go/doc/go1.15.html

<!--{
        "Title": "Go 1.15 Release Notes",
        "Path":  "/doc/go1.15"
}-->

<!--
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 1.15</h2>

<p>
  <strong>
    Go 1.15 is not yet released. These are work-in-progress
    release notes. Go 1.15 is expected to be released in August 2020.
  </strong>
</p>

<h2 id="language">Changes to the language</h2>

<p>
TODO
</p>

<h2 id="ports">Ports</h2>

<p> <!-- CL 214397 and CL 230217 -->
  Go 1.15 now generates Windows ASLR executables when -buildmode=pie
  cmd/link flag is provided. Go command uses -buildmode=pie by default
  on Windows.
</p>

<p>
TODO
</p>

<h2 id="tools">Tools</h2>

<p>
TODO
</p>

<h3 id="go-command">Go command</h3>

<p><!-- golang.org/issue/37367 -->
  The <code>GOPROXY</code> environment variable now supports skipping proxies
  that return errors. Proxy URLs may now be separated with either commas
  (<code>,</code>) or pipe characters (<code>|</code>). If a proxy URL is
  followed by a comma, the <code>go</code> command will only try the next proxy
  in the list after a 404 or 410 HTTP response. If a proxy URL is followed by a
  pipe character, the <code>go</code> command will try the next proxy in the
  list after any error. Note that the default value of <code>GOPROXY</code>
  remains <code>https://proxy.golang.org,direct</code>, which does not fall
  back to <code>direct</code> in case of errors.
</p>

<p>
TODO
</p>

<h4 id="go-test"><code>go</code> <code>test</code></h4>

<p><!-- https://golang.org/issue/36134 -->
  Changing the <code>-timeout</code> flag now invalidates cached test results. A
  cached result for a test run with a long timeout will no longer count as
  passing when <code>go</code> <code>test</code> is re-invoked with a short one.
</p>

<h4 id="go-flag-parsing">Flag parsing</h4>

<p><!-- https://golang.org/cl/211358 -->
  Various flag parsing issues in <code>go</code> <code>test</code> and
  <code>go</code> <code>vet</code> have been fixed. Notably, flags specified
  in <code>GOFLAGS</code> are handled more consistently, and
  the <code>-outputdir</code> flag now interprets relative paths relative to the
  working directory of the <code>go</code> command (rather than the working
  directory of each individual test).
</p>

<h4 id="module-cache">Module cache</h4>

<p><!-- https://golang.org/cl/219538 -->
  The location of the module cache may now be set with
  the <code>GOMODCACHE</code> environment variable. The default value of
  <code>GOMODCACHE</code> is <code>GOPATH[0]/pkg/mod</code>, the location of the
  module cache before this change.
</p>

<p><!-- https://golang.org/cl/221157 -->
  A workaround is now available for Windows "Access is denied" errors in
  <code>go</code> commands that access the module cache, caused by external
  programs concurrently scanning the file system (see
  <a href="https://golang.org/issue/36568">issue #36568</a>). The workaround is
  not enabled by default because it is not safe to use when Go versions lower
  than 1.14.2 and 1.13.10 are running concurrently with the same module cache.
  It can be enabled by explictly setting the environment variable
  <code>GODEBUG=modcacheunzipinplace=1</code>.
</p>

<h2 id="runtime">Runtime</h2>

<p>
TODO
</p>

<h2 id="compiler">Compiler</h2>

<p><!-- https://golang.org/cl/229578 -->
  Package <code>unsafe</code>'s <a href="/pkg/unsafe/#Pointer">safety
  rules</a> allow converting an <code>unsafe.Pointer</code>
  into <code>uintptr</code> when calling certain
  functions. Previously, in some cases, the compiler allowed multiple
  chained conversions (for example, <code>syscall.Syscall(…,
  uintptr(uintptr(ptr)), …)</code>). The compiler now requires exactly
  one conversion. Code that used multiple conversions should be
  updated to satisfy the safety rules.
</p>

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

<h3 id="time/tzdata">New embedded tzdata package</h3>

<p> <!-- CL 224588 -->
  Go 1.15 includes a new package,
  <a href="/pkg/time/tzdata/"><code>time/tzdata</code></a>,
  that permits embedding the timezone database into a program.
  Importing this package (as <code>import _ "time/tzdata"</code>)
  permits the program to find timezone information even if the
  timezone database is not available on the local system.
  You can also embed the timezone database by building
  with <code>-tags timetzdata</code>.
  Either approach increases the size of the program by about 800 KB.
</p>

