[WIP] der: clarify writer draft

der/Cargo.toml

@@ -26,12 +26,14 @@ pem-rfc7468 = { version = "1.0.0-rc.3", optional = true, features = ["alloc"] }
 time = { version = "0.3.4", optional = true, default-features = false }
 zeroize = { version = "1.8", optional = true, default-features = false }
 heapless = { version = "0.8", optional = true, default-features = false }
+tynm = { version = "0.2", optional = true, default-features = false }
 
 [dev-dependencies]
 hex-literal = "1"
 proptest = "1"
 
 [features]
+default = ["clarify"]
 alloc = ["zeroize?/alloc"]
 std = ["alloc"]
 
@@ -41,6 +43,7 @@ derive = ["dep:der_derive"]
 oid = ["dep:const-oid"]
 pem = ["dep:pem-rfc7468", "alloc", "zeroize"]
 real = []
+clarify = ["std", "pem", "dep:tynm", "derive"]
 
 [package.metadata.docs.rs]
 all-features = true

der/src/asn1/any.rs

@@ -56,6 +56,13 @@ impl<'a> AnyRef<'a> {
     pub fn value(self) -> &'a [u8] {
         self.value.as_slice()
     }
+    /// Returns [`Tag`] and [`Length`] of self.
+    pub fn header(&self) -> Header {
+        Header {
+            tag: self.tag,
+            length: self.value.len(),
+        }
+    }
 
     /// Attempt to decode this [`AnyRef`] type into the inner value.
     pub fn decode_as<T>(self) -> Result<T, <T as DecodeValue<'a>>::Error>
@@ -66,10 +73,7 @@ impl<'a> AnyRef<'a> {
             return Err(self.tag.unexpected_error(None).to_error().into());
         }
 
-        let header = Header {
-            tag: self.tag,
-            length: self.value.len(),
-        };
+        let header = self.header();
 
         let mut decoder = SliceReader::new(self.value())?;
         let result = T::decode_value(&mut decoder, header)?;

der/src/writer.rs

@@ -1,5 +1,7 @@
 //! Writer trait.
 
+#[cfg(feature = "clarify")]
+pub mod clarify;
 #[cfg(feature = "pem")]
 pub(crate) mod pem;
 pub(crate) mod slice;
@@ -18,6 +20,12 @@ pub trait Writer {
     fn write_byte(&mut self, byte: u8) -> Result<()> {
         self.write(&[byte])
     }
+
+    #[cfg(feature = "clarify")]
+    /// Should return Some(clarifier) for clarify writers
+    fn clarifier(&mut self) -> Option<&mut clarify::Clarifier> {
+        None
+    }
 }
 
 #[cfg(feature = "std")]