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<!--{
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<h2 id="introduction">DRAFT RELEASE NOTES — Introduction to Go 1.16</h2>
<p>
<strong>
Go 1.16 is not yet released. These are work-in-progress
release notes. Go 1.16 is expected to be released in February 2021.
</strong>
</p>
<h2 id="language">Changes to the language</h2>
<p>
TODO
</p>
<h2 id="ports">Ports</h2>
<h3 id="netbsd">NetBSD</h3>
<p><!-- golang.org/issue/30824 -->
Go now supports the 64-bit ARM architecture on NetBSD (the
<code>netbsd/arm64</code> port).
</p>
<h3 id="386">386</h3>
<p><!-- golang.org/issue/40255, golang.org/issue/41848, CL 258957, and CL 260017 -->
As <a href="go1.15#386">announced</a> in the Go 1.15 release notes,
Go 1.16 drops support for x87 mode compilation (<code>GO386=387</code>).
Support for non-SSE2 processors is now available using soft float
mode (<code>GO386=softfloat</code>).
Users running on non-SSE2 processors should replace <code>GO386=387</code>
with <code>GO386=softfloat</code>.
</p>
<h2 id="tools">Tools</h2>
<p>
TODO
</p>
<h3 id="go-command">Go command</h3>
<h4 id="modules">Modules</h4>
<p><!-- golang.org/issue/40276 -->
<code>go</code> <code>install</code> now accepts arguments with
version suffixes (for example, <code>go</code> <code>install</code>
<code>example.com/cmd@v1.0.0</code>). This causes <code>go</code>
<code>install</code> to build and install packages in module-aware mode,
ignoring the <code>go.mod</code> file in the current directory or any parent
directory, if there is one. This is useful for installing executables without
affecting the dependencies of the main module.<br>
TODO: write and link to section in golang.org/ref/mod<br>
TODO: write and link to blog post
</p>
<p><!-- golang.org/issue/24031 -->
<code>retract</code> directives may now be used in a <code>go.mod</code> file
to indicate that certain published versions of the module should not be used
by other modules. A module author may retract a version after a severe problem
is discovered or if the version was published unintentionally.<br>
TODO: write and link to section in golang.org/ref/mod<br>
TODO: write and link to tutorial or blog post
</p>
<p><!-- golang.org/issue/26603 -->
The <code>go</code> <code>mod</code> <code>vendor</code>
and <code>go</code> <code>mod</code> <code>tidy</code> subcommands now accept
the <code>-e</code> flag, which instructs them to proceed despite errors in
resolving missing packages.
</p>
<h4 id="go-test"><code>go</code> <code>test</code></h4>
<p><!-- golang.org/issue/29062 -->
When using <code>go</code> <code>test</code>, a test that
calls <code>os.Exit(0)</code> during execution of a test function
will now be considered to fail.
This will help catch cases in which a test calls code that calls
<code>os.Exit(0)</code> and thereby stops running all future tests.
If a <code>TestMain</code> function calls <code>os.Exit(0)</code>
that is still considered to be a passing test.
</p>
<p><!-- golang.org/issue/37519 -->
The <code>go</code> <code>get</code> <code>-insecure</code> flag is
deprecated and will be removed in a future version. This flag permits
fetching from repositories and resolving custom domains using insecure
schemes such as HTTP, and also bypassess module sum validation using the
checksum database. To permit the use of insecure schemes, use the
<code>GOINSECURE</code> environment variable instead. To bypass module
sum validation, use <code>GOPRIVATE</code> or <code>GONOSUMDB</code>.
See <code>go</code> <code>help</code> <code>environment</code> for details.
</p>
<h4 id="all-pattern">The <code>all</code> pattern</h4>
<p><!-- golang.org/cl/240623 -->
When the main module's <code>go.mod</code> file
declares <code>go</code> <code>1.16</code> or higher, the <code>all</code>
package pattern now matches only those packages that are transitively imported
by a package or test found in the main module. (Packages imported by <em>tests
of</em> packages imported by the main module are no longer included.) This is
the same set of packages retained
by <code>go</code> <code>mod</code> <code>vendor</code> since Go 1.11.
</p>
<h4 id="toolexec">The <code>-toolexec</code> build flag</h4>
<p><!-- golang.org/cl/263357 -->
When the <code>-toolexec</code> build flag is specified to use a program when
invoking toolchain programs like compile or asm, the environment variable
<code>TOOLEXEC_IMPORTPATH</code> is now set to the import path of the package
being built.
</p>
<h3 id="cgo">Cgo</h3>
<p> <!-- CL 252378 -->
The <a href="/cmd/cgo">cgo</a> tool will no longer try to translate
C struct bitfields into Go struct fields, even if their size can be
represented in Go. The order in which C bitfields appear in memory
is implementation dependent, so in some cases the cgo tool produced
results that were silently incorrect.
