2 "Title": "Go 1.21 Release Notes",
7 NOTE: In this document and others in this directory, the convention is to
8 set fixed-width phrases with non-fixed-width spaces, as in
9 <code>hello</code> <code>world</code>.
10 Do not send CLs removing the interior tags from such phrases.
14 main ul li { margin: 0.5em 0; }
17 <h2 id="introduction">DRAFT RELEASE NOTES — Introduction to Go 1.21</h2>
21 Go 1.21 is not yet released. These are work-in-progress
22 release notes. Go 1.21 is expected to be released in August 2023.
26 <h2 id="language">Changes to the language</h2>
29 Go 1.21 adds three new built-ins to the language.
32 <li><!-- https://go.dev/issue/59488 -->
33 The new functions <code>min</code> and <code>max</code> compute the
34 smallest (or largest, for <code>max</code>) value of a fixed number
36 See the language spec for
37 <a href="https://tip.golang.org/ref/spec#Min_and_max">details</a>.
39 <li><!-- https://go.dev/issue/56351 -->
40 The new function <code>clear</code> deletes all elements from a
41 map or zeroes all elements of a slice.
42 See the language spec for
43 <a href="https://tip.golang.org/ref/spec#Clear">details</a>.
48 <p><!-- https://go.dev/issue/57411 -->
49 Package initialization order is now specified more precisely. The
53 Sort all packages by import path.
55 <li>Repeat until the list of packages is empty:
58 Find the first package in the list for which all imports are
62 Initialize that package and remove it from the list.
67 This may change the behavior of some programs that rely on a
68 specific initialization ordering that was not expressed by explicit
69 imports. The behavior of such programs was not well defined by the
70 spec in past releases. The new rule provides an unambiguous definition.
73 <p><!-- https://go.dev/issue/59338 -->
74 TODO: <a href="https://go.dev/issue/59338">https://go.dev/issue/59338</a>: infer type arguments from assignments of generic functions (reverse type inference)
77 <p><!-- https://go.dev/issue/56986 -->
78 TODO: <a href="https://go.dev/issue/56986">https://go.dev/issue/56986</a>: extended backwards compatibility for Go
81 <!-- https://go.dev/issue/57969 -->
83 <!-- add GOEXPERIMENT=loopvar -->
88 TODO: complete this section
91 <h2 id="ports">Ports</h2>
95 <!-- cmd/dist: default to GOARM=7 on all non-arm systems -->
98 <!-- https://go.dev/issue/38248 -->
100 <!-- replace CallImport with go:wasmimport directive -->
103 <h3 id="wasm">WebAssembly</h3>
105 <!-- https://go.dev/issue/59149 -->
107 <!-- allow the use of go:wasmimport globally -->
112 <!-- cmd/compile: remove go:wasmimport restriction -->
115 <!-- https://go.dev/issue/56100 -->
117 The Go scheduler now interacts much more efficiently with the
118 JavaScript event loop, especially in applications that block
119 frequently on asynchronous events.
123 <h3 id="wasip1">WebAssembly System Interface</h3>
125 <p><!-- https://go.dev/issue/58141 -->
126 Go 1.21 adds an experimental port to the <a href="https://wasi.dev/">
127 WebAssembly System Interface (WASI)</a>, Preview 1
128 (<code>GOOS=wasip1</code>, <code>GOARCH=wasm</code>).
132 As a result of the addition of the new <code>GOOS</code> value
133 "<code>wasip1</code>", Go files named <code>*_wasip1.go</code>
134 will now be <a href="/pkg/go/build/#hdr-Build_Constraints">ignored
135 by Go tools</a> except when that <code>GOOS</code> value is being
137 If you have existing filenames matching that pattern, you will
141 <h2 id="tools">Tools</h2>
143 <!-- https://go.dev/issue/15513 -->
145 <!-- support compiling all tests without running -->
148 <h3 id="go-command">Go command</h3>
150 <p><!-- https://go.dev/issue/58099, CL 474236 -->
151 The <code>-pgo</code> build flag now defaults to <code>-pgo=auto</code>,
152 and the restriction of specifying a single main package on the command
153 line is now removed. If a file named <code>default.pgo</code> is present
154 in the main package's directory, the <code>go</code> command will use
155 it to enable profile-guided optimization for building the corresponding
159 <p><!-- https://go.dev/issue/37708, CL 463837 -->
160 The new <code>go</code> <code>test</code> option
161 <code>-fullpath</code> prints full path names in test log messages,
162 rather than just base names.
167 <!-- cmd/go: make go test build multiple executables; The go test command now supports using the -c flag with multiple packages. -->
170 <h2 id="runtime-changes">Runtime</h2>
173 TODO: complete this section, or delete if not needed
176 <p><!-- https://go.dev/issue/7181 -->
177 When printing very deep stacks, the runtime now prints the first 50
178 (innermost) frames followed by the bottom 50 (outermost) frames,
179 rather than just printing the first 100 frames. This makes it easier
180 to see how deeply recursive stacks started, and is especially
181 valuable for debugging stack overflows.
