macros: DeserializeRow uses Flavor

Instead of taking `enforce_order` as boolean flag, DeserializeRow now
takes a string (e.g., `flavor = "enforce_order"`) and converts it to
a variant of the Flavor enum. This way DeserializeRow is unified with
SerializeRow wrt flavor selection.

Author: wprzytula

scylla-cql/src/types/deserialize/row_tests.rs

@@ -91,7 +91,7 @@ struct TestUdtWithNoFieldsUnordered {}
 
 #[allow(unused)]
 #[derive(DeserializeRow)]
-#[scylla(crate = crate, enforce_order)]
+#[scylla(crate = crate, flavor = "enforce_order")]
 struct TestUdtWithNoFieldsOrdered {}
 
 #[test]
@@ -143,7 +143,7 @@ fn test_struct_deserialization_loose_ordering() {
 #[test]
 fn test_struct_deserialization_strict_ordering() {
     #[derive(DeserializeRow, PartialEq, Eq, Debug)]
-    #[scylla(crate = "crate", enforce_order)]
+    #[scylla(crate = "crate", flavor = "enforce_order")]
     struct MyRow<'a> {
         a: &'a str,
         b: Option<i32>,
@@ -180,7 +180,7 @@ fn test_struct_deserialization_strict_ordering() {
 #[test]
 fn test_struct_deserialization_no_name_check() {
     #[derive(DeserializeRow, PartialEq, Eq, Debug)]
-    #[scylla(crate = "crate", enforce_order, skip_name_checks)]
+    #[scylla(crate = "crate", flavor = "enforce_order", skip_name_checks)]
     struct MyRow<'a> {
         a: &'a str,
         b: Option<i32>,
@@ -623,7 +623,7 @@ fn test_struct_deserialization_errors() {
     // Strict ordering
     {
         #[derive(scylla_macros::DeserializeRow, PartialEq, Eq, Debug)]
-        #[scylla(crate = "crate", enforce_order)]
+        #[scylla(crate = "crate", flavor = "enforce_order")]
         struct MyRow<'a> {
             a: &'a str,
             #[scylla(skip)]

scylla-macros/src/deserialize/row.rs

@@ -5,6 +5,8 @@ use proc_macro2::Span;
 use syn::ext::IdentExt;
 use syn::parse_quote;
 
+use crate::Flavor;
+
 use super::{DeserializeCommonFieldAttrs, DeserializeCommonStructAttrs};
 
 #[derive(FromAttributes)]
@@ -13,12 +15,8 @@ struct StructAttrs {
     #[darling(rename = "crate")]
     crate_path: Option<syn::Path>,
 
-    // If true, then the type checking code will require the order of the fields
-    // to be the same in both the Rust struct and the columns. This allows the
-    // deserialization to be slightly faster because looking struct fields up
-    // by name can be avoided, though it is less convenient.
     #[darling(default)]
-    enforce_order: bool,
+    flavor: Flavor,
 
     // If true, then the type checking code won't verify the column names.
     // Columns will be matched to struct fields based solely on the order.
@@ -94,7 +92,7 @@ fn validate_attrs(attrs: &StructAttrs, fields: &[Field]) -> Result<(), darling::
 
     if attrs.skip_name_checks {
         // Skipping name checks is only available in enforce_order mode
-        if !attrs.enforce_order {
+        if attrs.flavor != Flavor::EnforceOrder {
             let error =
                 darling::Error::custom("attribute <skip_name_checks> requires <enforce_order>.");
             errors.push(error);
@@ -153,18 +151,16 @@ type StructDesc = super::StructDescForDeserialize<StructAttrs, Field>;
 
 impl StructDesc {
     fn generate_type_check_method(&self) -> syn::ImplItemFn {
-        if self.attrs.enforce_order {
-            TypeCheckAssumeOrderGenerator(self).generate()
-        } else {
-            TypeCheckUnorderedGenerator(self).generate()
+        match self.attrs.flavor {
+            Flavor::MatchByName => TypeCheckUnorderedGenerator(self).generate(),
+            Flavor::EnforceOrder => TypeCheckAssumeOrderGenerator(self).generate(),
         }
     }
 
     fn generate_deserialize_method(&self) -> syn::ImplItemFn {
-        if self.attrs.enforce_order {
-            DeserializeAssumeOrderGenerator(self).generate()
-        } else {
-            DeserializeUnorderedGenerator(self).generate()
+        match self.attrs.flavor {
+            Flavor::MatchByName => DeserializeUnorderedGenerator(self).generate(),
+            Flavor::EnforceOrder => DeserializeAssumeOrderGenerator(self).generate(),
         }
     }
 }

scylla/src/macros.rs

@@ -443,19 +443,25 @@ pub use scylla_macros::DeserializeValue;
 /// macro itself, so in those cases the user must provide an alternative path
 /// to either the `scylla` or `scylla-cql` crate.
 ///
-/// `#[scylla(enforce_order)]`
+/// `#[scylla(flavor = "flavor_name")]`
 ///
-/// By default, the generated deserialization code will be insensitive
-/// to the column order - when processing a column, the corresponding Rust field
-/// will be looked up and the column will be deserialized based on its type.
-/// However, if the column order and the Rust field order is known to be the
-/// same,  then the `enforce_order` annotation can be used so that a more
-/// efficient implementation that does not perform lookups is be generated.
-/// The generated code will still check that the column and field names match.
+/// Allows to choose one of the possible "flavors", i.e. the way how the
+/// generated code will approach deserialization. Possible flavors are:
+///
+/// - `"match_by_name"` (default) - the generated implementation _does not
+///   require_ the fields in the Rust struct to be in the same order as the
+///   columns in the row. During deserialization, the implementation will take
+///   care to deserialize the columns in the order which the database provided.
+/// - `"enforce_order"` - the generated implementation _requires_ the fields
+///   in the Rust struct to be in the same order as the columns in the row.
+///   If the order is incorrect, type checking/deserialization will fail.
+///   This is a less robust flavor than `"match_by_name"`, but should be
+///   slightly more performant as it doesn't need to perform lookups by name.
+///   The generated code will still check that the column and field names match.
 ///
 /// #[(scylla(skip_name_checks))]
 ///
-/// This attribute only works when used with `enforce_order`.
+/// This attribute only works when used with `flavor = "enforce_order"`.
 ///
 /// If set, the generated implementation will not verify the column names at
 /// all. Because it only works with `enforce_order`, it will deserialize first