Support derive(Debug) on enums (#194)

Related issue: #190 

Example:

```rs
// Rust

#[swift_bridge::bridge]
mod ffi {
    #[derive(Debug)]
    enum DeriveDebugEnum {
        Variant,
    }
}
```

```swift
// Swift

let debugString = String(reflecting: DeriveDebugEnum.Variant)
XCTAssertEqual(debugString, "Variant")
```

Author: amsam0

SwiftRustIntegrationTestRunner/SwiftRustIntegrationTestRunnerTests/SharedEnumAttributeTests.swift

@@ -30,5 +30,12 @@ class SharedEnumAttributeTests: XCTestCase {
             AlreadyDeclaredEnumTest.Variant
         )
     }
+    
+    
+    /// Verify that we can use the generated Debug impl.
+    func testSharedEnumDeriveDebug() throws {
+        let debugString = String(reflecting: DeriveDebugEnum.Variant)
+        XCTAssertEqual(debugString, "Variant")
+    }
 }
 

SwiftRustIntegrationTestRunner/build-rust.sh

@@ -15,7 +15,7 @@ if [[ -n "${DEVELOPER_SDK_DIR:-}" ]]; then
   export LIBRARY_PATH="${DEVELOPER_SDK_DIR}/MacOSX.sdk/usr/lib:${LIBRARY_PATH:-}"
 fi
 
-cd $PROJECT_DIR
+cd "$PROJECT_DIR"
 
 if [[ $CONFIGURATION == "Release" ]]; then
     echo "BUIlDING FOR RELEASE"

crates/swift-bridge-ir/src/bridged_type.rs

@@ -17,7 +17,7 @@ use crate::bridged_type::built_in_tuple::BuiltInTuple;
 use crate::parse::{HostLang, TypeDeclaration, TypeDeclarations};
 
 use self::bridged_option::BridgedOption;
-pub(crate) use self::shared_enum::{EnumVariant, SharedEnum};
+pub(crate) use self::shared_enum::{DeriveAttrs, EnumVariant, SharedEnum};
 pub(crate) use self::shared_struct::{SharedStruct, StructFields, StructSwiftRepr};
 
 pub(crate) mod boxed_fn;

crates/swift-bridge-ir/src/bridged_type/shared_enum.rs

@@ -9,12 +9,18 @@ pub(crate) use self::enum_variant::EnumVariant;
 
 use super::StructFields;
 
+#[derive(Default, Clone)]
+pub(crate) struct DeriveAttrs {
+    pub debug: bool,
+}
+
 #[derive(Clone)]
 pub(crate) struct SharedEnum {
     pub name: Ident,
     pub variants: Vec<EnumVariant>,
     pub already_declared: bool,
     pub swift_name: Option<LitStr>,
+    pub derive: DeriveAttrs,
 }
 
 impl SharedEnum {

crates/swift-bridge-ir/src/codegen/codegen_tests.rs

@@ -33,6 +33,7 @@ mod async_function_codegen_tests;
 mod boxed_fnonce_codegen_tests;
 mod built_in_tuple_codegen_tests;
 mod conditional_compilation_codegen_tests;
+mod derive_attribute_codegen_tests;
 mod derive_struct_attribute_codegen_tests;
 mod extern_rust_function_opaque_rust_type_argument_codegen_tests;
 mod extern_rust_function_opaque_rust_type_return_codegen_tests;

crates/swift-bridge-ir/src/codegen/codegen_tests/derive_attribute_codegen_tests.rs