184 <p><!-- https://go.dev/issue/59960 -->
185 On Linux platforms that support transparent huge pages, the Go runtime
186 now manages which parts of the heap may be backed by huge pages more
187 explicitly. This leads to better utilization of memory: small heaps
188 should see less memory used (up to 50% in pathological cases) while
189 large heaps should see fewer broken huge pages for dense parts of the
190 heap, improving CPU usage and latency by up to 1%.
193 <p><!-- https://go.dev/issue/57069, https://go.dev/issue/56966 -->
194 As a result of runtime-internal garbage collection tuning,
195 applications may see up to a 40% reduction in application tail latency
196 and a small decrease in memory use. Some applications may also observe
197 a small loss in throughput.
199 The memory use decrease should be proportional to the loss in
200 throughput, such that the previous release's throughput/memory
201 tradeoff may be recovered (with little change to latency) by
202 increasing <code>GOGC</code> and/or <code>GOMEMLIMIT</code> slightly.
205 <h2 id="compiler">Compiler</h2>
209 <!-- cmd/cgo: reject attempts to declare methods on C types -->
214 <!-- cmd/compile: enable deadcode of unreferenced large global maps -->
218 TODO: complete this section, or delete if not needed
221 <h2 id="assembler">Assembler</h2>
225 The verifier that checks for incorrect uses of <code>R15</code> when dynamic linking on amd64 has been improved.
228 <h2 id="linker">Linker</h2>
230 <p><!-- https://go.dev/issue/57302, CL 461749 -->
231 On Windows AMD64, the linker (with help from the compiler) now emits
232 SEH unwinding data by default, which improves the integration
233 of Go applications with Windows debuggers and other tools.
238 <!-- cmd/link: generate .xdata PE section -->
242 In Go 1.21 the linker (with help from the compiler) is now capable of
243 deleting dead (unreferenced) global map variables, if the number of
244 entries in the variable initializer is sufficiently large, and if the
245 initializer expressions are side-effect free.
248 TODO: complete this section, or delete if not needed
251 <h2 id="library">Core library</h2>
253 <h3 id="slog">New log/slog package</h3>
256 The new <a href="/pkg/log/slog">log/slog</a> package provides structured logging with levels.
257 Structured logging emits key-value pairs
258 to enable fast, accurate processing of large amounts of log data.
259 The package supports integration with popular log analysis tools and services.
262 <h3 id="slices">New slices package</h3>
264 <p><!-- https://go.dev/issue/45955, https://go.dev/issue/54768, https://go.dev/issue/57348, https://go.dev/issue/57433, CL 467417, CL 483175 -->
265 The new <a href="/pkg/slices">slices</a> package provides many common
266 operations on slices, using generic functions that work with slices
270 <h3 id="maps">New maps package</h3>
272 <p><!-- https://go.dev/issue/57436, CL 464343 -->
273 The new <a href="/pkg/maps/">maps</a> package provides several
274 common operations on maps, using generic functions that work with
275 maps of any key or element type.
278 <h3 id="minor_library_changes">Minor changes to the library</h3>
281 As always, there are various minor changes and updates to the library,
282 made with the Go 1 <a href="/doc/go1compat">promise of compatibility</a>
284 There are also various performance improvements, not enumerated here.
287 <p><!-- CL 456837 -->
288 TODO: <a href="https://go.dev/cl/456837">https://go.dev/cl/456837</a>: all: upgrade Unicode from 13.0.0 to 15.0.0; modified api/except.txt, api/next/55079.txt
292 TODO: complete this section
295 <dl id="archive/tar"><dt><a href="/pkg/archive/tar/">archive/tar</a></dt>
297 <p><!-- https://go.dev/issue/54451, CL 491175 -->
298 The implementation of the
299 <a href="/pkg/io/fs/#FileInfo"><code>io/fs.FileInfo</code></a>
300 interface returned by
301 <a href="/pkg/archive/tar/#Header.FileInfo"><code>Header.FileInfo</code></a>
302 now implements a <code>String</code> method that calls
303 <a href="/pkg/io/fs/#FormatFileInfo"><code>io/fs.FormatFileInfo</code></a>.
306 </dl><!-- archive/tar -->
308 <dl id="archive/zip"><dt><a href="/pkg/archive/zip/">archive/zip</a></dt>
310 <p><!-- https://go.dev/issue/54451, CL 491175 -->
311 The implementation of the
312 <a href="/pkg/io/fs/#FileInfo"><code>io/fs.FileInfo</code></a>
313 interface returned by
314 <a href="/pkg/archive/zip/#FileHeader.FileInfo"><code>FileHeader.FileInfo</code></a>
315 now implements a <code>String</code> method that calls
316 <a href="/pkg/io/fs/#FormatFileInfo"><code>io/fs.FormatFileInfo</code></a>.
