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<!--{
"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: <a href="https://go.dev/cl/398058">https://go.dev/cl/398058</a>: cmd/go: quote fragments in CGO_ env variables reported by 'go env'
</p>
<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>
<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>
<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="go.dev/x/crypto/ssh"><dt><a href="/pkg/go.dev/x/crypto/ssh/">go.dev/x/crypto/ssh</a></dt>
<dd>
<p><!-- CL 392134 -->
TODO: <a href="https://go.dev/cl/392134">https://go.dev/cl/392134</a>: ssh: add IUTF8 constant from RFC 8160
</p>
</dd>
</dl><!-- go.dev/x/crypto/ssh -->
<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="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 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>
<p><!-- CL 357331 -->
TODO: <a href="https://go.dev/cl/357331">https://go.dev/cl/357331</a>: allow Value.Bytes on addressable byte arrays
</p>
<p><!-- CL 400954 -->
TODO: <a href="https://go.dev/cl/400954">https://go.dev/cl/400954</a>: support Len and Cap on pointer-to-array Value
</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>
<p><!-- CL 333529 -->
TODO: <a href="https://go.dev/cl/333529">https://go.dev/cl/333529</a>: update runtime (v3)
</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 -->
The race detector has been updgraded 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="sort"><dt><a href="/pkg/sort/">sort</a></dt>
<dd>
<p><!-- CL 371574 -->
TODO: <a href="https://go.dev/cl/371574">https://go.dev/cl/371574</a>: use pdqsort
</p>
</dd>
</dl><!-- sort -->
<dl id="strconv"><dt><a href="/pkg/strconv/">strconv</a></dt>
<dd>
<p><!-- CL 397255 -->
<a href="/pkg/strconv/#strconv.Quote"><code>strconv.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 -->