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.
TODO: https://go.dev/issue/56986: extended backwards compatibility for Go
TODO: complete this section
The Go scheduler now interacts much more efficiently with the JavaScript event loop, especially in applications that block frequently on asynchronous events.
Go 1.21 adds an experimental port to the
WebAssembly System Interface (WASI), Preview 1
(GOOS=wasip1, GOARCH=wasm).
As a result of the addition of the new GOOS value
"wasip1", Go files named *_wasip1.go
will now be ignored
by Go tools except when that GOOS value is being
used.
If you have existing filenames matching that pattern, you will
need to rename them.
The -pgo build flag now defaults to -pgo=auto,
and the restriction of specifying a single main package on the command
line is now removed. If a file named default.pgo is present
in the main package's directory, the go command will use
it to enable profile-guided optimization for building the corresponding
program.
TODO: https://go.dev/cl/453603: cmd/go, go/build: parse directives in file headers; modified api/next/56986.txt
TODO: complete this section, or delete if not needed
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.
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%.
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 GOGC and/or GOMEMLIMIT slightly.
TODO: complete this section, or delete if not needed
TODO: complete this section, or delete if not needed
The new log/slog 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.
As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibility in mind. There are also various performance improvements, not enumerated here.
TODO: https://go.dev/cl/456837: all: upgrade Unicode from 13.0.0 to 15.0.0; modified api/except.txt, api/next/55079.txt
TODO: complete this section
TODO: https://go.dev/issue/53685: add Buffer.Available and Buffer.AvailableBuffer
TODO: https://go.dev/cl/474635: bytes: add Buffer.Available and Buffer.AvailableBuffer; modified api/next/53685.txt
The new WithoutCancel
function returns a copy of a context that is not canceled when the original
context is canceled.
The new WithDeadlineCause
and WithTimeoutCause
functions provide a way to set a context cancellation cause when a deadline or
timer expires. The cause may be retrieved with the
Cause function.
The new AfterFunc
function registers a function to run after a context has been cancelled.
TODO: https://go.dev/cl/459977: crypto/elliptic: deprecate unsafe APIs; modified api/next/34648.txt, api/next/52221.txt
TODO: https://go.dev/issue/56921: deprecate GenerateMultiPrimeKey and PrecomputedValues.CRTValues
TODO: https://go.dev/cl/459976: crypto/rsa: deprecate multiprime RSA support; modified api/next/56921.txt
TODO: https://go.dev/cl/483815: crypto/sha1: add WriteString and WriteByte method
TODO: https://go.dev/issue/50543: add native SHA256 instruction implementation for AMD64
TODO: https://go.dev/cl/408795: crypto/sha256: add sha-ni implementation; crypto/sha256 uses Intel SHA extensions on new enough x86 processors, making it 3-4X faster.
TODO: https://go.dev/cl/481478: crypto/sha256: add WriteString and WriteByte method
TODO: https://go.dev/cl/483816: crypto/sha512: add WriteString and WriteByte method
TODO: https://go.dev/issue/53573: surface ReasonCode inside x509.RevocationList entries
TODO: https://go.dev/cl/468875: crypto/x509: surface ReasonCode in RevocationList API; modified api/next/53573.txt
TODO: https://go.dev/issue/56887: add DT_FLAGS_1 (dynamic flags) constants
TODO: https://go.dev/issue/56892: add (*File).DynValue
TODO: https://go.dev/cl/452496: debug/elf: add DT_FLAGS_1 constants; modified api/next/56887.txt
TODO: https://go.dev/cl/452617: debug/elf: retrieve values for dynamic section tags; modified api/next/56892.txt
TODO: https://go.dev/cl/473256: debug/elf: support zstd compression; modified api/next/55107.txt
TODO: https://go.dev/cl/488475: debug/pe: return error on reading from section with uninitialized data
TODO: https://go.dev/issue/57803: openFile should implement ReaderAt
TODO: https://go.dev/cl/483235: embed: implement openFile.ReadAt
TODO: https://go.dev/issue/41198: add ErrUnsupported
TODO: https://go.dev/cl/473935: errors: add ErrUnsupported; modified api/next/41198.txt
TODO: https://go.dev/issue/53747: add BoolFunc(name, usage string, fn func(string)error)
TODO: https://go.dev/cl/476015: flag: add BoolFunc; FlagSet.BoolFunc; modified api/next/53747.txt