319 <p><!-- https://go.dev/issue/54451, CL 491175 -->
320 The implementation of the
321 <a href="/pkg/io/fs/#DirEntry"><code>io/fs.DirEntry</code></a>
322 interface returned by the
323 <a href="/pkg/io/fs/#ReadDirFile.ReadDir"><code>io/fs.ReadDirFile.ReadDir</code></a>
325 <a href="/pkg/io/fs/#File"><code>io/fs.File</code></a>
327 <a href="/pkg/archive/zip/#Reader.Open"><code>Reader.Open</code></a>
328 now implements a <code>String</code> method that calls
329 <a href="/pkg/io/fs/#FormatDirEntry"><code>io/fs.FormatDirEntry</code></a>.
332 </dl><!-- archive/zip -->
334 <dl id="bytes"><dt><a href="/pkg/bytes/">bytes</a></dt>
336 <p><!-- https://go.dev/issue/53685, CL 474635 -->
337 The <a href="/pkg/bytes/#Buffer"><code>Buffer</code></a> type
339 <a href="/pkg/bytes/#Buffer.Available"><code>Available</code></a>
340 and <a href="/pkg/bytes/#AvailableBuffer"><code>AvailableBuffer</code></a>.
341 These may be used along with the
342 <a href="/pkg/bytes/#Buffer.Write"><code>Write</code></a>
343 method to append directly to the <code>Buffer</code>.
348 <dl id="context"><dt><a href="/pkg/context/">context</a></dt>
350 <p><!-- https://go.dev/issue/40221, CL 479918 -->
351 The new <a href="/pkg/context/#WithoutCancel"><code>WithoutCancel</code></a>
352 function returns a copy of a context that is not canceled when the original
355 <p><!-- https://go.dev/issue/56661, CL 449318 -->
356 The new <a href="/pkg/context/#WithDeadlineCause"><code>WithDeadlineCause</code></a>
357 and <a href="/pkg/context/#WithTimeoutCause"><code>WithTimeoutCause</code></a>
358 functions provide a way to set a context cancellation cause when a deadline or
359 timer expires. The cause may be retrieved with the
360 <a href="/pkg/context/#Cause"><code>Cause</code></a> function.
362 <p><!-- https://go.dev/issue/57928, CL 482695 -->
363 The new <a href="/pkg/context/#AfterFunc"><code>AfterFunc</code></a>
364 function registers a function to run after a context has been cancelled.
369 <dl id="crypto/elliptic"><dt><a href="/pkg/crypto/elliptic/">crypto/elliptic</a></dt>
371 <p><!-- CL 459977 -->
372 TODO: <a href="https://go.dev/cl/459977">https://go.dev/cl/459977</a>: crypto/elliptic: deprecate unsafe APIs; modified api/next/34648.txt, api/next/52221.txt
375 </dl><!-- crypto/elliptic -->
377 <dl id="crypto/rsa"><dt><a href="/pkg/crypto/rsa/">crypto/rsa</a></dt>
379 <p><!-- https://go.dev/issue/56921 -->
380 TODO: <a href="https://go.dev/issue/56921">https://go.dev/issue/56921</a>: deprecate GenerateMultiPrimeKey and PrecomputedValues.CRTValues
383 <p><!-- CL 459976 -->
384 TODO: <a href="https://go.dev/cl/459976">https://go.dev/cl/459976</a>: crypto/rsa: deprecate multiprime RSA support; modified api/next/56921.txt
387 </dl><!-- crypto/rsa -->
389 <dl id="crypto/sha1"><dt><a href="/pkg/crypto/sha1/">crypto/sha1</a></dt>
391 <p><!-- CL 483815 -->
392 TODO: <a href="https://go.dev/cl/483815">https://go.dev/cl/483815</a>: crypto/sha1: add WriteString and WriteByte method
395 </dl><!-- crypto/sha1 -->
397 <dl id="crypto/sha256"><dt><a href="/pkg/crypto/sha256/">crypto/sha256</a></dt>
399 <p><!-- https://go.dev/issue/50543 -->
400 TODO: <a href="https://go.dev/issue/50543">https://go.dev/issue/50543</a>: add native SHA256 instruction implementation for AMD64
403 <p><!-- CL 408795 -->
404 TODO: <a href="https://go.dev/cl/408795">https://go.dev/cl/408795</a>: crypto/sha256: add sha-ni implementation; crypto/sha256 uses Intel SHA extensions on new enough x86 processors, making it 3-4X faster.
407 <p><!-- CL 481478 -->
408 TODO: <a href="https://go.dev/cl/481478">https://go.dev/cl/481478</a>: crypto/sha256: add WriteString and WriteByte method
411 </dl><!-- crypto/sha256 -->
413 <dl id="crypto/sha512"><dt><a href="/pkg/crypto/sha512/">crypto/sha512</a></dt>
415 <p><!-- CL 483816 -->
416 TODO: <a href="https://go.dev/cl/483816">https://go.dev/cl/483816</a>: crypto/sha512: add WriteString and WriteByte method
419 </dl><!-- crypto/sha512 -->
421 <dl id="crypto/x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt>
423 <p><!-- https://go.dev/issue/53573 -->
424 TODO: <a href="https://go.dev/issue/53573">https://go.dev/issue/53573</a>: surface ReasonCode inside x509.RevocationList entries
427 <p><!-- CL 468875 -->
428 TODO: <a href="https://go.dev/cl/468875">https://go.dev/cl/468875</a>: crypto/x509: surface ReasonCode in RevocationList API; modified api/next/53573.txt
431 </dl><!-- crypto/x509 -->
433 <dl id="debug/elf"><dt><a href="/pkg/debug/elf/">debug/elf</a></dt>
435 <p><!-- https://go.dev/issue/56892, CL 452617 -->
437 <a href="https:/pkg/debug/elf/#File.DynValue"><code>File.DynValue</code></a>
438 method may be used to retrieve the numeric values listed with a
442 <p><!-- https://go.dev/issue/56887, CL 452496 -->
443 The constant flags permitted in a <code>DT_FLAGS_1</code>
444 dynamic tag are now defined with type
445 <a href="/pkg/debug/elf/#DynFlag1"><code>DynFlag1</code></a>. These
446 tags have names starting with <code>DF_1</code>.
