Go 1.22 is not yet released. These are work-in-progress release notes. Go 1.22 is expected to be released in February 2024.
Go 1.22 makes two changes to "for" loops.
package main
import "fmt"
func main() {
for i := range 10 {
fmt.Println(10 - i)
}
fmt.Println("go1.22 has lift-off!")
}
See the spec for details.
Go 1.22 includes a preview of a language change we are considering
for a future version of Go: range-over-function iterators.
Building with GOEXPERIMENT=rangefunc enables this feature.
Commands in workspaces can now
use a vendor directory containing the dependencies of the
workspace. The directory is created by
go work vendor,
and used by build commands when the -mod flag is set to
vendor, which is the default when a workspace vendor
directory is present.
Note that the vendor directory's contents for a workspace are different
from those of a single module: if the directory at the root of a workspace also
contains one of the modules in the workspace, its vendor directory
can contain the dependencies of either the workspace or of the module,
but not both.
go get is no longer supported outside of a module in the
legacy GOPATH mode (that is, with GO111MODULE=off).
Other build commands, such as go build and
go test, will continue to work indefinitely
for legacy GOPATH programs.
go test -cover now prints coverage summaries for covered
packages that do not have their own test files. Prior to Go 1.22 a
go test -cover run for such a package would report
? mymod/mypack [no test files]
and now with Go 1.22, functions in the package are treated as uncovered:
mymod/mypack coverage: 0.0% of statements
The trace tool's web UI has been gently refreshed as part of the
work to support the new tracer, resolving several issues and improving the
readability of various sub-pages.
The web UI now supports exploring traces in a thread-oriented view.
The trace viewer also now displays the full duration of all system calls.
These improvements only apply for viewing traces produced by programs built with
Go 1.22 or newer.
A future release will bring some of these improvements to traces produced by older
version of Go.
TODO: https://go.dev/cl/539016: go/analysis/passes/loopclosure: disable checker after go1.22.; loopclosure was modified to only not report in files with GoVersion after 1.22.
The vet tool now reports calls to
append that pass
no values to be appended to the slice, such as slice = append(slice).
Such a statement has no effect, and experience has shown that is nearly always a mistake.
time.Since
The vet tool now reports a non-deferred call to
time.Since(t) within a defer statement.
This is equivalent to calling time.Now().Sub(t) before the defer statement,
not when the deferred function is called. In nearly all cases, the correct code
requires deferring the time.Since call. For example:
t := time.Now()
defer log.Println(time.Since(t)) // non-deferred call to time.Since
tmp := time.Since(t); defer log.Println(tmp) // equivalent to the previous defer
defer func() {
log.Println(time.Since(t)) // a correctly deferred call to time.Since
}()
log/slog calls
The vet tool now reports invalid arguments in calls to functions and methods
in the structured logging package, log/slog,
that accept alternating key/value pairs.
It reports calls where an argument in a key position is neither a
string nor a slog.Attr, and where a final key is missing its value.
The runtime now keeps type-based garbage collection metadata nearer to each heap object, improving the CPU performance (latency or throughput) of Go programs by 1–3%. This change also reduces the memory overhead of the majority Go programs by approximately 1% by deduplicating redundant metadata. Some programs may see a smaller improvement because this change adjusts the size class boundaries of the memory allocator, so some objects may be moved up a size class.
A consequence of this change is that some objects' addresses that were previously
always aligned to a 16 byte (or higher) boundary will now only be aligned to an 8
byte boundary.
Some programs that use assembly instructions that require memory addresses to be
more than 8-byte aligned and rely on the memory allocator's previous alignment behavior
may break, but we expect such programs to be rare.
Such programs may be built with GOEXPERIMENT=noallocheaders to revert
to the old metadata layout and restore the previous alignment behavior, but package
owners should update their assembly code to avoid the alignment assumption, as this
workaround will be removed in a future release.
On the windows/amd64 port, programs linking or loading Go libraries built with
-buildmode=c-archive or -buildmode=c-shared can now use
the SetUnhandledExceptionFilter Win32 function to catch exceptions not handled
by the Go runtime. Note that this was already supported on the windows/386 port.
Profile-guided Optimization (PGO) builds can now devirtualize a higher proportion of calls than previously possible. Most programs from a representative set of Go programs now see between 2 and 14% improvement from enabling PGO.
