+++ /dev/null
-<!--{
- "Title": "Go 1.21 Release Notes",
- "Path": "/doc/go1.21"
-}-->
-
-<!--
-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 1.21</h2>
-
-<p>
- <strong>
- Go 1.21 is not yet released. These are work-in-progress
- release notes. Go 1.21 is expected to be released in August 2023.
- </strong>
-</p>
-
-<p>
- The latest Go release, version 1.21, arrives six months after <a href="/doc/go1.20">Go 1.20</a>.
- Most of its changes are in the implementation of the toolchain, runtime, and libraries.
- As always, the release maintains the Go 1 <a href="/doc/go1compat">promise of compatibility</a>;
- in fact, Go 1.21 <a href="#godebug">improves upon that promise</a>.
- We expect almost all Go programs to continue to compile and run as before.
-</p>
-
-<p><!-- https://go.dev/issue/57631 -->
- Go 1.21 introduces a small change to the numbering of releases.
- In the past, we used Go 1.<i>N</i> to refer to both the overall Go language version and release family
- as well as the first release in that family.
- Starting in Go 1.21, the first release is now Go 1.<i>N</i>.0.
- Today we are releasing both the Go 1.21 language and its initial implementation, the Go 1.21.0 release.
- These notes refer to “Go 1.21”; tools like <code>go</code> <code>version</code> will report “<code>go1.21.0</code>”
- (until you upgrade to Go 1.21.1).
- See “<a href="/doc/toolchain#versions">Go versions</a>” in the “Go Toolchains” documentation for details
- about the new version numbering.
-</p>
-
-<h2 id="language">Changes to the language</h2>
-
-<p>
- Go 1.21 adds three new built-ins to the language.
-
- <ul>
- <li><!-- https://go.dev/issue/59488 -->
- The new functions <code>min</code> and <code>max</code> compute the
- smallest (or largest, for <code>max</code>) value of a fixed number
- of given arguments.
- See the language spec for
- <a href="https://tip.golang.org/ref/spec#Min_and_max">details</a>.
- </li>
- <li><!-- https://go.dev/issue/56351 -->
- The new function <code>clear</code> deletes all elements from a
- map or zeroes all elements of a slice.
- See the language spec for
- <a href="https://tip.golang.org/ref/spec#Clear">details</a>.
- </li>
- </ul>
-</p>
-
-<p><!-- https://go.dev/issue/57411 -->
- Package initialization order is now specified more precisely. The
- new algorithm is:
- <ul>
- <li>
- Sort all packages by import path.
- </li>
- <li>Repeat until the list of packages is empty:
- <ul>
- <li>
- Find the first package in the list for which all imports are
- already initialized.
- </li>
- <li>
- Initialize that package and remove it from the list.
- </li>
- </ul>
- </li>
- </ul>
- This may change the behavior of some programs that rely on a
- specific initialization ordering that was not expressed by explicit
- imports. The behavior of such programs was not well defined by the
- spec in past releases. The new rule provides an unambiguous definition.
-</p>
-
-<p>
- Multiple improvements that increase the power and precision of type inference have been made.
-</p>
-<ul>
- <li><!-- https://go.dev/issue/59338 -->
- A (possibly partially instantiated generic) function may now be called with arguments that are
- themselves (possibly partially instantiated) generic functions.
- The compiler will attempt to infer the missing type arguments of the callee (as before) and,
- for each argument that is a generic function that is not fully instantiated,
- its missing type arguments (new).
- Typical use cases are calls to generic functions operating on containers
- (such as <a href="/pkg/slices#IndexFunc">slices.IndexFunc</a>) where a function argument
- may also be generic, and where the type argument of the called function and its arguments
- are inferred from the container type.
- More generally, a generic function may now be used without explicit instantiation when
- it is assigned to a variable or returned as a result value if the type arguments can
- be inferred from the assignment.
- </li>
- <li><!-- https://go.dev/issue/60353, https://go.dev/issue/57192, https://go.dev/issue/52397, https://go.dev/issue/41176 -->
- Type inference now also considers methods when a value is assigned to an interface:
- type arguments for type parameters used in method signatures may be inferred from
- the corresponding parameter types of matching methods.
- </li>
- <li><!-- https://go.dev/issue/51593 https://go.dev/issue/39661 -->
- Similarly, since a type argument must implement all the methods of its corresponding constraint,
- the methods of the type argument and constraint are matched which may lead to the inference of
- additional type arguments.
- </li>
- <li><!-- https://go.dev/issue/58671 -->
- If multiple untyped constant arguments of different kinds (such as an untyped int and
- an untyped floating-point constant) are passed to parameters with the same (not otherwise
- specified) type parameter type, instead of an error, now type inference determines the
- type using the same approach as an operator with untyped constant operands.
- This change brings the types inferred from untyped constant arguments in line with the
- types of constant expressions.
- </li>
- <li><!-- https://go.dev/issue/59750 -->
- Type inference is now precise when matching corresponding types in assignments:
- component types (such as the elements of slices, or the parameter types in function signatures)
- must be identical (given suitable type arguments) to match, otherwise inference fails.
- This change produces more accurate error messages:
- where in the past type inference may have succeeded incorrectly and lead to an invalid assignment,
- the compiler now reports an inference error if two types can't possibly match.
- </li>
-</ul>
-
-<p><!-- https://go.dev/issue/58650 -->
- More generally, the description of
- <a href="https://tip.golang.org/ref/spec#Type_inference">type inference</a>
- in the language spec has been clarified.
- Together, all these changes make type inference more powerful and inference failures less surprising.
-</p>
-
-<!-- https://go.dev/issue/57969 -->
-<p>
- Go 1.21 includes a preview of a language change we are considering for a future version of Go:
- making for loop variables per-iteration instead of per-loop, to avoid accidental sharing bugs.
- For details about how to try that language change, see <a href="https://go.dev/wiki/LoopvarExperiment">the LoopvarExperiment wiki page</a>.
-</p>
-
-<h2 id="tools">Tools</h2>
-<p>
- Go 1.21 adds improved support for backwards compatibility and forwards compatibility
- in the Go toolchain.
-</p>
-
-<p><!-- https://go.dev/issue/56986 -->
- To improve backwards compatibility, Go 1.21 formalizes
- Go's use of the GODEBUG environment variable to control
- the default behavior for changes that are non-breaking according to the
- <a href="/doc/go1compat">compatibility policy</a>
- but nonetheless may cause existing programs to break.
- (For example, programs that depend on buggy behavior may break
- when a bug is fixed, but bug fixes are not considered breaking changes.)
- When Go must make this kind of behavior change,
- it now chooses between the old and new behavior based on the
- <code>go</code> line in the workspace's <code>go.work</code> file
- or else the main module's <code>go.mod</code> file.
- Upgrading to a new Go toolchain but leaving the <code>go</code> line
- set to its original (older) Go version preserves the behavior of the older
- toolchain.
- With this compatibility support, the latest Go toolchain should always
- be the best, most secure, implementation of an older version of Go.
- See “<a href="/doc/godebug">Go, Backwards Compatibility, and GODEBUG</a>” for details.
-</p>
-
-<p><!-- https://go.dev/issue/57001 -->
- To improve forwards compatibility, Go 1.21 now reads the <code>go</code> line
- in a <code>go.work</code> or <code>go.mod</code> file as a strict
- minimum requirement: <code>go</code> <code>1.21.0</code> means
- that the workspace or module cannot be used with Go 1.20 or with Go 1.21rc1.
- This allows projects that depend on fixes made in later versions of Go
- to ensure that they are not used with earlier versions.