449 <p><!-- CL 473256 -->
450 The package now defines the constant
451 <a href="/pkg/debug/elf/#COMPRESS_ZSTD"><code>COMPRESS_ZSTD</code></a>.
454 </dl><!-- debug/elf -->
456 <dl id="debug/pe"><dt><a href="/pkg/debug/pe/">debug/pe</a></dt>
458 <p><!-- CL 488475 -->
459 Attempts to read from a section containing uninitialized data
461 <a href="/pkg/debug/pe/#Section.Data"><code>Section.Data</code></a>
462 or the reader returned by <a href="/pkg/debug/pe/#Section.Open"><code>Section.Open</code></a>
466 </dl><!-- debug/pe -->
468 <dl id="embed"><dt><a href="/pkg/embed/">embed</a></dt>
470 <p><!-- https://go.dev/issue/57803, CL 483235 -->
471 The <a href="/pkg/io/fs/#File"><code>io/fs.File</code></a>
473 <a href="/pkg/embed/#FS.Open"><code>FS.Open</code></a> now
474 has a <code>ReadAt</code> method that
475 implements <a href="/pkg/io/#ReaderAt"><code>io.ReaderAt</code></a>.
478 <p><!-- https://go.dev/issue/54451, CL 491175 -->
479 Calling <code><a href="/pkg/embed/FS.Open">FS.Open</a>.<a href="/pkg/io/fs/#File.Stat">Stat</a></code>
480 will return a type that now implements a <code>String</code>
482 <a href="/pkg/io/fs/#FormatFileInfo"><code>io/fs.FormatFileInfo</code></a>.
487 <dl id="errors"><dt><a href="/pkg/errors/">errors</a></dt>
489 <p><!-- https://go.dev/issue/41198, CL 473935 -->
491 <a href="/pkg/errors/#ErrUnsupported"><code>ErrUnsupported</code></a>
492 error provides a standardized way to indicate that a requested
493 operation may not be performed because it is unsupported.
494 For example, a call to
495 <a href="/pkg/os/#Link"><code>os.Link</code></a> when using a
496 file system that does not support hard links.
501 <dl id="flag"><dt><a href="/pkg/flag/">flag</a></dt>
503 <p><!-- https://go.dev/issue/53747, CL 476015 -->
504 The new <a href="/pkg/flag/#BoolFunc"><code>BoolFunc</code></a>
506 <a href="/pkg/flag/#FlagSet.BoolFunc"><code>FlagSet.BoolFunc</code></a>
507 method define a flag that does not require an argument and calls
508 a function when the flag is used. This is similar to
509 <a href="/pkg/flag/#Func"><code>Func</code></a> but for a
513 <p><!-- CL 480215 -->
514 A flag definition (via <code>Bool</code>, <code>BoolVar</code>, <code>Int</code>, <code>IntVar</code>, etc.) will panic if <code>Set</code> has already been called on a flag with the same name.
516 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 <code>Set</code> operations.
521 <dl id="go/ast"><dt><a href="/pkg/go/ast/">go/ast</a></dt>
523 <p><!-- https://go.dev/issue/28089, CL 487935 -->
524 The new <a href="/pkg/go/ast/#IsGenerated"><code>IsGenerated</code></a> predicate
525 reports whether a file syntax tree contains the
526 <a href="https://go.dev/s/generatedcode">special comment</a>
527 that conventionally indicates that the file was generated by a tool.
532 <p><!-- https://go.dev/issue/59033, CL 476276 -->
534 <a href="/pkg/go/ast/#File.GoVersion"><code>File.GoVersion</code></a>
535 field records the minimum Go version required by
536 any <code>//go:build</code> or <code>// +build</code>
542 <dl id="go/build"><dt><a href="/pkg/go/build/">go/build</a></dt>
544 <p><!-- https://go.dev/issue/56986, CL 453603 -->
545 The package now parses build directives (comments that start
546 with <code>//go:</code>) in file headers (before
547 the <code>package</code> declaration). These directives are
549 <a href="/pkg/go/build/Package"><code>Package</code></a> fields
550 <a href="/pkg/go/build/Package.Directives"><code>Directives</code></a>,
551 <a href="/pkg/go/build/Package.TestDirectives"><code>TestDirectives</code></a>,
553 <a href="/pkg/go/build/Package.XTestDirectives"><code>XTestDirectives</code></a>.
