From a4b6685c4c94152cdb9cb80061478e20c9fc2e88 Mon Sep 17 00:00:00 2001 From: David Chase Date: Fri, 4 Aug 2023 12:57:32 -0400 Subject: [PATCH] doc: move Go 1.21 release notes to x/website Now that the development of the Go 1.21 release is almost done, its release notes are moved to their eventual long-term home in x/website in CL 516095. Delete the initial development copy here. For golang/go#58645. Change-Id: I5207d21289b2e7b9328c943a088f45bc81c710a4 Reviewed-on: https://go-review.googlesource.com/c/go/+/516075 Run-TryBot: David Chase TryBot-Result: Gopher Robot Reviewed-by: Heschi Kreinick --- doc/go1.21.html | 1339 ----------------------------------------------- 1 file changed, 1339 deletions(-) delete mode 100644 doc/go1.21.html diff --git a/doc/go1.21.html b/doc/go1.21.html deleted file mode 100644 index 3e98e1fa1556b..0000000000000 --- a/doc/go1.21.html +++ /dev/null @@ -1,1339 +0,0 @@ - - - - - - -

DRAFT RELEASE NOTES — Introduction to Go 1.21

- -

- - 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. - -

- -

- The latest Go release, version 1.21, arrives six months after Go 1.20. - Most of its changes are in the implementation of the toolchain, runtime, and libraries. - As always, the release maintains the Go 1 promise of compatibility; - in fact, Go 1.21 improves upon that promise. - We expect almost all Go programs to continue to compile and run as before. -

- -

- Go 1.21 introduces a small change to the numbering of releases. - In the past, we used Go 1.N 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.N.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 go version will report “go1.21.0” - (until you upgrade to Go 1.21.1). - See “Go versions” in the “Go Toolchains” documentation for details - about the new version numbering. -

- -

Changes to the language

- -

- Go 1.21 adds three new built-ins to the language. - -

    -
  • - The new functions min and max compute the - smallest (or largest, for max) value of a fixed number - of given arguments. - See the language spec for - details. -
    • -
  • - The new function clear deletes all elements from a - map or zeroes all elements of a slice. - See the language spec for - details. -
    • -
-

- -

- Package initialization order is now specified more precisely. The - new algorithm is: -

    -
  • - Sort all packages by import path. -
    • -
  • Repeat until the list of packages is empty: -
      -
    • - Find the first package in the list for which all imports are - already initialized. -
      • -
    • - Initialize that package and remove it from the list. -
      • -
    -
    • -
- 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. -

- -

- Multiple improvements that increase the power and precision of type inference have been made. -

-
    -
  • - 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 slices.IndexFunc) 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. -
    • -
  • - 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. -
    • -
  • - 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. -
    • -
  • - 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. -
    • -
  • - 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. -
    • -
- -

- More generally, the description of - type inference - in the language spec has been clarified. - Together, all these changes make type inference more powerful and inference failures less surprising. -

- - -

- 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 the LoopvarExperiment wiki page. -

- -

Tools

-

- Go 1.21 adds improved support for backwards compatibility and forwards compatibility - in the Go toolchain. -

- -

- 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 - compatibility policy - 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 - go line in the workspace's go.work file - or else the main module's go.mod file. - Upgrading to a new Go toolchain but leaving the go 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 “Go, Backwards Compatibility, and GODEBUG” for details. -

- -

- To improve forwards compatibility, Go 1.21 now reads the go line - in a go.work or go.mod file as a strict - minimum requirement: go 1.21.0 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. -

- -

- To make these new stricter version requirements easier to manage, - the go 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 go.mod or go.work go line - declares a minimum requirement on a newer version of Go, the go - command will find and run that version automatically. - The new toolchain directive sets a suggested minimum toolchain to use, - which may be newer than the strict go minimum. - See “Go Toolchains” for details. -

- -

Go command

- -

- 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. -

- -

- The -C dir flag must now be the first - flag on the command-line when used. -

- -

- The new go test option - -fullpath prints full path names in test log messages, - rather than just base names. -

