Go 1.17 is not yet released. These are work-in-progress release notes. Go 1.17 is expected to be released in August 2021.
Go 1.17 includes three small enhancements to the language.
s of
type []T may now be converted to array pointer type
*[N]T. If a is the result of such a
conversion, then corresponding indices that are in range refer to
the same underlying elements: &a[i] == &s[i]
for 0 <= i < N. The conversion panics if
len(s) is less than N.
unsafe.Add:
unsafe.Add(ptr, len) adds len
to ptr and returns the updated pointer
unsafe.Pointer(uintptr(ptr) + uintptr(len)).
unsafe.Slice:
For expression ptr of type *T,
unsafe.Slice(ptr, len) returns a slice of
type []T whose underlying array starts
at ptr and whose length and capacity
are len.
These enhancements were added to simplify writing code that conforms
to unsafe.Pointer's safety
rules, but the rules remain unchanged. In particular, existing
programs that correctly use unsafe.Pointer remain
valid, and new programs must still follow the rules when
using unsafe.Add or unsafe.Slice.
As announced in the Go 1.16 release notes, Go 1.17 requires macOS 10.13 High Sierra or later; support for previous versions has been discontinued.
Go 1.17 adds support of 64-bit ARM architecture on Windows (the
windows/arm64 port). This port supports cgo.
The 64-bit MIPS architecture on OpenBSD (the openbsd/mips64
port) now supports cgo.
In Go 1.16, on the 64-bit x86 and 64-bit ARM architectures on
OpenBSD (the openbsd/amd64 and openbsd/arm64
ports) system calls are made through libc, instead
of directly using the machine instructions. In Go 1.17, this is
also done on the 32-bit x86 and 32-bit ARM architectures on OpenBSD
(the openbsd/386 and openbsd/arm ports).
This ensures forward-compatibility with future versions of
OpenBSD.
Go programs now maintain stack frame pointers on the 64-bit ARM architecture on all operating systems. Previously it maintained stack frame pointers only on Linux, macOS, and iOS.
TODO: complete the Ports section
TODO: complete the Tools section
If a module specifies go 1.17 or higher in its
go.mod file, its transitive requirements are now loaded lazily,
avoiding the need to download or read go.mod files for
otherwise-irrelevant dependencies. To support lazy loading, in Go 1.17 modules
the go command maintains explicit requirements in
the go.mod file for every dependency that provides any package
transitively imported by any package or test within the module.
See the design
document for more detail.
To facilitate the upgrade to lazy loading, the
go mod tidy subcommand now supports
a -go flag to set or change the go version in
the go.mod file. To enable lazy loading for an existing module
without changing the selected versions of its dependencies, run:
go mod tidy -go=1.17
By default, go mod tidy verifies that
the selected versions of dependencies relevant to the main module are the same
versions that would be used by the prior Go release (Go 1.16 for a module that
spsecifies go 1.17), and preserves
the go.sum entries needed by that release even for dependencies
that are not normally needed by other commands.
The -compat flag allows that version to be overridden to support
older (or only newer) versions, up to the version specified by
the go directive in the go.mod file. To tidy
a go 1.17 module for Go 1.17 only, without saving
checksums for (or checking for consistency with) Go 1.16:
go mod tidy -compat=1.17
Note that even if the main module is tidied with -compat=1.17,
users who require the module from a
go 1.16 or earlier module will still be able to
use it, provided that the packages use only compatible language and library
features.
Module authors may deprecate a module by adding a
// Deprecated:
comment to go.mod, then tagging a new version.
go get now prints a warning if a module needed to
build packages named on the command line is deprecated. go
list -m -u prints deprecations for all
dependencies (use -f or -json to show the full
message). The go command considers different major versions to
be distinct modules, so this mechanism may be used, for example, to provide
users with migration instructions for a new major version.
go get
The go get -insecure flag is
deprecated and has been removed. To permit the use of insecure schemes
when fetching dependencies, please use the GOINSECURE
environment variable. The -insecure flag also bypassed module
sum validation, use GOPRIVATE or GONOSUMDB if
you need that functionality. See go help
environment for details.
go.mod files missing go directives
If the main module's go.mod file does not contain
a go directive and
the go command cannot update the go.mod file, the
go command now assumes go 1.11 instead of the
current release. (go mod init has added
go directives automatically since
Go 1.12.)
If a module dependency lacks an explicit go.mod file, or
its go.mod file does not contain
a go directive,
the go command now assumes go 1.16 for that
dependency instead of the current release. (Dependencies developed in GOPATH
mode may lack a go.mod file, and
the vendor/modules.txt has to date never recorded
the go versions indicated by dependencies' go.mod
files.)
vendor contents
If the main module specifies go 1.17 or higher,
go mod vendor now annotates
vendor/modules.txt with the go version indicated by
each vendored module in its own go.mod file. The annotated
version is used when building the module's packages from vendored source code.
