reflect: deprecate (Slice|String)Header

As discussed in CL 401434 there are substantial misuses of these in the
wild, and they are a potential source of unsafety even for code that
does not use them directly.

We should either keep them as-is and document when/how they can be used
safely, or deprecate them so that uses will eventually die out.

After some discussion, it was decided to deprecate them outright.
Since the docs already mentioned that they may be unstable across
releases, it should be possible to get rid of them completely later on.

Change-Id: I3b75819409177b5a286c1e9861a2edb6fd1301b8
Reviewed-on: https://go-review.googlesource.com/c/go/+/401434
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

diff --git a/doc/go1.19.html b/doc/go1.19.html
index 164f967bdd0bae70d8d49a929e074cf21ebddd19..0bf5472246e3b3c268cac526c920d344c1c68a5c 100644 (file)
--- a/doc/go1.19.html
+++ b/doc/go1.19.html
@@ -166,6 +166,16 @@ Do not send CLs removing the interior tags from such phrases.
   </dd>
 </dl> <!-- os/exec -->
 
+<dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
+  <dd>
+    <p><!-- CL 401434 -->
+      <a href="/pkg/strconv/#reflect.SliceHeader"></a><code>reflect.SliceHeader</code>
+      and <a href="/pkg/strconv/#reflect.StringHeader"></a><code>reflect.StringHeader</code>
+      are now deprecated, and their use should be avoided.
+    </p>
+  </dd>
+</dl><!-- reflect -->
+
 <dl id="runtime"><dt><a href="/pkg/runtime/">runtime</a></dt>
   <dd>
     <p><!-- https://go.dev/issue/51461 -->

diff --git a/src/reflect/value.go b/src/reflect/value.go
index d68f7ad2e642b9616f541faa14ba760cb0401c0a..0fc19ef101f324db910a8bc826d9e737704cd67c 100644 (file)
--- a/src/reflect/value.go
+++ b/src/reflect/value.go
@@ -2660,6 +2660,9 @@ func (v Value) UnsafePointer() unsafe.Pointer {
 // Moreover, the Data field is not sufficient to guarantee the data
 // it references will not be garbage collected, so programs must keep
 // a separate, correctly typed pointer to the underlying data.
+//
+// Deprecated: this type should not be used, it exists only for
+// backward compatibility.
 type StringHeader struct {
        Data uintptr
        Len  int
@@ -2671,6 +2674,9 @@ type StringHeader struct {
 // Moreover, the Data field is not sufficient to guarantee the data
 // it references will not be garbage collected, so programs must keep
 // a separate, correctly typed pointer to the underlying data.
+//
+// Deprecated: this type should not be used, it exists only for
+// backward compatibility.
 type SliceHeader struct {
        Data uintptr
        Len  int