- -

- The go test -c flag now - supports writing test binaries for multiple packages, each to - pkg.test where pkg is the package name. - It is an error if more than one test package being compiled has a given package name.] -

- -

- The go test -o flag now - accepts a directory argument, in which case test binaries are written to that - directory instead of the current directory. -

- -

Cgo

- -

- In files that import "C", the Go toolchain now - correctly reports errors for attempts to declare Go methods on C types. -

- -

Runtime

- -

- 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. -

- -

- 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. -

- -

Compiler

- -

- 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 - Go command section, PGO is enabled by default for - binaries that contain a default.pgo 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 - PGO user guide for detailed documentation. -

- - -

- 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. -

- - -

- Go 1.21 improves build speed by up to 6%, largely thanks to building the - compiler itself with PGO. -

- -

Assembler

- - -

- On amd64, frameless nosplit assembly functions are no longer automatically marked as NOFRAME. - Instead, the NOFRAME 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. -

- - -

- The verifier that checks for incorrect uses of R15 when dynamic linking on amd64 has been improved. -

- -

Linker

- -

- 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. -

- - -

- 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. -

- -

Core library

- -

New log/slog package

- -

- 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. -

- -

New testing/slogtest package

- -

- The new testing/slogtest package can help - to validate slog.Handler implementations. -

- -

New slices package

- -

- - - - - - The new slices package provides many common - operations on slices, using generic functions that work with slices - of any element type. -

- -

New maps package

- -

- The new maps package provides several - common operations on maps, using generic functions that work with - maps of any key or element type. -

- -

New cmp package

- -

- The new cmp package defines the type - constraint Ordered and - two new generic functions - Less - and Compare that are - useful with ordered - types. -

- -

Minor changes to the library

- -

- 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. -

- -
archive/tar
-
-

- The implementation of the - io/fs.FileInfo - interface returned by - Header.FileInfo - now implements a String method that calls - io/fs.FormatFileInfo. -

-
-
- -
archive/zip
-
-

- The implementation of the - io/fs.FileInfo - interface returned by - FileHeader.FileInfo - now implements a String method that calls - io/fs.FormatFileInfo. -

- -

- The implementation of the - io/fs.DirEntry - interface returned by the - io/fs.ReadDirFile.ReadDir - method of the - io/fs.File - returned by - Reader.Open - now implements a String method that calls - io/fs.FormatDirEntry. -

-
-
- -
bytes
-
-

- The Buffer type - has two new methods: - Available - and AvailableBuffer. - These may be used along with the - Write - method to append directly to the Buffer. -

-
-
- -
context
-
-

- 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. -

- -

- An optimization means that the results of calling - Background - and TODO and - converting them to a shared type can be considered equal. - In previous releases they were always different. Comparing - Context values - for equality has never been well-defined, so this is not - considered to be an incompatible change. -

-
-
- - -
crypto/ecdsa
-
-

- PublicKey.Equal and - PrivateKey.Equal - now execute in constant time. -

-
-
- -
crypto/elliptic
-
-

- All of the Curve methods have been deprecated, along with GenerateKey, Marshal, and Unmarshal. For ECDH operations, the new crypto/ecdh package should be used instead. For lower-level operations, use third-party modules such as filippo.io/nistec. -

-
-
- -
crypto/rand
-
-

- The crypto/rand package now uses the getrandom system call on NetBSD 10.0 and later. -

-
-
- -
crypto/rsa
-
-

- The performance of private RSA operations (decryption and signing) is now better than Go 1.19 for GOARCH=amd64 and GOARCH=arm64. It had regressed in Go 1.20. -

-

- Due to the addition of private fields to PrecomputedValues, PrivateKey.Precompute must be called for optimal performance even if deserializing (for example from JSON) a previously-precomputed private key. -

-

- PublicKey.Equal and - PrivateKey.Equal - now execute in constant time. -

-

- The GenerateMultiPrimeKey function and the PrecomputedValues.CRTValues field have been deprecated. PrecomputedValues.CRTValues will still be populated when PrivateKey.Precompute is called, but the values will not be used during decryption operations. -