- It also gives better error reporting for projects that make use of new Go features:
- when the problem is that a newer Go version is needed,
- that problem is reported clearly, instead of attempting to build the code
- and instead printing errors about unresolved imports or syntax errors.
-</p>
-
-<p>
- To make these new stricter version requirements easier to manage,
- the <code>go</code> command can now invoke not just the toolchain
- bundled in its own release but also other Go toolchain versions found in the PATH
- or downloaded on demand.
- If a <code>go.mod</code> or <code>go.work</code> <code>go</code> line
- declares a minimum requirement on a newer version of Go, the <code>go</code>
- command will find and run that version automatically.
- The new <code>toolchain</code> directive sets a suggested minimum toolchain to use,
- which may be newer than the strict <code>go</code> minimum.
- See “<a href="/doc/toolchain">Go Toolchains</a>” for details.
-</p>
-
-<h3 id="go-command">Go command</h3>
-
-<p><!-- https://go.dev/issue/58099, CL 474236 -->
- The <code>-pgo</code> build flag now defaults to <code>-pgo=auto</code>,
- and the restriction of specifying a single main package on the command
- line is now removed. If a file named <code>default.pgo</code> is present
- in the main package's directory, the <code>go</code> command will use
- it to enable profile-guided optimization for building the corresponding
- program.
-</p>
-
-<p>
- The <code>-C</code> <code>dir</code> flag must now be the first
- flag on the command-line when used.
-</p>
-
-<p><!-- https://go.dev/issue/37708, CL 463837 -->
- The new <code>go</code> <code>test</code> option
- <code>-fullpath</code> prints full path names in test log messages,
- rather than just base names.
-</p>
-
-<p><!-- https://go.dev/issue/15513, CL 466397 -->
- The <code>go</code> <code>test</code> <code>-c</code> flag now
- supports writing test binaries for multiple packages, each to
- <code>pkg.test</code> where <code>pkg</code> is the package name.
- It is an error if more than one test package being compiled has a given package name.]
-</p>
-
-<p><!-- https://go.dev/issue/15513, CL 466397 -->
- The <code>go</code> <code>test</code> <code>-o</code> flag now
- accepts a directory argument, in which case test binaries are written to that
- directory instead of the current directory.
-</p>
-
-<h3 id="cgo">Cgo</h3>
-
-<p><!-- CL 490819 -->
- In files that <code>import "C"</code>, the Go toolchain now
- correctly reports errors for attempts to declare Go methods on C types.
-</p>
-
-<h2 id="runtime-changes">Runtime</h2>
-
-<p><!-- https://go.dev/issue/7181 -->
- When printing very deep stacks, the runtime now prints the first 50
- (innermost) frames followed by the bottom 50 (outermost) frames,
- rather than just printing the first 100 frames. This makes it easier
- to see how deeply recursive stacks started, and is especially
- valuable for debugging stack overflows.
-</p>
-
-<p><!-- https://go.dev/issue/59960 -->
- On Linux platforms that support transparent huge pages, the Go runtime
- now manages which parts of the heap may be backed by huge pages more
- explicitly. This leads to better utilization of memory: small heaps
- should see less memory used (up to 50% in pathological cases) while
- large heaps should see fewer broken huge pages for dense parts of the
- heap, improving CPU usage and latency by up to 1%.
-</p>
-
-<p><!-- https://go.dev/issue/57069, https://go.dev/issue/56966 -->
- As a result of runtime-internal garbage collection tuning,
- applications may see up to a 40% reduction in application tail latency
- and a small decrease in memory use. Some applications may also observe
- a small loss in throughput.
-
- The memory use decrease should be proportional to the loss in
- throughput, such that the previous release's throughput/memory
- tradeoff may be recovered (with little change to latency) by
- increasing <code>GOGC</code> and/or <code>GOMEMLIMIT</code> slightly.
-</p>
-
-<p><!-- https://go.dev/issue/51676 -->
- Calls from C to Go on threads created in C require some setup to prepare for
- Go execution. On Unix platforms, this setup is now preserved across multiple
- calls from the same thread. This significantly reduces the overhead of
- subsequent C to Go calls from ~1-3 microseconds per call to ~100-200
- nanoseconds per call.
-</p>
-
-<h2 id="compiler">Compiler</h2>
-
-<p>
- Profile-guide optimization (PGO), added as a preview in Go 1.20, is now ready
- for general use. PGO enables additional optimizations on code identified as
- hot by profiles of production workloads. As mentioned in the
- <a href="#go-command">Go command section</a>, PGO is enabled by default for
- binaries that contain a <code>default.pgo</code> profile in the main
- package directory. Performance improvements vary depending on application
- behavior, with most programs from a representative set of Go programs seeing
- between 2 and 7% improvement from enabling PGO. See the
- <a href="/doc/pgo">PGO user guide</a> for detailed documentation.
-</p>
-
-<!-- https://go.dev/issue/59959 -->
-<p>
- PGO builds can now devirtualize some interface method calls, adding a
- concrete call to the most common callee. This enables further optimization,
- such as inlining the callee.
-</p>
-
-<!-- CL 497455 -->
-<p>
- Go 1.21 improves build speed by up to 6%, largely thanks to building the
- compiler itself with PGO.
-</p>
-
-<h2 id="assembler">Assembler</h2>
-
-<!-- https://go.dev/issue/58378 -->
-<p>
- On amd64, frameless nosplit assembly functions are no longer automatically marked as <code>NOFRAME</code>.
- Instead, the <code>NOFRAME</code> attribute must be explicitly specified if desired,
- which is already the behavior on other architectures supporting frame pointers.
- With this, the runtime now maintains the frame pointers for stack transitions.
-</p>
-
-<!-- CL 476295 -->
-<p>
- The verifier that checks for incorrect uses of <code>R15</code> when dynamic linking on amd64 has been improved.
-</p>
-
-<h2 id="linker">Linker</h2>
-
-<p><!-- https://go.dev/issue/57302, CL 461749, CL 457455 -->
- On windows/amd64, the linker (with help from the compiler) now emits
- SEH unwinding data by default, which improves the integration
- of Go applications with Windows debuggers and other tools.
-</p>
-
-<!-- CL 463395, CL 461315 -->
-<p>
- In Go 1.21 the linker (with help from the compiler) is now capable of
- deleting dead (unreferenced) global map variables, if the number of
- entries in the variable initializer is sufficiently large, and if the
- initializer expressions are side-effect free.
-</p>
-
-<h2 id="library">Core library</h2>
-
-<h3 id="slog">New log/slog package</h3>
-
-<p><!-- https://go.dev/issue/59060, https://go.dev/issue/59141, https://go.dev/issue/59204, https://go.dev/issue/59280,
- https://go.dev/issue/59282, https://go.dev/issue/59339, https://go.dev/issue/59345, https://go.dev/issue/61200,
- CL 477295, CL 484096, CL 486376, CL 486415, CL 487855, CL 508195 -->
- The new <a href="/pkg/log/slog">log/slog</a> package provides structured logging with levels.
- Structured logging emits key-value pairs
- to enable fast, accurate processing of large amounts of log data.
- The package supports integration with popular log analysis tools and services.
-</p>
-
-<h3 id="slogtest">New testing/slogtest package</h3>
-
-<p><!-- CL 487895 -->
- The new <a href="/pkg/testing/slogtest">testing/slogtest</a> package can help
- to validate <a href="/pkg/log/slog#Handler">slog.Handler</a> implementations.