The compiler now interleaves devirtualization and inlining, so interface method calls are better optimized.
Go 1.22 also includes a preview of an enhanced implementation of the compiler's inlining phase that uses heuristics to boost inlinability at call sites deemed "important" (for example, in loops) and discourage inlining at call sites deemed "unimportant" (for example, on panic paths).
Building with GOEXPERIMENT=newinliner enables the new call-site
heuristics; see issue #61502 for
more info and to provide feedback.
The linker's -s and -w flags are now behave more
consistently across all platforms.
The -w flag suppresses DWARF debug information generation.
The -s flag suppresses symbol table generation.
The -s flag also implies the -w flag, which can be
negated with -w=0.
That is, -s -w=0 will generate a binary with DWARF
debug information generation but without the symbol table.
On ELF platforms, the -B linker flag now accepts a special form:
with -B gobuildid, the linker will generate a GNU
build ID (the ELF NT_GNU_BUILD_ID note) derived from the Go
build ID.
On Windows, when building with -linkmode=internal, the linker now
preserves SEH information from C object files by copying the .pdata
and .xdata sections into the final binary.
This helps with debugging and profiling binaries using native tools, such as WinDbg.
Note that until now, C functions' SEH exception handlers were not being honored,
so this change may cause some programs to behave differently.
-linkmode=external is not affected by this change, as external linkers
already preserve SEH information.
As mentioned in the Go 1.20 release notes, Go 1.22 now requires the final point release of Go 1.20 or later for bootstrap. We expect that Go 1.24 will require the final point release of Go 1.22 or later for bootstrap.
Go 1.22 includes the first “v2” package in the standard library,
math/rand/v2.
The changes compared to math/rand are
detailed in proposal #61716. The most important changes are:
Read method, deprecated in math/rand,
was not carried forward for math/rand/v2.
(It remains available in math/rand.)
The vast majority of calls to Read should use
crypto/rand’s Read instead.
Otherwise a custom Read can be constructed using the Uint64 method.
Source
interface now has a single Uint64 method;
there is no Source64 interface.
math/rand
because they changed the output streams.
Intn,
Int31,
Int31n,
Int63,
and
Int64n
top-level functions and methods from math/rand
are spelled more idiomatically in math/rand/v2:
IntN,
Int32,
Int32N,
Int64,
and
Int64N.
There are also new top-level functions and methods
Uint32,
Uint32N,
Uint64,
Uint64N,
Uint,
and
UintN.
N
is like
Int64N or
Uint64N
but works for any integer type.
For example a random duration from 0 up to 5 minutes is
rand.N(5*time.Minute).
math/rand’s Source
has been replaced by two more modern pseudo-random generator sources:
ChaCha8
PCG.
ChaCha8 is a new, cryptographically strong random number generator
roughly similar to PCG in efficiency.
ChaCha8 is the algorithm used for the top-level functions in math/rand/v2.
As of Go 1.22, math/rand's top-level functions (when not explicitly seeded)
and the Go runtime also use ChaCha8 for randomness.
We plan to include an API migration tool in a future release, likely Go 1.23.
HTTP routing in the standard library is now more expressive.
The patterns used by net/http.ServeMux have been enhanced to accept methods and wildcards.
Registering a handler with a method, like "POST /items/create", restricts
invocations of the handler to requests with the given method. A pattern with a method takes precedence over a matching pattern without one.
As a special case, registering a handler with "GET" also registers it with "HEAD".
Wildcards in patterns, like /items/{id}, match segments of the URL path.
The actual segment value may be accessed by calling the Request.PathValue method.
A wildcard ending in "...", like /files/{path...}, must occur at the end of a pattern and matches all the remaining segments.
A pattern that ends in "/" matches all paths that have it as a prefix, as always.
To match the exact pattern including the trailing slash, end it with {$},
as in /exact/match/{$}.
If two patterns overlap in the requests that they match, then the more specific pattern takes precedence. If neither is more specific, the patterns conflict. This rule generalizes the original precedence rules and maintains the property that the order in which patterns are registered does not matter.
This change breaks backwards compatiblity in small ways, some obvious—patterns with "{" and "}" behave differently—
and some less so—treatment of escaped paths has been improved.
The change is controlled by a GODEBUG field named httpmuxgo121.
Set httpmuxgo121=1 to restore the old behavior.
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: complete this section
The new method Writer.AddFS adds all of the files from an fs.FS to the archive.