-
-
- - - -
crypto/sha256
-
-

- SHA-224 and SHA-256 operations now use native instructions when available when GOARCH=amd64, providing a performance improvement on the order of 3-4x. -

-
-
- - - - -
crypto/tls
-
-

- Servers now skip verifying client certificates (including not running - Config.VerifyPeerCertificate) - 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 Config.InsecureSkipVerify - is set. -

- -

- Applications can now control the content of session tickets. -

-

- -

- 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 Conn.SetSessionTicketKeys, - this might lead to a noticeable performance cost. -

- -

- Both clients and servers now implement the Extended Master Secret extension (RFC 7627). - The deprecation of ConnectionState.TLSUnique - has been reverted, and is now set for resumed connections that support Extended Master Secret. -

- -

- The new QUICConn 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. -

- -

- The new VersionName function - returns the name for a TLS version number. -

- -

- 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: -

    -
  • - For TLS 1.3 connections, if the server is configured to require client authentication using - RequireAnyClientCert or - RequireAndVerifyClientCert, - and the client does not provide any certificate, the server will now return the "certificate required" alert. -
    • -
  • - 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. -
    • -
  • - If the client provides a certificate that is either expired or not yet valid, - the server will return the "expired certificate" alert. -
    • -
  • - In all other scenarios related to client authentication failures, the server still returns "bad certificate". -
    • -
-

-
-
- -
crypto/x509
-
-

- RevocationList.RevokedCertificates has been deprecated and replaced with the new RevokedCertificateEntries field, which is a slice of RevocationListEntry. RevocationListEntry contains all of the fields in pkix.RevokedCertificate, as well as the revocation reason code. -

- -

- Name constraints are now correctly enforced on non-leaf certificates, and - not on the certificates where they are expressed. -

-
-
- -
debug/elf
-
-

- The new - File.DynValue - method may be used to retrieve the numeric values listed with a - given dynamic tag. -

- -

- The constant flags permitted in a DT_FLAGS_1 - dynamic tag are now defined with type - DynFlag1. These - tags have names starting with DF_1. -

- -

- The package now defines the constant - COMPRESS_ZSTD. -

- -

- The package now defines the constant - R_PPC64_REL24_P9NOTOC. -

-
-
- -
debug/pe
-
-

- Attempts to read from a section containing uninitialized data - using - Section.Data - or the reader returned by Section.Open - now return an error. -

-
-
- -
embed
-
-

- The io/fs.File - returned by - FS.Open now - has a ReadAt method that - implements io.ReaderAt. -

- -

- Calling FS.Open.Stat - will return a type that now implements a String - method that calls - io/fs.FormatFileInfo. -

-
-
- -
errors
-
-

- The new - ErrUnsupported - error provides a standardized way to indicate that a requested - operation may not be performed because it is unsupported. - For example, a call to - os.Link when using a - file system that does not support hard links. -

-
-
- -
flag
-
-

- The new BoolFunc - function and - FlagSet.BoolFunc - method define a flag that does not require an argument and calls - a function when the flag is used. This is similar to - Func but for a - boolean flag. -

- -

- A flag definition - (via Bool, - BoolVar, - Int, - IntVar, etc.) - will panic if Set has - already been called on a flag with the same name. This change is - intended to detect cases where changes in - initialization order 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 - Set operations. -

-
-
- -
go/ast
-
-

- The new IsGenerated predicate - reports whether a file syntax tree contains the - special comment - that conventionally indicates that the file was generated by a tool. -

-
- -
-

- The new - File.GoVersion - field records the minimum Go version required by - any //go:build or // +build - directives. -

-
-
- -
go/build
-
-

- The package now parses build directives (comments that start - with //go:) in file headers (before - the package declaration). These directives are - available in the new - Package fields - Directives, - TestDirectives, - and - XTestDirectives. -

-
-
- -
go/build/constraint
-
-

- The new - GoVersion - function returns the minimum Go version implied by a build - expression. -

-
-
- -
go/token
-
-

- The new File.Lines method - returns the file's line-number table in the same form as accepted by - File.SetLines. -

