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go/doc/go1.19.html
Austin Clements 0c3a0543c2 doc/go1.19: compiler section is complete, modulo TODOs 
For #51400

Change-Id: I964e52e0a36e7bbe77175670e93ce8c99e7dab6d
Reviewed-on: https://go-review.googlesource.com/c/go/+/410367
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
2022-06-07 16:59:48 +00:00

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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>
<p><!-- https://go.dev/issue/52038 -->
TODO: <a href="https://go.dev/issue/52038">https://go.dev/issue/52038</a>: adjust scope of type parameters declared by method receivers
</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>
<p><!-- https://go.dev/issue/47528 -->:
TODO: https://go.dev/issue/47528 warn when errors.As target has type *error
</p>
<h3 id="go-doc">Doc Comments</h3>
<p><!-- https://go.dev/issue/51082 -->
TODO: complete this section.
</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 --><!-- https://go.dev/issue/20322 --><!-- https://go.dev/issue/51572 -->
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><!-- https://go.dev/issue/48409 --><!-- CL 397018 -->
The runtime now includes support for a soft memory limit. This memory limit
includes all memory mapped and managed by the runtime, and excludes external
memory sources such as binary size, memory managed in other languages, and
memory held by the operating system on behalf of the Go program. This limit
may be managed via the <code>GOMEMLIMIT</code> environment variable or the
<code>SetMemoryLimit</code> function in the runtime/debug package. The limit
works in conjunction with <code>GOGC</code> and <code>SetGCPercent</code>,
and will be respected even if <code>GOGC=off</code>, allowing Go programs to
always make maximal use of their memory limit, improving resource efficiency
in some cases. Please note that small memory limits, on the order of tens of
megabytes or less, are less likely to be adhered to due to external latency
factors, such as OS scheduling. See https://go.dev/issue/52433 for more
details. Larger memory limits, on the order of hundreds of megabytes or more,
are stable and production-ready.
</p>
<p><!-- CL 353989 -->
In order to limit the effects of GC thrashing when the program's live heap
size approaches the soft memory limit, the Go runtime also attempts to limit
total GC CPU utilization to 50%, excluding idle time, choosing to use more
memory over preventing application progress. In practice, we expect this limit
to only play a role in exceptional cases, and the new runtime/metrics metric
<code>/gc/limiter/last-enabled:gc-cycle</code> reports when this last
occurred.
</p>
<p><!-- https://go.dev/issue/44163 -->
The runtime now schedules many fewer GC worker goroutines on idle operating
system threads when the application is idle enough to force a periodic GC
cycle.
</p>
<p><!-- https://go.dev/issue/18138 --><!-- CL 345889 -->
The runtime will now allocate initial goroutine stacks based on the historic
average stack usage of goroutines. This avoids some of the early stack growth
and copying needed in the average case in exchange for at most 2x wasted
space on below-average goroutines.
</p>
<p><!-- https://go.dev/issue/46279 --><!-- CL 393354 -->
On Unix operating systems, Go programs that import package
<a href="/pkg/os/">os</a> now automatically increase the open file limit
(<code>RLIMIT_NOFILE</code>) to the maximum allowed value. Programs that need
a lower limit (for compatibility with <code>select</code>, for example) can
set the limit back as needed, or lower the hard limit prior to starting the
Go program.
</p>
<p><!-- https://go.dev/issue/51485 --><!-- CL 390421 -->
Unrecoverable fatal errors (such as concurrent map writes, or unlock of
unlocked mutexes) now print a simpler traceback excluding runtime metadata
(equivalent to a fatal panic) unless <code>GOTRACEBACK=system</code> or
<code>crash</code>. Runtime-internal fatal error tracebacks always include
full metadata regardless of the value of <code>GOTRACEBACK</code>
</p>
<p><!-- https://go.dev/issue/50614 --><!-- CL 395754 -->
Support for debugger-injected function calls has been added on ARM64,
enabling users to call functions from their binary in an interactive
debugging session when using a debugger that is updated to make use of this
functionality.
</p>
<p><!-- https://go.dev/issue/44853 -->
TODO: <a href="https://go.dev/issue/44853">https://go.dev/issue/44853</a>: enable address sanitizer in Go
</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><!-- CL 402374 -->
TODO: <a href="https://go.dev/cl/402374">https://go.dev/cl/402374</a>: enable regabi on riscv64 by default
</p>
<p><!-- CL 391014 -->
The Go compiler now requires the <code>-p=importpath</code> flag to
build a linkable object file. This is already supplied by
the <code>go</code> 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.
