meta| {
+                for &v in VALID {
+                    if meta.path.is_ident(v) {
+                        repr_type = Some(meta.path);
+                        return Ok(())
+                    }
+                }
+                Err(meta.error("unrecognized repr"))
+            });
+            repr_type
+        }).next();
+
+    let repr = match repr_type {
+        Some(repr) => repr,
+        None => {
+            return TokenStream::from(quote::quote! {
+                compile_error!("PrimitiveEnum requires the #[repr(u/i*)] attribute");
+            })
+        }
+    };
+
+    let values = edata.variants.iter().filter_map(|variant| {
+        if let Some((_, desc)) = &variant.discriminant {
+            let variant = &variant.ident;
+            Some(quote::quote! {
+                #desc => Some(Self::#variant),
+            })
+        } else { None }
+    });
+
+    let name = &ident;
+    TokenStream::from(quote::quote! {
+        impl eset::FromRepr for #name {
+            type Repr = #repr;
+            fn from_repr(repr: #repr) -> Option<Self>  {
+                match repr {
+                    #(#values)*
+                    _ => None
+                }
+            }
+        }
+    })
+}
\ No newline at end of file
diff --git a/proc_macro/src/lib.rs b/proc_macro/src/lib.rs
index 62ac1d9..cd62d47 100644
--- a/proc_macro/src/lib.rs
+++ b/proc_macro/src/lib.rs
@@ -5,8 +5,14 @@
 use proc_macro::*;
 
 mod sigscan;
+mod from_repr;
 
 #[proc_macro]
 pub fn signature(input: TokenStream) -> TokenStream {
     sigscan::macro_proc(input)
+}
+
+#[proc_macro_derive(FromRepr)]
+pub fn derive_from_repr(input: TokenStream) -> TokenStream {
+    from_repr::derive_from_repr(input)
 }
\ No newline at end of file
diff --git a/src/lib.rs b/src/lib.rs
index 2116162..390f8d9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -32,9 +32,6 @@ pub mod win32;
 #[cfg(feature = "win32")]
 pub use win32::{ image_base, image_header, find_kernel32, process_executable };
 
-/// re-export the signature macro
-pub use xgen::signature;
-
 mod time;
 pub use time::dur;
 
@@ -45,4 +42,12 @@ mod strings;
 pub use strings::*;
 
 mod iter_tools;
-pub use iter_tools::*;
\ No newline at end of file
+pub use iter_tools::*;
+
+/// re-export the signature macro
+pub use xgen::signature;
+pub use xgen::FromRepr;
+pub trait FromRepr: Sized {
+    type Repr;
+    fn from_repr(repr: Self::Repr) -> Option<Self>;
+}