From 11caeadfef6c1ac72e3cf80c824315c320acddec Mon Sep 17 00:00:00 2001
From: Pierre Chifflier <chifflier@wzdftpd.net>
Date: Thu, 14 Nov 2024 12:26:13 +0100
Subject: [PATCH] Add `ToStatic` custom derive attribute

---
 derive/src/lib.rs      |  6 +++
 derive/src/tostatic.rs | 99 ++++++++++++++++++++++++++++++++++++++++++
 src/derive.rs          | 31 +++++++++++++
 src/traits.rs          | 16 +++++++
 4 files changed, 152 insertions(+)
 create mode 100644 derive/src/tostatic.rs

diff --git a/derive/src/lib.rs b/derive/src/lib.rs
index c75cf37..b2a486a 100644
--- a/derive/src/lib.rs
+++ b/derive/src/lib.rs
@@ -2,9 +2,11 @@ mod alias;
 mod container;
 mod sequence;
 mod set;
+mod tostatic;
 use alias::*;
 use sequence::*;
 use set::*;
+use tostatic::derive_tostatic;
 
 synstructure::decl_derive!([BerAlias, attributes(
     debug_derive,
@@ -62,3 +64,7 @@ synstructure::decl_derive!([DerSet, attributes(
     error,
     map_err
 )] => derive_der_set);
+
+synstructure::decl_derive!([ToStatic, attributes(
+    debug_derive
+)] => derive_tostatic);
diff --git a/derive/src/tostatic.rs b/derive/src/tostatic.rs
new file mode 100644
index 0000000..d99e60e
--- /dev/null
+++ b/derive/src/tostatic.rs
@@ -0,0 +1,99 @@
+use proc_macro2::Span;
+use quote::quote;
+use syn::{Data, DeriveInput, FieldsNamed, FieldsUnnamed, Ident, LitInt};
+
+pub fn derive_tostatic(s: synstructure::Structure) -> proc_macro2::TokenStream {
+    let ast = s.ast();
+
+    let debug_derive = ast.attrs.iter().any(|attr| {
+        attr.meta
+            .path()
+            .is_ident(&Ident::new("debug_derive", Span::call_site()))
+    });
+
+    let ds = match &ast.data {
+        Data::Struct(ds) => ds,
+        _ => panic!("Unsupported type, cannot derive"),
+    };
+
+    let ts = match &ds.fields {
+        syn::Fields::Unit => derive_unit_struct(ast),
+        syn::Fields::Named(fields) => derive_named_struct(fields, ast),
+        syn::Fields::Unnamed(fields) => derive_unnamed_struct(fields, ast),
+    };
+
+    let ts = s.gen_impl(ts);
+
+    if debug_derive {
+        eprintln!("{ts}");
+    }
+    ts
+}
+
+fn derive_unit_struct(ast: &DeriveInput) -> proc_macro2::TokenStream {
+    let struct_ident = &ast.ident;
+
+    quote! {
+        gen impl asn1_rs::ToStatic for @Self {
+            type Owned = #struct_ident;
+
+            fn to_static(&self) -> Self::Owned {
+                #struct_ident
+            }
+        }
+    }
+}
+
+fn derive_named_struct(fields: &FieldsNamed, ast: &DeriveInput) -> proc_macro2::TokenStream {
+    let fields: Vec<_> = fields.named.iter().collect();
+
+    let field_idents: Vec<_> = fields.iter().map(|f| f.ident.clone()).collect();
+
+    let field_instrs = field_idents.iter().map(|ident| {
+        quote! { let #ident = self.#ident.to_static(); }
+    });
+
+    let struct_ident = &ast.ident;
+
+    quote! {
+        gen impl asn1_rs::ToStatic for @Self {
+            type Owned = #struct_ident<'static>;
+
+            fn to_static(&self) -> Self::Owned {
+                #(#field_instrs)*
+                #struct_ident{
+                    #(#field_idents,)*
+                }
+            }
+        }
+    }
+}
+
+fn derive_unnamed_struct(fields: &FieldsUnnamed, ast: &DeriveInput) -> proc_macro2::TokenStream {
+    // TODO: if unnamed, check that there is only one lifetime in ast.generics
+    let fields: Vec<_> = fields.unnamed.iter().collect();
+
+    let field_idents: Vec<_> = (0..fields.len())
+        .map(|idx| Ident::new(&format!("_{idx}"), Span::call_site()))
+        .collect();
+
+    let field_instrs = field_idents.iter().enumerate().map(|(idx, ident)| {
+        let idx = LitInt::new(&format!("{idx}"), Span::call_site());
+        quote! { let #ident = self.#idx.to_static(); }
+    });
+
+    let struct_ident = &ast.ident;
+
+    quote! {
+        gen impl asn1_rs::ToStatic for @Self {
+            type Owned = #struct_ident<'static>;
+
+            fn to_static(&self) -> Self::Owned {
+                #(#field_instrs)*
+                #struct_ident(
+                    #(#field_idents,)*
+                )
+            }
+        }
+    }
+}
diff --git a/src/derive.rs b/src/derive.rs
index faf862e..eae33a8 100644
--- a/src/derive.rs
+++ b/src/derive.rs
@@ -320,3 +320,34 @@ pub use asn1_rs_derive::BerAlias;
 /// struct S(pub u32);
 /// ```
 pub use asn1_rs_derive::DerAlias;
+
+/// # ToStatic custom derive
+///
+/// `ToStatic` is a custom derive attribute, to derive the [`ToStatic`](ToStatic) trait automatically from the structure definition.
+///
+/// ## Example
+///
+/// ```rust
+/// use asn1_rs::ToStatic;
+/// use std::borrow::Cow;
+///
+/// #[derive(ToStatic)]
+/// struct S<'a>(pub Cow<'a, str>);
+/// ```
+///
+/// ## Debugging
+///
+/// To help debugging the generated code, the `#[debug_derive]` attribute has been added.
+///
+/// When this attribute is specified, the generated code will be printed to `stderr` during compilation.
+///
+/// Example:
+/// ```rust
+/// use asn1_rs::ToStatic;
+/// use std::borrow::Cow;
+///
+/// #[derive(ToStatic)]
+/// #[debug_derive]
+/// struct S<'a>(pub Cow<'a, str>);
+/// ```
+pub use asn1_rs_derive::ToStatic;
diff --git a/src/traits.rs b/src/traits.rs
index 1f8a3da..cddbd53 100644
--- a/src/traits.rs
+++ b/src/traits.rs
@@ -1,6 +1,8 @@
 use crate::debug::{trace, trace_generic};
 use crate::error::*;
 use crate::{parse_der_any, Any, Class, Explicit, Implicit, Tag, TaggedParser};
+use alloc::borrow::Cow;
+use alloc::string::ToString;
 use core::convert::{TryFrom, TryInto};
 use core::fmt::{Debug, Display};
 #[cfg(feature = "std")]
@@ -355,3 +357,17 @@ pub trait ToStatic {
     type Owned: 'static;
     fn to_static(&self) -> Self::Owned;
 }
+
+impl ToStatic for Cow<'_, str> {
+    type Owned = Cow<'static, str>;
+    fn to_static(&self) -> <Self as ToStatic>::Owned {
+        Cow::Owned(self.to_string())
+    }
+}
+
+impl ToStatic for Cow<'_, [u8]> {
+    type Owned = Cow<'static, [u8]>;
+    fn to_static(&self) -> <Self as ToStatic>::Owned {
+        Cow::Owned(self.to_vec())
+    }
+}