-</p>
-
-<h3 id="slices">New slices package</h3>
-
-<p>
- <!-- https://go.dev/issue/45955, https://go.dev/issue/54768 -->
- <!-- https://go.dev/issue/57348, https://go.dev/issue/57433 -->
- <!-- https://go.dev/issue/58565, https://go.dev/issue/60091 -->
- <!-- https://go.dev/issue/60546 -->
- <!-- CL 467417, CL 468855, CL 483175, CL 496078, CL 498175, CL 502955 -->
- The new <a href="/pkg/slices">slices</a> package provides many common
- operations on slices, using generic functions that work with slices
- of any element type.
-</p>
-
-<h3 id="maps">New maps package</h3>
-
-<p><!-- https://go.dev/issue/57436, CL 464343 -->
- The new <a href="/pkg/maps/">maps</a> package provides several
- common operations on maps, using generic functions that work with
- maps of any key or element type.
-</p>
-
-<h3 id="cmp">New cmp package</h3>
-
-<p><!-- https://go.dev/issue/59488, CL 496356 -->
- The new <a href="/pkg/cmp/">cmp</a> package defines the type
- constraint <a href="/pkg/cmp/#Ordered"><code>Ordered</code></a> and
- two new generic functions
- <a href="/pkg/cmp/#Less"><code>Less</code></a>
- and <a href="/pkg/cmp/#Compare"><code>Compare</code></a> that are
- useful with <a href="/ref/spec/#Comparison_operators">ordered
- types</a>.
-</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.
- There are also various performance improvements, not enumerated here.
-</p>
-
-<dl id="archive/tar"><dt><a href="/pkg/archive/tar/">archive/tar</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/54451, CL 491175 -->
- The implementation of the
- <a href="/pkg/io/fs/#FileInfo"><code>io/fs.FileInfo</code></a>
- interface returned by
- <a href="/pkg/archive/tar/#Header.FileInfo"><code>Header.FileInfo</code></a>
- now implements a <code>String</code> method that calls
- <a href="/pkg/io/fs/#FormatFileInfo"><code>io/fs.FormatFileInfo</code></a>.
- </p>
- </dd>
-</dl><!-- archive/tar -->
-
-<dl id="archive/zip"><dt><a href="/pkg/archive/zip/">archive/zip</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/54451, CL 491175 -->
- The implementation of the
- <a href="/pkg/io/fs/#FileInfo"><code>io/fs.FileInfo</code></a>
- interface returned by
- <a href="/pkg/archive/zip/#FileHeader.FileInfo"><code>FileHeader.FileInfo</code></a>
- now implements a <code>String</code> method that calls
- <a href="/pkg/io/fs/#FormatFileInfo"><code>io/fs.FormatFileInfo</code></a>.
- </p>
-
- <p><!-- https://go.dev/issue/54451, CL 491175 -->
- The implementation of the
- <a href="/pkg/io/fs/#DirEntry"><code>io/fs.DirEntry</code></a>
- interface returned by the
- <a href="/pkg/io/fs/#ReadDirFile.ReadDir"><code>io/fs.ReadDirFile.ReadDir</code></a>
- method of the
- <a href="/pkg/io/fs/#File"><code>io/fs.File</code></a>
- returned by
- <a href="/pkg/archive/zip/#Reader.Open"><code>Reader.Open</code></a>
- now implements a <code>String</code> method that calls
- <a href="/pkg/io/fs/#FormatDirEntry"><code>io/fs.FormatDirEntry</code></a>.
- </p>
- </dd>
-</dl><!-- archive/zip -->
-
-<dl id="bytes"><dt><a href="/pkg/bytes/">bytes</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/53685, CL 474635 -->
- The <a href="/pkg/bytes/#Buffer"><code>Buffer</code></a> type
- has two new methods:
- <a href="/pkg/bytes/#Buffer.Available"><code>Available</code></a>
- and <a href="/pkg/bytes/#AvailableBuffer"><code>AvailableBuffer</code></a>.
- These may be used along with the
- <a href="/pkg/bytes/#Buffer.Write"><code>Write</code></a>
- method to append directly to the <code>Buffer</code>.
- </p>
- </dd>
-</dl><!-- bytes -->
-
-<dl id="context"><dt><a href="/pkg/context/">context</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/40221, CL 479918 -->
- The new <a href="/pkg/context/#WithoutCancel"><code>WithoutCancel</code></a>
- function returns a copy of a context that is not canceled when the original
- context is canceled.
- </p>
- <p><!-- https://go.dev/issue/56661, CL 449318 -->
- The new <a href="/pkg/context/#WithDeadlineCause"><code>WithDeadlineCause</code></a>
- and <a href="/pkg/context/#WithTimeoutCause"><code>WithTimeoutCause</code></a>
- functions provide a way to set a context cancellation cause when a deadline or
- timer expires. The cause may be retrieved with the
- <a href="/pkg/context/#Cause"><code>Cause</code></a> function.
- </p>
- <p><!-- https://go.dev/issue/57928, CL 482695 -->
- The new <a href="/pkg/context/#AfterFunc"><code>AfterFunc</code></a>
- function registers a function to run after a context has been cancelled.
- </p>
-
- <p><!-- CL 455455 -->
- An optimization means that the results of calling
- <a href="/pkg/context/#Background"><code>Background</code></a>
- and <a href="/pkg/context/#TODO"><code>TODO</code></a> and
- converting them to a shared type can be considered equal.
- In previous releases they were always different. Comparing
- <a href="/pkg/context/#Context"><code>Context</code></a> values
- for equality has never been well-defined, so this is not
- considered to be an incompatible change.
- </p>
- </dd>
-</dl>
-
-
-<dl id="crypto/ecdsa"><dt><a href="/pkg/crypto/ecdsa/">crypto/ecdsa</a></dt>
- <dd>
- <p><!-- CL 492955 -->
- <a href="/pkg/crypto/ecdsa/#PublicKey.Equal"><code>PublicKey.Equal</code></a> and
- <a href="/pkg/crypto/ecdsa/#PrivateKey.Equal"><code>PrivateKey.Equal</code></a>
- now execute in constant time.
- </p>
- </dd>
-</dl><!-- crypto/ecdsa -->
-
-<dl id="crypto/elliptic"><dt><a href="/pkg/crypto/elliptic/">crypto/elliptic</a></dt>
- <dd>
- <p><!-- CL 459977 -->
- All of the <a href="/pkg/crypto/elliptic/#Curve"><code>Curve</code></a> methods have been deprecated, along with <a href="/pkg/crypto/elliptic/#GenerateKey"><code>GenerateKey</code></a>, <a href="/pkg/crypto/elliptic/#Marshal"><code>Marshal</code></a>, and <a href="/pkg/crypto/elliptic/#Unmarshal"><code>Unmarshal</code></a>. For ECDH operations, the new <a href="/pkg/crypto/ecdh/"><code>crypto/ecdh</code></a> package should be used instead. For lower-level operations, use third-party modules such as <a href="https://pkg.go.dev/filippo.io/nistec">filippo.io/nistec</a>.
- </p>
- </dd>
-</dl><!-- crypto/elliptic -->
-
-<dl id="crypto/rand"><dt><a href="/pkg/crypto/rand/">crypto/rand</a></dt>
- <dd>
- <p><!-- CL 463123 -->
- The <a href="/pkg/crypto/rand/"><code>crypto/rand</code></a> package now uses the <code>getrandom</code> system call on NetBSD 10.0 and later.
- </p>
- </dd>
-</dl><!-- crypto/rand -->
-
-<dl id="crypto/rsa"><dt><a href="/pkg/crypto/rsa/">crypto/rsa</a></dt>
- <dd>
- <p><!-- CL 471259, CL 492935 -->
- The performance of private RSA operations (decryption and signing) is now better than Go 1.19 for <code>GOARCH=amd64</code> and <code>GOARCH=arm64</code>. It had regressed in Go 1.20.