@@ -0,0 +1,68 @@
+use super::{CodegenTest, ExpectedCHeader, ExpectedRustTokens, ExpectedSwiftCode};
+use proc_macro2::TokenStream;
+use quote::quote;
+
+/// Verify that we generate debugDescription in Swift and Debug function in Rust when using #\[derive(Debug)]
+mod derive_debug_enum {
+    use super::*;
+
+    fn bridge_module_tokens() -> TokenStream {
+        quote! {
+            #[swift_bridge::bridge]
+            mod ffi {
+                #[derive(Debug)]
+                enum SomeEnum {
+                    Variant1
+                }
+            }
+        }
+    }
+
+    fn expected_rust_tokens() -> ExpectedRustTokens {
+        ExpectedRustTokens::ContainsMany(vec![
+            quote! {
+                #[derive(Copy, Clone, ::std::fmt::Debug)]
+                pub enum SomeEnum {
+                    Variant1
+                }
+            },
+            quote! {
+                #[export_name = "__swift_bridge__$SomeEnum$Debug"]
+                pub extern "C" fn __swift_bridge__SomeEnum_Debug(this: __swift_bridge__SomeEnum) -> *mut swift_bridge::string::RustString {
+                    swift_bridge::string::RustString(format!("{:?}", this.into_rust_repr())).box_into_raw()
+                }
+            },
+        ])
+    }
+
+    fn expected_swift_code() -> ExpectedSwiftCode {
+        ExpectedSwiftCode::ContainsAfterTrim(
+            r#" 
+extension SomeEnum: CustomDebugStringConvertible {
+    public var debugDescription: String {
+        RustString(ptr: __swift_bridge__$SomeEnum$Debug(self.intoFfiRepr())).toString()
+    }
+}
+"#,
+        )
+    }
+
+    fn expected_c_header() -> ExpectedCHeader {
+        ExpectedCHeader::ContainsAfterTrim(
+            r#" 
+void* __swift_bridge__$SomeEnum$Debug(__swift_bridge__$SomeEnum this);
+"#,
+        )
+    }
+
+    #[test]
+    fn generates_enum_to_and_from_ffi_conversions_no_data() {
+        CodegenTest {
+            bridge_module: bridge_module_tokens().into(),
+            expected_rust_tokens: expected_rust_tokens(),
+            expected_swift_code: expected_swift_code(),
+            expected_c_header: expected_c_header(),
+        }
+        .test();
+    }
+}

crates/swift-bridge-ir/src/codegen/generate_c_header.rs

@@ -152,6 +152,12 @@ typedef struct {option_ffi_name} {{ bool is_some; {ffi_name} val; }} {option_ffi
                             variants += &variant;
                         }
 
+                        let derive_debug_impl = if ty_enum.derive.debug {
+                            format!("void* {ffi_name}$Debug({ffi_name} this);")
+                        } else {
+                            "".to_string()
+                        };
+
                         let maybe_vec_support = if ty_enum.has_one_or_more_variants_with_data() {
                             "".to_string()
                         } else {
@@ -162,7 +168,8 @@ typedef struct {option_ffi_name} {{ bool is_some; {ffi_name} val; }} {option_ffi
                             let enum_decl = format!(
                                 r#"typedef enum {ffi_tag_name} {{ {variants}}} {ffi_tag_name};
 typedef struct {ffi_name} {{ {ffi_tag_name} tag; }} {ffi_name};
-typedef struct {option_ffi_name} {{ bool is_some; {ffi_name} val; }} {option_ffi_name};{maybe_vec_support}"#,
+typedef struct {option_ffi_name} {{ bool is_some; {ffi_name} val; }} {option_ffi_name};
+{derive_debug_impl}{maybe_vec_support}"#,
                                 ffi_name = ffi_name,
                                 ffi_tag_name = ffi_tag_name,
                                 option_ffi_name = option_ffi_name,
@@ -223,7 +230,8 @@ typedef struct {option_ffi_name} {{ bool is_some; {ffi_name} val; }} {option_ffi
                                 r#"{variant_fields}union {ffi_union_name} {union_fields};
 typedef enum {ffi_tag_name} {{ {variants}}} {ffi_tag_name};
 typedef struct {ffi_name} {{ {ffi_tag_name} tag; union {ffi_union_name} payload;}} {ffi_name};
-typedef struct {option_ffi_name} {{ bool is_some; {ffi_name} val; }} {option_ffi_name};{maybe_vec_support}"#,
+typedef struct {option_ffi_name} {{ bool is_some; {ffi_name} val; }} {option_ffi_name};
+{derive_debug_impl}{maybe_vec_support}"#,
                                 union_fields = ffi_union_field_names,
                                 variant_fields = variant_fields,
                                 ffi_name = ffi_name,

crates/swift-bridge-ir/src/codegen/generate_rust_tokens/shared_enum.rs

@@ -130,14 +130,34 @@ impl SwiftBridgeModule {
             convert_ffi_variants_to_rust.push(convert_ffi_variant_to_rust);
         }
 