</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="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>
<h3 id="go/doc/comment">Doc comment parsing</h3>
<p><!-- CL 384265 --><!-- CL 397276 --><!-- CL 397278 --><!-- CL 397279 --><!-- CL 397281 --><!-- CL 397284 -->
TODO: <a href="https://go.dev/cl/384265">https://go.dev/cl/384265</a>: go/doc: use go/doc/comment; modified api/next/51082.txt
TODO: <a href="https://go.dev/cl/397276">https://go.dev/cl/397276</a>: go/doc/comment: add data structures; modified api/next/51082.txt
TODO: <a href="https://go.dev/cl/397278">https://go.dev/cl/397278</a>: go/doc/comment: add paragraph parsing and test framework; modified api/next/51082.txt
TODO: <a href="https://go.dev/cl/397279">https://go.dev/cl/397279</a>: go/doc/comment: add Printer and basic comment printing; modified api/next/51082.txt
TODO: <a href="https://go.dev/cl/397281">https://go.dev/cl/397281</a>: go/doc/comment: parse and print doc links; modified api/next/51082.txt
TODO: <a href="https://go.dev/cl/397284">https://go.dev/cl/397284</a>: go/doc/comment: parse and print headings; modified api/next/51082.txt
</p>
<h3 id="os-exec-path">PATH lookups</h3>
<p><!-- https://go.dev/issue/43724 --><!-- CL 381374 --><!-- CL 403274 -->
TODO: <a href="https://go.dev/issue/43724">https://go.dev/issue/43724</a>: return error when PATH lookup would use current directory
</p>
<p><!-- https://go.dev/issue/43947 -->
TODO: <a href="https://go.dev/issue/43947">https://go.dev/issue/43947</a>: on Windows use NeedCurrentDirectoryForExePathW for LookPath behavior
</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 --><!-- CL 390038 -->
<a href="/pkg/crypto/rand/#Read"><code>Read</code></a> no longer buffers
random data obtained from the operating system between calls.
</p>
<p><!-- CL 375215 -->
On Plan 9, <code>Read</code> has been reimplemented, replacing the ANSI
X9.31 algorithm with fast key erasure.
</p>
</dd>
</dl><!-- crypto/rand -->
<dl id="crypto/tls"><dt><a href="/pkg/crypto/tls/">crypto/tls</a></dt>
<dd>
<p><!-- CL 400974 --><!-- https://go.dev/issue/45428 -->
The <code>tls10default</code> <code>GODEBUG</code> option has been
removed. It is still possible to enable TLS 1.0 client-side by setting
<a href="/pkg/crypto/tls#Config.MinVersion"><code>Config.MinVersion</code></a>.
</p>
<p><!-- CL 384894 -->
The TLS server and client now reject duplicate extensions in TLS
handshakes, as required by RFC 5246, Section 7.4.1.4 and RFC 8446, Section
4.2.
</p>
</dd>
</dl><!-- crypto/tls -->
<dl id="crypto/x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt>
<dd>
<p><!-- CL 285872 -->
<a href="/pkg/crypto/x509/#CreateCertificate"><code>CreateCertificate</code></a>
no longer supports creating certificates with <code>SignatureAlgorithm</code>
set to <code>MD5WithRSA</code>.
</p>
<p><!-- CL 400494 -->
<code>CreateCertificate</code> no longer accepts negative serial numbers.
</p>
<p><!-- CL 383215 -->
<a href="/pkg/crypto/x509/#ParseCertificate"><code>ParseCertificate</code></a>
and <a href="/pkg/crypto/x509/#ParseCertificateRequest"><code>ParseCertificateRequest</code></a>
now reject certificates and CSRs which contain duplicate extensions.
</p>
<p><!-- CL 400175 --><!-- CL 388915 -->
The new <a href="/pkg/crypto/x509/#CertPool.Clone"><code>CertPool.Clone</code></a>
and <a href="/pkg/crypto/x509/#CertPool.Equal"><code>CertPool.Equal</code></a>
methods allow cloning a <code>CertPool</code> and checking the equality of two
<code>CertPool</code>s respectively.