-
-
- -
go/types
-
-

- The new Package.GoVersion - method returns the Go language version used to check the package. -

-
-
- -
hash/maphash
-
-

- The hash/maphash package now has a pure Go implementation, selectable with the purego build tag. -

-
-
- -
html/template
-
-

- The new error - ErrJSTemplate - is returned when an action appears in a JavaScript template - literal. Previously an unexported error was returned. -

-
-
- -
io/fs
-
-

- The new - FormatFileInfo - function returns a formatted version of a - FileInfo. - The new - FormatDirEntry - function returns a formatted version of a - DirEntry. - The implementation of - DirEntry - returned by - ReadDir now - implements a String method that calls - FormatDirEntry, - and the same is true for - the DirEntry - value passed to - WalkDirFunc. -

-
-
- - - - - -
math/big
-
-

- The new Int.Float64 - method returns the nearest floating-point value to a - multi-precision integer, along with an indication of any - rounding that occurred. -

-
-
- -
net
-
-

- - - On Linux, the net 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 - Dialer.SetMultipathTCP - method before calling the - Dialer.Dial or - Dialer.DialContext - methods. To use Multipath TCP when available on a server, call - the - ListenConfig.SetMultipathTCP - method before calling the - ListenConfig.Listen - method. Specify the network as "tcp" or - "tcp4" or "tcp6" 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 - TCPConn.MultipathTCP - method. -

-

- In a future Go release we may enable Multipath TCP by default on - systems that support it. -

-
-
- -
net/http
-
-

- The new ResponseController.EnableFullDuplex - 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 - EnableFullDuplex method disables this behavior. -

- -

- The new ErrSchemeMismatch error is returned by Client and Transport when the server responds to an HTTPS request with an HTTP response. -

- -

- The net/http package now supports - errors.ErrUnsupported, - in that the expression - errors.Is(http.ErrNotSupported, errors.ErrUnsupported) - will return true. -

-
-
- -
os
-
-

- Programs may now pass an empty time.Time value to - the Chtimes function - to leave either the access time or the modification time unchanged. -

- -

- On Windows the - File.Chdir method - now changes the current directory to the file, rather than - always returning an error. -

- -

- On Unix systems, if a non-blocking descriptor is passed - to NewFile, calling - the File.Fd method - will now return a non-blocking descriptor. Previously the - descriptor was converted to blocking mode. -

- -

- On Windows calling - Truncate on a - non-existent file used to create an empty file. It now returns - an error indicating that the file does not exist. -

- -

- On Windows calling - TempDir 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. -

- -

- On Windows the os package now supports working with files whose - names, stored as UTF-16, can't be represented as valid UTF-8. -

- -

- On Windows Lstat now resolves - symbolic links for paths ending with a path separator, consistent with its - behavior on POSIX platforms. -

- -

- The implementation of the - io/fs.DirEntry - interface returned by the - ReadDir function and - the File.ReadDir - method now implements a String method that calls - io/fs.FormatDirEntry. -

- -

- The implementation of the - io/fs.FS interface returned by - the DirFS function now implements - the io/fs.ReadFileFS and - the io/fs.ReadDirFS - interfaces. -

-
-
- -
path/filepath
-
-

- The implementation of the - io/fs.DirEntry - interface passed to the function argument of - WalkDir - now implements a String method that calls - io/fs.FormatDirEntry. -

-
-
- - - -
reflect
-
-

- 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. -

- -

- The new Value - method Value.Clear - clears the contents of a map or zeros the contents of a slice. - This corresponds to the new clear built-in - added to the language. -

- -

- The SliceHeader - and StringHeader - types are now deprecated. In new code - prefer unsafe.Slice, - unsafe.SliceData, - unsafe.String, - or unsafe.StringData. -

-
-
- -
regexp
-
-

- Regexp now defines - MarshalText - and UnmarshalText - methods. These implement - encoding.TextMarshaler - and - encoding.TextUnmarshaler - and will be used by packages such as - encoding/json. -

-
-
- -
runtime
-
-

- Textual stack traces produced by Go programs, such as those - produced when crashing, calling runtime.Stack, or - collecting a goroutine profile with debug=2, now - include the IDs of the goroutines that created each goroutine in - the stack trace. -