- </p>
- <p>
- Due to the addition of private fields to <a href="/pkg/crypto/rsa/#PrecomputedValues"><code>PrecomputedValues</code></a>, <a href="/pkg/crypto/rsa/#PrivateKey.Precompute"><code>PrivateKey.Precompute</code></a> must be called for optimal performance even if deserializing (for example from JSON) a previously-precomputed private key.
- </p>
- <p><!-- CL 492955 -->
- <a href="/pkg/crypto/rsa/#PublicKey.Equal"><code>PublicKey.Equal</code></a> and
- <a href="/pkg/crypto/rsa/#PrivateKey.Equal"><code>PrivateKey.Equal</code></a>
- now execute in constant time.
- </p>
- <p><!-- https://go.dev/issue/56921, CL 459976 -->
- The <a href="/pkg/crypto/rsa/#GenerateMultiPrimeKey"><code>GenerateMultiPrimeKey</code></a> function and the <a href="/pkg/crypto/rsa/#PrecomputedValues.CRTValues"><code>PrecomputedValues.CRTValues</code></a> field have been deprecated. <a href="/pkg/crypto/rsa/#PrecomputedValues.CRTValues"><code>PrecomputedValues.CRTValues</code></a> will still be populated when <a href="/pkg/crypto/rsa/#PrivateKey.Precompute"><code>PrivateKey.Precompute</code></a> is called, but the values will not be used during decryption operations.
- </p>
- </dd>
-</dl><!-- crypto/rsa -->
-
-<!-- CL 483815 reverted -->
-
-<dl id="crypto/sha256"><dt><a href="/pkg/crypto/sha256/">crypto/sha256</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/50543, CL 408795 -->
- SHA-224 and SHA-256 operations now use native instructions when available when <code>GOARCH=amd64</code>, providing a performance improvement on the order of 3-4x.
- </p>
- </dd>
-</dl><!-- crypto/sha256 -->
-
-<!-- CL 481478 reverted -->
-<!-- CL 483816 reverted -->
-
-<dl id="crypto/tls"><dt><a href="/pkg/crypto/tls/">crypto/tls</a></dt>
- <dd>
- <p><!-- CL 497895 -->
- Servers now skip verifying client certificates (including not running
- <a href="/pkg/crypto/tls/#Config.VerifyPeerCertificate"><code>Config.VerifyPeerCertificate</code></a>)
- for resumed connections, besides checking the expiration time. This makes
- session tickets larger when client certificates are in use. Clients were
- already skipping verification on resumption, but now check the expiration
- time even if <a href="/pkg/crypto/tls/#Config.InsecureSkipVerify"><code>Config.InsecureSkipVerify</code></a>
- is set.
- </p>
-
- <p><!-- https://go.dev/issue/60105, CL 496818, CL 496820, CL 496822, CL 496821, CL 501675 -->
- Applications can now control the content of session tickets.
- <ul>
- <li>
- The new <a href="/pkg/crypto/tls/#SessionState"><code>SessionState</code></a> type
- describes a resumable session.
- </li>
- <li>
- The <a href="/pkg/crypto/tls/#SessionState.Bytes"><code>SessionState.Bytes</code></a>
- method and <a href="/pkg/crypto/tls/#ParseSessionState"><code>ParseSessionState</code></a>
- function serialize and deserialize a <code>SessionState</code>.
- </li>
- <li>
- The <a href="/pkg/crypto/tls/#Config.WrapSession"><code>Config.WrapSession</code></a> and
- <a href="/pkg/crypto/tls/#Config.UnwrapSession"><code>Config.UnwrapSession</code></a>
- hooks convert a <code>SessionState</code> to and from a ticket on the server side.
- </li>
- <li>
- The <a href="/pkg/crypto/tls/#Config.EncryptTicket"><code>Config.EncryptTicket</code></a>
- and <a href="/pkg/crypto/tls/#Config.DecryptTicket"><code>Config.DecryptTicket</code></a>
- methods provide a default implementation of <code>WrapSession</code> and
- <code>UnwrapSession</code>.
- </li>
- <li>
- The <a href="/pkg/crypto/tls/#ClientSessionState.ResumptionState"><code>ClientSessionState.ResumptionState</code></a> method and
- <a href="/pkg/crypto/tls/#NewResumptionState"><code>NewResumptionState</code></a> function
- may be used by a <code>ClientSessionCache</code> implementation to store and
- resume sessions on the client side.
- </li>
- </ul>
- </p>
-
- <p><!-- CL 496817 -->
- To reduce the potential for session tickets to be used as a tracking
- mechanism across connections, the server now issues new tickets on every
- resumption (if they are supported and not disabled) and tickets don't bear
- an identifier for the key that encrypted them anymore. If passing a large
- number of keys to <a href="/pkg/crypto/tls/#Conn.SetSessionTicketKeys"><code>Conn.SetSessionTicketKeys</code></a>,
- this might lead to a noticeable performance cost.
- </p>
-
- <p><!-- CL 497376 -->
- Both clients and servers now implement the Extended Master Secret extension (RFC 7627).
- The deprecation of <a href="/pkg/crypto/tls/#ConnectionState.TLSUnique"><code>ConnectionState.TLSUnique</code></a>
- has been reverted, and is now set for resumed connections that support Extended Master Secret.
- </p>
-
- <p><!-- https://go.dev/issue/44886, https://go.dev/issue/60107, CL 493655, CL 496995 -->
- The new <a href="/pkg/crypto/tls/#QUICConn"><code>QUICConn</code></a> type
- provides support for QUIC implementations, including 0-RTT support. Note
- that this is not itself a QUIC implementation, and 0-RTT is still not
- supported in TLS.
- </p>
-
- <p><!-- https://go.dev/issue/46308, CL 497377 -->
- The new <a href="/pkg/crypto/tls/#VersionName"><code>VersionName</code></a> function
- returns the name for a TLS version number.
- </p>
-
- <p><!-- https://go.dev/issue/52113, CL 410496 -->
- The TLS alert codes sent from the server for client authentication failures have
- been improved. Previously, these failures always resulted in a "bad certificate" alert.
- Now, certain failures will result in more appropriate alert codes,
- as defined by RFC 5246 and RFC 8446:
- <ul>
- <li>
- For TLS 1.3 connections, if the server is configured to require client authentication using
- <a href="/pkg/crypto/tls/#RequireAnyClientCert"></code>RequireAnyClientCert</code></a> or
- <a href="/pkg/crypto/tls/#RequireAndVerifyClientCert"></code>RequireAndVerifyClientCert</code></a>,
- and the client does not provide any certificate, the server will now return the "certificate required" alert.
- </li>
- <li>
- If the client provides a certificate that is not signed by the set of trusted certificate authorities
- configured on the server, the server will return the "unknown certificate authority" alert.
- </li>
- <li>
- If the client provides a certificate that is either expired or not yet valid,
- the server will return the "expired certificate" alert.
- </li>
- <li>
- In all other scenarios related to client authentication failures, the server still returns "bad certificate".
- </li>
- </ul>
- </p>
- </dd>
-</dl><!-- crypto/tls -->
-
-<dl id="crypto/x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/53573, CL 468875 -->
- <a href="/pkg/crypto/x509/#RevocationList.RevokedCertificates"><code>RevocationList.RevokedCertificates</code></a> has been deprecated and replaced with the new <a href="/pkg/crypto/x509/#RevocationList.RevokedCertificateEntries"><code>RevokedCertificateEntries</code></a> field, which is a slice of <a href="/pkg/crypto/x509/#RevocationListEntry"><code>RevocationListEntry</code></a>. <a href="/pkg/crypto/x509/#RevocationListEntry"><code>RevocationListEntry</code></a> contains all of the fields in <a href="/pkg/crypto/x509/pkix#RevokedCertificate"><code>pkix.RevokedCertificate</code></a>, as well as the revocation reason code.