</p>
<p><!-- CL 390834 -->
The new function <a href="/pkg/crypto/x509/#ParseRevocationList"><code>ParseRevocationList</code></a>
provides a faster, safer to use CRL parser which returns a
<a href="/pkg/crypto/x509/#RevocationList"><code>RevocationList</code></a>.
To support this addition, <code>RevocationList</code> adds new fields
<code>RawIssuer</code>, <code>Signature</code>,
<code>AuthorityKeyId</code>, and <code>Extensions</code>.
The new method <a href="/pkg/crypto/x509/#RevocationList.CheckSignatureFrom"><code>RevocationList.CheckSignatureFrom</a>
checks that the signature on a CRL is a valid signature from a
<a href="/pkg/crypto/x509/#Certificate">Certificate</a>.
With the new CRL functionality, the existing functions
<a href="/pkg/crypto/x509/#ParseCRL"><code>ParseCRL</code></a> and
<a href="/pkg/crypto/x509/#ParseDERCRL"><code>ParseDERCRL</code></a> are deprecated.
Additionally the method <a href="/pkg/crypto/x509#Certificate.CheckCRLSignature"><code>Certificate.CheckCRLSignature</code></a>
is deprecated.
</p>
<p><!-- CL 389555 -->
When building paths, <a href="/pkg/crypto/x509/#Certificate.Verify"><code>Certificate.Verify</code></a>
now considers certificates to be equal when the subjects, public keys, and SANs
are all equal. Before, it required byte-for-byte equality.
</p>
<p><!-- https://go.dev/issue/46057 --><!-- CL 398237 -->
TODO: <a href="https://go.dev/issue/46057">https://go.dev/issue/46057</a>: add CertPool.Equal
</p>
<p><!-- https://go.dev/issue/50674 -->
TODO: <a href="https://go.dev/issue/50674">https://go.dev/issue/50674</a>: add ParseRevocationList, deprecate ParseCRL &amp; ParseDERCRL
</p>
<p><!-- CL 390834 -->
TODO: <a href="https://go.dev/cl/390834">https://go.dev/cl/390834</a>: crypto/x509: add new CRL parser, deprecate old one; modified api/next/50674.txt
</p>
<p><!-- https://go.dev/issue/35044 --><!-- CL 400175 -->
TODO: <a href="https://go.dev/cl/400175">https://go.dev/cl/400175</a>: crypto/x509: add CertPool.Clone; modified api/next/35044.txt
TODO: <a href="https://go.dev/issue/35044">https://go.dev/issue/35044</a>: add CertPool.Clone
</p>
</dd>
</dl><!-- crypto/x509 -->
<dl id="crypto/x509/pkix"><dt><a href="/pkg/crypto/x509/pkix">crypto/x509/pkix</a></dt>
<dd>
<p><!-- CL 390834 -->
The types <a href="/pkg/crypto/x509/pkix#CertificateList"><code>CertificateList</code></a> and
<a href="/pkg/crypto/x509/pkix#TBSCertificateList"><code>TBSCertificateList</code></a>
have been deprecated. The new <a href="#crypto/x509"><code>crypto/x509</code></code> CRL functionality</a>
should be used instead.