TODO: https://go.dev/cl/480215: flag: panic if a flag is defined after being set
TODO: https://go.dev/issue/54451: standard implementations of FileInfo and DirEntry should implement fmt.Stringer
TODO: https://go.dev/issue/28089: add func IsGenerated(*File) bool
TODO: https://go.dev/cl/476276: go/ast: add File.GoVersion; modified api/next/59033.txt
TODO: https://go.dev/cl/487935: go/ast: add IsGenerated(*File) predicate; modified api/next/28089.txt
TODO: https://go.dev/cl/453603: cmd/go, go/build: parse directives in file headers; modified api/next/56986.txt
TODO: https://go.dev/cl/476275: go/build/constraint: add GoVersion; modified api/next/59033.txt
TODO: https://go.dev/cl/464515: go/token: add (*File).Lines method; modified api/next/57708.txt
TODO: https://go.dev/issue/47342: Provide a `purego` implementation
TODO: https://go.dev/cl/468795: hash/maphash: add purego implementation
TODO: https://go.dev/cl/489555: io/fs: add FormatFileInfo and FormatDirEntry functions; modified api/next/54451.txt
TODO: https://go.dev/issue/59060: arg to Record.Attrs should return bool
TODO: https://go.dev/issue/59141: handle panics in LogValuer.LogValue
TODO: https://go.dev/issue/59204: change slog.Group signature to ...any
TODO: https://go.dev/issue/59280: ReplaceAttr gets Source struct instead of file:line
TODO: https://go.dev/issue/59282: drop only completely empty Attrs
TODO: https://go.dev/issue/59339: change constructors to NewXXXHandler(io.Writer, *HandlerOptions)
TODO: https://go.dev/issue/59345: JSONHandler should format everything like json.Marshal
TODO: https://go.dev/cl/477295: log/slog: initial commit; modified api/next/56345.txt
TODO: https://go.dev/cl/484096: log/slog: function argument to Record.Attrs returns bool; modified api/next/59060.txt
TODO: https://go.dev/cl/486376: log/slog: add Source type for source location; modified api/next/59280.txt
TODO: https://go.dev/cl/486415: log/slog: built-in handler constructors take options as a second arg; modified api/next/56345.txt, api/next/59339.txt
TODO: https://go.dev/cl/487855: log/slog: Group takes ...any; modified api/next/56345.txt, api/next/59204.txt
TODO: https://go.dev/issue/57436: new standard library package based on x/exp/maps
TODO: https://go.dev/cl/464343: maps: new package; modified api/next/57436.txt
TODO: https://go.dev/issue/56491: add Compare and Compare32
TODO: https://go.dev/cl/459435: math: add Compare and Compare32; modified api/next/56491.txt
TODO: https://go.dev/cl/467515: math: add Compare and Compare32; modified api/next/56491.txt
TODO: https://go.dev/issue/56984: add Int.Float64 conversion (was initially: {ToInt64,ToUint64,Float64})
TODO: https://go.dev/cl/453115: math/big: add Int.Float64 conversion; modified api/next/56984.txt
TODO: https://go.dev/issue/56539: add support for MPTCP
TODO: https://go.dev/issue/59166: add func (*TCPConn) MultipathTCP() (bool, error)
TODO: https://go.dev/cl/471136: net: mptcp: implement dialMPTCP; modified api/next/56539.txt
TODO: https://go.dev/cl/471137: net: mptcp: implement listenMPTCP; modified api/next/56539.txt
TODO: https://go.dev/cl/471140: net: mptcp: add TCPConn's MultipathTCP checker; modified api/next/59166.txt
TODO: https://go.dev/issue/44855: add ErrSchemeMismatch
TODO: https://go.dev/cl/382117: net/http: expose "http: server gave HTTP response to HTTPS client" error; modified api/next/44855.txt
TODO: https://go.dev/cl/472636: net/http: support full-duplex HTTP/1 responses; modified api/next/57786.txt
TODO: https://go.dev/cl/494122: net/http: let ErrNotSupported match errors.ErrUnsupported; modified api/next/41198.txt
TODO: https://go.dev/issue/32558: allow Chtimes with time.Time{} to avoid setting time
TODO: https://go.dev/cl/219638: os: make Chtimes accept empty time values to skip file time modification
TODO: https://go.dev/cl/477215: os: avoid creating a new file in Truncate on Windows; os.Truncate on Windows no longer now fails if the file does not exist, consistent with other platforms
TODO: https://go.dev/cl/493036: os, syscall: support ill-formed UTF-16 strings on Windows
TODO: https://go.dev/cl/459455: os/user: lookup Linux users and groups via systemd userdb
In Go 1.21, ValueOf
no longer forces its argument to be allocated on the heap, allowing
a Value's content to be allocated on the stack. Most
operations on a Value also allow the underlying value
to be stack allocated.