- </p>
-
- <p><!-- CL 478216 -->
- Name constraints are now correctly enforced on non-leaf certificates, and
- not on the certificates where they are expressed.
- </p>
- </dd>
-</dl><!-- crypto/x509 -->
-
-<dl id="debug/elf"><dt><a href="/pkg/debug/elf/">debug/elf</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/56892, CL 452617 -->
- The new
- <a href="/pkg/debug/elf/#File.DynValue"><code>File.DynValue</code></a>
- method may be used to retrieve the numeric values listed with a
- given dynamic tag.
- </p>
-
- <p><!-- https://go.dev/issue/56887, CL 452496 -->
- The constant flags permitted in a <code>DT_FLAGS_1</code>
- dynamic tag are now defined with type
- <a href="/pkg/debug/elf/#DynFlag1"><code>DynFlag1</code></a>. These
- tags have names starting with <code>DF_1</code>.
- </p>
-
- <p><!-- CL 473256 -->
- The package now defines the constant
- <a href="/pkg/debug/elf/#COMPRESS_ZSTD"><code>COMPRESS_ZSTD</code></a>.
- </p>
-
- <p><!-- https://go.dev/issue/60348, CL 496918 -->
- The package now defines the constant
- <a href="/pkg/debug/elf/#R_PPC64_REL24_P9NOTOC"><code>R_PPC64_REL24_P9NOTOC</code></a>.
- </p>
- </dd>
-</dl><!-- debug/elf -->
-
-<dl id="debug/pe"><dt><a href="/pkg/debug/pe/">debug/pe</a></dt>
- <dd>
- <p><!-- CL 488475 -->
- Attempts to read from a section containing uninitialized data
- using
- <a href="/pkg/debug/pe/#Section.Data"><code>Section.Data</code></a>
- or the reader returned by <a href="/pkg/debug/pe/#Section.Open"><code>Section.Open</code></a>
- now return an error.
- </p>
- </dd>
-</dl><!-- debug/pe -->
-
-<dl id="embed"><dt><a href="/pkg/embed/">embed</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/57803, CL 483235 -->
- The <a href="/pkg/io/fs/#File"><code>io/fs.File</code></a>
- returned by
- <a href="/pkg/embed/#FS.Open"><code>FS.Open</code></a> now
- has a <code>ReadAt</code> method that
- implements <a href="/pkg/io/#ReaderAt"><code>io.ReaderAt</code></a>.
- </p>
-
- <p><!-- https://go.dev/issue/54451, CL 491175 -->
- Calling <code><a href="/pkg/embed/FS.Open">FS.Open</a>.<a href="/pkg/io/fs/#File.Stat">Stat</a></code>
- will return a type that now implements a <code>String</code>
- method that calls
- <a href="/pkg/io/fs/#FormatFileInfo"><code>io/fs.FormatFileInfo</code></a>.
- </p>
- </dd>
-</dl><!-- embed -->
-
-<dl id="errors"><dt><a href="/pkg/errors/">errors</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/41198, CL 473935 -->
- The new
- <a href="/pkg/errors/#ErrUnsupported"><code>ErrUnsupported</code></a>
- error provides a standardized way to indicate that a requested
- operation may not be performed because it is unsupported.
- For example, a call to
- <a href="/pkg/os/#Link"><code>os.Link</code></a> when using a
- file system that does not support hard links.
- </p>
- </dd>
-</dl><!-- errors -->
-
-<dl id="flag"><dt><a href="/pkg/flag/">flag</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/53747, CL 476015 -->
- The new <a href="/pkg/flag/#BoolFunc"><code>BoolFunc</code></a>
- function and
- <a href="/pkg/flag/#FlagSet.BoolFunc"><code>FlagSet.BoolFunc</code></a>
- method define a flag that does not require an argument and calls
- a function when the flag is used. This is similar to
- <a href="/pkg/flag/#Func"><code>Func</code></a> but for a
- boolean flag.
- </p>
-
- <p><!-- CL 480215 -->
- A flag definition
- (via <a href="/pkg/flag/#Bool"><code>Bool</code></a>,
- <a href="/pkg/flag/#BoolVar"><code>BoolVar</code></a>,
- <a href="/pkg/flag/#Int"><code>Int</code></a>,
- <a href="/pkg/flag/#IntVar"><code>IntVar</code></a>, etc.)
- will panic if <a href="/pkg/flag/#Set"><code>Set</code></a> has
- already been called on a flag with the same name. This change is
- intended to detect cases where <a href="#language">changes in
- initialization order</a> cause flag operations to occur in a
- different order than expected. In many cases the fix to this
- problem is to introduce a explicit package dependence to
- correctly order the definition before any
- <a href="/pkg/flag/#Set"><code>Set</code></a> operations.
- </p>
- </dd>
-</dl><!-- flag -->
-
-<dl id="go/ast"><dt><a href="/pkg/go/ast/">go/ast</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/28089, CL 487935 -->
- The new <a href="/pkg/go/ast/#IsGenerated"><code>IsGenerated</code></a> predicate
- reports whether a file syntax tree contains the
- <a href="https://go.dev/s/generatedcode">special comment</a>
- that conventionally indicates that the file was generated by a tool.
- </p>
- </dd>
-
- <dd>
- <p><!-- https://go.dev/issue/59033, CL 476276 -->
- The new
- <a href="/pkg/go/ast/#File.GoVersion"><code>File.GoVersion</code></a>
- field records the minimum Go version required by
- any <code>//go:build</code> or <code>// +build</code>
- directives.
- </p>
- </dd>
-</dl><!-- go/ast -->
-
-<dl id="go/build"><dt><a href="/pkg/go/build/">go/build</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/56986, CL 453603 -->
- The package now parses build directives (comments that start
- with <code>//go:</code>) in file headers (before
- the <code>package</code> declaration). These directives are
- available in the new
- <a href="/pkg/go/build#Package"><code>Package</code></a> fields
- <a href="/pkg/go/build#Package.Directives"><code>Directives</code></a>,
- <a href="/pkg/go/build#Package.TestDirectives"><code>TestDirectives</code></a>,
- and
- <a href="/pkg/go/build#Package.XTestDirectives"><code>XTestDirectives</code></a>.
- </p>
- </dd>
-</dl><!-- go/build -->
-
-<dl id="go/build/constraint"><dt><a href="/pkg/go/build/constraint/">go/build/constraint</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/59033, CL 476275 -->
- The new
- <a href="/pkg/go/build/constraint/#GoVersion"><code>GoVersion</code></a>
- function returns the minimum Go version implied by a build
- expression.
- </p>
- </dd>
-</dl><!-- go/build/constraint -->
-
-<dl id="go/token"><dt><a href="/pkg/go/token/">go/token</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/57708, CL 464515 -->
- The new <a href="/pkg/go/token/#File.Lines"><code>File.Lines</code></a> method
- returns the file's line-number table in the same form as accepted by
- <code>File.SetLines</code>.
- </p>
- </dd>
-</dl><!-- go/token -->
-
-<dl id="go/types"><dt><a href="/pkg/go/types/">go/types</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/61175, CL 507975 -->
- The new <a href="/pkg/go/types/#Package.GoVersion"><code>Package.GoVersion</code></a>
- method returns the Go language version used to check the package.
- </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/47342, CL 468795 -->
- The <code>hash/maphash</code> package now has a pure Go implementation, selectable with the <code>purego</code> build tag.