<p>
TODO
</p>

<dl id="testing"><dt><a href="/pkg/testing/">testing</a></dt>
  <dd>
    <p><!-- golang.org/issue/28135 -->
      The <code>testing.T</code> type now has a <code>Deadline</code> method
      that reports the time at which the test binary will have exceeded its
      timeout.
    </p>
    <p><!-- golang.org/issue/34129 -->
      A <code>TestMain</code> function is no longer required to call
      <code>os.Exit</code>. If a <code>TestMain</code> function returns,
      the test binary will call <code>os.Exit</code> with the value returned
      by <code>m.Run</code>.
    </p>
  </dd>
</dl><!-- testing -->

<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/tls"><dt><a href="/crypto/tls/">crypto/tls</a></dt>
  <dd>
    <p><!-- CL 214977 -->
      The new
      <a href="/pkg/crypto/tls/#Dialer"><code>Dialer</code></a>
      type and its
      <a href="/pkg/crypto/tls/#Dialer.DialContext"><code>DialContext</code></a>
      method permits using a context to both connect and handshake with a TLS server.
    </p>
  </dd>
</dl>

<dl id="flag"><dt><a href="/pkg/flag/">flag</a></dt>
  <dd>
    <p><!-- CL 221427 -->
      When the flag package sees <code>-h</code> or <code>-help</code>, and
      those flags are not defined, the flag package prints a usage message.
      If the <a href="/pkg/flag/#FlagSet"><code>FlagSet</code></a> was created with
      <a href="/pkg/flag/#ExitOnError"><code>ExitOnError</code></a>,
      <a href="/pkg/flag/#FlagSet.Parse"><code>FlagSet.Parse</code></a> would then
      exit with a status of 2. In this release, the exit status for <code>-h</code>
      or <code>-help</code> has been changed to 0. In particular, this applies to
      the default handling of command line flags.
    </p>
  </dd>
</dl>

<dl id="net"><dt><a href="/pkg/net/">net</a></dt>
  <dd>
    <p><!-- CL -->
      If an I/O operation exceeds a deadline set by
      the <a href="/pkg/net/#Conn"><code>Conn.SetDeadline</code></a>,
      <code>Conn.SetReadDeadline</code>,
      or <code>Conn.SetWriteDeadline</code> methods, it will now
      return an error that is or wraps
      <a href="/pkg/os#ErrDeadlineExceeded"><code>os.ErrDeadlineExceeded</code></a>.
      This may be used to reliably detect whether an error is due to
      an exceeded deadline.
      Earlier releases recommended calling the <code>Timeout</code>
      method on the error, but I/O operations can return errors for
      which <code>Timeout</code> returns <code>true</code> although a
      deadline has not been exceeded.
    </p>
  </dd>
</dl>

<dl id="net/http/pprof"><dt><a href="/pkg/net/http/pprof/">net/http/pprof</a></dt>
  <dd>
    <p><!-- CL 147598, 229537 -->
      All profile endpoints now support a "seconds" parameter. When present,
      the endpoint profiles for the specified number of seconds and reports the difference.
      The meaning of the "seconds" parameter in the <code>cpu</code> profile and
      the trace endpoints is unchanged.
    </p>
  </dd>
</dl>

<dl id="net/url"><dt><a href="/pkg/net/url/">net/url</a></dt>
  <dd>
    <p><!-- CL 227645 -->
      The new <a href="/pkg/net/url/#URL"><code>URL</code></a> field
      <code>RawFragment</code> and method <a href="/pkg/net/url/#URL.EscapedFragment"><code>EscapedFragment</code></a>
      provide detail about and control over the exact encoding of a particular fragment.
      These are analogous to
      <code>RawPath</code> and <a href="/pkg/net/url/#URL.EscapedPath"><code>EscapedPath</code></a>.
    </p>
    <p><!-- CL 207082 -->
      The new <a href="/pkg/net/url/#URL"><code>URL</code></a>
      method <a href="/pkg/net/url/#URL.Redacted"><code>Redacted</code></a>
      returns the URL in string form with any password replaced with <code>xxxxx</code>.
    </p>
  </dd>
</dl>

