go/doc/go1.19.html

<!--{
	"Title": "Go 1.19 Release Notes",
	"Path":  "/doc/go1.19"
}-->
<!--
NOTE: In this document and others in this directory, the convention is to
set fixed-width phrases with non-fixed-width spaces, as in
<code>hello</code> <code>world</code>.
Do not send CLs removing the interior tags from such phrases.
-->
<style>
  main ul li { margin: 0.5em 0; }
</style>
<h2 id="introduction">DRAFT RELEASE NOTES — Introduction to Go 1.19</h2>
<p>
  <strong>
    Go 1.19 is not yet released. These are work-in-progress
    release notes. Go 1.19 is expected to be released in August 2022.
  </strong>
</p>
<h2 id="language">Changes to the language</h2>
<p>
  TODO: complete this section
</p>
<h2 id="ports">Ports</h2>
<p>
  TODO: complete this section, or delete if not needed
</p>
<h2 id="tools">Tools</h2>
<p>
  TODO: complete this section, or delete if not needed
</p>
<h3 id="go-command">Go command</h3>
<p>
  TODO: complete this section.
</p>

<!-- https://go.dev/issue/51461 -->
<p>
  The <code>-trimpath</code> flag, if set, is now included in the build settings
  stamped into Go binaries by <code>go</code> <code>build</code>, and can be
  examined using
  <a href="https://pkg.go.dev/cmd/go#hdr-Print_Go_version"><code>go</code> <code>version</code> <code>-m</code></a>
  or <a href="https://pkg.go.dev/runtime/debug#ReadBuildInfo"><code>debug.ReadBuildInfo</code></a>.
</p>
<p>
  <code>go</code> <code>generate</code> now sets the <code>GOROOT</code>
  environment variable explicitly in the generator's environment, so that
  generators can locate the correct <code>GOROOT</code> even if built
  with <code>-trimpath</code>.
</p>

<p><!-- CL 404134 -->
  <code>go</code> <code>test</code> and <code>go</code> <code>generate</code> now place
  <code>GOROOT/bin</code> at the beginning of the <code>PATH</code> used for the
  subprocess, so tests and generators that execute the <code>go</code> command
  will resolve it to same <code>GOROOT</code>.
</p>

<p><!-- CL 398058 -->
  <code>go</code> <code>env</code> now quotes entries that contain spaces in
  the <code>CGO_CFLAGS</code>, <code>CGO_CPPFLAGS</code>, <code>CGO_CXXFLAGS</code>, <code>CGO_FFLAGS</code>, <code>CGO_LDFLAGS</code>,
  and <code>GOGCCFLAGS</code> variables it reports.
</p>


<h4 id="go-unix">New <code>unix</code> build constraint</h4>

<p><!-- CL 389934 -->
  The build constraint <code>unix</code> is now recognized
  in <code>//go:build</code> lines. The constraint is satisfied
  if the target operating system, also known as <code>GOOS</code>, is
  a Unix or Unix-like system. For the 1.19 release it is satisfied
  if <code>GOOS</code> is one of
  <code>aix</code>, <code>android</code>, <code>darwin</code>,
  <code>dragonfly</code>, <code>freebsd</code>, <code>hurd</code>,
  <code>illumos</code>, <code>ios</code>, <code>linux</code>,
  <code>netbsd</code>, <code>openbsd</code>, or <code>solaris</code>.
  In future releases the <code>unix</code> constraint may match
  additional newly supported operating systems.
</p>

<h2 id="runtime">Runtime</h2>
<p>
  TODO: complete this section, or delete if not needed
</p>
<h2 id="compiler">Compiler</h2>

<p><!-- https://go.dev/issue/5496 CL 357330, 395714, 403979 -->
  The compiler now uses
  a <a href="https://en.wikipedia.org/wiki/Branch_table">jump
  table</a> to implement large integer and string switch statements.
  Performance improvements for the switch statement vary but can be
  on the order of 20% faster.
  (<code>GOARCH=amd64</code> and <code>GOARCH=arm64</code> only)
</p>
<p>
  TODO: <a href="https://go.dev/cl/402374">https://go.dev/cl/402374</a>: enable regabi on riscv64 by default
</p>
<p>
  TODO: <a href="https://go.dev/cl/391014">https://go.dev/cl/391014</a>: The Go compiler now requires the -p=importpath flag, which is already supplied by the go command and by Bazel. Any other build systems that invoke the Go compiler directly will need to make sure they pass this flag as well in order to use Go 1.19.: cmd/compile: require -p flag
</p>
<p>
  TODO: complete this section, or delete if not needed
</p>
<h2 id="linker">Linker</h2>
<p>
  TODO: complete this section, or delete if not needed
</p>