If the main module specifies go 1.17 or higher,
go mod vendor now omits go.mod
and go.sum files for vendored dependencies, which can otherwise
interfere with the ability of the go command to identify the correct
module root when invoked within the vendor tree.
The go command by default now suppresses SSH password prompts and
Git Credential Manager prompts when fetching Git repositories using SSH, as it
already did previously for other Git password prompts. Users authenticating to
private Git repos with password-protected SSH may configure
an ssh-agent to enable the go command to use
password-protected SSH keys.
go mod download
When go mod download is invoked without
arguments, it will no longer save sums for downloaded module content to
go.sum. It may still make changes to go.mod and
go.sum needed to load the build list. This is the same as the
behavior in Go 1.15. To save sums for all modules, use go
mod download all.
TODO: https://golang.org/cl/249759: cmd/cover: replace code using optimized golang.org/x/tools/cover
TODO: https://golang.org/cl/299532: cmd/vet: bring in sigchanyzer to report unbuffered channels to signal.Notify
TODO: complete the Vet section
Go 1.17 implements a new way of passing function arguments and results using
registers instead of the stack. This work is enabled for Linux, MacOS, and
Windows on the 64-bit x86 architecture (the linux/amd64,
darwin/amd64, windows/amd64 ports). For a
representative set of Go packages and programs, benchmarking has shown
performance improvements of about 5%, and a typical reduction in binary size
of about 2%.
This change does not affect the functionality of any safe Go code. It can affect
code outside the compatibility guidelines with
minimal impact. To maintain compatibility with existing assembly functions,
adapter functions converting between the new register-based calling convention
and the previous stack-based calling convention (also known as ABI wrappers)
are sometimes used. This is mostly invisible to users, except for assembly
functions that have their addresses taken in Go. Using reflect.ValueOf(fn).Pointer()
(or similar approaches such as via unsafe.Pointer) to get the address
of an assembly function will now return the address of the ABI wrapper. This is
mostly harmless, except for special-purpose assembly code (such as accessing
thread-local storage or requiring a special stack alignment). Assembly functions
called indirectly from Go via func values will now be made through
ABI wrappers, which may cause a very small performance overhead. Also, calling
Go functions from assembly may now go through ABI wrappers, with a very small
performance overhead.
The format of stack traces from the runtime (printed when an uncaught panic
occurs, or when runtime.Stack is called) is improved. Previously,
the function arguments were printed as hexadecimal words based on the memory
layout. Now each argument in the source code is printed separately, separated
by commas. Aggregate-typed (struct, array, string, slice, interface, and complex)
arguments are delimited by curly braces. A caveat is that the value of an
argument that only lives in a register and is not stored to memory may be
inaccurate. Results (which were usually inaccurate) are no longer printed.
Functions containing closures can now be inlined. One effect of this change is that a function with a closure may actually produce a distinct closure function for each place that the function is inlined. Hence, this change could reveal bugs where Go functions are compared (incorrectly) by pointer value. Go functions are by definition not comparable.
TODO: complete the Core library section
(*Conn).HandshakeContext was added to allow the user to control cancellation of an in-progress TLS Handshake. The context provided is propagated into the ClientHelloInfo and CertificateRequestInfo structs and accessible through the new (*ClientHelloInfo).Context and (*CertificateRequestInfo).Context methods respectively. Canceling the context after the handshake has finished has no effect.
When Config.NextProtos is set, servers now
enforce that there is an overlap between the configured protocols and the protocols
advertised by the client, if any. If there is no overlap the connection is closed
with the no_application_protocol alert, as required by RFC 7301.
The runtime/cgo package now provides a new facility that allows to turn any Go values to a safe representation that can be used to pass values between C and Go safely. See runtime/cgo.Handle for more information.
As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibility in mind.
The new methods File.OpenRaw, Writer.CreateRaw, Writer.Copy provide support for cases where performance is a primary concern.
The Writer.WriteRune method
now writes the replacement character U+FFFD for negative rune values,
as it does for other invalid runes.
The Buffer.WriteRune method
now writes the replacement character U+FFFD for negative rune values,
as it does for other invalid runes.
The NewReader
function is guaranteed to return a value of the new
type Reader,
and similarly NewWriter
is guaranteed to return a value of the new
type Writer.
These new types both implement a Reset method
(Reader.Reset,
Writer.Reset)
that allows reuse of the Reader or Writer.
TODO: https://golang.org/cl/302230: fix salt length calculation with PSSSaltLengthAuto
The DB.Close method now closes
the connector field if the type in this field implements the
io.Closer interface.
The new
NullInt16
and
NullByte
structs represent the int16 and byte values that may be null. These can be used as
destinations of the Scan method,
similar to NullString.
