Implement DerefMut for Own<Resource> in Rust component export (#647)

juntyr · web-flow · commit a7533653cfc3 · 2023-08-21T14:56:52.000-05:00
diff --git a/crates/rust/src/lib.rs b/crates/rust/src/lib.rs
@@ -833,6 +833,26 @@ impl InterfaceGenerator<'_> {
                         }}
                     }}
 
+                    impl core::ops::DerefMut for Own{camel} {{
+                        fn deref_mut(&mut self) -> &mut Rep{camel} {{
+                            unsafe {{
+                                #[cfg(target_arch = "wasm32")]
+                                #[link(wasm_import_module = "[export]{module}")]
+                                extern "C" {{
+                                    #[link_name = "[resource-rep]{name}"]
+                                    fn wit_import(_: i32) -> i32;
+                                }}
+
+                                #[cfg(not(target_arch = "wasm32"))]
+                                unsafe fn wit_import(_n: i32) -> i32 {{ unreachable!() }}
+
+                                ::core::mem::transmute::<isize, &mut Rep{camel}>(
+                                    wit_import(self.handle).try_into().unwrap()
+                                )
+                            }}
+                        }}
+                    }}
+
                     impl Drop for Own{camel} {{
                         fn drop(&mut self) {{
                             unsafe {{
diff --git a/crates/rust/tests/codegen.rs b/crates/rust/tests/codegen.rs
@@ -225,3 +225,50 @@ mod alternative_bitflags_path {
         }
     }
 }
+
+mod owned_resource_deref_mut {
+    wit_bindgen::generate!({
+        inline: "
+            package my:inline
+
+            interface foo {
+                resource bar {
+                    constructor(data: u32)
+                    get-data: func() -> u32
+                    consume: static func(%self: bar) -> u32
+                }
+            }
+
+            world baz {
+                export foo
+            }
+        ",
+        exports: {
+            "my:inline/foo/bar": Resource
+        }
+    });
+
+    pub struct Resource {
+        data: u32,
+    }
+
+    impl exports::my::inline::foo::Bar for Resource {
+        fn new(data: u32) -> Self {
+            Self { data }
+        }
+
+        fn get_data(&self) -> u32 {
+            self.data
+        }
+
+        fn consume(mut this: exports::my::inline::foo::OwnBar) -> u32 {
+            // Check that Deref<Target = Self> is implemented
+            let prior_data: &u32 = &this.data;
+            let new_data = prior_data + 1;
+            // Check that DerefMut<Target = Self> is implemented
+            let mutable_data: &mut u32 = &mut this.data;
+            *mutable_data = new_data;
+            this.data
+        }
+    }
+}
