Add error handling and string test for C# interop (#3658)

Author: kennykerr

crates/samples/csharp/client/client.cs

@@ -3,4 +3,10 @@
 [DllImport("csharp_component.dll", PreserveSig = false)]
 static extern uint Add(uint left, uint right);
 
-Console.WriteLine("result = {0:D}", Add(4, 5));
+Console.WriteLine("Add: {0}", Add(4, 5));
+
+[DllImport("csharp_component.dll", PreserveSig = false)]
+[return: MarshalAs(UnmanagedType.BStr)]
+static extern string Concat([MarshalAs(UnmanagedType.LPWStr)] string left, [MarshalAs(UnmanagedType.LPWStr)] string right);
+
+Console.WriteLine("Concat: {0}", Concat("hello ", "world"));

crates/samples/csharp/client/src/lib.rs

@@ -12,6 +12,8 @@ fn test() {
         panic!("{}", String::from_utf8_lossy(&output.stderr));
     }
 
-    let result = String::from_utf8_lossy(&output.stdout).to_string();
-    assert_eq!(result.trim(), "result = 9");
+    let result = String::from_utf8_lossy(&output.stdout);
+    let result: Vec<&str> = result.lines().collect();
+
+    assert_eq!(result, ["Add: 9", "Concat: hello world"]);
 }

crates/samples/csharp/component/Cargo.toml

@@ -5,3 +5,6 @@ edition = "2021"
 
 [lib]
 crate-type = ["cdylib"]
+
+[dependencies]
+windows-core = { workspace = true }

crates/samples/csharp/component/src/lib.rs

@@ -1,5 +1,28 @@
+use windows_core::*;
+
+pub const S_OK: HRESULT = HRESULT(0);
+pub const E_POINTER: HRESULT = HRESULT(0x80004003_u32 as _);
+
 #[no_mangle]
-unsafe extern "system" fn Add(left: u32, right: u32, result: *mut u32) -> i32 {
+unsafe extern "system" fn Add(left: u32, right: u32, result: *mut u32) -> HRESULT {
+    if result.is_null() {
+        return E_POINTER;
+    }
+
     *result = left + right;
-    0 // S_OK
+    S_OK
+}
+
+#[no_mangle]
+unsafe extern "system" fn Concat(left: PCWSTR, right: PCWSTR, result: *mut BSTR) -> HRESULT {
+    if left.is_null() || right.is_null() || result.is_null() {
+        return E_POINTER;
+    }
+
+    let left = left.as_wide();
+    let right = right.as_wide();
+    let combined: Vec<u16> = [left, right].concat();
+
+    *result = BSTR::from_wide(&combined);
+    S_OK
 }