556 </dl><!-- go/build -->
558 <dl id="go/build/constraint"><dt><a href="/pkg/go/build/constraint/">go/build/constraint</a></dt>
560 <p><!-- https://go.dev/issue/59033, CL 476275 -->
562 <a href="/pkg/go/build/constraint/#GoVersion"><code>GoVersion</code></a>
563 function returns the minimum Go version implied by a build
567 </dl><!-- go/build/constraint -->
569 <dl id="go/token"><dt><a href="/pkg/go/token/">go/token</a></dt>
571 <p><!-- https://go.dev/issue/57708, CL 464515 -->
572 The new <a href="/pkg/go/token/#File.Lines"><code>File.Lines</code></a> method
573 returns the file's line-number table in the same form as accepted by
574 <code>File.SetLines</code>.
577 </dl><!-- go/token -->
579 <dl id="hash/maphash"><dt><a href="/pkg/hash/maphash/">hash/maphash</a></dt>
581 <p><!-- https://go.dev/issue/47342, CL 468795 -->
582 The <code>hash/maphash</code> package now has a pure Go implementation, selectable with the <code>purego</code> build tag.
585 </dl><!-- hash/maphash -->
587 <dl id="io/fs"><dt><a href="/pkg/io/fs/">io/fs</a></dt>
589 <p><!-- https://go.dev/issue/54451, CL 489555 -->
591 <a href="/pkg/io/fs/#FormatFileInfo"><code>FormatFileInfo</code></a>
592 function returns a formatted version of a
593 <a href="/pkg/io/fs/#FileInfo"><code>FileInfo</code></a>.
595 <a href="/pkg/io/fs/#FormatDirEntry"><code>FormatDirEntry</code></a>
596 function returns a formatted version of a
597 <a href="/pkg/io/fs/#FileInfo"><code>DirEntry</code></a>.
598 The implementation of
599 <a href="/pkg/io/fs/#DirEntry"><code>DirEntry</code></a>
601 <a href="/pkg/io/fs/#ReadDir"><code>ReadDir</code></a> now
602 implements a <code>String</code> method that calls
603 <a href="/pkg/io/fs/#FormatDirEntry"><code>FormatDirEntry</code></a>,
604 and the same is true for
605 the <a href="/pkg/io/fs/#DirEntry"><code>DirEntry</code></a>
607 <a href="/pkg/io/fs/#WalkDirFunc"><code>WalkDirFunc</code></a>.
612 <dl id="log/slog"><dt><a href="/pkg/log/slog/">log/slog</a></dt>
614 <p><!-- https://go.dev/issue/59060 -->
615 TODO: <a href="https://go.dev/issue/59060">https://go.dev/issue/59060</a>: arg to Record.Attrs should return bool
618 <p><!-- https://go.dev/issue/59141 -->
619 TODO: <a href="https://go.dev/issue/59141">https://go.dev/issue/59141</a>: handle panics in LogValuer.LogValue
622 <p><!-- https://go.dev/issue/59204 -->
623 TODO: <a href="https://go.dev/issue/59204">https://go.dev/issue/59204</a>: change slog.Group signature to ...any
626 <p><!-- https://go.dev/issue/59280 -->
627 TODO: <a href="https://go.dev/issue/59280">https://go.dev/issue/59280</a>: ReplaceAttr gets Source struct instead of file:line
630 <p><!-- https://go.dev/issue/59282 -->
631 TODO: <a href="https://go.dev/issue/59282">https://go.dev/issue/59282</a>: drop only completely empty Attrs
634 <p><!-- https://go.dev/issue/59339 -->
635 TODO: <a href="https://go.dev/issue/59339">https://go.dev/issue/59339</a>: change constructors to NewXXXHandler(io.Writer, *HandlerOptions)
638 <p><!-- https://go.dev/issue/59345 -->
639 TODO: <a href="https://go.dev/issue/59345">https://go.dev/issue/59345</a>: JSONHandler should format everything like json.Marshal
642 <p><!-- CL 477295 -->
643 TODO: <a href="https://go.dev/cl/477295">https://go.dev/cl/477295</a>: log/slog: initial commit; modified api/next/56345.txt
646 <p><!-- CL 484096 -->
647 TODO: <a href="https://go.dev/cl/484096">https://go.dev/cl/484096</a>: log/slog: function argument to Record.Attrs returns bool; modified api/next/59060.txt
650 <p><!-- CL 486376 -->
651 TODO: <a href="https://go.dev/cl/486376">https://go.dev/cl/486376</a>: log/slog: add Source type for source location; modified api/next/59280.txt
654 <p><!-- CL 486415 -->
655 TODO: <a href="https://go.dev/cl/486415">https://go.dev/cl/486415</a>: log/slog: built-in handler constructors take options as a second arg; modified api/next/56345.txt, api/next/59339.txt
658 <p><!-- CL 487855 -->
659 TODO: <a href="https://go.dev/cl/487855">https://go.dev/cl/487855</a>: log/slog: Group takes ...any; modified api/next/56345.txt, api/next/59204.txt
662 </dl><!-- log/slog -->
664 <dl id="math"><dt><a href="/pkg/math/">math</a></dt>
666 <p><!-- https://go.dev/issue/56491 -->
667 TODO: <a href="https://go.dev/issue/56491">https://go.dev/issue/56491</a>: add Compare and Compare32
670 <p><!-- CL 459435 -->
671 TODO: <a href="https://go.dev/cl/459435">https://go.dev/cl/459435</a>: math: add Compare and Compare32; modified api/next/56491.txt
674 <p><!-- CL 467515 -->
675 TODO: <a href="https://go.dev/cl/467515">https://go.dev/cl/467515</a>: math: add Compare and Compare32; modified api/next/56491.txt
680 <dl id="math/big"><dt><a href="/pkg/math/big/">math/big</a></dt>
682 <p><!-- https://go.dev/issue/56984, CL 453115 -->
683 The new <a href="/pkg/math/big/#Int.ToFloat64"><code>Int.ToFloat64</code></a>
684 method returns the nearest floating-point value to a
685 multi-precision integer, along with an indication of any
686 rounding that occurred.