-        // TODO:
-        //  Parse any derives that the user has specified and combine those with our auto derives.
-        let automatic_derives = if shared_enum.has_one_or_more_variants_with_data() {
+        // Auto derives
+        let mut derives = if shared_enum.has_one_or_more_variants_with_data() {
             vec![]
         } else {
             vec![quote! {Copy}, quote! {Clone}]
         };
 
+        // User derives
+        let mut derive_impl_ffi_bridges = vec![];
+
+        // We currently only allow derive(Debug) on non data carrying enums in order
+        // to prevent a potential memory safety issue.
+        // https://github.com/chinedufn/swift-bridge/pull/194#discussion_r1134386788
+        if shared_enum.derive.debug && !shared_enum.has_one_or_more_variants_with_data() {
+            derives.push(quote! {::std::fmt::Debug});
+
+            // __swift_bridge__$SomeEnum$Debug
+            let export_name = format!("{}$Debug", shared_enum.ffi_name_string());
+            // __swift_bridge__SomeEnum_Debug
+            let fn_name = format_ident!("{}_Debug", enum_ffi_name);
+            derive_impl_ffi_bridges.push(quote! {
+                #[export_name = #export_name]
+                pub extern "C" fn #fn_name(this: #enum_ffi_name) -> *mut swift_bridge::string::RustString {
+                    swift_bridge::string::RustString(format!("{:?}", this.into_rust_repr())).box_into_raw()
+                }
+            });
+        }
+
         let vec_support = if shared_enum.has_one_or_more_variants_with_data() {
             // Enums with variants that contain data are not yet supported.
             quote! {}
@@ -146,7 +166,7 @@ impl SwiftBridgeModule {
         };
 
         let definition = quote! {
-            #[derive(#(#automatic_derives),*)]
+            #[derive(#(#derives),*)]
             pub enum #enum_name {
                 #(#enum_variants),*
             }
@@ -217,6 +237,8 @@ impl SwiftBridgeModule {
             }
 
             #vec_support
+
+            #(#derive_impl_ffi_bridges),*
         };
 
         Some(definition)

crates/swift-bridge-ir/src/codegen/generate_rust_tokens/vec/vec_of_transparent_enum.rs

@@ -96,7 +96,7 @@ pub(in super::super) fn generate_vec_of_transparent_enum_functions(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::test_utils::assert_tokens_eq;
+    use crate::{bridged_type::DeriveAttrs, test_utils::assert_tokens_eq};
     use proc_macro2::{Ident, Span};
 
     /// Verify that we can generate the functions for an opaque Rust type that get exposed to Swift
@@ -168,6 +168,7 @@ mod tests {
             variants: vec![],
             already_declared: false,
             swift_name: None,
+            derive: DeriveAttrs::default(),
         };
         assert_tokens_eq(
             &generate_vec_of_transparent_enum_functions(&shared_enum),

crates/swift-bridge-ir/src/codegen/generate_swift/shared_enum.rs

@@ -130,6 +130,19 @@ extension {enum_name}: Vectorizable {{
             )
         };
 
+        let derive_debug_impl = if shared_enum.derive.debug {
+            format!(
+                r#"
+extension {enum_name}: CustomDebugStringConvertible {{
+    public var debugDescription: String {{
+        RustString(ptr: __swift_bridge__${enum_name}$Debug(self.intoFfiRepr())).toString()
+    }}
+}}"#
+            )
+        } else {
+            "".to_string()
+        };
+
         let swift_enum = format!(
             r#"public enum {enum_name} {{{variants}}}
 extension {enum_name} {{
@@ -159,7 +172,7 @@ extension {option_ffi_name} {{
             return {option_ffi_name}(is_some: false, val: {ffi_repr_name}())
         }}
     }}
-}}{vectorizable_impl}"#,
+}}{vectorizable_impl}{derive_debug_impl}"#,
             enum_name = enum_name,
             enum_ffi_name = enum_ffi_name,
             option_ffi_name = option_ffi_name,