Revert changes and require Clone if Copy

This commit aligns `wiggle` a little bit closer with Rust proper in
the sense that now `GuestTypeCopy` implies `GuestTypeClone` which
in turn implies that any type implementing `GuestTypeCopy` will have
to provide `read_from_guest` and `write_to_guest` methods. As a result,
we can safely revert changes introduced in the previous commit.

crates/runtime/src/guest_type.rs

@@ -10,11 +10,12 @@ pub trait GuestType: Sized {
     fn validate<'a>(location: &GuestPtr<'a, Self>) -> Result<(), GuestError>;
 }
 
-pub trait GuestTypeCopy: GuestType + Copy {}
 pub trait GuestTypeClone<'a>: GuestType + Clone {
     fn read_from_guest(location: &GuestPtr<'a, Self>) -> Result<Self, GuestError>;
     fn write_to_guest(&self, location: &GuestPtrMut<'a, Self>);
 }
+// Following trait system in Rust, Copy implies Clone
+pub trait GuestTypeCopy<'a>: GuestTypeClone<'a> + Copy {}
 
 macro_rules! builtin_type {
     ( $( $t:ident ), * ) => {
@@ -33,7 +34,15 @@ macro_rules! builtin_type {
                 Ok(())
             }
         }
-        impl GuestTypeCopy for $t {}
+        impl<'a> GuestTypeClone<'a> for $t {
+            fn read_from_guest(location: &GuestPtr<'a, Self>) -> Result<Self, GuestError> {
+                Ok(*location.as_ref()?)
+            }
+            fn write_to_guest(&self, location: &GuestPtrMut<'a, Self>) {
+                unsafe { (location.as_raw() as *mut $t).write(*self) };
+            }
+        }
+        impl<'a> GuestTypeCopy<'a> for $t {}
         )*
     };
 }

crates/runtime/src/memory/array.rs

@@ -79,7 +79,7 @@ where
 
 impl<'a, T> GuestArray<'a, T>
 where
-    T: GuestTypeCopy,
+    T: GuestTypeCopy<'a>,
 {
     pub fn as_ref(&self) -> Result<GuestArrayRef<'a, T>, GuestError> {
         let mut next = self.ptr.elem(0)?;
@@ -109,7 +109,7 @@ where
 
 pub struct GuestArrayRef<'a, T>
 where
-    T: GuestTypeCopy,
+    T: GuestTypeCopy<'a>,
 {
     ref_: GuestRef<'a, T>,
     num_elems: u32,
@@ -117,7 +117,7 @@ where
 
 impl<'a, T> fmt::Debug for GuestArrayRef<'a, T>
 where
-    T: GuestTypeCopy + fmt::Debug,
+    T: GuestTypeCopy<'a> + fmt::Debug,
 {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(
@@ -130,7 +130,7 @@ where
 
 impl<'a, T> Deref for GuestArrayRef<'a, T>
 where
-    T: GuestTypeCopy,
+    T: GuestTypeCopy<'a>,
 {
     type Target = [T];
 

crates/runtime/src/memory/ptr.rs

@@ -57,7 +57,7 @@ impl<'a, T: GuestType> GuestPtr<'a, T> {
 
 impl<'a, T> GuestPtr<'a, T>
 where
-    T: GuestTypeCopy,
+    T: GuestTypeCopy<'a>,
 {
     pub fn as_ref(&self) -> Result<GuestRef<'a, T>, GuestError> {
         T::validate(&self)?;
@@ -183,7 +183,7 @@ where
 
 impl<'a, T> GuestPtrMut<'a, T>
 where
-    T: GuestTypeCopy,
+    T: GuestTypeCopy<'a>,
 {
     pub fn as_ref(&self) -> Result<GuestRef<'a, T>, GuestError> {
         self.as_immut().as_ref()
@@ -298,7 +298,7 @@ impl<'a, T> GuestRef<'a, T> {
 
 impl<'a, T> Deref for GuestRef<'a, T>
 where
-    T: GuestTypeCopy,
+    T: GuestTypeCopy<'a>,
 {
     type Target = T;
 
@@ -357,7 +357,7 @@ impl<'a, T> GuestRefMut<'a, T> {
 
 impl<'a, T> ::std::ops::Deref for GuestRefMut<'a, T>
 where
-    T: GuestTypeCopy,
+    T: GuestTypeCopy<'a>,
 {
     type Target = T;
 
@@ -372,7 +372,7 @@ where
 
 impl<'a, T> DerefMut for GuestRefMut<'a, T>
 where
-    T: GuestTypeCopy,
+    T: GuestTypeCopy<'a>,
 {
     fn deref_mut(&mut self) -> &mut Self::Target {
         unsafe {