<h2 id="library">Core library</h2>

<h3 id="atomic_types">New atomic types</h3>
<p><!-- https://go.dev/issue/50860 --><!-- CL 381317 -->
  The <a href="/pkg/sync/atomic/"><code>sync/atomic</code></a> package defines new atomic types
  <a href="/pkg/sync/atomic/#Bool"><code>Bool</code></a>,
  <a href="/pkg/sync/atomic/#Int32"><code>Int32</code></a>,
  <a href="/pkg/sync/atomic/#Int64"><code>Int64</code></a>,
  <a href="/pkg/sync/atomic/#Uint32"><code>Uint32</code></a>,
  <a href="/pkg/sync/atomic/#Uint64"><code>Uint64</code></a>,
  <a href="/pkg/sync/atomic/#Uintptr"><code>Uintptr</code></a>, and
  <a href="/pkg/sync/atomic/#Pointer"><code>Pointer</code></a>.
  These types hide the underlying values so that all accesses are forced to use
  the atomic APIs.
  <a href="/pkg/sync/atomic/#Pointer"><code>Pointer</code></a> also avoids
  the need to convert to
  <a href="/pkg/unsafe/#Pointer"><code>unsafe.Pointer</code></a> at call sites.
  <a href="/pkg/sync/atomic/#Int64"><code>Int64</code></a> and
  <a href="/pkg/sync/atomic/#Uint64"><code>Uint64</code></a> automatically
  receive 64-bit alignment on ARM, 386, and 32-bit MIPS required for 64-bit
  atomics on these systems.
</p>

<p>
  TODO: complete this section
</p>

<h3 id="minor_library_changes">Minor changes to the library</h3>
<p>
  As always, there are various minor changes and updates to the library,
  made with the Go 1 <a href="/doc/go1compat">promise of compatibility</a>
  in mind.
</p>
<p>
  TODO: complete this section
</p>

<dl id="archive/zip"><dt><a href="/pkg/archive/zip/">archive/zip</a></dt>
  <dd>
    <p><!-- CL 387976 -->
      TODO: <a href="https://go.dev/cl/387976">https://go.dev/cl/387976</a>: permit zip files to have prefixes
    </p>
  </dd>
</dl><!-- archive/zip -->

<dl id="crypto/rand"><dt><a href="/pkg/crypto/rand/">crypto/rand</a></dt>
  <dd>
    <p><!-- CL 370894 -->
      TODO: <a href="https://go.dev/cl/370894">https://go.dev/cl/370894</a>: batch and buffer calls to getrandom/getentropy
    </p>

    <p><!-- CL 375215 -->
      TODO: <a href="https://go.dev/cl/375215">https://go.dev/cl/375215</a>: use fast key erasure RNG on plan9 instead of ANSI X9.31
    </p>

    <p><!-- CL 390038 -->
      TODO: <a href="https://go.dev/cl/390038">https://go.dev/cl/390038</a>: remove all buffering
    </p>
  </dd>
</dl><!-- crypto/rand -->

<dl id="crypto/tls"><dt><a href="/pkg/crypto/tls/">crypto/tls</a></dt>
  <dd>
    <p><!-- CL 400974 -->
      The <code>tls10default</code> <code>GODEBUG</code> option has been
      removed. It is still possible to enable TLS 1.0 client-side by setting
      <code>Config.MinVersion</code>.
    </p>
  </dd>
</dl><!-- crypto/tls -->

<dl id="crypto/x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt>
  <dd>
    <p><!-- CL 285872 -->
      TODO: <a href="https://go.dev/cl/285872">https://go.dev/cl/285872</a>: disable signing with MD5WithRSA
    </p>
  </dd>
</dl><!-- crypto/x509 -->

<dl id="encoding/binary"><dt><a href="/pkg/encoding/binary/">encoding/binary</a></dt>
  <dd>
    <p><!-- CL 386017 -->
      TODO: <a href="https://go.dev/cl/386017">https://go.dev/cl/386017</a>: add AppendByteOrder
    </p>
  </dd>
</dl><!-- encoding/binary -->

<dl id="encoding/csv"><dt><a href="/pkg/encoding/csv/">encoding/csv</a></dt>
  <dd>
    <p><!-- CL 405675 -->
      TODO: <a href="https://go.dev/cl/405675">https://go.dev/cl/405675</a>: add Reader.InputOffset method
    </p>
  </dd>
</dl><!-- encoding/csv -->