</p>
</dd>
</dl><!-- crypto/x509/pkix -->
<dl id="debug"><dt><a href="/pkg/debug/">debug</a></dt>
<dd>
<p><!-- CL 396735 -->
TODO: <a href="https://go.dev/cl/396735">https://go.dev/cl/396735</a>: debug: define ELF relocation for loong64; modified api/next/46229.txt
</p>
</dd>
</dl><!-- debug -->
<dl id="debug/pe"><dt><a href="/pkg/debug/pe/">debug/pe</a></dt>
<dd>
<p><!-- https://go.dev/issue/51868 -->
TODO: <a href="https://go.dev/issue/51868">https://go.dev/issue/51868</a>: add APIs to support reading COMDAT info for sections
</p>
<p><!-- CL 394534 -->
TODO: <a href="https://go.dev/cl/394534">https://go.dev/cl/394534</a>: debug/pe: add APIs for reading section def aux info; modified api/next/51868.txt
</p>
</dd>
</dl><!-- debug/pe -->
<dl id="encoding/binary"><dt><a href="/pkg/encoding/binary/">encoding/binary</a></dt>
<dd>
<p><!-- https://go.dev/issue/50601 --><!-- CL 386017 --><!-- CL 389636 -->
TODO: <a href="https://go.dev/cl/386017">https://go.dev/cl/386017</a>: add AppendByteOrder
</p>
<p><!-- https://go.dev/issue/51644 --><!-- CL 400176 -->
TODO: <a href="https://go.dev/issue/51644">https://go.dev/issue/51644</a>: add AppendUvarint and AppendVarint
</p>
</dd>
</dl><!-- encoding/binary -->
<dl id="encoding/csv"><dt><a href="/pkg/encoding/csv/">encoding/csv</a></dt>
<dd>
<p><!-- https://go.dev/issue/43401 --><!-- 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="encoding/xml"><dt><a href="/pkg/encoding/xml/">encoding/xml</a></dt>
<dd>
<p><!-- https://go.dev/issue/45628 --><!-- CL 311270 -->
TODO: <a href="https://go.dev/issue/45628">https://go.dev/issue/45628</a>: add Decoder.InputPos
TODO: <a href="https://go.dev/cl/311270">https://go.dev/cl/311270</a>: encoding/xml: expose decoder line and column; modified api/next/45628.txt
</p>
</dd>
</dl><!-- encoding/xml -->
<dl id="flag"><dt><a href="/pkg/flag/">flag</a></dt>
<dd>
<p><!-- https://go.dev/issue/45754 --><!-- 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><!-- https://go.dev/issue/47579 --><!-- 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/types"><dt><a href="/pkg/go/types/">go/types</a></dt>
<dd>
<p><!-- https://go.dev/issue/51682 --><!-- CL 395535 -->
The new methods <a href="/pkg/go/types/#Func.Origin"><code>Func.Origin</code></a>
and <a href="/pkg/go/types/#Var.Origin"><code>Var.Origin</code></a> return the
corresponding <a href="/pkg/go/types/#Object"><code>Object</code></a> of the
generic type for synthetic <a href="/pkg/go/types/#Func"><code>Func</code></a>
and <a href="/pkg/go/types/#Var"><code>Var</code></a> objects created during type
instantiation.
</p>
<p><!-- https://go.dev/issue/52728 --><!-- CL 404885 -->
It is no longer possible to produce an infinite number of distinct-but-identical
<a href="/pkg/go/types/#Named"><code>Named</code></a> type instantiations via
recursive calls to
<a href="/pkg/go/types/#Named.Underlying"><code>Named.Underlying</code></a> or
<a href="/pkg/go/types/#Named.Method"><code>Named.Method</code></a>.
</p>
</dd>
</dl><!-- go/types -->
<dl id="hash/maphash"><dt><a href="/pkg/hash/maphash/">hash/maphash</a></dt>
<dd>
<p><!-- https://go.dev/issue/42710 --><!-- CL 392494 -->
TODO: <a href="https://go.dev/cl/392494">https://go.dev/cl/392494</a>: hash/maphash: add Bytes and String; modified api/next/42710.txt
TODO: <a href="https://go.dev/issue/42710">https://go.dev/issue/42710</a>: add Bytes and String
</p>
</dd>
</dl><!-- hash/maphash -->
<dl id="html/template"><dt><a href="/pkg/html/template/">html/template</a></dt>
<dd>
<p><!-- https://go.dev/issue/46121 --><!-- CL 389156 -->
TODO: <a href="https://go.dev/issue/46121">https://go.dev/issue/46121</a>: make FuncMap an alias for text/template.FuncMap
TODO: <a href="https://go.dev/cl/389156">https://go.dev/cl/389156</a>: html/template: make FuncMap a type alias of text/template.FuncMap; modified api/except.txt, api/next/46121.txt
</p>
</dd>
</dl><!-- html/template -->
<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><!-- https://go.dev/issue/51566 --><!-- 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>
<p><!-- https://go.dev/issue/50842 -->
TODO: <a href="https://go.dev/issue/50842">https://go.dev/issue/50842</a>: implement WriterTo on result of MultiReader
</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><!-- https://go.dev/issue/51428 --><!-- 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>
<p><!-- https://go.dev/issue/33097 --><!-- CL 400654 -->
<a href="/pkg/net/#Resolver.PreferGo"><code>Resolver.PreferGo</code></a>
is now implemented on Windows and Plan 9. It previously only worked on Unix
platforms. Combined with
<a href="/pkg/net/#Dialer.Resolver"><code>Dialer.Resolver</code></a> and
<a href="/pkg/net/#Resolver.Dial"><code>Resolver.Dial</code></a>, it's now
possible to write portable programs and be in control of all DNS name lookups
when dialing.