If the argument to FileInfoHeader implements the new FileInfoNames interface, then the interface methods will be used to set the UID/GID of the file header. This allows applications to override the default UID/GID resolution.
The new method Writer.AddFS adds all of the files from an fs.FS to the archive.
When a SplitFunc returns ErrFinalToken with a nil token, Scanner will now stop immediately.
Previously, it would report a final empty token before stopping, which was usually not desired.
Callers that do want to report a final empty token can do so by returning []byte{} rather than nil.
The new function Or returns the first in a sequence of values that is not the zero value.
ConnectionState.ExportKeyingMaterial will now
return an error unless TLS 1.3 is in use, or the extended_master_secret extension is supported by both the server and
client. crypto/tls has supported this extension since Go 1.20. This can be disabled with the
tlsunsafeekm=1 GODEBUG setting.
By default, the minimum version offered by crypto/tls servers is now TLS 1.2 if not specified with
config.MinimumVersion, matching the behavior of crypto/tls
clients. This change can be reverted with the tls10server=1 GODEBUG setting.
By default, cipher suites without ECDHE support are no longer offered by either clients or servers during pre-TLS 1.3
handshakes. This change can be reverted with the tlsrsakex=1 GODEBUG setting.
The new CertPool.AddCertWithConstraint
method can be used to add customized constraints to root certificates to be applied during chain building.
On Android, root certificates will now be loaded from /data/misc/keychain/certs-added as well as /system/etc/security/cacerts.
A new type, OID, supports ASN.1 Object Identifiers with individual
components larger than 31 bits. A new field which uses this type, Policies,
is added to the Certificate struct, and is now populated during parsing. Any OIDs which cannot be represented
using a asn1.ObjectIdentifier will appear in Policies,
but not in the old PolicyIdentifiers field.
When calling CreateCertificate, the Policies field is ignored, and
policies are taken from the PolicyIdentifiers field. Using the x509usepolicies=1 GODEBUG setting inverts this,
populating certificate policies from the Policies field, and ignoring the PolicyIdentifiers field. We may change the
default value of x509usepolicies in Go 1.23, making Policies the default field for marshaling.
The new Null[T] type
provide a way to scan nullable columns for any column types.
Constant R_MIPS_PC32 is defined for use with MIPS64 systems.
Additional R_LARCH_* constants are defined for use with LoongArch systems.
The new methods AppendEncode and AppendDecode added to
each of the Encoding types in the packages
encoding/base32,
encoding/base64, and
encoding/hex
simplify encoding and decoding from and to byte slices by taking care of byte slice buffer management.
The methods
base32.Encoding.WithPadding and
base64.Encoding.WithPadding
now panic if the padding argument is a negative value other than
NoPadding.
Marshaling and encoding functionality now escapes
'\b' and '\f' characters as
\b and \f instead of
\u0008 and \u000c.
The following declarations related to
syntactic identifier resolution
are now deprecated:
Ident.Obj,
Object,
Scope,
File.Scope,
File.Unresolved,
Importer,
Package,
NewPackage.
Identifiers cannot be accurately resolved without type information.
Consider, for example, the identifier K
in T{K: ""}: it could be the name of a local variable
if T is a map type, or the name of a field if T is a struct type.
New programs should use the go/types
package to resolve identifiers;
see Object, Info.Uses,
and Info.Defs for details.
The new ast.Unparen
function removes any enclosing
parentheses from
an expression.
The new Alias type represents type aliases.
Previously, type aliases were not represented explicitly, so a reference to a type alias was equivalent
to spelling out the aliased type, and the name of the alias was lost.
The new representation retains the intermediate Alias.
This enables improved error reporting (the name of a type alias can be reported), and allows for better handling
of cyclic type declarations involving type aliases.
In a future release, Alias types will also carry type parameter information.
The new function Unalias returns the actual type denoted by an
Alias type (or any other Type for that matter).
Because Alias types may break existing type switches that do not know to check for them,
this functionality is controlled by a GODEBUG field named gotypesalias.
With gotypesalias=0, everything behaves as before, and Alias types are never created.
With gotypesalias=1, Alias types are created and clients must expect them.
The default is gotypesalias=0.
In a future release, the default will be changed to gotypesalias=1.
Clients of go/types are urged to adjust their code as soon as possible
to work with gotypesalias=1 to eliminate problems early.