<dl id="flag"><dt><a href="/pkg/flag/">flag</a></dt>
  <dd>
    <p><!-- CL 313329 -->
      TODO: <a href="https://go.dev/cl/313329">https://go.dev/cl/313329</a>: add TextVar function
    </p>
  </dd>
</dl><!-- flag -->

<dl id="fmt"><dt><a href="/pkg/fmt/">fmt</a></dt>
  <dd>
    <p><!-- CL 406177 -->
      TODO: <a href="https://go.dev/cl/406177">https://go.dev/cl/406177</a>: add Append, Appendln, Appendf
    </p>
  </dd>
</dl><!-- fmt -->

<dl id="go/parser"><dt><a href="/pkg/go/parser/">go/parser</a></dt>
  <dd>
    <p><!-- CL 403696 -->
      TODO: <a href="https://go.dev/cl/403696">https://go.dev/cl/403696</a>: parser to accept ~x as unary expression
    </p>
  </dd>
</dl><!-- go/parser -->

<dl id="image/draw"><dt><a href="/pkg/image/draw/">image/draw</a></dt>
  <dd>
    <p><!-- CL 396795 -->
      <code>Draw</code> with the <code>Src</code> operator preserves
      non-premultiplied-alpha colors when destination and source images are
      both <code>*image.NRGBA</code> (or both <code>*image.NRGBA64</code>).
      This reverts a behavior change accidentally introduced by a Go 1.18
      library optimization, to match the behavior in Go 1.17 and earlier.
    </p>
  </dd>
</dl><!-- image/draw -->

<dl id="io"><dt><a href="/pkg/io/">io</a></dt>
  <dd>
    <p><!-- CL 396215 -->
      TODO: <a href="https://go.dev/cl/396215">https://go.dev/cl/396215</a>: add an Err field to LimitedReader
    </p>

    <p><!-- CL 400236 -->
      TODO: <a href="https://go.dev/cl/400236">https://go.dev/cl/400236</a>: NopCloser forward WriterTo implementations if the reader supports it
    </p>
  </dd>
</dl><!-- io -->

<dl id="mime"><dt><a href="/pkg/mime/">mime</a></dt>
  <dd>
    <p><!-- CL 406894 -->
      On Windows only, the mime package now ignores a registry entry
      recording that the extension <code>.js</code> should have MIME
      type <code>text/plain</code>. This is a common unintentional
      misconfiguration on Windows systems. The effect is
      that <code>.js</code> will have the default MIME
      type <code>text/javascript; charset=utf-8</code>.
      Applications that expect <code>text/plain</code> on Windows must
      now explicitly call
      <a href="/pkg/mime#AddExtensionType"><code>AddExtensionType</code></a>.
    </p>
  </dd>
</dl>

<dl id="net"><dt><a href="/pkg/net/">net</a></dt>
  <dd>
    <p><!-- CL 386016 -->
      The pure Go resolver will now use EDNS(0) to include a suggested
      maximum reply packet length, permitting reply packets to contain
      up to 1232 bytes (the previous maximum was 512).
      In the unlikely event that this causes problems with a local DNS
      resolver, setting the environment variable
      <code>GODEBUG=netdns=cgo</code> to use the cgo-based resolver
      should work.
      Please report any such problems on <a href="/issue/new">the
      issue tracker</a>.
    </p>

    <p><!-- CL 396877 -->
      When a net package function or method returns an "I/O timeout"
      error, the error will now satisfy <code>errors.Is(err,
      context.DeadlineExceeded)</code>.  When a net package function
      returns an "operation was canceled" error, the error will now
      satisfy <code>errors.Is(err, context.Canceled)</code>.
      These changes are intended to make it easier for code to test
      for cases in which a context cancellation or timeout causes a net
      package function or method to return an error, while preserving
      backward compatibility for error messages.
    </p>
  </dd>
  <dd>
    <p><!-- CL 400654 -->
      TODO: <a href="https://go.dev/cl/400654">https://go.dev/cl/400654</a>: permit use of Resolver.PreferGo, netgo on Windows and Plan 9
    </p>
  </dd>
</dl><!-- net -->

<dl id="net/http"><dt><a href="/pkg/net/http/">net/http</a></dt>
  <dd>
    <p><!-- CL 269997 -->
      TODO: <a href="https://go.dev/cl/269997">https://go.dev/cl/269997</a>: allow sending 1xx responses
    </p>
  </dd>
</dl><!-- net/http -->

