knickish · knickish · Feb 22, 2025 · Feb 22, 2025
diff --git a/Cargo.toml b/Cargo.toml
@@ -7,6 +7,7 @@ repository = "https://github.com/knickish/structdiff"
 description = """zero-dependency crate for generating and applying partial diffs between struct instances"""
 keywords      = ["delta-compression", "difference"]
 categories    = ["compression"]
+rust-version = "1.82.0"
 
 [dependencies]
 nanoserde           = { version = "^0.1.37", optional = true }

diff --git a/README.md b/README.md
@@ -48,19 +48,22 @@ assert_ne!(diffed, second);
 For more examples take a look at [integration tests](/tests)
 
 ## Derive macro attributes
-- `#[difference(skip)]` - Do not consider this field when creating a diff
-- `#[difference(recurse)]` - Generate a StructDiff for this field when creating a diff
-- `#[difference(collection_strategy = {})]`
-    - `"ordered_array_like"` - Generates a minimal changeset for ordered, array-like collections of items which implement `PartialEq`. (uses levenshtein difference)
-    - `"unordered_array_like"` - Generates a minimal changeset for unordered, array-like collections of items which implement `Hash + Eq`.
-    - `"unordered_map_like"` - Generates a minimal changeset for unordered, map-like collections for which the key implements `Hash + Eq`.
-- `#[difference(map_equality = {})]` - Used with `unordered_map_like`
-    - `"key_only"` - only replace a key-value pair for which the key has changed
-    - `"key_and_value"` - replace a key-value pair if either the key or value has changed
-- `#[difference(setters)]` - Generate setters for all fields in the struct (used on struct)
-    - Example: for the `field1` of the `Example` struct used above, a function with the signature `set_field1_with_diff(&mut self, value: Option<usize>) -> Option<<Self as StructDiff>::Diff>` will be generated. Useful when a single field will be changed in a struct with many fields, as it saves the comparison of all other fields. 
-- `#[difference(setter)]` - Generate setters for this struct field (used on field)
-- `#[difference(setter_name = {})]` - Use this name instead of the default value when generating a setter for this field (used on field)
+- Field level
+    - `#[difference(skip)]` - Do not consider this field when creating a diff
+    - `#[difference(recurse)]` - Generate a StructDiff for this field when creating a diff
+    - `#[difference(collection_strategy = {})]`
+        - `"ordered_array_like"` - Generates a minimal changeset for ordered, array-like collections of items which implement `PartialEq`. (uses levenshtein difference)
+        - `"unordered_array_like"` - Generates a minimal changeset for unordered, array-like collections of items which implement `Hash + Eq`.
+        - `"unordered_map_like"` - Generates a minimal changeset for unordered, map-like collections for which the key implements `Hash + Eq`.
+    - `#[difference(map_equality = {})]` - Used with `unordered_map_like`
+        - `"key_only"` - only replace a key-value pair for which the key has changed
+        - `"key_and_value"` - replace a key-value pair if either the key or value has changed
+    - `#[difference(setter)]` - Generate setters for this struct field
+    - `#[difference(setter_name = {})]` - Use this name instead of the default value when generating a setter for this field (used on field)
+- Struct Level
+    - `#[difference(setters)]` - Generate setters for all fields in the struct 
+        - Example: for the `field1` of the `Example` struct used above, a function with the signature `set_field1_with_diff(&mut self, value: Option<usize>) -> Option<<Self as StructDiff>::Diff>` will be generated. Useful when a single field will be changed in a struct with many fields, as it saves the comparison of all other fields. 
+    - `#[difference(expose)]`/`#[difference(expose = "MyDiffTypeName")]` - expose the generated difference type (optionally, with the specified name)
 
 ## Optional features
 - [`nanoserde`, `serde`] - Serialization of `Difference` derived associated types. Allows diffs to easily be sent over network.

diff --git a/derive/src/difference.rs b/derive/src/difference.rs
@@ -6,7 +6,7 @@ use alloc::string::String;
 use crate::parse::{Category, ConstValType, Enum, Generic, Struct, Type};
 #[cfg(feature = "generated_setters")]
 use crate::shared::{attrs_all_setters, attrs_setter};
-use crate::shared::{attrs_collection_type, attrs_recurse, attrs_skip};
+use crate::shared::{attrs_collection_type, attrs_expose, attrs_recurse, attrs_skip};
 use proc_macro::TokenStream;
 
 fn get_used_lifetimes(ty: &Type) -> Vec<String> {
@@ -108,8 +108,16 @@ pub(crate) fn derive_struct_diff_struct(struct_: &Struct) -> TokenStream {
     #[cfg(feature = "generated_setters")]
     let mut setters_body = String::new();
 
