Add DstLayout::extend

src/util.rs

@@ -512,6 +512,22 @@ pub(crate) const fn _round_down_to_next_multiple_of_alignment(
     n & mask
 }
 
+pub(crate) const fn max(a: NonZeroUsize, b: NonZeroUsize) -> NonZeroUsize {
+    if a.get() < b.get() {
+        b
+    } else {
+        a
+    }
+}
+
+pub(crate) const fn min(a: NonZeroUsize, b: NonZeroUsize) -> NonZeroUsize {
+    if a.get() > b.get() {
+        b
+    } else {
+        a
+    }
+}
+
 /// Since we support multiple versions of Rust, there are often features which
 /// have been stabilized in the most recent stable release which do not yet
 /// exist (stably) on our MSRV. This module provides polyfills for those

tests/ui-msrv/max-align.rs

@@ -0,0 +1 @@
+../ui-nightly/max-align.rs

tests/ui-msrv/max-align.stderr

@@ -0,0 +1,5 @@
+error[E0589]: invalid `repr(align)` attribute: larger than 2^29
+  --> tests/ui-msrv/max-align.rs:96:11
+   |
+96 | #[repr(C, align(1073741824))]
+   |           ^^^^^^^^^^^^^^^^^

tests/ui-nightly/max-align.rs

@@ -0,0 +1,99 @@
+// Copyright 2023 The Fuchsia Authors
+//
+// Licensed under a BSD-style license <LICENSE-BSD>, Apache License, Version 2.0
+// <LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0>, or the MIT
+// license <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your option.
+// This file may not be copied, modified, or distributed except according to
+// those terms.
+
+#[repr(C, align(1))]
+struct Align1;
+
+#[repr(C, align(2))]
+struct Align2;
+
+#[repr(C, align(4))]
+struct Align4;
+
+#[repr(C, align(8))]
+struct Align8;
+
+#[repr(C, align(16))]
+struct Align16;
+
+#[repr(C, align(32))]
+struct Align32;
+
+#[repr(C, align(64))]
+struct Align64;
+
+#[repr(C, align(128))]
+struct Align128;
+
+#[repr(C, align(256))]
+struct Align256;
+
+#[repr(C, align(512))]
+struct Align512;
+
+#[repr(C, align(1024))]
+struct Align1024;
+
+#[repr(C, align(2048))]
+struct Align2048;
+
+#[repr(C, align(4096))]
+struct Align4096;
+
+#[repr(C, align(8192))]
+struct Align8192;
+
+#[repr(C, align(16384))]
+struct Align16384;
+
+#[repr(C, align(32768))]
+struct Align32768;
+
+#[repr(C, align(65536))]
+struct Align65536;
+
+#[repr(C, align(131072))]
+struct Align131072;
+
+#[repr(C, align(262144))]
+struct Align262144;
+
+#[repr(C, align(524288))]
+struct Align524288;
+
+#[repr(C, align(1048576))]
+struct Align1048576;
+
+#[repr(C, align(2097152))]
+struct Align2097152;
+
+#[repr(C, align(4194304))]
+struct Align4194304;
+
+#[repr(C, align(8388608))]
+struct Align8388608;
+
+#[repr(C, align(16777216))]
+struct Align16777216;
+
+#[repr(C, align(33554432))]
+struct Align33554432;
+
+#[repr(C, align(67108864))]
+struct Align67108864;
+
+#[repr(C, align(134217728))]
+struct Align13421772;
+
+#[repr(C, align(268435456))]
+struct Align26843545;
+
+#[repr(C, align(1073741824))]
+struct Align1073741824;
+
+fn main() {}

tests/ui-nightly/max-align.stderr

@@ -0,0 +1,5 @@
+error[E0589]: invalid `repr(align)` attribute: larger than 2^29
+  --> tests/ui-nightly/max-align.rs:96:11
+   |
+96 | #[repr(C, align(1073741824))]
+   |           ^^^^^^^^^^^^^^^^^

tests/ui-stable/max-align.rs

@@ -0,0 +1 @@
+../ui-nightly/max-align.rs

tests/ui-stable/max-align.stderr

@@ -0,0 +1,5 @@
+error[E0589]: invalid `repr(align)` attribute: larger than 2^29
+  --> tests/ui-stable/max-align.rs:96:11
+   |
+96 | #[repr(C, align(1073741824))]
+   |           ^^^^^^^^^^^^^^^^^