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<!--{
"Title": "Go 1.16 Release Notes",
"Path": "/doc/go1.16"
}-->
<!--
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 1.16</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>
<p>
TODO
</p>
<h2 id="tools">Tools</h2>
<p>
TODO
</p>
<h3 id="go-command">Go command</h3>
<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/29062 -->
When using <code>go 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
os.Exit(0) 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>
<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>
<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>
<h2 id="library">Core library</h2>
<p>
TODO
</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>
<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="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>
</dd>
</dl><!-- net/http -->
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