- </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/59584, CL 496395 -->
- The new error
- <a href="/pkg/html/template/#ErrJSTemplate"><code>ErrJSTemplate</code></a>
- is returned when an action appears in a JavaScript template
- literal. Previously an unexported error was returned.
- </p>
- </dd>
-</dl><!-- html/template -->
-
-<dl id="io/fs"><dt><a href="/pkg/io/fs/">io/fs</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/54451, CL 489555 -->
- The new
- <a href="/pkg/io/fs/#FormatFileInfo"><code>FormatFileInfo</code></a>
- function returns a formatted version of a
- <a href="/pkg/io/fs/#FileInfo"><code>FileInfo</code></a>.
- The new
- <a href="/pkg/io/fs/#FormatDirEntry"><code>FormatDirEntry</code></a>
- function returns a formatted version of a
- <a href="/pkg/io/fs/#FileInfo"><code>DirEntry</code></a>.
- The implementation of
- <a href="/pkg/io/fs/#DirEntry"><code>DirEntry</code></a>
- returned by
- <a href="/pkg/io/fs/#ReadDir"><code>ReadDir</code></a> now
- implements a <code>String</code> method that calls
- <a href="/pkg/io/fs/#FormatDirEntry"><code>FormatDirEntry</code></a>,
- and the same is true for
- the <a href="/pkg/io/fs/#DirEntry"><code>DirEntry</code></a>
- value passed to
- <a href="/pkg/io/fs/#WalkDirFunc"><code>WalkDirFunc</code></a>.
- </p>
- </dd>
-</dl><!-- io/fs -->
-
-<!-- https://go.dev/issue/56491 rolled back by https://go.dev/issue/60519 -->
-<!-- CL 459435 reverted by CL 467255 -->
-<!-- CL 467515 reverted by CL 499416 -->
-
-<dl id="math/big"><dt><a href="/pkg/math/big/">math/big</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/56984, CL 453115, CL 500116 -->
- The new <a href="/pkg/math/big/#Int.Float64"><code>Int.Float64</code></a>
- method returns the nearest floating-point value to a
- multi-precision integer, along with an indication of any
- rounding that occurred.
- </p>
- </dd>
-</dl><!-- math/big -->
-
-<dl id="net"><dt><a href="/pkg/net/">net</a></dt>
- <dd>
- <p>
- <!-- https://go.dev/issue/59166, https://go.dev/issue/56539 -->
- <!-- CL 471136, CL 471137, CL 471140 -->
- On Linux, the <a href="/pkg/net/">net</a> package can now use
- Multipath TCP when the kernel supports it. It is not used by
- default. To use Multipath TCP when available on a client, call
- the
- <a href="/pkg/net/#Dialer.SetMultipathTCP"><code>Dialer.SetMultipathTCP</code></a>
- method before calling the
- <a href="/pkg/net/#Dialer.Dial"><code>Dialer.Dial</code></a> or
- <a href="/pkg/net/#Dialer.DialContext"><code>Dialer.DialContext</code></a>
- methods. To use Multipath TCP when available on a server, call
- the
- <a href="/pkg/net/#ListenConfig.SetMultipathTCP"><code>ListenConfig.SetMultipathTCP</code></a>
- method before calling the
- <a href="/pkg/net/#ListenConfig.Listen"><code>ListenConfig.Listen</code></a>
- method. Specify the network as <code>"tcp"</code> or
- <code>"tcp4"</code> or <code>"tcp6"</code> as usual. If
- Multipath TCP is not supported by the kernel or the remote host,
- the connection will silently fall back to TCP. To test whether a
- particular connection is using Multipath TCP, use the
- <a href="/pkg/net/#TCPConn.MultipathTCP"><code>TCPConn.MultipathTCP</code></a>
- method.
- </p>
- <p>
- In a future Go release we may enable Multipath TCP by default on
- systems that support it.
- </p>
- </dd>
-</dl><!-- net -->
-
-<dl id="net/http"><dt><a href="/pkg/net/http/">net/http</a></dt>
- <dd>
- <p><!-- CL 472636 -->
- The new <a href="/pkg/net/http#ResponseController.EnableFullDuplex"><code>ResponseController.EnableFullDuplex</code></a>
- method allows server handlers to concurrently read from an HTTP/1
- request body while writing the response. Normally, the HTTP/1 server
- automatically consumes any remaining request body before starting to
- write the response, to avoid deadlocking clients which attempt to
- write a complete request before reading the response. The
- <code>EnableFullDuplex</code> method disables this behavior.
- </p>
-
- <p><!-- https://go.dev/issue/44855, CL 382117 -->
- The new <a href="/pkg/net/http/#ErrSchemeMismatch"><code>ErrSchemeMismatch</code></a> error is returned by <a href="/pkg/net/http/#Client"><code>Client</code></a> and <a href="/pkg/net/http/#Transport"><code>Transport</code></a> when the server responds to an HTTPS request with an HTTP response.
- </p>
-
- <p><!-- CL 494122 -->
- The <a href="/pkg/net/http/">net/http</a> package now supports
- <a href="/pkg/errors/#ErrUnsupported"><code>errors.ErrUnsupported</code></a>,
- in that the expression
- <code>errors.Is(http.ErrNotSupported, errors.ErrUnsupported)</code>
- will return true.
- </p>
- </dd>
-</dl><!-- net/http -->
-
-<dl id="os"><dt><a href="/pkg/os/">os</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/32558, CL 219638 -->
- Programs may now pass an empty <code>time.Time</code> value to
- the <a href="/pkg/os/#Chtimes"><code>Chtimes</code></a> function
- to leave either the access time or the modification time unchanged.
- </p>
-
- <p><!-- CL 480135 -->
- On Windows the
- <a href="/pkg/os#File.Chdir"><code>File.Chdir</code></a> method
- now changes the current directory to the file, rather than
- always returning an error.
- </p>
-
- <p><!-- CL 495079 -->
- On Unix systems, if a non-blocking descriptor is passed
- to <a href="/pkg/os/#NewFile"><code>NewFile</code></a>, calling
- the <a href="/pkg/os/#File.Fd"><code>File.Fd</code></a> method
- will now return a non-blocking descriptor. Previously the
- descriptor was converted to blocking mode.
- </p>
-
- <p><!-- CL 477215 -->
- On Windows calling
- <a href="/pkg/os/#Truncate"><code>Truncate</code></a> on a
- non-existent file used to create an empty file. It now returns
- an error indicating that the file does not exist.
- </p>
-
- <p><!-- https://go.dev/issue/56899, CL 463219 -->
- On Windows calling
- <a href="/pkg/os/#TempDir"><code>TempDir</code></a> now uses
- GetTempPath2W when available, instead of GetTempPathW. The
- new behavior is a security hardening measure that prevents
- temporary files created by processes running as SYSTEM to
- be accessed by non-SYSTEM processes.
- </p>
-
- <p><!-- CL 493036 -->
- On Windows the os package now supports working with files whose
- names, stored as UTF-16, can't be represented as valid UTF-8.
- </p>
-
- <p><!-- CL 463177 -->
- On Windows <a href="/pkg/os/#Lstat"><code>Lstat</code></a> now resolves
- symbolic links for paths ending with a path separator, consistent with its
- behavior on POSIX platforms.
- </p>
-
- <p><!-- https://go.dev/issue/54451, CL 491175 -->
- The implementation of the
- <a href="/pkg/io/fs/#DirEntry"><code>io/fs.DirEntry</code></a>
- interface returned by the
- <a href="/pkg/os/#ReadDir"><code>ReadDir</code></a> function and
- the <a href="/pkg/os/#File.ReadDir"><code>File.ReadDir</code></a>
- method now implements a <code>String</code> method that calls
- <a href="/pkg/io/fs/#FormatDirEntry"><code>io/fs.FormatDirEntry</code></a>.