689 </dl><!-- math/big -->
691 <dl id="net"><dt><a href="/pkg/net/">net</a></dt>
694 <!-- https://go.dev/issue/59166, https://go.dev/issue/56539 -->
695 <!-- CL 471136, CL 471137, CL 471140 -->
696 On Linux, the <a href="/pkg/net/">net</a> package can now use
697 Multipath TCP when the kernel supports it. It is not used by
698 default. To use Multipath TCP when available on a client, call
700 <a href="/pkg/net/#Dialer.SetMultipathTCP"><code>Dialer.SetMultipathTCP</code></a>
701 method before calling the
702 <a href="/pkg/net/#Dialer.Dial"><code>Dialer.Dial</code></a> or
703 <a href="/pkg/net/#Dialer.DialContext"><code>Dialer.DialContext</code></a>
704 methods. To use Multipath TCP when available on a server, call
706 <a href="/pkg/net/#ListenConfig.SetMultipathTCP"><code>ListenConfig.SetMultipathTCP</code></a>
707 method before calling the
708 <a href="/pkg/net/#ListenConfig.Listen"><code>ListenConfig.Listen</code></a>
709 method. Specify the network as <code>"tcp"</code> or
710 <code>"tcp4"</code> or <code>"tcp6"</code> as usual. If
711 Multipath TCP is not supported by the kernel or the remote host,
712 the connection will silently fall back to TCP. To test whether a
713 particular connection is using Multipath TCP, use the
714 <a href="/pkg/net/#TCPConn.MultipathTCP"><code>TCPConn.MultipathTCP</code></a>
718 In a future Go release we may enable Multipath TCP by default on
719 systems that support it.
724 <dl id="net/http"><dt><a href="/pkg/net/http/">net/http</a></dt>
726 <p><!-- https://go.dev/issue/44855, CL 382117 -->
727 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.
730 <p><!-- CL 472636 -->
731 TODO: <a href="https://go.dev/cl/472636">https://go.dev/cl/472636</a>: net/http: support full-duplex HTTP/1 responses; modified api/next/57786.txt
734 <p><!-- CL 494122 -->
735 The <a href="/pkg/net/http/">net/http</a> package now supports
736 <a href="/pkg/errors/#ErrUnsupported"><code>errors.ErrUnsupported</code></a>,
737 in that the expression
738 <code>errors.Is(http.ErrNotSupported, errors.ErrUnsupported)</code>
742 </dl><!-- net/http -->
744 <dl id="os"><dt><a href="/pkg/os/">os</a></dt>
746 <p><!-- https://go.dev/issue/32558, CL 219638 -->
747 Programs may now pass an empty <code>time.Time</code> value to
748 the <a href="/pkg/os/#Chtimes"><code>Chtimes</code></a> function
749 to leave either the access time or the modification time unchanged.
752 <p><!-- CL 480135 -->
754 <a href="/pkg/os#File.Chdir"><code>File.Chdir</code></a> method
755 now changes the current directory to the file, rather than
756 always returning an error.
759 <p><!-- CL 477215 -->
761 <a href="/pkg/os/#Truncate"><code>Truncate</code></a> on a
762 non-existent file used to create an empty file. It now returns
763 an error indicating that the file does not exist.
766 <p><!-- CL 493036 -->
767 On Windows the os package now supports working with files whose
768 names, stored as UTF-16, can't be represented as valid UTF-8.
771 <p><!-- https://go.dev/issue/54451, CL 491175 -->
772 The implementation of the
773 <a href="/pkg/io/fs/#DirEntry"><code>io/fs.DirEntry</code></a>
774 interface returned by the
775 <a href="/pkg/os/#ReadDir"><code>ReadDir</code></a> function and
776 the <a href="/pkg/os/#File.ReadDir"><code>File.ReadDir</code>
777 method now implements a <code>String</code> method that calls
778 <a href="/pkg/io/fs/#FormatDirEntry"><code>io/fs.FormatDirEntry</code></a>.
