Go 1.20 is not yet released. These are work-in-progress release notes. Go 1.20 is expected to be released in February 2023.
Go 1.20 includes three changes to the language.
Go 1.17 added conversions from slice to an array pointer.
Go 1.20 extends this to allow conversions from a slice to an array:
given a slice x, [4]byte(x) can now be written
instead of *(*[4]byte)(x).
The unsafe package defines
three new functions SliceData, String, and StringData.
Along with Go 1.17's Slice, these functions now provide the complete ability to
construct and deconstruct slice and string values, without depending on their exact representation.
The specification now defines that struct values are compared one field at a time, considering fields in the order they appear in the struct type definition, and stopping at the first mismatch. The specification could previously have been read as if all fields needed to be compared beyond the first mismatch. Similarly, the specification now defines that array values are compared one element at a time, in increasing index order. In both cases, the difference affects whether certain comparisons must panic. Existing programs are unchanged: the new spec wording describes what the implementations have always done.
TODO: complete this section, or delete if not needed
TODO: https://go.dev/issue/53466: add freebsd/riscv64 port
The directory $GOROOT/pkg no longer stores
pre-compiled package archives for the standard library:
go install no longer writes them,
the go build no longer checks for them,
and the Go distribution no longer ships them.
Instead, packages in the standard library are built as needed
and cached in the build cache, just like packages outside GOROOT.
This change reduces the size of the Go distribution and also
avoids C toolchain skew for packages that use cgo.
The implementation of go test -json
has been improved to make it more robust.
Programs that run go test -json
do not need any updates.
Programs that invoke go tool test2json
directly should now run the test binary with -v=json
(for example, go test -v=json
or ./pkg.test -test.v=json)
instead of plain -v.
A related change to go test -json
is the addition of an event with Action set to start
at the beginning of each test program's execution.
When running multiple tests using the go command,
these start events are guaranteed to be emitted in the same order as
the packages named on the command line.
The go command now defines
architecture feature build tags, such as amd64.v2,
to allow selecting a package implementation file based on the presence
or absence of a particular architecture feature.
See go help buildconstraint for details.
The go subcommands now accept
-C <dir> to change directory to <dir>
before performing the command, which may be useful for scripts that need to
execute commands in multiple different modules.
The go build and go test
commands no longer accept the -i flag,
which has been deprecated since Go 1.16.
The go generate command now accepts
-skip <pattern> to skip //go:generate directives
matching <pattern>.
The go test command now accepts
-skip <pattern> to skip tests, subtests, or examples
matching <pattern>.
When the main module is located within GOPATH/src,
go install no longer installs libraries for
non-main packages to GOPATH/pkg,
and go list no longer reports a Target
field for such packages. (In module mode, compiled packages are stored in the
build cache
only, but a bug had caused
the GOPATH install targets to unexpectedly remain in effect.)
go version
The go version -m command
now supports reading more types of Go binaries, most notably, Windows DLLs
built with go build -buildmode=c-shared
and Linux binaries without execute permission.
The go command now disables cgo by default
on systems without a C toolchain.
More specifically, when the CGO_ENABLED environment variable is unset,
the CC environment variable is unset,
and the default C compiler (typically clang or gcc)
is not found in the path,
CGO_ENABLED defaults to 0.
As always, you can override the default by setting CGO_ENABLED explicitly.
The most important effect of the default change is that when Go is installed on a system without a C compiler, it will now use pure Go builds for packages in the standard library that use cgo, instead of using pre-distributed package archives (which have been removed, as noted above) or attempting to use cgo and failing. This makes Go work better in some minimal container environments as well as on macOS, where pre-distributed package archives have not been used for cgo-based packages since Go 1.16.
The packages in the standard library that use cgo are net, os/user, and plugin. On macOS, the net and os/user packages have been rewritten not to use cgo: the same code is now used for cgo and non-cgo builds as well as cross-compiled builds. On Windows, the net and os/user packages have never used cgo. On other systems, builds with cgo disabled will use a pure Go version of these packages.
On macOS, the race detector has been rewritten not to use cgo: race-detector-enabled programs can be built and run without Xcode. On Linux and other Unix systems, and on Windows, a host C toolchain is required to use the race detector.
TODO coverage
The vet tool now reports references to loop variables following
a call to T.Parallel()
within subtest function bodies. Such references may observe the value of the
variable from a different iteration (typically causing test cases to be
skipped) or an invalid state due to unsynchronized concurrent access.
The tool also detects reference mistakes in more places. Previously it would only consider the last statement of the loop body, but now it recursively inspects the last statements within if, switch, and select statements.
The vet tool now reports use of the time format 2006-02-01 (yyyy-dd-mm)
with Time.Format and
time.Parse.