<dl id="os"><dt><a href="/pkg/os/">os</a></dt>
  <dd>
    <p><!-- CL -->
      If an I/O operation exceeds a deadline set by
      the <a href="/pkg/os/#File.SetDeadline"><code>File.SetDeadline</code></a>,
      <a href="/pkg/os/#File.SetReadDeadline"><code>File.SetReadDeadline</code></a>,
      or <a href="/pkg/os/#File.SetWriteDeadline"><code>File.SetWriteDeadline</code></a>
      methods, it will now return an error that is or wraps
      <a href="/pkg/os#ErrDeadlineExceeded"><code>os.ErrDeadlineExceeded</code></a>.
      This may be used to reliably detect whether an error is due to
      an exceeded deadline.
      Earlier releases recommended calling the <code>Timeout</code>
      method on the error, but I/O operations can return errors for
      which <code>Timeout</code> returns <code>true</code> although a
      deadline has not been exceeded.
    </p>
  </dd>
</dl>

<dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
  <dd>
    <p><!-- CL 228902 -->
      Package reflect now disallows accessing methods of all
      non-exported fields, whereas previously it allowed accessing
      those of non-exported, embedded fields. Code that relies on the
      previous behavior should be updated to instead access the
      corresponding promoted method of the enclosing variable.
    </p>
  </dd>
</dl>

<dl id="pkg-runtime"><dt><a href="/pkg/runtime/">runtime</a></dt>
  <dd>
    <p><!-- CL 221779 -->
      If <code>panic</code> is invoked with a value whose type is derived from any
      of: <code>bool</code>, <code>complex64</code>, <code>complex128</code>, <code>float32</code>, <code>float64</code>,
      <code>int</code>, <code>int8</code>, <code>int16</code>, <code>int32</code>, <code>int64</code>, <code>string</code>,
      <code>uint</code>, <code>uint8</code>, <code>uint16</code>, <code>uint32</code>, <code>uint64</code>, <code>uintptr</code>,
      then the value will be printed, instead of just its address.
    </p>

    <p><!-- CL -->
      On a Unix system, if the <code>kill</code> command
      or <code>kill</code> system call is used to send
      a <code>SIGSEGV</code>, <code>SIGBUS</code>,
      or <code>SIGFPE</code> signal to a Go program, and if the signal
      is not being handled via
      <a href="/pkg/os/signal/#Notify"><code>os/signal.Notify</code></a>,
      the Go program will now reliably crash with a stack trace.
      In earlier releases the behavior was unpredictable.
    </p>
  </dd>
</dl>

<dl id="pkg-runtime-pprof"><dt><a href="/pkg/runtime/pprof">runtime/pprof</a></dt>
  <dd>
    <p><!-- CL 189318 -->
      The goroutine profile includes the profile labels associated with each goroutine
      at the time of profiling. This feature is not yet implemented for the profile
      reported with <code>debug=2</code>.
    </p>
  </dd>
</dl>

<dl id="sync"><dt><a href="/pkg/sync/">sync</a></dt>
  <dd>
    <p><!-- CL 205899, golang.org/issue/33762 -->
      The new method
      <a href="/pkg/sync/#Map.LoadAndDelete"><code>Map.LoadAndDelete</code></a>
      atomically deletes a key and returns the previous value if present.
    </p>
    <p><!-- CL 205899 -->
      The method
      <a href="/pkg/sync/#Map.Delete"><code>Map.Delete</code></a>
      is more efficient.
    </p>
</dl><!-- sync -->

<dl id="testing"><dt><a href="/pkg/testing/">testing</a></dt>
  <dd>
    <p><!-- CL 226877, golang.org/issue/35998 -->
       The new methods
       <a href="/pkg/testing/#T.TempDir"><code>T.TempDir</code></a> and
       <a href="/pkg/testing/#B.TempDir"><code>B.TempDir</code></a> and
       return temporary directories that are automatically cleaned up
       at the end of the test.
    </p>
  </dd>
</dl><!-- testing -->

<dl id="time"><dt><a href="/pkg/time/">time</a></dt>
  <dd>
    <p><!-- CL 220424, CL 217362, golang.org/issue/33184 -->
       The new method
       <a href="/pkg/time/#Ticker.Reset"><code>Ticker.Reset</code></a>
       supports changing the duration of a ticker.
    </p>
  </dd>
</dl><!-- time -->