-    let enum_name =
-        String::from("__".to_owned() + struct_.name.as_ref().unwrap().as_str() + "StructDiffEnum");
+    let exposed = attrs_expose(&struct_.attributes);
+
+    let enum_name = match exposed.clone() {
+        Some(Some(name)) => name,
+        Some(None) => String::from(struct_.name.as_ref().unwrap().to_string() + "StructDiffEnum"),
+        _ => String::from(
+            "__".to_owned() + struct_.name.as_ref().unwrap().as_str() + "StructDiffEnum",
+        ),
+    };
+
     let struct_generics_names_hash: HashSet<String> =
         struct_.generics.iter().map(|x| x.full()).collect();
 
@@ -1000,14 +1008,13 @@ pub(crate) fn derive_struct_diff_struct(struct_: &Struct) -> TokenStream {
         ""
     };
 
+    let const_start = "#[allow(non_camel_case_types)]\nconst _: () = {";
+
     format!(
-        "#[allow(non_camel_case_types)]
-        const _: () = {{
-            use structdiff::collections::*;
+        "{non_exposed_const_start}
             {type_aliases}
             {ref_type_aliases}
             {nanoserde_hack}
-
             #[allow(non_camel_case_types)]
             /// Generated type from StructDiff
             #[derive({owned_derives})]{serde_bounds}
@@ -1027,6 +1034,9 @@ pub(crate) fn derive_struct_diff_struct(struct_: &Struct) -> TokenStream {
             {{
                 {diff_ref_enum_body}
             }}
+        {exposed_const_start}
+
+
 
             impl{ref_enum_def_generics} Into<{enum_name}{owned_enum_impl_generics}> for {enum_name}Ref{ref_enum_impl_generics}
             where
@@ -1070,6 +1080,8 @@ pub(crate) fn derive_struct_diff_struct(struct_: &Struct) -> TokenStream {
 
             {setters}
         }};",
+        non_exposed_const_start = if exposed.is_some() { "" } else { const_start },
+        exposed_const_start = if exposed.is_some() { const_start } else { "" },
         type_aliases = owned_type_aliases,
         ref_type_aliases = ref_type_aliases,
         nanoserde_hack = nanoserde_hack,
@@ -1253,7 +1265,14 @@ pub(crate) fn derive_struct_diff_enum(enum_: &Enum) -> TokenStream {
     let mut type_aliases = String::new();
     let mut used_generics: Vec<&Generic> = Vec::new();
 
-    let enum_name = String::from("__".to_owned() + enum_.name.as_str() + "StructDiffEnum");
+    let exposed = attrs_expose(&enum_.attributes);
+
+    let enum_name = match exposed.clone() {
+        Some(Some(name)) => name,
+        Some(None) => String::from(enum_.name.clone() + "StructDiffEnum"),
+        _ => String::from("__".to_owned() + &enum_.name + "StructDiffEnum"),
+    };
+
     let ref_into_owned_body = format!(
         "Self::Replace(variant) => {}::Replace(variant.clone()),",
         &enum_name
@@ -1425,12 +1444,10 @@ pub(crate) fn derive_struct_diff_enum(enum_: &Enum) -> TokenStream {
     #[cfg(not(feature = "serde"))]
     let serde_bound = "";
 
-    format!(
-        "const _: () = {{
-            use structdiff::collections::*;
-            {type_aliases}
-            {nanoserde_hack}
+    let const_start = "#[allow(non_camel_case_types)]\nconst _: () = {";
 