</p>
<p>
The <code>net</code> package now has initial support for the <code>netgo</code>
build tag on Windows. When used, the package uses the Go DNS client (as used
by <code>Resolver.PreferGo</code>) instead of asking Windows for
DNS results. The upstream DNS server it discovers from Windows
may not yet be correct with complex system network configurations, however.
</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>
<p><!-- https://go.dev/issue/30715 --><!-- CL 361397 -->
TODO: <a href="https://go.dev/cl/361397">https://go.dev/cl/361397</a>: net/http: add MaxBytesError; modified api/next/30715.txt
TODO: <a href="https://go.dev/issue/30715">https://go.dev/issue/30715</a>: add MaxBytesError
</p>
</dd>
</dl><!-- net/http -->
<dl id="net/url"><dt><a href="/pkg/net/url/">net/url</a></dt>
<dd>
<p><!-- https://go.dev/issue/47005 --><!-- CL 374654 -->
TODO: <a href="https://go.dev/cl/374654">https://go.dev/cl/374654</a>: add JoinPath, URL.JoinPath
</p>
<p><!-- https://go.dev/issue/46059 -->
TODO: <a href="https://go.dev/issue/46059">https://go.dev/issue/46059</a>: add OmitHost bool to URL
</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>
<p><!-- https://go.dev/issue/50599 --><!-- CL 401340 -->
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><!-- https://go.dev/issue/47066 --><!-- 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="regexp"><dt><a href="/pkg/regexp/">regexp</a></dt>
<dd>
<p><!-- https://go.dev/issue/51684 --><!-- CL 401076 -->
TODO: <a href="https://go.dev/issue/51684">https://go.dev/issue/51684</a>: add ErrNestingDepth error
TODO: <a href="https://go.dev/cl/401076">https://go.dev/cl/401076</a>: regexp: change ErrInvalidDepth message to match proposal; modified api/next/51684.txt, api/next/regexpdepth.txt
</p>
</dd>
</dl><!-- regexp -->
<dl id="regexp/syntax"><dt><a href="/pkg/regexp/syntax/">regexp/syntax</a></dt>
<dd>
<p><!-- CL 384617 --><!-- CL 401854 -->
TODO: <a href="https://go.dev/cl/384617">https://go.dev/cl/384617</a>: regexp/syntax: add and use ErrInvalidDepth; modified api/next/regexpdepth.txt
TODO: <a href="https://go.dev/cl/401854">https://go.dev/cl/401854</a>: regexp/syntax: rename ErrInvalidDepth to ErrNestingDepth; modified api/next/51684.txt
</p>
</dd>
</dl><!-- regexp/syntax -->
<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/debug"><dt><a href="/pkg/runtime/debug/">runtime/debug</a></dt>
<dd>
<p><!-- CL 397018 -->
TODO: <a href="https://go.dev/cl/397018">https://go.dev/cl/397018</a>: runtime/debug: export SetMemoryLimit; modified api/next/48409.txt
</p>
</dd>
</dl><!-- runtime/debug -->
<dl id="runtime/metrics"><dt><a href="/pkg/runtime/metrics/">runtime/metrics</a></dt>
<dd>
<p><!-- https://go.dev/issue/47216 --><!-- CL 404305 -->
The new <code>/sched/gomaxprocs:threads</code> metric reports the current
<code>runtime.GOMAXPROCS</code> value.
</p>
<p><!-- https://go.dev/issue/47216 --><!-- CL 404306 -->
The new <code>/cgo/go-to-c-calls:calls</code> metric reports the total
number of calls made from Go to C. This metric is identical to the <a
href="/pkg/runtime/#NumCgoCall"><code>runtime.NumCgoCall</code></a>
function.
</p>
<p><!-- https://go.dev/issue/48409 --><!-- CL 403614 -->
The new <code>/gc/limiter/last-enabled:gc-cycle</code> metric reports the
last GC cycle when the GC CPU limiter was enabled.
