Improved error messages

Author: vigna

epserde/src/deser/mod.rs

@@ -400,6 +400,7 @@ pub fn check_header<T: SerInner<SerType: TypeHash + AlignHash>>(
     backend: &mut impl ReadWithPos,
 ) -> Result<()> {
     let self_type_name = core::any::type_name::<T>().to_string();
+    let self_ser_type_name = core::any::type_name::<T::SerType>().to_string();
     let mut type_hasher = xxhash_rust::xxh3::Xxh3::new();
     T::SerType::type_hash(&mut type_hasher);
     let self_type_hash = type_hasher.finish();
@@ -438,18 +439,20 @@ pub fn check_header<T: SerInner<SerType: TypeHash + AlignHash>>(
 
     if ser_type_hash != self_type_hash {
         return Err(Error::WrongTypeHash {
-            self_type_name,
             ser_type_name,
-            self_type_hash,
             ser_type_hash,
+            self_type_name,
+            self_ser_type_name,
+            self_type_hash,
         });
     }
     if ser_align_hash != self_align_hash {
         return Err(Error::WrongAlignHash {
-            self_type_name,
             ser_type_name,
-            self_align_hash,
             ser_align_hash,
+            self_type_name,
+            self_ser_type_name,
+            self_align_hash,
         });
     }
 
@@ -521,13 +524,21 @@ pub enum Error {
     /// A tag is wrong (e.g., for [`Option`]).
     InvalidTag(usize),
     #[error(
-        r#"Wrong type hash: actual = 0x{ser_type_hash:016x}, expected = 0x{self_type_hash:016x}.
-You are trying to deserialize a file with the wrong type. You might also be trying to deserialize
-a tuple of mixed zero-copy types, which is no longer supported since 0.8.0,
-an instance containing tuples, whose type hash was fixed in 0.9.0,
-or an instance containing a vector or a string that was serialized before 0.10.0.
-The serialized type is '{ser_type_name}',
-but the deserializable type on which the deserialization method was invoked is '{self_type_name}'."#
+        r#"Wrong type hash
+Actual: 0x{ser_type_hash:016x}; expected: 0x{self_type_hash:016x}.
+
+The serialized type is
+    '{ser_type_name}',
+but the deserializable type on which the deserialization method was invoked is
+    '{self_type_name}',
+which has serialization type
+    {self_ser_type_name}.
+
+You are trying to deserialize a file with the wrong type. You might also be
+trying to deserialize a tuple of mixed zero-copy types, which is no longer
+supported since 0.8.0, an instance containing tuples, whose type hash was fixed
+in 0.9.0, or an instance containing a vector or a string that was serialized
+before 0.10.0."#
     )]
     /// The type hash is wrong. Probably the user is trying to deserialize a
     /// file with the wrong type.
@@ -538,19 +549,28 @@ but the deserializable type on which the deserialization method was invoked is '
         ser_type_hash: u64,
         // The name of the type on which the deserialization method was called.
         self_type_name: String,
+        // The name of the serialization type of `self_type_name`.
+        self_ser_type_name: String,
         // The [`TypeHash`] of the type on which the deserialization method was called.
         self_type_hash: u64,
     },
     #[error(
-r#"Wrong alignment hash: actual = 0x{ser_align_hash:016x}, expected = 0x{self_align_hash:016x}.
-You might be trying to deserialize a file that was serialized on an architecture
-with different alignment requirements, or some of the fields of the type
-might have changed their copy type (zero or deep). You might also be trying to deserialize
-an array, whose alignment hash has been fixed in 0.8.0. It is also
-possible that you are trying to deserialize a file serialized before version 0.10.0
-in which repr attributes were not sorted lexicographically.
-The serialized type is '{ser_type_name}',  but the deserializable type on which the the deserialization
-method was invoked is '{self_type_name}'."#
+        r#"Wrong alignment hash
+Actual: 0x{ser_align_hash:016x}; expected: 0x{self_align_hash:016x}.
+
+The serialized type is
+    '{ser_type_name}',
+but the deserializable type on which the deserialization method was invoked is
+    '{self_type_name}',
+which has serialization type
+    {self_ser_type_name}.
+
+You might be trying to deserialize a file that was serialized on an
+architecture with different alignment requirements, or some of the fields of
+the type might have changed their copy type (zero or deep). You might also be
+trying to deserialize an array, whose alignment hash has been fixed in 0.8.0.
+It is also possible that you are trying to deserialize a file serialized before
+version 0.10.0 in which repr attributes were not sorted lexicographically."#
     )]
     /// The type representation hash is wrong. Probably the user is trying to
     /// deserialize a file with some zero-copy type that has different
@@ -564,6 +584,8 @@ method was invoked is '{self_type_name}'."#
         ser_align_hash: u64,
         // The name of the type on which the deserialization method was called.
         self_type_name: String,
+        // The name of the serialization type of `self_type_name`.
+        self_ser_type_name: String,
         // The [`AlignHash`] of the type on which the deserialization method was called.
         self_align_hash: u64,
     },

epserde/src/ser/mod.rs

@@ -206,7 +206,7 @@ pub fn write_header<S: TypeHash + AlignHash>(backend: &mut impl WriteWithNames)
 
     backend.write("TYPE_HASH", &type_hasher.finish())?;
     backend.write("REPR_HASH", &align_hasher.finish())?;
-    backend.write("TYPE_NAME", &core::any::type_name::<S>().to_string())
+    backend.write("TYPE_NAME", &core::any::type_name::<S>())
 }
 
 /// A helper trait that makes it possible to implement differently serialization