+    format!(
+        "{non_exposed_const_start}
             /// Generated type from StructDiff
             #[derive({owned_derives})]{serde_bounds}
             #[allow(non_camel_case_types)]
@@ -1450,6 +1467,10 @@ pub(crate) fn derive_struct_diff_enum(enum_: &Enum) -> TokenStream {
             {{
                 Replace(&'__diff_target {struct_name}{struct_generics})
             }}
+        {exposed_const_start}
+
+            {type_aliases}
+            {nanoserde_hack}
 
             impl{ref_enum_def_generics} Into<{enum_name}{enum_impl_generics}> for {enum_name}Ref{ref_enum_impl_generics}
             where
@@ -1500,6 +1521,8 @@ pub(crate) fn derive_struct_diff_enum(enum_: &Enum) -> TokenStream {
                 }}
             }}
         }};",
+        non_exposed_const_start = if exposed.is_some() { "" } else { const_start },
+        exposed_const_start = if exposed.is_some() { const_start } else { "" },
         type_aliases = type_aliases,
         nanoserde_hack = nanoserde_hack,
         owned_derives = owned_derives,

diff --git a/derive/src/lib.rs b/derive/src/lib.rs
@@ -16,11 +16,10 @@ mod parse;
 pub fn derive_struct_diff(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let input = parse::parse_data(input);
 
-    // ok we have an ident, hopefully it's a struct
     let ts = match &input {
         parse::Data::Struct(struct_) if struct_.named => derive_struct_diff_struct(struct_),
         parse::Data::Enum(enum_) => derive_struct_diff_enum(enum_),
-        _ => unimplemented!("Only structs are supported"),
+        _ => unimplemented!("Only structs and enums are supported"),
     };
 
     ts

diff --git a/derive/src/shared.rs b/derive/src/shared.rs
@@ -100,3 +100,11 @@ pub fn attrs_map_strategy(attributes: &[crate::parse::Attribute]) -> Option<MapS
         }
     })
 }
+
+pub fn attrs_expose(attributes: &[crate::parse::Attribute]) -> Option<Option<String>> {
+    attributes.iter().find_map(|attr| match attr.tokens.len() {
+        1 if attr.tokens[0].starts_with("expose") => Some(None),
+        2.. if attr.tokens[0] == "expose" => Some(Some((&attr.tokens[1]).to_string())),
+        _ => return None,
+    })
+}
diff --git a/src/collections/ordered_array_like.rs b/src/collections/ordered_array_like.rs
@@ -237,6 +237,7 @@ fn create_last_change_row<'src, 'target: 'src, T: Clone + PartialEq + 'target>(
     let mut target_forward = target_start..target_end;
     let mut target_rev = (target_end..target_start).rev();
 
+    #[allow(clippy::type_complexity)]
     let (target_range, source_range): (
         &mut dyn Iterator<Item = usize>,
         Box<dyn Fn() -> Box<dyn Iterator<Item = usize>>>,
@@ -750,9 +751,7 @@ mod test {
                 return;
             };
 
-            let changed = apply(changes, s2.chars().collect::<Vec<_>>())
-                .into_iter()
-                .collect::<String>();
+            let changed = apply(changes, s2.chars().collect::<Vec<_>>()).collect::<String>();
             assert_eq!(s1, changed)
         }
     }
@@ -765,18 +764,14 @@ mod test {
         let s1_vec = s1.chars().collect::<Vec<_>>();
         let s2_vec = s2.chars().collect::<Vec<_>>();
 
-        for diff_type in [
-            // levenshtein,
-            hirschberg,
-        ] {
+        {
+            let diff_type = hirschberg;
             let Some(changes) = diff_type(&s1_vec, &s2_vec) else {
                 assert_eq!(&s1_vec, &s2_vec);
                 return;
             };
 
-            let changed = apply(changes, s2.chars().collect::<Vec<_>>())
-                .into_iter()
-                .collect::<String>();
+            let changed = apply(changes, s2.chars().collect::<Vec<_>>()).collect::<String>();
             assert_eq!(s1, changed)
         }
     }
@@ -786,10 +781,8 @@ mod test {
         let s1: Vec<char> = "abc".chars().collect();
         let s2: Vec<char> = "".chars().collect();
 
-        for diff_type in [
-            // levenshtein,
-            hirschberg,
-        ] {
+        {
+            let diff_type = hirschberg;
             let Some(changes) = diff_type(&s1, &s2) else {
                 assert_eq!(s1, s2);
                 return;
@@ -870,9 +863,7 @@ mod test {
                     continue;
                 };
 
-                let changed = apply(changes, s2_vec.clone())
-                    .into_iter()
-                    .collect::<Vec<char>>();
+                let changed = apply(changes, s2_vec.clone()).collect::<Vec<char>>();
                 assert_eq!(&s1_vec, &changed);
             }
         }
@@ -1005,9 +996,7 @@ mod test {
                 return;
             };
 
