add an (optional) syn backend

.github/workflows/rust.yml

@@ -64,6 +64,29 @@ jobs:
           command: test
           args: --all-features
 
+  test_backends:
+    name: TestBackends
+    runs-on: ${{ matrix.config.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        config:
+          - { os: ubuntu-latest, target: 'x86_64-unknown-linux-gnu' }
+          - { os: macos-latest, target: 'x86_64-apple-darwin' }
+        backends: ["syn", ""]
+
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          target: ${{ matrix.config.target }}
+          override: true      
+      - uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --features "debug_asserts, rustc_hash, generated_setters, debug_diffs, serde, nanoserde, ${{ matrix.backends.target }}"
+
   test_serde:
     name: TestSerde
     runs-on: ${{ matrix.config.os }}

Cargo.toml

@@ -19,6 +19,7 @@ structdiff-derive   = { path = "derive", version = "=0.7.4" }
 "default"       = []
 "nanoserde"     = ["dep:nanoserde", "structdiff-derive/nanoserde"]
 "serde"         = ["dep:serde", "structdiff-derive/serde"]
+"syn"           = ["structdiff-derive/syn"]
 "debug_diffs"   = ["structdiff-derive/debug_diffs"]
 "generated_setters" = ["structdiff-derive/generated_setters"]
 "rustc_hash"    = ["dep:rustc-hash"]

README.md

@@ -70,6 +70,7 @@ For more examples take a look at [integration tests](/tests)
 - `debug_diffs` - Derive `Debug` on the generated diff type
 - `generated_setters` - Enable generation of setters for struct fields. These setters automatically return a diff if a field's value is changed by the assignment.
 - `rustc_hash` - Use the (non-cryptographic) hash implementation from the `rustc-hash` crate instead of the default hasher. Much faster diff generation for collections at the cost of a dependency.
+- `syn` - Use a `syn`-based backend for the `Difference` derive macro. This adds the `syn`, `quote`, and `proc-macro2` dependencies, but supports Rust syntax through `syn`'s parser instead of structdiff's zero-dependency derive parser.
 
 ### Development status 
 This is being used actively for my own projects, although it's mostly working now. PRs will be accepted for either more tests or functionality.

derive/Cargo.toml

@@ -11,12 +11,16 @@ proc-macro = true
 
 [dependencies]
 nanoserde           = { version = "^0.1.37", optional = true }
+proc-macro2         = { version = "1.0", optional = true }
+quote               = { version = "1.0", optional = true }
 serde               = { version = "^1.0.0", optional = true, features = ["derive"] }
+syn                 = { version = "2.0", optional = true, features = ["derive", "full", "parsing"] }
 
 [features]
 "default"   = []
 "nanoserde" = ["dep:nanoserde"]
 "serde"     = ["dep:serde"]
+"syn"       = ["dep:proc-macro2", "dep:quote", "dep:syn"]
 "debug_diffs" = []
 "generated_setters" = []
 

derive/src/lib.rs

@@ -5,22 +5,36 @@ extern crate proc_macro;
 mod shared;
 
 mod difference;
+#[cfg(feature = "syn")]
+mod syn_backend;
+
+#[cfg(not(feature = "syn"))]
 use difference::derive_struct_diff_enum;
 
+#[cfg(not(feature = "syn"))]
 use crate::difference::derive_struct_diff_struct;
 
+#[cfg_attr(feature = "syn", allow(dead_code))]
 mod parse;
 
 /// Derive macro generating an impl of the trait `StructDiff`
 #[proc_macro_derive(Difference, attributes(difference))]
 pub fn derive_struct_diff(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    derive_struct_diff_impl(input)
+}
+
+#[cfg(feature = "syn")]
+fn derive_struct_diff_impl(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    syn_backend::derive_struct_diff(input)
+}
+
+#[cfg(not(feature = "syn"))]
+fn derive_struct_diff_impl(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
     let input = parse::parse_data(input);
 
-    let ts = match &input {
+    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 and enums are supported"),
-    };
-
-    ts
+    }
 }