compiler/rust: Add a unit test for the memstream abstraction

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31718>

src/compiler/rust/memstream.rs

@@ -148,3 +148,24 @@ impl Drop for MemStream {
         }
     }
 }
+
+#[test]
+fn test_memstream() {
+    use std::ffi::CString;
+
+    let mut s = MemStream::new().unwrap();
+    let test_str = "Test string";
+    let test_c_str = CString::new(test_str).unwrap();
+    let test_bytes = test_c_str.as_bytes();
+
+    unsafe {
+        bindings::compiler_rs_fwrite(
+            test_bytes.as_ptr().cast(),
+            1,
+            test_bytes.len(),
+            s.c_file(),
+        );
+    }
+    let res = s.take_utf8_string_lossy().unwrap();
+    assert_eq!(res, test_str);
+}

src/compiler/rust/rust_helpers.c

@@ -26,3 +26,10 @@ int compiler_rs_fseek(FILE *f, long offset, int whence)
 {
    return fseek(f, offset, whence);
 }
+
+size_t compiler_rs_fwrite(const void *ptr,
+                          size_t size, size_t nmemb,
+                          FILE *stream)
+{
+   return fwrite(ptr, size, nmemb, stream);
+}

src/compiler/rust/rust_helpers.h

@@ -8,3 +8,6 @@
 void compiler_rs_free(void *ptr);
 long compiler_rs_ftell(FILE *f);
 int compiler_rs_fseek(FILE *f, long offset, int whence);
+size_t compiler_rs_fwrite(const void *ptr,
+                          size_t size, size_t nmemb,
+                          FILE *stream);