This format does not appear in common date standards, but is frequently
used by mistake when attempting to use the ISO 8601 date format
(yyyy-mm-dd).
TODO: complete this section, or delete if not needed
TODO: https://go.dev/issue/49390: clarify whether "-l" and "-N" compiler flags are actually supported
TODO: complete this section, or delete if not needed
When building a Go release from source and GOROOT_BOOTSTRAP is not set, previous versions of Go looked for a Go 1.4 or later bootstrap toolchain in the directory $HOME/go1.4 (%HOMEDRIVE%%HOMEPATH%\go1.4 on Windows). Go 1.18 and Go 1.19 looked first for $HOME/go1.17 or $HOME/sdk/go1.17 before falling back to $HOME/go1.4, in ancitipation of requiring Go 1.17 for use when bootstrapping Go 1.20. Go 1.20 does require a Go 1.17 release for bootstrapping, but we realized that we should adopt the latest point release of the bootstrap toolchain, so it requires Go 1.17.13. Go 1.20 looks for $HOME/go1.17.13 or $HOME/sdk/go1.17.13 before falling back to $HOME/go1.4 (to support systems that hard-coded the path $HOME/go1.4 but have installed a newer Go toolchain there). In the future, we plan to move the bootstrap toolchain forward approximately once a year, and in particular we expect that Go 1.22 will require the final point release of Go 1.20 for bootstrap.
crypto/ecdh packageTODO: complete this section
Go 1.20 expands support for error wrapping to permit an error to wrap multiple other errors.
An error e can wrap more than one error by providing
an Unwrap method that returns a []error.
The errors.Is and
errors.As functions
have been updated to inspect multiply wrapped errors.
The fmt.Errorf function
now supports multiple occurrances of the %w format verb,
which will cause it to return an error that wraps all of those error operands.
The new function errors.Join
returns an error wrapping a list of errors.
The new
"net/http".ResponseController
type provides access to extended per-request functionality not handled by the
"net/http".ResponseWriter interface.
Previously, we have added new per-request functionality by defining optional
interfaces which a ResponseWriter can implement, such as
Flusher. These interfaces
are not discoverable and clumsy to use.
The ResponseController type provides a clearer, more discoverable way
to add per-handler controls. Two such controls also added in Go 1.20 are
SetReadDeadline and SetWriteDeadline, which allow setting
per-request read and write deadlines. For example:
func RequestHandler(w ResponseWriter, r *Request) {
rc := http.NewResponseController(w)
rc.SetWriteDeadline(0) // disable Server.WriteTimeout when sending a large response
io.Copy(w, bigData)
}
The httputil.ReverseProxy
forwarding proxy includes a new Rewrite hook function, superseding the
previous Director hook.
The Rewrite hook accepts a
ProxyRequest parameter,
which includes both the inbound request received by the proxy and the outbound
request that it will send.
Unlike Director hooks, which only operate on the outbound request,
this permits Rewrite hooks to avoid certain scenarios where
a malicious inbound request may cause headers added by the hook
to be removed before forwarding.
See issue #50580.
The ProxyRequest.SetURL
method routes the outbound request to a provided destination
and supersedes the NewSingleHostReverseProxy function.
Unlike NewSingleHostReverseProxy, SetURL
also sets the Host header of the outbound request.
The
ProxyRequest.SetXForwarded
method sets the X-Forwarded-For, X-Forwarded-Host,
and X-Forwarded-Proto headers of the outbound request.
When using a Rewrite, these headers are not added by default.
An example of a Rewrite hook using these features is:
proxyHandler := &httputil.ReverseProxy{
Rewrite: func(r *httputil.ProxyRequest) {
r.SetURL(outboundURL) // Forward request to outboundURL.
r.SetXForwarded() // Set X-Forwarded-* headers.
r.Out.Header.Set("X-Additional-Header", "header set by the proxy")
},
}
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
When the GODEBUG=tarinsecurepath=0 environment variable
is set, (*Reader).Next will return the error
ErrInsecurePath when opening an archive which contains
file names that are absolute, refer to a location outside the current
directory, contain invalid characters, or (on Windows) are reserved
names such as NUL. Programs that perform their own
name sanitization can ignore this error. This behavior will be made
the default in a future version of Go.
When the GODEBUG=zipinsecurepath=0 environment variable
is set, NewReader will return the error
ErrInsecurePath when opening an archive which contains
file names that are absolute, refer to a location outside the current
irectory, contain invalid characters, or (on Windows) are reserved
names such as NUL. Programs that perform their own
name sanitization can ignore this error. This behavior will be made
the default in a future version of Go.
Reading from a directory file that contains file data will now return an error. The zip specification does not permit directory files to contain file data, so this change only affects reading from invalid archives.