- -

- Crashing Go applications can now opt-in to Windows Error Reporting (WER) by setting the environment variable - GOTRACEBACK=wer or calling debug.SetTraceback("wer") - before the crash. Other than enabling WER, the runtime will behave as with GOTRACEBACK=crash. - On non-Windows systems, GOTRACEBACK=wer is ignored. -

- -

- GODEBUG=cgocheck=2, a thorough checker of cgo pointer passing rules, - is no longer available as a debug option. - Instead, it is available as an experiment using GOEXPERIMENT=cgocheck2. - In particular this means that this mode has to be selected at build time instead of startup time. -

- -

- GODEBUG=cgocheck=1 is still available (and is still the default). -

- -

- 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. -

- - -
-
- -
runtime/metrics
-
-

- A few previously-internal GC metrics, such as live heap size, are - now available. - - GOGC and GOMEMLIMIT are also now - available as metrics. -

-
-
- -
runtime/trace
-
-

- 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. -

-
-
- -
sync
-
-

- The new OnceFunc, - OnceValue, and - OnceValues - functions capture a common use of Once to - lazily initialize a value on first use. -

-
-
- -
syscall
-
-

- On Windows the - Fchdir function - now changes the current directory to its argument, rather than - always returning an error. -

- -

- On FreeBSD - SysProcAttr - has a new field Jail that may be used to put the - newly created process in a jailed environment. -

- -

- 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 UTF16ToString - and UTF16FromString - functions now convert between UTF-16 data and - WTF-8 strings. - This is backward compatible as WTF-8 is a superset of the UTF-8 - format that was used in earlier releases. -

- -

- Several error values match the new - errors.ErrUnsupported, - such that errors.Is(err, errors.ErrUnsupported) - returns true. -

    -
  • ENOSYS
    • -
  • ENOTSUP
    • -
  • EOPNOTSUPP
    • -
  • EPLAN9 (Plan 9 only)
    • -
  • ERROR_CALL_NOT_IMPLEMENTED (Windows only)
    • -
  • ERROR_NOT_SUPPORTED (Windows only)
    • -
  • EWINDOWS (Windows only)
    • -
-

-
-
- -
testing
-
-

- The new -test.fullpath option will print full path - names in test log messages, rather than just base names. -

- -

- The new Testing function reports whether the program is a test created by go test. -

-
-
- -
testing/fstest
-
-

- Calling Open.Stat - will return a type that now implements a String - method that calls - io/fs.FormatFileInfo. -

-
-
- -
unicode
-
-

- The unicode package and - associated support throughout the system has been upgraded to - Unicode 15.0.0. -

-
-
- -

Ports

- -

Darwin

- -

- As announced in the Go 1.20 release notes, - Go 1.21 requires macOS 10.15 Catalina or later; - support for previous versions has been discontinued. -

- -

Windows

- -

- As announced 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. -

- - -

- -

- -

WebAssembly

- -

- The new go:wasmimport directive can now be used in Go programs - to import functions from the WebAssembly host. -

- - -

- The Go scheduler now interacts much more efficiently with the - JavaScript event loop, especially in applications that block - frequently on asynchronous events. -

- - -

WebAssembly System Interface

- -

- 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. -

- -

ppc64/ppc64le

- -

- On Linux, GOPPC64=power10 now generates PC-relative instructions, prefixed - instructions, and other new Power10 instructions. On AIX, GOPPC64=power10 - generates Power10 instructions, but does not generate PC-relative instructions. -

- -

- When building position-independent binaries for GOPPC64=power10 - GOOS=linux GOARCH=ppc64le, users can expect reduced binary - sizes in most cases, in some cases 3.5%. Position-independent binaries are built for - ppc64le with the following -buildmode values: - c-archive, c-shared, shared, pie, plugin. -

- -

loong64

- -

- The linux/loong64 port now supports -buildmode=c-archive, - -buildmode=c-shared and -buildmode=pie. -

- - - - - - - - - - - - - - - - - -