</p>
<p>
TODO
</p>
<h2 id="runtime">Runtime</h2>
<p>
TODO
</p>
<h2 id="compiler">Compiler</h2>
<p>
TODO
</p>
<h2 id="linker">Linker</h2>
<p>
This release includes additional improvements to the Go linker,
reducing linker resource usage (both time and memory) and improving
code robustness/maintainability. These changes form the second half
of a two-release project to
<a href="https://golang.org/s/better-linker">modernize the Go
linker</a>.
</p>
<p>
The linker changes in 1.16 extend the 1.15 improvements to all
supported architecture/OS combinations (the 1.15 performance improvements
were primarily focused on <code>ELF</code>-based OSes and
<code>amd64</code> architectures). For a representative set of
large Go programs, linking is 20-35% faster than 1.15 and requires
5-15% less memory on average for <code>linux/amd64</code>, with larger
improvements for other architectures and OSes.
</p>
<p>
TODO: update with final numbers later in the release.
</p>
<p> <!-- CL 255259 -->
On Windows, <code>go build -buildmode=c-shared</code> now generates Windows
ASLR DLLs by default. ASLR can be disabled with <code>--ldflags=-aslr=false</code>.
</p>
<h2 id="library">Core library</h2>
<p>
TODO
</p>
<h3 id="crypto/hmac"><a href="/pkg/crypto/hmac">crypto/hmac</a></h3>
<p><!-- CL 261960 -->
<a href="/pkg/crypto/hmac/#New">New</a> will now panic if separate calls to
the hash generation function fail to return new values. Previously, the
behavior was undefined and invalid outputs were sometimes generated.
</p>
<h3 id="crypto/tls"><a href="/pkg/crypto/tls">crypto/tls</a></h3>
<p><!-- CL 256897 -->
I/O operations on closing or closed TLS connections can now be detected using
the new <a href="/pkg/net/#ErrClosed">ErrClosed</a> error. A typical use
would be <code>errors.Is(err, net.ErrClosed)</code>. In earlier releases
the only way to reliably detect this case was to match the string returned
by the <code>Error</code> method with <code>"tls: use of closed connection"</code>.
</p>
<h3 id="crypto/x509"><a href="/pkg/crypto/x509">crypto/x509</a></h3>
<p><!-- CL 235078 -->
<a href="/pkg/crypto/x509/#ParseCertificate">ParseCertificate</a> and
<a href="/pkg/crypto/x509/#CreateCertificate">CreateCertificate</a> both
now enforce string encoding restrictions for the fields <code>DNSNames</code>,
<code>EmailAddresses</code>, and <code>URIs</code>. These fields can only
contain strings with characters within the ASCII range.
</p>
<p><!-- CL 259697 -->
<a href="/pkg/crypto/x509/#CreateCertificate">CreateCertificate</a> now
verifies the generated certificate's signature using the signer's
public key. If the signature is invalid, an error is returned, instead
of a malformed certificate.
</p>
<h3 id="encoding/json"><a href="/pkg/encoding/json">encoding/json</a></h3>
<p><!-- CL 263619 -->
The error message for
<a href="/pkg/encoding/json/#SyntaxError">SyntaxError</a>
now begins with "json: ", matching the other errors in the package.
</p>
<h3 id="net"><a href="/pkg/net/">net</a></h3>
<p><!-- CL 250357 -->
The case of I/O on a closed network connection, or I/O on a network
connection that is closed before any of the I/O completes, can now
be detected using the new <a href="/pkg/net/#ErrClosed">ErrClosed</a> error.
A typical use would be <code>errors.Is(err, net.ErrClosed)</code>.
In earlier releases the only way to reliably detect this case was to
match the string returned by the <code>Error</code> method
with <code>"use of closed network connection"</code>.
</p>
<p><!-- CL 255898 -->
In previous Go releases the default TCP listener backlog size on Linux systems,
set by <code>/proc/sys/net/core/somaxconn</code>, was limited to a maximum of <code>65535</code>.
On Linux kernel version 4.1 and above, the maximum is now <code>4294967295</code>.
</p>
<h3 id="reflect"><a href="/pkg/reflect/">reflect</a></h3>
<p><!-- CL 259237, golang.org/issue/22075 -->
For interface types and values, <a href="/pkg/reflect/#Value.Method">Method</a>,
<a href="/pkg/reflect/#Value.MethodByName">MethodByName</a>, and
<a href="/pkg/reflect/#Value.NumMethod">NumMethod</a> now
operate on the interface's exported method set, rather than its full method set.