- </p>
-
- <p><!-- https://go.dev/issue/53761, CL 416775, CL 498015-->
- The implementation of the
- <a href="/pkg/io/fs/#FS"><code>io/fs.FS</code></a> interface returned by
- the <a href="/pkg/os/#DirFS"><code>DirFS</code></a> function now implements
- the <a href="/pkg/io/fs/#ReadFileFS"><code>io/fs.ReadFileFS</code></a> and
- the <a href="/pkg/io/fs/#ReadDirFS"><code>io/fs.ReadDirFS</code></a>
- interfaces.
- </p>
- </dd>
-</dl><!-- os -->
-
-<dl id="path/filepath"><dt><a href="/pkg/path/filepath/">path/filepath</a></dt>
- <dd>
- <p>
- The implementation of the
- <a href="/pkg/io/fs/#DirEntry"><code>io/fs.DirEntry</code></a>
- interface passed to the function argument of
- <a href="/pkg/path/filepath/#WalkDir"><code>WalkDir</code></a>
- now implements a <code>String</code> method that calls
- <a href="/pkg/io/fs/#FormatDirEntry"><code>io/fs.FormatDirEntry</code></a>.
- </p>
- </dd>
-</dl><!-- path/filepath -->
-
-<!-- CL 459455 reverted -->
-
-<dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
- <dd>
- <p><!-- CL 408826, CL 413474 -->
- In Go 1.21, <a href="/pkg/reflect/#ValueOf"><code>ValueOf</code></a>
- no longer forces its argument to be allocated on the heap, allowing
- a <code>Value</code>'s content to be allocated on the stack. Most
- operations on a <code>Value</code> also allow the underlying value
- to be stack allocated.
- </p>
-
- <p><!-- https://go.dev/issue/55002 -->
- The new <a href="/pkg/reflect/#Value"><code>Value</code></a>
- method <a href="/pkg/reflect/#Value.Clear"><code>Value.Clear</code></a>
- clears the contents of a map or zeros the contents of a slice.
- This corresponds to the new <code>clear</code> built-in
- <a href="#language">added to the language</a>.
- </p>
-
- <p><!-- https://go.dev/issue/56906, CL 452762 -->
- The <a href="/pkg/reflect/#SliceHeader"><code>SliceHeader</code></a>
- and <a href="/pkg/reflect/#StringHeader"><code>StringHeader</code></a>
- types are now deprecated. In new code
- prefer <a href="/pkg/unsafe/#Slice"><code>unsafe.Slice</code></a>,
- <a href="/pkg/unsafe/#SliceData"><code>unsafe.SliceData</code></a>,
- <a href="/pkg/unsafe/#String"><code>unsafe.String</code></a>,
- or <a href="/pkg/unsafe/#StringData"><code>unsafe.StringData</code></a>.
- </p>
- </dd>
-</dl><!-- reflect -->
-
-<dl id="regexp"><dt><a href="/pkg/regexp/">regexp</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/46159, CL 479401 -->
- <a href="/pkg/regexp#Regexp"><code>Regexp</code></a> now defines
- <a href="/pkg/regexp#Regexp.MarshalText"><code>MarshalText</code></a>
- and <a href="/pkg/regexp#Regexp.UnmarshalText"><code>UnmarshalText</code></a>
- methods. These implement
- <a href="/pkg/encoding#TextMarshaler"><code>encoding.TextMarshaler</code></a>
- and
- <a href="/pkg/encoding#TextUnmarshaler"><code>encoding.TextUnmarshaler</code></a>
- and will be used by packages such as
- <a href="/pkg/encoding/json">encoding/json</a>.
- </p>
- </dd>
-</dl><!-- regexp -->
-
-<dl id="runtime"><dt><a href="/pkg/runtime/">runtime</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/38651, CL 435337 -->
- Textual stack traces produced by Go programs, such as those
- produced when crashing, calling <code>runtime.Stack</code>, or
- collecting a goroutine profile with <code>debug=2</code>, now
- include the IDs of the goroutines that created each goroutine in
- the stack trace.
- </p>
-
- <p><!-- https://go.dev/issue/57441, CL 474915 -->
- Crashing Go applications can now opt-in to Windows Error Reporting (WER) by setting the environment variable
- <code>GOTRACEBACK=wer</code> or calling <a href="/pkg/runtime/debug/#SetTraceback"><code>debug.SetTraceback("wer")</code></a>
- before the crash. Other than enabling WER, the runtime will behave as with <code>GOTRACEBACK=crash</code>.
- On non-Windows systems, <code>GOTRACEBACK=wer</code> is ignored.
- </p>
-
- <p><!-- CL 447778 -->
- <code>GODEBUG=cgocheck=2</code>, a thorough checker of cgo pointer passing rules,
- is no longer available as a <a href="/pkg/runtime#hdr-Environment_Variables">debug option</a>.
- Instead, it is available as an experiment using <code>GOEXPERIMENT=cgocheck2</code>.
- In particular this means that this mode has to be selected at build time instead of startup time.
- </p>
-
- <p>
- <code>GODEBUG=cgocheck=1</code> is still available (and is still the default).
- </p>
-
- <p><!-- https://go.dev/issue/46787, CL 367296 -->
- A new type <code>Pinner</code> has been added to the runtime
- package. <code>Pinner</code>s may be used to "pin" Go memory
- such that it may be used more freely by non-Go code. For instance,
- passing Go values that reference pinned Go memory to C code is
- now allowed. Previously, passing any such nested reference was
- disallowed by the
- <a href="https://pkg.go.dev/cmd/cgo#hdr-Passing_pointers">cgo pointer passing rules.</a>
-
- See <a href="/pkg/runtime#Pinner">the docs</a> for more details.
- </p>
-
- <!-- CL 472195 no release note needed -->
- </dd>
-</dl><!-- runtime -->
-
-<dl id="runtime/metrics"><dt><a href="/pkg/runtime/metrics/">runtime/metrics</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/56857, CL 497315 -->
- A few previously-internal GC metrics, such as live heap size, are
- now available.
-
- <code>GOGC</code> and <code>GOMEMLIMIT</code> are also now
- available as metrics.
- </p>
- </dd>
-</dl><!-- runtime/metrics -->
-
-<dl id="runtime/trace"><dt><a href="/pkg/runtime/trace/">runtime/trace</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/16638 -->
- Collecting traces on amd64 and arm64 now incurs a substantially
- smaller CPU cost: up to a 10x improvement over the previous release.
- </p>
-
- <p><!-- CL 494495 -->
- Traces now contain explicit stop-the-world events for every reason
- the Go runtime might stop-the-world, not just garbage collection.
- </p>
- </dd>
-</dl><!-- runtime/trace -->
-
-<dl id="sync"><dt><a href="/pkg/sync/">sync</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/56102, CL 451356 -->
- The new <a href="/pkg/sync/#OnceFunc"><code>OnceFunc</code></a>,
- <a href="/pkg/sync/#OnceValue"><code>OnceValue</code></a>, and
- <a href="/pkg/sync/#OnceValues"><code>OnceValues</code></a>
- functions capture a common use of <a href="/pkg/sync/#Once">Once</a> to
- lazily initialize a value on first use.
- </p>
- </dd>
-</dl>
-
-<dl id="syscall"><dt><a href="/pkg/syscall/">syscall</a></dt>
- <dd>
- <p><!-- CL 480135 -->
- On Windows the
- <a href="/pkg/syscall#Fchdir"><code>Fchdir</code></a> function
- now changes the current directory to its argument, rather than
- always returning an error.
