nak,nir: Stop using std::mem::zeroed()

We can replace all of these with safe alternatives if we ask bindgen for
implementations of Default.

Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35390>

src/compiler/rust/memstream.rs

@@ -23,7 +23,7 @@ pub struct MemStream(Pin<Box<MemStreamImpl>>);
 impl MemStream {
     pub fn new() -> io::Result<Self> {
         let mut stream_impl = Box::pin(MemStreamImpl {
-            stream: unsafe { std::mem::zeroed() },
+            stream: Default::default(),
             buffer: std::ptr::null_mut(),
             buffer_size: 0,
             _pin: PhantomPinned,

src/compiler/rust/meson.build

@@ -47,6 +47,7 @@ _compiler_bindgen_args = [
   '--allowlist-function', 'u_memstream.*',
   '--allowlist-type', 'u_memstream',
   '--no-prepend-enum-name',
+  '--with-derive-default',
 ]
 
 foreach type : _compiler_binding_types

src/nouveau/compiler/meson.build

@@ -66,6 +66,7 @@ _nak_bindings_rs = rust.bindgen(
     '--allowlist-function', 'nak_.*',
     '--allowlist-function', 'nouveau_ws_.*',
     '--no-prepend-enum-name',
+    '--with-derive-default',
   ],
   dependencies : [
     dep_libdrm,

src/nouveau/compiler/nak/api.rs

@@ -108,7 +108,7 @@ pub extern "C" fn nak_should_print_nir() -> bool {
 }
 
 fn nir_options(dev: &nv_device_info) -> nir_shader_compiler_options {
-    let mut op: nir_shader_compiler_options = unsafe { std::mem::zeroed() };
+    let mut op: nir_shader_compiler_options = Default::default();
 
     op.lower_fdiv = true;
     op.fuse_ffma16 = true;
@@ -319,11 +319,11 @@ impl ShaderBin {
                     xfb: if let Some(xfb) = &io.xfb {
                         **xfb
                     } else {
-                        unsafe { std::mem::zeroed() }
+                        Default::default()
                     },
                     _pad: Default::default(),
                 },
-                _ => unsafe { std::mem::zeroed() },
+                _ => Default::default(),
             },
             hdr: sph::encode_header(sm, info, fs_key),
         };

src/nouveau/compiler/nak/hw_runner.rs

@@ -46,7 +46,7 @@ struct DrmDevices {
 impl DrmDevices {
     fn get() -> io::Result<Self> {
         unsafe {
-            let mut devices: [drmDevicePtr; 16] = std::mem::zeroed();
+            let mut devices: [drmDevicePtr; 16] = [std::ptr::null_mut(); 16];
             let num_devices = drmGetDevices(
                 devices.as_mut_ptr(),
                 devices.len().try_into().unwrap(),
@@ -465,7 +465,7 @@ impl<'a> Runner {
         );
 
         // Populate and upload the QMD
-        let mut qmd_cbufs: [nak_qmd_cbuf; 8] = unsafe { std::mem::zeroed() };
+        let mut qmd_cbufs: [nak_qmd_cbuf; 8] = Default::default();
         qmd_cbufs[0] = nak_qmd_cbuf {
             index: 0,
             size: std::mem::size_of::<CB0>()