783 <dl id="path/filepath"><dt><a href="/pkg/path/filepath/">path/filepath</a></dt>
786 The implementation of the
787 <a href="/pkg/io/fs/#DirEntry"><code>io/fs.DirEntry</code></a>
788 interface passed to the function argument of
789 <a href="/pkg/path/filepath/#WalkDir"><code>WalkDir</code></a>
790 now implements a <code>String</code> method that calls
791 <a href="/pkg/io/fs/#FormatDirEntry"><code>io/fs.FormatDirEntry</code></a>.
794 </dl><!-- path/filepath -->
796 <!-- CL 459455 reverted -->
798 <dl id="reflect"><dt><a href="/pkg/reflect/">reflect</a></dt>
800 <p><!-- CL 408826, CL 413474 -->
801 In Go 1.21, <a href="/pkg/reflect/#ValueOf"><code>ValueOf</code></a>
802 no longer forces its argument to be allocated on the heap, allowing
803 a <code>Value</code>'s content to be allocated on the stack. Most
804 operations on a <code>Value</code> also allow the underlying value
805 to be stack allocated.
808 <p><!-- https://go.dev/issue/55002 -->
809 The new <a href="/pkg/reflect/#Value"><code>Value</code></a>
810 method <a href="/pkg/reflect/#Value.Clear"><code>Value.Clear</code></a>
811 clears the contents of a map or zeros the contents of a slice.
812 This corresponds to the new <code>clear</code> built-in
813 <a href="#language">added to the language</a>.
816 <p><!-- https://go.dev/issue/56906, CL 452762 -->
817 The <a href="/pkg/reflect/#SliceHeader"><code>SliceHeader</code></a>
818 and <a href="/pkg/reflect/#StringHeader"><code>StringHeader</code></a>
819 types are now deprecated. In new code
820 prefer <a href="/pkg/unsafe/#Slice"><code>unsafe.Slice</code></a>,
821 <a href="/pkg/unsafe/#SliceData"><code>unsafe.SliceData</code></a>,
822 <a href="/pkg/unsafe/#String"><code>unsafe.String</code></a>,
823 or <a href="/pkg/unsafe/#StringData"><code>unsafe.StringData</code></a>.
826 </dl><!-- reflect -->
828 <dl id="regexp"><dt><a href="/pkg/regexp/">regexp</a></dt>
830 <p><!-- https://go.dev/issue/46159, CL 479401 -->
831 <a href="/pkg/regexp#Regexp"><code>Regexp</code></a> now defines
832 <a href="/pkg/regexp#Regexp.MarshalText"><code>MarshalText</code></a>
833 and <a href="/pkg/regexp#Regexp.UnmarshalText"><code>UnmarshalText</code></a>
834 methods. These implement
835 <a href="/pkg/encoding#TextMarshaler"><code>encoding.TextMarshaler</code></a>
837 <a href="/pkg/encoding#TextUnmarshaler"><code>encoding.TextUnmarshaler</code></a>
838 and will be used by packages such as
839 <a href="/pkg/encoding/json">encoding/json</a>.
844 <dl id="runtime"><dt><a href="/pkg/runtime/">runtime</a></dt>
846 <p><!-- https://go.dev/issue/38651 -->
847 TODO: <a href="https://go.dev/issue/38651">https://go.dev/issue/38651</a>: add 'created by goroutine number' to stack traces
850 <p><!-- https://go.dev/issue/57441, CL 474915 -->
851 Crashing Go applications can now opt-in to Windows Error Reporting (WER) by setting the environment variable
852 <code>GOTRACEBACK=wer</code> or calling <a href="/pkg/runtime/debug/#SetTraceback"><code>debug.SetTraceback("wer")</code></a>
853 before the crash. Other than enabling WER, the runtime will behave as with <code>GOTRACEBACK=crash</code>.
854 On non-Windows systems, <code>GOTRACEBACK=wer</code> is ignored.
857 <p><!-- CL 447778 -->
858 <code>GODEBUG=cgocheck=2</code>, a thorough checker of cgo pointer passing rules,
859 is no longer available as a <a href="/pkg/runtime#hdr-Environment_Variables">debug option</a>.
860 Instead, it is available as an experiment using <code>GOEXPERIMENT=cgocheck2</code>.
861 In particular this means that this mode has to be selected at build time instead of startup time.
863 <code>GODEBUG=cgocheck=1</code> is still available (and is still the default).
866 <p><!-- https://go.dev/issue/46787 -->
867 A new type <code>Pinner</code> has been added to the runtime
868 package. <code>Pinner</code>s may be used to "pin" Go memory
869 such that it may be used more freely by non-Go code. For instance,
870 passing Go values that reference pinned Go memory to C code is
871 now allowed. Previously, passing any such nested reference was
873 <a href="https://pkg.go.dev/cmd/cgo#hdr-Passing_pointers">cgo pointer passing rules.</a>
875 See <a href="/pkg/runtime#Pinner">the docs</a> for more details.
878 </dl><!-- runtime -->
880 <dl id="runtime/trace"><dt><a href="/pkg/runtime/trace/">runtime/trace</a></dt>
882 <p><!-- https://go.dev/issue/16638 -->
883 Collecting traces on amd64 and arm64 now incurs a substantially
884 smaller CPU cost: up to a 10x improvement over the previous release.