-            let changed = apply(changes, s2.chars().collect::<Vec<_>>())
-                .into_iter()
-                .collect::<String>();
+            let changed = apply(changes, s2.chars().collect::<Vec<_>>()).collect::<String>();
             assert_eq!(s1, changed)
         }
 
@@ -1024,9 +1013,7 @@ mod test {
                 return;
             };
 
-            let changed = apply(changes, s2.chars().collect::<Vec<_>>())
-                .into_iter()
-                .collect::<String>();
+            let changed = apply(changes, s2.chars().collect::<Vec<_>>()).collect::<String>();
             assert_eq!(s1, changed)
         }
 
@@ -1043,9 +1030,7 @@ mod test {
                     return;
                 };
 
-                let changed = apply(changes, s2.chars().collect::<Vec<_>>())
-                    .into_iter()
-                    .collect::<String>();
+                let changed = apply(changes, s2.chars().collect::<Vec<_>>()).collect::<String>();
                 assert_eq!(s1, changed)
             }
         }
@@ -1063,9 +1048,7 @@ mod test {
                     return;
                 };
 
-                let changed = apply(changes, s2.chars().collect::<Vec<_>>())
-                    .into_iter()
-                    .collect::<String>();
+                let changed = apply(changes, s2.chars().collect::<Vec<_>>()).collect::<String>();
                 assert_eq!(s1, changed)
             }
         }
@@ -1083,9 +1066,7 @@ mod test {
                     return;
                 };
 
-                let changed = apply(changes, s2.chars().collect::<Vec<_>>())
-                    .into_iter()
-                    .collect::<String>();
+                let changed = apply(changes, s2.chars().collect::<Vec<_>>()).collect::<String>();
                 assert_eq!(s1, changed)
             }
         }
@@ -1103,9 +1084,7 @@ mod test {
                     return;
                 };
 
-                let changed = apply(changes, s2.chars().collect::<Vec<_>>())
-                    .into_iter()
-                    .collect::<String>();
+                let changed = apply(changes, s2.chars().collect::<Vec<_>>()).collect::<String>();
                 assert_eq!(s1, changed)
             }
         }

diff --git a/src/collections/unordered_array_like.rs b/src/collections/unordered_array_like.rs
@@ -166,7 +166,7 @@ pub fn unordered_hashcmp<
             UnorderedArrayLikeDiffInternal::Replace(
                 current
                     .into_iter()
-                    .flat_map(|(k, v)| std::iter::repeat(k).take(v))
+                    .flat_map(|(k, v)| std::iter::repeat_n(k, v))
                     .collect(),
             ),
         ));
@@ -333,7 +333,7 @@ where
     Box::new(
         list_hash
             .into_iter()
-            .flat_map(|(k, v)| std::iter::repeat(k).take(v)),
+            .flat_map(|(k, v)| std::iter::repeat_n(k, v)),
     )
 }
 

diff --git a/src/collections/unordered_map_like.rs b/src/collections/unordered_map_like.rs
@@ -167,7 +167,7 @@ pub fn unordered_hashcmp<
         return Some(UnorderedMapLikeDiff(UnorderedMapLikeDiffInternal::Replace(
             current
                 .into_iter()
-                .flat_map(|(k, (v, count))| std::iter::repeat((k, v)).take(count))
+                .flat_map(|(k, (v, count))| std::iter::repeat_n((k, v), count))
                 .collect(),
         )));
     }
@@ -319,7 +319,7 @@ pub fn apply_unordered_hashdiffs<
     Box::new(
         list_hash
             .into_iter()
-            .flat_map(|(k, (v, count))| std::iter::repeat((k.clone(), v.clone())).take(count))
+            .flat_map(|(k, (v, count))| std::iter::repeat_n((k.clone(), v.clone()), count))
             .collect::<Vec<_>>()
             .into_iter(),
     )

diff --git a/tests/derives.rs b/tests/derives.rs
@@ -1,4 +1,4 @@
-#![allow(unused_imports)]
+#![allow(unused_imports, clippy::type_complexity)]
 
 use std::{
     collections::{BTreeMap, BTreeSet, HashMap, HashSet},