The Info struct now exports the
FileVersions map
which provides per-file Go version information.
The new helper method PkgNameOf returns the local package name
for the given import declaration.
The implementation of SizesFor has been adjusted to compute
the same type sizes as the compiler when the compiler argument for SizesFor is "gc".
The default Sizes implementation used by the type checker is now
types.SizesFor("gc", "amd64").
The start position (Pos)
of the lexical environment block (Scope)
that represents a function body has changed:
it used to start at the opening curly brace of the function body,
but now starts at the function's func token.
The new go/version package implements functions
for validating and comparing Go version strings.
TODO: https://go.dev/issue/61619: allow actions in JS template literals
TODO: https://go.dev/cl/507995: html/template: support parsing complex JS template literals; modified api/next/61619.txt
The new SectionReader.Outer method returns the ReaderAt, offset, and size passed to NewSectionReader.
The new SetLogLoggerLevel function
controls the level for the bridge between the `slog` and `log` packages. It sets the minimum level
for calls to the top-level `slog` logging functions, and it sets the level for calls to `log.Logger`
that go through `slog`.
The new method Rat.FloatPrec computes the number of fractional decimal digits required to represent a rational number accurately as a floating-point number, and whether accurate decimal representation is possible in the first place.
When io.Copy copies
from a TCPConn to a UnixConn,
it will now use Linux's splice(2) system call if possible,
using the new method TCPConn.WriteTo.
The Go DNS Resolver, used when building with "-tags=netgo",
now searches for a matching name in the Windows hosts file,
located at %SystemRoot%\System32\drivers\etc\hosts,
before making a DNS query.
The new functions
ServeFileFS,
FileServerFS, and
NewFileTransportFS
are versions of the existing
ServeFile, FileServer, and NewFileTransport,
operating on an fs.FS.
The HTTP server and client now reject requests and responses containing
an invalid empty Content-Length header.
The previous behavior may be restored by setting
GODEBUG field httplaxcontentlength=1.
TODO: https://go.dev/cl/528355: net/http: implement path value methods on Request; modified api/next/61410.txt
TODO: https://go.dev/cl/539615: net/http/cgi: the PATH_INFO should be empty or start with a slash
TODO: https://go.dev/issue/61642: add Prefix.Compare and AddrPort.Compare
TODO: https://go.dev/cl/524616: net/netip: add AddrPort.Compare and Prefix.Compare; modified api/next/61642.txt
On Windows, the Stat function now follows all reparse points
that link to another named entity in the system.
It was previously only following IO_REPARSE_TAG_SYMLINK and
IO_REPARSE_TAG_MOUNT_POINT reparse points.
On Windows, passing O_SYNC to OpenFile now causes write operations to go directly to disk, equivalent to O_SYNC on Unix platforms.
On Windows, the ReadDir,
File.ReadDir,
File.Readdir,
and File.Readdirnames functions
now read directory entries in batches to reduce the number of system calls,
improving performance up to 30%.
When io.Copy copies
from a File to a net.UnixConn,
it will now use Linux's sendfile(2) system call if possible,
using the new method File.WriteTo.
On Windows, LookPath now
ignores empty entries in %PATH%, and returns
ErrNotFound (instead of ErrNotExist) if
no executable file extension is found to resolve an otherwise-unambiguous
name.
On Windows, Command and
Cmd.Start no
longer call LookPath if the path to the executable is already
absolute and has an executable file extension. In addition,
Cmd.Start no longer writes the resolved extension back to
the Path field,
so it is now safe to call the String method concurrently
with a call to Start.
The Value.IsZero
method will now return true for a floating-point or complex
negative zero, and will return true for a struct value if a
blank field (a field named _) somehow has a
non-zero value.
These changes make IsZero consistent with comparing
a value to zero using the language == operator.
The PtrTo function is deprecated,
in favor of PointerTo.
The new function TypeFor
returns the Type that represents
the type argument T.
Previously, to get the reflect.Type value for a type, one had to use
reflect.TypeOf((*T)(nil)).Elem().
This may now be written as reflect.TypeFor[T]().
Four new histogram metrics
/sched/pauses/stopping/gc:seconds,
/sched/pauses/stopping/other:seconds,
/sched/pauses/total/gc:seconds, and
/sched/pauses/total/other:seconds provide additional details
about stop-the-world pauses.