<dl id="net/url"><dt><a href="/pkg/net/url/">net/url</a></dt>
  <dd>
    <p><!-- CL 374654 -->
      TODO: <a href="https://go.dev/cl/374654">https://go.dev/cl/374654</a>: add JoinPath, URL.JoinPath
    </p>
  </dd>
</dl><!-- net/url -->

<dl id="os"><dt><a href="/pkg/os/">os</a></dt>
  <dd>
    <p><!-- CL 392415 -->
      TODO: <a href="https://go.dev/cl/392415">https://go.dev/cl/392415</a>: raise open file rlimit at startup
    </p>
  </dd>
</dl><!-- os -->


<dl id="os/exec"><dt><a href="/pkg/os/exec/">os/exec</a></dt>
  <dd><!-- https://go.dev/issue/50599 -->
    <p>
      An <code>exec.Cmd</code> with a non-empty <code>Dir</code> and a
      nil <code>Env</code> now implicitly sets the <code>PWD</code> environment
      variable for the subprocess to match <code>Dir</code>.
    </p>
    <p>
      The new method <code>(*exec.Cmd).Environ</code> reports the
      environment that would be used to run the command, including the
      aforementioned <code>PWD</code> variable.
    </p>
  </dd>
</dl> <!-- os/exec -->

<dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
  <dd>
    <p><!-- CL 357331 -->
      The method <a href="/pkg/reflect/#Value.Bytes"><code>Value.Bytes</code></a> now accepts addressable arrays in addition to slices.
    </p>
    <p><!-- CL 400954 -->
      The methods <a href="/pkg/reflect/#Value.Len"><code>Value.Len</code></a> and <a href="/pkg/reflect/#Value.Cap"><code>Value.Cap</code></a> now successfully operate on a pointer to an array and return the length of that array, to match what the <a href="https://go.dev/ref/spec#Length_and_capacity">builtin <code>len</code> and <code>cap</code> functions do</a>.
    </p>
  </dd>
</dl><!-- reflect -->

<dl id="runtime"><dt><a href="/pkg/runtime/">runtime</a></dt>
  <dd>
    <p><!-- https://go.dev/issue/51461 -->
      The <code>GOROOT</code> function now returns the empty string
      (instead of <code>"go"</code>) when the binary was built with
      the <code>-trimpath</code> flag set and the <code>GOROOT</code>
      variable is not set in the process environment.
    </p>
  </dd>
</dl><!-- runtime -->

<dl id="runtime/race"><dt><a href="/pkg/runtime/race/">runtime/race</a></dt>
  <dd>
    <p><!-- https://go.dev/issue/49761 --><!-- CL 333529 -->
      The race detector has been upgraded to use thread sanitizer
      version v3.
      <ul>
        <li>
          Faster (typically 1.5 to 2 times faster)
        </li>
        <li>
          Uses less memory (typically 1/2 as much)
        </li>
        <li>
          Supports unlimited numbers of goroutines
        </li>
      </ul>
    </p>
  </dd>
</dl><!-- runtime/race -->

<dl id="runtime/trace"><dt><a href="/pkg/runtime/trace/">runtime/trace</a></dt>
  <dd>
    <p><!-- CL 400795 -->
      When used together with the
      <a href="/pkg/runtime/pprof#StartCPUProfile">CPU profiler</a>, the
      execution trace includes CPU profile samples.
    </p>
  </dd>
</dl><!-- runtime/trace -->

<dl id="sort"><dt><a href="/pkg/sort/">sort</a></dt>
  <dd>
    <p><!-- CL 371574 -->
      The sorting algorithm has been rewritten to use
      <a href="https://arxiv.org/pdf/2106.05123.pdf">pattern-defeating quicksort</a>, which
      is faster for several common scenarios.
    </p>
  </dd>
</dl><!-- sort -->

<dl id="strconv"><dt><a href="/pkg/strconv/">strconv</a></dt>
  <dd>
    <p><!-- CL 397255 -->
      <a href="/pkg/strconv/#Quote"><code>Quote</code></a>
      and related functions now quote the rune 007F as <code>\x7f</code>,
      not <code>\u007f</code>.
    </p>
  </dd>
</dl><!-- strconv -->

<dl id="time"><dt><a href="/pkg/time/">time</a></dt>
  <dd>
    <p><!-- CL 393515 -->
      TODO: <a href="https://go.dev/cl/393515">https://go.dev/cl/393515</a>: add Duration.Abs
    </p>
  </dd>
</dl><!-- time -->