TODO: https://go.dev/issue/55002: add Value.Clear
TODO: https://go.dev/issue/56906: deprecate SliceHeader and StringHeader
TODO: https://go.dev/cl/452762: reflect: deprecate SliceHeader and StringHeader; modified api/next/56906.txt
TODO: https://go.dev/issue/46159: support encoding.TextMarshaler
TODO: https://go.dev/cl/479401: regexp: add Regexp.TextMarshaler/TextUnmarshaler; modified api/next/46159.txt
TODO: https://go.dev/issue/38651: add 'created by goroutine number' to stack traces
TODO: https://go.dev/issue/57441: use WER for GOTRACEBACK=wer on Windows
TODO: https://go.dev/cl/447778: runtime: reimplement GODEBUG=cgocheck=2 as a GOEXPERIMENT
TODO: https://go.dev/cl/472195: runtime: remove NOFRAME from asmcgocall, systemstack and mcall
TODO: https://go.dev/cl/474915: runtime: support GOTRACEBACK=wer on Windows
A new type Pinner has been added to the runtime
package. Pinners 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
cgo pointer passing rules.
See the docs for more details.
Collecting traces on amd64 and arm64 now incurs a substantially smaller CPU cost: up to a 10x improvement over the previous release.
Traces now contain explicit stop-the-world events for every reason the Go runtime might stop-the-world, not just garbage collection.
A few previously-internal GC metrics, such as live heap size, are
now available.
GOGC and GOMEMLIMIT are also now
available as metrics.
TODO: https://go.dev/issue/54768: add DeleteFunc
TODO: https://go.dev/issue/57433: new standard library package based on x/exp/slices
TODO: https://go.dev/cl/467417: slices: new package; modified api/next/57433.txt
TODO: https://go.dev/cl/483175: slices: add DeleteFunc; modified api/next/54768.txt
TODO: https://go.dev/issue/56351: add clear(x) builtin, to clear map, zero content of slice
TODO: https://go.dev/issue/57411: define initialization order more precisely
TODO: https://go.dev/issue/59338: infer type arguments from assignments of generic functions (reverse type inference)
The new slices package
provides many common operations on slices, using generic
functions that work with slices of any element type.
The new OnceFunc,
OnceValue, and
OnceValues
functions capture a common use of Once to
lazily initialize a value on first use.
TODO: https://go.dev/issue/46259: add Jail int32 to SysProcAttr on FreeBSD
TODO: https://go.dev/cl/458335: syscall: add jail support to ForkExec on FreeBSD; modified api/next/46259.txt
TODO: https://go.dev/cl/480135: syscall: implement Fchdir on Windows
TODO: https://go.dev/issue/37708: optionally include full (or relative) path name
The new Testing function reports whether the program is a test created by go test.
TODO: https://go.dev/cl/487895: testing/slogtest: tests for slog handlers; modified api/next/56345.txt
TODO: https://go.dev/issue/57348: Allow different types for haystack/needle in BinarySearchFunc
TODO: https://go.dev/issue/54232: Add WSALookupService
TODO: https://go.dev/issue/57906: add Analyzer.URL and Diagnostic.URL fields
TODO: https://go.dev/issue/58668: add Encoder type, to amortize Scope.Names