The "stopping" metrics report the time taken from deciding to stop the
world until all goroutines are stopped.
The "total" metrics report the time taken from deciding to stop the world
until it is started again.
The /gc/pauses:seconds metric is deprecated, as it is
equivalent to the new /sched/pauses/total/gc:seconds metric.
/sync/mutex/wait/total:seconds now includes contention on
runtime-internal locks in addition to
sync.Mutex and
sync.RWMutex.
Mutex profiles now scale contention by the number of goroutines blocked on the mutex. This provides a more accurate representation of the degree to which a mutex is a bottleneck in a Go program. For instance, if 100 goroutines are blocked on a mutex for 10 milliseconds, a mutex profile will now record 1 second of delay instead of 10 milliseconds of delay.
Mutex profiles also now include contention on runtime-internal locks in addition to
sync.Mutex and
sync.RWMutex.
Contention on runtime-internal locks is always reported at runtime._LostContendedRuntimeLock.
A future release will add complete stack traces in these cases.
CPU profiles on Darwin platforms now contain the process's memory map, enabling the disassembly view in the pprof tool.
The execution tracer has been completely overhauled in this release, resolving several long-standing issues and paving the way for new use-cases for execution traces.
Execution traces now use the operating system's clock on most platforms (Windows excluded) so it is possible to correlate them with traces produced by lower-level components. Execution traces no longer depend on the reliability of the platform's clock to produce a correct trace. Execution traces are now partitioned regularly on-the-fly and as a result may be processed in a streamable way. Execution traces now contain complete durations for all system calls. Execution traces now contain information about the operating system threads that goroutines executed on. The latency impact of starting and stopping execution traces has been dramatically reduced. Execution traces may now begin or end during the garbage collection mark phase.
To allow Go developers to take advantage of these improvements, an experimental trace reading package is available at golang.org/x/exp/trace. Note that this package only works on traces produced by programs built with Go 1.22 at the moment. Please try out the package and provide feedback on the corresponding proposal issue.
If you experience any issues with the new execution tracer implementation, you may switch back to the
old implementation by building your Go program with GOEXPERIMENT=noexectracer2.
If you do, please file an issue, otherwise this option will be removed in a future release.
The new function Concat concatenates multiple slices.
Functions that shrink the size of a slice (Delete, DeleteFunc, Compact, CompactFunc, and Replace) now zero the elements between the new length and the old length.
Insert now always panics if the argument i is out of range. Previously it did not panic in this situation if there were no elements to be inserted.
The syscall package has been frozen since Go 1.4 and was marked as deprecated in Go 1.11, causing many editors to warn about any use of the package.
However, some non-deprecated functionality requires use of the syscall package, such as the os/exec.Cmd.SysProcAttr field.
To avoid unnecesary complaints on such code, the syscall package is no longer marked as deprecated.
The package remains frozen to most new functionality, and new code remains encouraged to use golang.org/x/sys/unix or golang.org/x/sys/windows where possible.
On Linux, the new SysProcAttr.PidFD field allows obtaining a PID FD when starting a child process via StartProcess or os/exec.
On Windows, passing O_SYNC to Open now causes write operations to go directly to disk, equivalent to O_SYNC on Unix platforms.
The new Run function uses sub-tests to run test cases,
providing finer-grained control.
On macOS on 64-bit x86 architecture (the darwin/amd64 port),
the Go toolchain now generates position-independent executables (PIE) by default.
Non-PIE binaries can be generated by specifying the -buildmode=exe
build flag.
On 64-bit ARM-based macOS (the darwin/arm64 port),
the Go toolchain already generates PIE by default.
Go 1.22 is the last release that will run on macOS 10.15 Catalina. Go 1.23 will require macOS 11 Big Sur or later.
The GOARM environment variable now allows you to select whether to use software or hardware floating point.
Previously, valid GOARM values were 5, 6, or 7. Now those same values can
be optionally followed by ,softfloat or ,hardfloat to select the floating-point implementation.
This new option defaults to softfloat for version 5 and hardfloat for versions
6 and 7.
The loong64 port now supports passing function arguments and results using registers.
The linux/loong64 port now supports the address sanitizer, memory sanitizer, new-style linker relocations, and the plugin build mode.
Go 1.22 adds an experimental port to OpenBSD on big-endian 64-bit PowerPC
(openbsd/ppc64).