TODO: https://go.dev/cl/407176: strings, bytes: add CutPrefix and CutSuffix
TODO: https://go.dev/cl/359675: bytes: add Clone function
TODO: https://go.dev/cl/375977: context: add APIs for writing and reading cancelation cause; modified api/next/51365.txt
TODO: https://go.dev/cl/373076: crypto/ed25519: implement Ed25519ph in Sign and VerifyWithOptions; modified api/next/31804.txt
TODO: https://go.dev/issue/34648: automatically upgrade CurveParams for known curves and deprecate custom ones
TODO: https://go.dev/issue/19974: allow hash.Hash for OAEP and MGF1 to be specified independently
TODO: https://go.dev/issue/53021: add XORBytes
TODO: https://go.dev/cl/421435: crypto/subtle: add XORBytes; modified api/next/53021.txt
TODO: https://go.dev/cl/426455: crypto/tls: use certificate cache in client
TODO: https://go.dev/cl/420982: debug/elf: add new-style LoongArch reloc types; modified api/next/54222.txt
TODO: https://go.dev/cl/411915: debug/elf: fix reloc number of R_PPC64_SECTOFF_LO_DS; modified api/except.txt, api/next/53356.txt
TODO: https://go.dev/cl/425555: debug/elf: define additional PPC64 ELFv2 relocations; modified api/next/54345.txt
TODO: https://go.dev/cl/429601: debug/elf: return error on reading from SHT_NOBITS sections
TODO: https://go.dev/cl/435415: debug/elf: fix typo in R_PPC64_TPREL34 and R_PPC64_DTPREL34; modified api/next/54345.txt
TODO: https://go.dev/cl/421357: debug/pe: add IMAGE_FILE_MACHINE_RISCV{32,64,128}; modified api/next/54251.txt
The ReadVarint and
ReadUvarint
functions will now return io.ErrUnexpectedEOF after reading a partial value,
rather than io.EOF.
TODO: https://go.dev/issue/53346: Add (*Encoder).Close() to check for unclosed elements
TODO: https://go.dev/cl/424777: encoding/xml: add (*Encoder).Close
TODO: https://go.dev/cl/103875: encoding/xml: error when more than one colon in qualified names
TODO: https://go.dev/cl/107255: encoding/xml: error when closing tag does not match opening tag
The new Join function returns an error wrapping a list of errors.
The Errorf function supports multiple occurrances of
the %w format verb.
TODO: https://go.dev/issue/51668: add FormatString(State) string
TODO: https://go.dev/cl/400875: fmt: add a function to recover the original format string given a State; modified api/next/51668.txt
TODO: https://go.dev/cl/426091: go/ast: add Range token.Pos to RangeStmt
TODO: https://go.dev/cl/427955: go/ast: record start and end of file in File.File{Start,End}; modified api/next/53202.txt
TODO: https://go.dev/cl/421434: go/build: add GO$GOARCH-based ToolTags
TODO: https://go.dev/cl/410114: go/token: add (*FileSet).RemoveFile(*File) method
TODO: https://go.dev/issue/45899: add OffsetWriter, NewOffsetWriter
TODO: https://go.dev/cl/406776: io: add OffsetWriter, NewOffsetWriter; modified api/next/45899.txt
TODO: https://go.dev/cl/363814: path/filepath, io/fs: add SkipAll; modified api/next/47209.txt
The math/rand package now automatically seeds
the global random number generator
(used by top-level functions like Float64 and Int) with a random value,
and the top-level Seed function has been deprecated.
Programs that need a reproducible sequence of random numbers
should prefer to allocate their own random source, using rand.New(rand.NewSource(seed)).
Programs that need the earlier consistent global seeding behavior can set
GODEBUG=randautoseed=0 in their environment.
The ParseMediaType function now allows duplicate parameter names,
so long as the values of the names are the same.
Methods of the Reader type now wrap errors
returned by the underlying io.Reader.
The LookupCNAME function now consistently returns the contents
of a CNAME record when one exists. Previously on Unix systems and
when using the pure Go resolver, LookupCNAME would return an error
if a CNAME record referred to a name that with no A,
AAAA, or CNAME record. This change modifies
LookupCNAME to match the previous behavior on Windows,
allowing allowing LookupCNAME to succeed whenever a
CNAME exists.
Interface.Flags now includes the new flag FlagRunning,
indicating an operationally active interface. An interface which is administratively
configured but not active (for example, because the network cable is not connected)
will have FlagUp set but not FlagRunning.
The new Dialer.ControlContext field contains a callback function
similar to the existing Dialer.Control hook, that additionally
accepts the dial context as a parameter.
Control is ignored when ControlContext is not nil.
The Go DNS resolver recognizes the trust-ad resolver option.
When options trust-ad is set in resolv.conf,
the Go resolver will set the AD bit in DNS queries. The resolver does not
make use of the AD bit in responses.