</p>
<h3 id="text/template/parse"><a href="/pkg/text/template/parse/">text/template/parse</a></h3>
<p><!-- CL 229398, golang.org/issue/34652 -->
A new <a href="/pkg/text/template/parse/#CommentNode"><code>CommentNode</code></a>
was added to the parse tree. The <a href="/pkg/text/template/parse/#Mode"><code>Mode</code></a>
field in the <code>parse.Tree</code> enables access to it.
</p>
<!-- text/template/parse -->
<h3 id="unicode"><a href="/pkg/unicode/">unicode</a></h3>
<p><!-- CL 248765 -->
The <a href="/pkg/unicode/"><code>unicode</code></a> package and associated
support throughout the system has been upgraded from Unicode 12.0.0 to
<a href="https://www.unicode.org/versions/Unicode13.0.0/">Unicode 13.0.0</a>,
which adds 5,930 new characters, including four new scripts, and 55 new emoji.
Unicode 13.0.0 also designates plane 3 (U+30000-U+3FFFF) as the tertiary
ideographic plane.
</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
</p>
<dl id="crypto/dsa"><dt><a href="/pkg/crypto/dsa/">crypto/dsa</a></dt>
<dd>
<p><!-- CL 257939 -->
The <a href="/pkg/crypto/dsa/"><code>crypto/dsa</code></a> package is now deprecated.
See <a href="https://golang.org/issue/40337">issue #40337</a>.
</p>
</dd>
</dl><!-- crypto/dsa -->
<dl id="crypto/x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt>
<dd>
<p><!-- CL 257939 -->
DSA signature verification is no longer supported. Note that DSA signature
generation was never supported.
See <a href="https://golang.org/issue/40337">issue #40337</a>.
</p>
</dd>
</dl><!-- crypto/x509 -->
<dl id="encoding/xml"><dt><a href="/pkg/encoding/xml/">encoding/xml</a></dt>
<dd>
<p><!-- CL 264024 -->
The encoder has always taken care to avoid using namespace prefixes
beginning with <code>xml</code>, which are reserved by the XML
specification.
Now, following the specification more closely, that check is
case-insensitive, so that prefixes beginning
with <code>XML</code>, <code>XmL</code>, and so on are also
avoided.
</p>
</dd>
</dl><!-- encoding/xml -->
<dl id="net/http"><dt><a href="/pkg/net/http/">net/http</a></dt>
<dd>
<p><!-- CL 233637 -->
In the <a href="/pkg/net/http/"><code>net/http</code></a> package, the
behavior of <a href="/pkg/net/http/#StripPrefix"><code>StripPrefix</code></a>
has been changed to strip the prefix from the request URL's
<code>RawPath</code> field in addition to its <code>Path</code> field.
In past releases, only the <code>Path</code> field was trimmed, and so if the
request URL contained any escaped characters the URL would be modified to
have mismatched <code>Path</code> and <code>RawPath</code> fields.
In Go 1.16, <code>StripPrefix</code> trims both fields.
If there are escaped characters in the prefix part of the request URL the
handler serves a 404 instead of its previous behavior of invoking the
underlying handler with a mismatched <code>Path</code>/<code>RawPath</code> pair.
</p>
<p><!-- CL 252497 -->
The <a href="/pkg/net/http/"><code>net/http</code></a> package now rejects HTTP range requests
of the form <code>"Range": "bytes=--N"</code> where <code>"-N"</code> is a negative suffix length, for
example <code>"Range": "bytes=--2"</code>. It now replies with a <code>416 "Range Not Satisfiable"</code> response.
</p>
<p><!-- CL 256498, golang.org/issue/36990 -->
Cookies set with <code>SameSiteDefaultMode</code> now behave according to the current
spec (no attribute is set) instead of generating a SameSite key without a value.
</p>
</dd>
</dl><!-- net/http -->
<dl id="runtime/debug"><dt><a href="/pkg/runtime/debug/">runtime/debug</a></dt>
<dd>
<p><!-- CL 249677 -->
TODO: <a href="https://golang.org/cl/249677">https://golang.org/cl/249677</a>: provide Addr method for errors from SetPanicOnFault
</p>
</dd>
</dl><!-- runtime/debug -->
<dl id="strconv"><dt><a href="/pkg/strconv/">strconv</a></dt>
<dd>
<p><!-- CL 260858 -->
<a href="/pkg/strconv/#ParseFloat"><code>ParseFloat</code></a> now uses
the <a
href="https://nigeltao.github.io/blog/2020/eisel-lemire.html">Eisel-Lemire
algorithm</a>, improving performance by up to a factor of 2. This can
also speed up decoding textual formats like <a
href="/pkg/encoding/json/"><code>encoding/json</code></a>.
</p>
</dd>
</dl><!-- strconv -->