887 <p><!-- CL 494495 -->
888 Traces now contain explicit stop-the-world events for every reason
889 the Go runtime might stop-the-world, not just garbage collection.
892 </dl><!-- runtime/trace -->
894 <dl id="runtime/metrics"><dt><a href="/pkg/runtime/metrics/">runtime/metrics</a></dt>
896 <p><!-- https://go.dev/issue/56857 -->
897 A few previously-internal GC metrics, such as live heap size, are
900 <code>GOGC</code> and <code>GOMEMLIMIT</code> are also now
901 available as metrics.
904 </dl><!-- runtime/metrics -->
906 <dl id="sync"><dt><a href="/pkg/sync/">sync</a></dt>
908 <p><!-- https://go.dev/issue/56102, CL 451356 -->
909 The new <a href="/pkg/sync/#OnceFunc"><code>OnceFunc</code></a>,
910 <a href="/pkg/sync/#OnceValue"><code>OnceValue</code></a>, and
911 <a href="/pkg/sync/#OnceValues"><code>OnceValues</code></a>
912 functions capture a common use of <a href="/pkg/sync/#Once">Once</a> to
913 lazily initialize a value on first use.
918 <dl id="syscall"><dt><a href="/pkg/syscall/">syscall</a></dt>
920 <p><!-- CL 480135 -->
922 <a href="/pkg/syscall#Fchdir"><code>Fchdir</code></a> function
923 now changes the current directory to its argument, rather than
924 always returning an error.
927 <p><!-- https://go.dev/issue/46259, CL 458335 -->
929 <a href="/pkg/syscall#SysProcAttr"><code>SysProcAttr</code></a>
930 has a new field <code>Jail</code> that may be used to put the
931 newly created process in a jailed environment.
934 <p><!-- CL 493036 -->
935 On Windows the syscall package now supports working with files whose
936 names, stored as UTF-16, can't be represented as valid UTF-8.
937 The <a href="/pkg/syscall#UTF16ToString"><code>UTF16ToString</code></a>
938 and <a href="/pkg/syscall#UTF16FromString"><code>UTF16FromString</code></a>
939 functions now convert between UTF-16 data and
940 <a href=http://simonsapin.github.io/wtf-8/"">WTF-8</a> strings.
941 This is backward compatible as WTF-8 is a superset of the UTF-8
942 format that was used in earlier releases.
945 <p><!-- CL 476578, CL 476875, CL 476916 -->
946 Several error values match the new
947 <a href="/pkg/errors/#ErrUnsupported"><code>errors.ErrUnsupported</code></a>,
948 such that <code>errors.Is(err, errors.ErrUnsupported)</code>
951 <li><code>ENOSYS</code></li>
952 <li><code>ENOTSUP</code></li>
953 <li><code>EOPNOTSUPP</code></li>
954 <li><code>EPLAN9</code> (Plan 9 only)</li>
955 <li><code>ERROR_CALL_NOT_IMPLEMENTED</code> (Windows only)</li>
956 <li><code>ERROR_NOT_SUPPORTED</code> (Windows only)</li>
957 <li><code>EWINDOWS</code> (Windows only)</li>
961 </dl><!-- syscall -->
963 <dl id="testing"><dt><a href="/pkg/testing/">testing</a></dt>
965 <p><!-- https://go.dev/issue/37708, CL 463837 -->
966 The new <code>-test.fullpath</code> option will print full path
967 names in test log messages, rather than just base names.
970 <p><!-- https://go.dev/issue/52600, CL 475496 -->
971 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>.
974 </dl><!-- testing -->
976 <dl id="testing/fstest"><dt><a href="/pkg/testing/fstest/">testing/fstest</a></dt>
978 <p><!-- https://go.dev/issue/54451, CL 491175 -->
979 Calling <code><a href="/pkg/testing/fstest/MapFS.Open">Open</a>.<a href="/pkg/io/fs/#File.Stat">Stat</a></code>
980 will return a type that now implements a <code>String</code>
982 <a href="/pkg/io/fs/#FormatFileInfo"><code>io/fs.FormatFileInfo</code></a>.
985 </dl><!-- testing/fstest -->
987 <dl id="testing/slogtest"><dt><a href="/pkg/testing/slogtest/">testing/slogtest</a></dt>
989 <p><!-- CL 487895 -->
990 TODO: <a href="https://go.dev/cl/487895">https://go.dev/cl/487895</a>: testing/slogtest: tests for slog handlers; modified api/next/56345.txt
993 </dl><!-- testing/slogtest -->
995 <!-- proposals for x repos that don't need to be mentioned here but
996 are picked up by the relnote tool. -->
997 <!-- https://go.dev/issue/54232 -->
998 <!-- https://go.dev/issue/57906 -->
999 <!-- https://go.dev/issue/58668 -->