Create macros for writing Translator functions

This is the first commit in a series of two in order to remove the
PkTranslator trait. The triat has a general implementation of Tranlator
like `impl Translator for PkTranslator where P::Sha256 ...`.

However, this blanket implemented has constraints on associated types
and makes it impossible to implement the trait for a generic type
downstream. Rust compiler does not support for trait specialization yet,
and so we should only provide a macro to ease implementation rather than
a blanket implementation that causes duplicate conflicts downstream

Author: sanket1729

src/macros.rs

@@ -2,6 +2,48 @@
 //!
 //! Macros meant to be used inside the Rust Miniscript library
 
+/// Macro for failing translation for other associated types.
+/// Handy for testing String -> concrete keys as we don't want to specify these
+/// functions repeatedly.
+#[macro_export]
+macro_rules! translate_assoc_fail {
+    ($source: ty, $target:ty, $error_ty: ty) => {
+        fn sha256(
+            &mut self,
+            _sha256: &<$source as MiniscriptKey>::Sha256,
+        ) -> Result<<$target as MiniscriptKey>::Sha256, $error_ty> {
+            panic!("Called sha256 on translate_only_pk")
+        }
+
+        fn hash256(
+            &mut self,
+            _hash256: &<$source as MiniscriptKey>::Hash256,
+        ) -> Result<<$target as MiniscriptKey>::Hash256, $error_ty> {
+            panic!("Called hash256 on translate_only_pk")
+        }
+    };
+}
+
+/// Macro for translation of associated types where the associated type is the same
+/// Handy for Derived -> concrete keys where the associated types are the same.
+#[macro_export]
+macro_rules! translate_assoc_clone {
+    ($source: ty, $target:ty, $error_ty: ty) => {
+        fn sha256(
+            &mut self,
+            _sha256: &<$source as MiniscriptKey>::Sha256,
+        ) -> Result<<$target as MiniscriptKey>::Sha256, $error_ty> {
+            Ok(sha256.clone())
+        }
+
+        fn hash256(
+            &mut self,
+            _hash256: &<$source as MiniscriptKey>::Hash256,
+        ) -> Result<<$target as MiniscriptKey>::Hash256, $error_ty> {
+            Ok(hash256.clone())
+        }
+    };
+}
 /// Allows tests to create a miniscript directly from string as
 /// `ms_str!("c:or_i(pk({}),pk({}))", pk1, pk2)`
 #[cfg(test)]