The SHT_MIPS_ABIFLAGS
constant has been added.
binary.Uvarint will stop reading after 10 bytes to avoid
wasted computations. If more than 10 bytes are needed, the byte count returned is -11.
Previous Go versions could return larger negative counts when reading incorrectly encoded varints.
The new
Reader.FieldPos
method returns the line and column corresponding to the start of
a given field in the record most recently returned by
Read.
Flag declarations now panic if an invalid name is specified.
The new
Context.ToolTags
field holds the build tags appropriate to the current Go
toolchain configuration.
The new FileInfoToDirEntry function converts a FileInfo to a DirEntry.
The math package now defines three more constants: MaxUint, MaxInt and MinInt.
For 32-bit systems their values are 2^32 - 1, 2^31 - 1 and -2^31, respectively.
For 64-bit systems their values are 2^64 - 1, 2^63 - 1 and -2^63, respectively.
On Unix systems, the table of MIME types is now read from the local system's Shared MIME-info Database when available.
The new method IP.IsPrivate reports whether an address is
a private IPv4 address according to RFC 1918
or a local IPv6 address according RFC 4193.
The Go DNS resolver now only sends one DNS query when resolving an address for an IPv4-only or IPv6-only network, rather than querying for both address families.
The ErrClosed sentinel error and
ParseError error type now implement
the net.Error interface.
The net/http package now uses the new
(*tls.Conn).HandshakeContext
with the Request context
when performing TLS handshakes in the client or server.
Setting the Server
ReadTimeout or WriteTimeout fields to a negative value now indicates no timeout
rather than an immediate timeout.
The ReadRequest function
now returns an error when the request has multiple Host headers.
ResponseRecorder.WriteHeader>
now panics when the provided code is not a valid three-digit HTTP status code.
This matches the behavior of ResponseWriter>
implementations in the net/http package.
The new method Values.Has
reports whether a query parameter is set.
The File.WriteString method
has been optimized to no longer make a copy of the input string.
The new
StructField.IsExported
and
Method.IsExported
methods report whether a struct field or type method is exported.
They provide a more readable alternative to checking whether PkgPath
is empty.
The new VisibleFields function
returns all the visible fields in a struct type, including fields inside anonymous struct members.
The ArrayOf function now panics when
called with a negative length.
New metrics were added that track total bytes and objects allocated and freed. A new metric tracking the distribution of goroutine scheduling latencies was also added.
TODO: https://golang.org/cl/170079: implement Ryū-like algorithm for fixed precision ftoa
TODO: https://golang.org/cl/170080: Implement Ryū algorithm for ftoa shortest mode
The new QuotedPrefix function
returns the quoted string (as understood by
Unquote)
at the start of input.
The Builder.WriteRune method
now writes the replacement character U+FFFD for negative rune values,
as it does for other invalid runes.
atomic.Value now has Swap and
CompareAndSwap methods that provide
additional atomic operations.
The GetQueuedCompletionStatus and
PostQueuedCompletionStatus
functions are now deprecated. These functions have incorrect signatures and are superseded by
equivalents in the golang.org/x/sys/windows package.
On Unix-like systems, the process group of a child process is now set with signals blocked.
This avoids sending a SIGTTOU to the child when the parent is in a background process group.
The Windows version of
SysProcAttr
has two new fields. AdditionalInheritedHandles is
a list of additional handles to be inherited by the new child
process. ParentProcess permits specifying the
parent process of the new process.
The constant MSG_CMSG_CLOEXEC is now defined on
DragonFly and all OpenBSD systems (it was already defined on
some OpenBSD systems and all FreeBSD, NetBSD, and Linux systems).
The constants SYS_WAIT6 and WEXITED
are now defined on NetBSD systems (SYS_WAIT6 was
already defined on DragonFly and FreeBSD systems;
WEXITED was already defined on Darwin, DragonFly,
FreeBSD, Linux, and Solaris systems).
Added a new testing flag -shuffle which controls the execution order of tests and benchmarks.
The new
T.Setenv
and B.Setenv
methods support setting an environment variable for the duration
of the test or benchmark.
The new SkipFuncCheck Mode
value changes the template parser to not verify that functions are defined.
The Time type now has a
GoString method that
will return a more useful value for times when printed with the
%#v format specifier in the fmt package.
The new Time.IsDST method can be used to check whether the time
is in Daylight Savings Time in its configured location.
The new Time.UnixMilli and
Time.UnixMicro methods return the number of milliseconds and
microseconds elapsed since January 1, 1970 UTC respectively.
The new UnixMilli and UnixMicro functions return local Time corresponding to given
Unix time.
The package now accepts comma "," as a separator for fractional seconds when parsing and formatting time. The following time formats are now accepted:
The new constant Layout
defines the reference time.