</p>
</dd>
</dl><!-- runtime/metrics -->
<dl id="runtime/pprof"><dt><a href="/pkg/runtime/pprof/">runtime/pprof</a></dt>
<dd>
<p><!-- https://go.dev/issue/33250 --><!-- CL 387415 -->
Stop-the-world pause times have been significantly reduced when
collecting goroutine profiles, reducing the overall latency impact to the
application.
</p>
<p><!-- CL 391434 -->
<code>MaxRSS</code> is now reported in heap profiles for all Unix
operating systems (it was previously only reported for
<code>GOOS=android</code>, <code>darwin</code>, <code>ios</code>, and
<code>linux</code>).
</p>
</dd>
</dl><!-- runtime/pprof -->
<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. Compared to v2, it is now typically 1.5x to 2x
faster, uses half as much memory, and it supports an unlimited
number of goroutines.
</p>
<p><!-- CL 336549 -->
The race detector is now supported on <code>GOARCH=s390x</code>.
</p>
</dd>
</dl><!-- runtime/race -->
<dl id="runtime/trace"><dt><a href="/pkg/runtime/trace/">runtime/trace</a></dt>
<dd>
<p><!-- CL 400795 -->
When tracing and the
<a href="/pkg/runtime/pprof#StartCPUProfile">CPU profiler</a> are
enabled simultaneously, the execution trace includes CPU profile
samples as instantaneous events.
</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>
<p><!-- https://go.dev/issue/50340 --><!-- CL 396514 -->
TODO: <a href="https://go.dev/issue/50340">https://go.dev/issue/50340</a>: add Find
TODO: <a href="https://go.dev/cl/396514">https://go.dev/cl/396514</a>: sort: add Find function; modified api/next/50340.txt
</p>
</dd>
</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="syscall"><dt><a href="/pkg/syscall/">syscall</a></dt>
<dd>
<p><!-- https://go.dev/issue/51192 --><!-- CL 385796 -->
On PowerPC (<code>GOARCH=ppc64</code>, <code>ppc64le</code>),
<a href="/pkg/syscall/#Syscall"><code>Syscall</code></a>,
<a href="/pkg/syscall/#Syscall6"><code>Syscall6</code></a>,
<a href="/pkg/syscall/#RawSyscall"><code>RawSyscall</code></a>, and
<a href="/pkg/syscall/#RawSyscall6"><code>RawSyscall6</code></a>
now always return 0 for return value <code>r2</code> instead of an
undefined value.
</p>
<p><!-- CL 391434 -->
On AIX and Solaris, <code>Getrusage</code> is now defined.
</p>
</dd>
</dl><!-- syscall -->
<dl id="time"><dt><a href="/pkg/time/">time</a></dt>
<dd>
<p><!-- https://go.dev/issue/51414 --><!-- CL 393515 -->
TODO: <a href="https://go.dev/cl/393515">https://go.dev/cl/393515</a>: add Duration.Abs
TODO: <a href="https://go.dev/issue/51414">https://go.dev/issue/51414</a>: add Duration.Abs
</p>
<p><!-- https://go.dev/issue/50062 --><!-- CL 405374 -->
TODO: <a href="https://go.dev/issue/50062">https://go.dev/issue/50062</a>: add Time.ZoneBounds
TODO: <a href="https://go.dev/cl/405374">https://go.dev/cl/405374</a>: time: add Time.ZoneBounds; modified api/next/50062.txt
</p>
</dd>
</dl><!-- time -->
<!-- Silence these false positives from x/build/cmd/relnote: -->
<!-- CL 382460 -->
<!-- CL 384154 -->
<!-- CL 384554 -->
<!-- CL 392134 -->
<!-- CL 392414 -->
<!-- CL 396215 -->
<!-- CL 403058 -->
<!-- CL 410133 -->
<!-- https://go.dev/issue/27837 -->
<!-- https://go.dev/issue/38340 -->
<!-- https://go.dev/issue/42516 -->
<!-- https://go.dev/issue/45713 -->
<!-- https://go.dev/issue/46654 -->
<!-- https://go.dev/issue/48257 -->
<!-- https://go.dev/issue/50447 -->
<!-- https://go.dev/issue/50720 -->
<!-- https://go.dev/issue/50792 -->
<!-- https://go.dev/issue/51115 -->
<!-- https://go.dev/issue/51447 -->
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