- </p>
-
- <p><!-- https://go.dev/issue/46259, CL 458335 -->
- On FreeBSD
- <a href="/pkg/syscall#SysProcAttr"><code>SysProcAttr</code></a>
- has a new field <code>Jail</code> that may be used to put the
- newly created process in a jailed environment.
- </p>
-
- <p><!-- CL 493036 -->
- On Windows the syscall package now supports working with files whose
- names, stored as UTF-16, can't be represented as valid UTF-8.
- The <a href="/pkg/syscall#UTF16ToString"><code>UTF16ToString</code></a>
- and <a href="/pkg/syscall#UTF16FromString"><code>UTF16FromString</code></a>
- functions now convert between UTF-16 data and
- <a href="https://simonsapin.github.io/wtf-8/">WTF-8</a> strings.
- This is backward compatible as WTF-8 is a superset of the UTF-8
- format that was used in earlier releases.
- </p>
-
- <p><!-- CL 476578, CL 476875, CL 476916 -->
- Several error values match the new
- <a href="/pkg/errors/#ErrUnsupported"><code>errors.ErrUnsupported</code></a>,
- such that <code>errors.Is(err, errors.ErrUnsupported)</code>
- returns true.
- <ul>
- <li><code>ENOSYS</code></li>
- <li><code>ENOTSUP</code></li>
- <li><code>EOPNOTSUPP</code></li>
- <li><code>EPLAN9</code> (Plan 9 only)</li>
- <li><code>ERROR_CALL_NOT_IMPLEMENTED</code> (Windows only)</li>
- <li><code>ERROR_NOT_SUPPORTED</code> (Windows only)</li>
- <li><code>EWINDOWS</code> (Windows only)</li>
- </ul>
- </p>
- </dd>
-</dl><!-- syscall -->
-
-<dl id="testing"><dt><a href="/pkg/testing/">testing</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/37708, CL 463837 -->
- The new <code>-test.fullpath</code> option will print full path
- names in test log messages, rather than just base names.
- </p>
-
- <p><!-- https://go.dev/issue/52600, CL 475496 -->
- The new <a href="/pkg/testing/#Testing"><code>Testing</code></a> function reports whether the program is a test created by <code>go</code> <code>test</code>.
- </p>
- </dd>
-</dl><!-- testing -->
-
-<dl id="testing/fstest"><dt><a href="/pkg/testing/fstest/">testing/fstest</a></dt>
- <dd>
- <p><!-- https://go.dev/issue/54451, CL 491175 -->
- Calling <code><a href="/pkg/testing/fstest/MapFS.Open">Open</a>.<a href="/pkg/io/fs/#File.Stat">Stat</a></code>
- will return a type that now implements a <code>String</code>
- method that calls
- <a href="/pkg/io/fs/#FormatFileInfo"><code>io/fs.FormatFileInfo</code></a>.
- </p>
- </dd>
-</dl><!-- testing/fstest -->
-
-<dl id="unicode"><dt><a href="/pkg/unicode/">unicode</a></dt>
- <dd>
- <p><!-- CL 456837 -->
- The <a href="/pkg/unicode/"><code>unicode</code></a> package and
- associated support throughout the system has been upgraded to
- <a href="https://www.unicode.org/versions/Unicode15.0.0/">Unicode 15.0.0</a>.
- </p>
- </dd>
-</dl><!-- unicode -->
-
-<h2 id="ports">Ports</h2>
-
-<h3 id="darwin">Darwin</h3>
-
-<p><!-- https://go.dev/issue/57125 -->
- As <a href="go1.20#darwin">announced</a> in the Go 1.20 release notes,
- Go 1.21 requires macOS 10.15 Catalina or later;
- support for previous versions has been discontinued.
-</p>
-
-<h3 id="windows">Windows</h3>
-
-<p><!-- https://go.dev/issue/57003, https://go.dev/issue/57004 -->
- As <a href="go1.20#windows">announced</a> in the Go 1.20 release notes,
- Go 1.21 requires at least Windows 10 or Windows Server 2016;
- support for previous versions has been discontinued.
-</p>
-
-<!-- CL 470695 -->
-<p>
- <!-- cmd/dist: default to GOARM=7 on all non-arm systems -->
-</p>
-
-<h3 id="wasm">WebAssembly</h3>
-
-<p><!-- https://go.dev/issue/38248, https://go.dev/issue/59149, CL 489255 -->
- The new <code>go:wasmimport</code> directive can now be used in Go programs
- to import functions from the WebAssembly host.
-</p>
-
-<!-- https://go.dev/issue/56100 -->
-<p>
- The Go scheduler now interacts much more efficiently with the
- JavaScript event loop, especially in applications that block
- frequently on asynchronous events.
-</p>
-
-
-<h3 id="wasip1">WebAssembly System Interface</h3>
-
-<p><!-- https://go.dev/issue/58141 -->
- Go 1.21 adds an experimental port to the <a href="https://wasi.dev/">
- WebAssembly System Interface (WASI)</a>, Preview 1
- (<code>GOOS=wasip1</code>, <code>GOARCH=wasm</code>).
-</p>
-
-<p>
- As a result of the addition of the new <code>GOOS</code> value
- "<code>wasip1</code>", Go files named <code>*_wasip1.go</code>
- will now be <a href="/pkg/go/build/#hdr-Build_Constraints">ignored
- by Go tools</a> except when that <code>GOOS</code> value is being
- used.
- If you have existing filenames matching that pattern, you will
- need to rename them.
-</p>
-
-<h3 id="PPC64">ppc64/ppc64le</h3>
-
-<p><!-- go.dev/issue/44549 -->
- On Linux, <code>GOPPC64=power10</code> now generates PC-relative instructions, prefixed
- instructions, and other new Power10 instructions. On AIX, <code>GOPPC64=power10</code>
- generates Power10 instructions, but does not generate PC-relative instructions.
-</p>
-
-<p>
- When building position-independent binaries for <code>GOPPC64=power10</code>
- <code>GOOS=linux</code> <code>GOARCH=ppc64le</code>, users can expect reduced binary
- sizes in most cases, in some cases 3.5%. Position-independent binaries are built for
- ppc64le with the following <code>-buildmode</code> values:
- <code>c-archive</code>, <code>c-shared</code>, <code>shared</code>, <code>pie</code>, <code>plugin</code>.
-</p>
-
-<h3 id="loong64">loong64</h3>
-
-<p><!-- go.dev/issue/53301, CL 455075, CL 425474, CL 425476, CL 425478, CL 489576 -->
- The <code>linux/loong64</code> port now supports <code>-buildmode=c-archive</code>,
- <code>-buildmode=c-shared</code> and <code>-buildmode=pie</code>.
-</p>
-
-<!-- proposals for x repos that don't need to be mentioned here but
- are picked up by the relnote tool. -->
-<!-- https://go.dev/issue/54232 -->
-<!-- https://go.dev/issue/57051 -->
-<!-- https://go.dev/issue/57792 -->
-<!-- https://go.dev/issue/57906 -->
-<!-- https://go.dev/issue/58668 -->
-<!-- https://go.dev/issue/59016 -->
-<!-- https://go.dev/issue/59676 -->
-<!-- https://go.dev/issue/60409 -->
-<!-- https://go.dev/issue/61176 -->
-
-<!-- changes to cmd/api that don't need release notes. -->
-<!-- CL 469115, CL 469135, CL 499981 -->
-
-<!-- proposals that don't need release notes. -->
-<!-- https://go.dev/issue/10275 -->
-<!-- https://go.dev/issue/59719 -->