DNS resolution will detect changes to /etc/nsswitch.conf
and reload the file when it changes. Checks are made at most once every
five seconds, matching the previous handling of /etc/hosts
and /etc/resolv.conf.
The new
The new
The
The new
The new
The HTTP server now accepts HEAD requests containing a body,
rather than rejecting them as invalid.
HTTP/2 stream errors returned by
Leading and trailing spaces are trimmed from cookie names,
rather than being rejected as invalid.
For example, a cookie setting of "name =value"
is now accepted as setting the cookie "name".
ResponseController type provides access to extended per-request
functionality not handled by the ResponseWriter interface.
ResponseController.SetReadDeadline and
ResponseController.SetWriteDeadline methods permit setting
per-request read and write deadlines.
ResponseWriter.WriteHeader function now supports sending
1xx status codes.
Server.DisableGeneralOptionsHandler configuration setting
allows disabling the default OPTIONS * handler.
Transport.OnProxyConnectResponse hook is called
when a Transport receives an HTTP response from a proxy
for a CONNECT request.
net/http functions may be converted
to a "golang.org/x/net/http2".StreamError using errors.As.
The new ReverseProxy hook supersedes the existing Rewrite hook.
ReverseProxy now adds
X-Forwarded-Proto and X-Forwarded-Host headers
to forwarded requests.
These headers are added to all requests forwarded by a Director hook,
and to requests forwarded by a Rewrite hook which calls the
ProxyRequest.SetXForwarded function.
ReverseProxy no longer adds a User-Agent header
to forwarded requests when the incoming request does not have one.
TODO: https://go.dev/issue/51766: add IPv6LinkLocalAllRouters
TODO: https://go.dev/issue/51777: add IPv6Loopback
TODO: https://go.dev/cl/412475: net/netip: add IPv6LinkLocalAllRouters and IPv6Loopback; modified api/next/51766.txt, api/next/51777.txt
TODO: https://go.dev/cl/448897: os: remove special casing of NUL in Windows file operations
The new Cmd fields Cancel and WaitDelay
specify the behavior of the Cmd when its associated
Context is canceled or its process exits with I/O pipes still
held open by a child process.
TODO: https://go.dev/cl/363814: path/filepath, io/fs: add SkipAll; modified api/next/47209.txt
The new IsLocal function reports whether a path is
lexically local to a directory.
For example, if IsLocal(p) is true,
then Open(p) will refer to a file that is lexically
within the subtree rooted at the current directory.
TODO: https://go.dev/issue/46746: add Value.Equal, Value.Comparable
TODO: https://go.dev/issue/48000: add reflect.Value.Grow
TODO: https://go.dev/issue/52376: add Value.SetZero
TODO: https://go.dev/cl/389635: reflect: add Value.Grow
TODO: https://go.dev/cl/411476: reflect: add Value.SetZero
TODO: https://go.dev/cl/423794: reflect: add Value.{Comparable,Equal}
TODO: https://go.dev/cl/425184: reflect: fix Value.SetIterXXX to check for the read-only bit
TODO: https://go.dev/cl/428757: reflect: deprecate SliceHeader and StringHeader
TODO: https://go.dev/cl/444817: regexp: add ErrLarge error; modified api/next/56041.txt
TODO: https://go.dev/issue/47216: add GOMAXPROCS, NumCgoCall, GC CPU time
TODO: https://go.dev/cl/345488: strconv: optimize Parse for []byte arguments
TODO: https://go.dev/issue/42537: add CutPrefix and CutSuffix
TODO: https://go.dev/issue/45038: bytes, strings: add Clone
The new methods Map.Swap,
Map.CompareAndSwap, and
Map.CompareAndDelete
allow existing map entries to be updated atomically.
TODO: https://go.dev/cl/407574: syscall: add new CLONE_ flags for Linux
TODO: https://go.dev/cl/411596: syscall: remove FreeBSD 11 and below 64bit inode compatibility shims
TODO: https://go.dev/cl/417695: syscall: add CgroupFD support for ForkExec on Linux
The new method B.Elapsed
reports the current elapsed time of the benchmark, which may be useful for
calculating rates to report with ReportMetric.
TODO: https://go.dev/issue/52746: add DateTime, DateOnly, TimeOnly format constants
TODO: https://go.dev/cl/412495: time: add DateTime, DateOnly, and TimeOnly
TODO: https://go.dev/cl/382734: time: implement Compare method
TODO: https://go.dev/cl/425037: time: fix Parse to ignore extra sub-nanosecond digits
TODO: https://go.dev/cl/444277: time: implement strict RFC 3339 during marshal and unmarshal
TODO: https://go.dev/issue/51896: add AppendRune
TODO: https://go.dev/cl/409054: unicode/utf16: add AppendRune; modified api/next/51896.txt