Go 1.8 is not yet released. These are work-in-progress release notes. Go 1.8 is expected to be released in February 2017.
The latest Go release, version 1.8, arrives six months after Go 1.7. Most of its changes are in the implementation of the toolchain, runtime, and libraries. There is one minor change to the language specification. As always, the release maintains the Go 1 promise of compatibility. We expect almost all Go programs to continue to compile and run as before.
The release adds support for 32-bit MIPS, updates the compiler back end to generate more efficient code, reduces GC pauses by eliminating stop-the-world stack rescanning, adds HTTP/2 Push support, adds HTTP graceful shutdown, more context support, and simplifies sorting slices.
When explicitly converting structs, tags are now ignored for structural type identity. See the language specification for details.
The language specification now only requires that implementations
support up to 16-bit exponents in floating-point constants. This does not affect
either the “gc” or
gccgo compilers, both of
which still support 32-bit exponents.
Go now supports 32-bit MIPS on Linux for both big-endian
(linux/mips) and little-endian machines
(linux/mipsle).
Go now requires DragonFly BSD 4.4.4 or later.
The Plan 9 port's networking support is now much more complete and matches the behavior of Unix and Windows with respect to deadlines and cancelation.
Go 1.8 now only supports OS X 10.8 or later. This is likely the last Go release to support 10.8. Compiling Go or running binaries on older OS X versions is untested.
There are some instabilities on FreeBSD and NetBSD that are known but not understood. These can lead to program crashes in rare cases. See issue 15658, issue 16396, and issue 16511. Any help in solving these issues would be appreciated.
For 64-bit x86 systems, the following instructions have been added:
VBROADCASTSD,
BROADCASTSS,
MOVDDUP,
MOVSHDUP,
MOVSLDUP,
VMOVDDUP,
VMOVSHDUP,
and VMOVSLDUP.
For 64-bit PPC systems, the common vector scalar instructions have been
added:
LXS,
LXSDX,
LXSI,
LXSIWAX,
LXSIWZX,
LXV,
LXVD2X,
LXVDSX,
LXVW4X,
MFVSR,
MFVSRD,
MFVSRWZ,
MTVSR,
MTVSRD,
MTVSRWA,
MTVSRWZ,
STXS,
STXSDX,
STXSI,
STXSIWX,
STXV,
STXVD2X,
STXVW4X,
XSCV,
XSCVDPSP,
XSCVDPSPN,
XSCVDPSXDS,
XSCVDPSXWS,
XSCVDPUXDS,
XSCVDPUXWS,
XSCVSPDP,
XSCVSPDPN,
XSCVSXDDP,
XSCVSXDSP,
XSCVUXDDP,
XSCVUXDSP,
XSCVX,
XSCVXP,
XVCV,
XVCVDPSP,
XVCVDPSXDS,
XVCVDPSXWS,
XVCVDPUXDS,
XVCVDPUXWS,
XVCVSPDP,
XVCVSPSXDS,
XVCVSPSXWS,
XVCVSPUXDS,
XVCVSPUXWS,
XVCVSXDDP,
XVCVSXDSP,
XVCVSXWDP,
XVCVSXWSP,
XVCVUXDDP,
XVCVUXDSP,
XVCVUXWDP,
XVCVUXWSP,
XVCVX,
XVCVXP,
XXLAND,
XXLANDC,
XXLANDQ,
XXLEQV,
XXLNAND,
XXLNOR,
XXLOR,
XXLORC,
XXLORQ,
XXLXOR,
XXMRG,
XXMRGHW,
XXMRGLW,
XXPERM,
XXPERMDI,
XXSEL,
XXSI,
XXSLDWI,
XXSPLT, and
XXSPLTW.
The yacc tool (previously available via
“go tool yacc”)
has been removed. As of Go 1.7 it was no longer used by the Go compiler.
It has moved to the “tools” repository and is and is available via
go get golang.org/x/tools/cmd/goyacc.
Go 1.7 introduced a new compiler back end for 64-bit x86 systems. In Go 1.8, that back end has been developed further and is now used for all architectures.
The new back end, based on SSA, generates more compact, more efficient code and provides a better platform for optimizations such as bounds check elimination. The new back end reduces the CPU time required by our benchmark programs by 20-30% on 32-bit ARM systems. For 64-bit x86 systems, which already used the SSA backend in Go 1.7, the gains are a more modest 0-10%. Other architectures will likely see improvements closer to the 32-bit ARM numbers.
The temporary -ssa=0 compiler flag introduced in Go 1.7
to disable the new backend has been removed in Go 1.8.
In addition to enabling the new compiler back end for all systems, Go 1.8 also introduces a new compiler front end. The new compiler front end should not be noticeable to users but is the foundation for future performance work.
The compiler and linker have been optimized and run faster in this release than in Go 1.7, although they are still slower than we would like and will continue to be optimized in future releases. Compared to the previous release, Go 1.8 is about 15% faster.
TODO
TODO
The go command's basic operation
is unchanged, but there is one addition worth noting.
The new
“go
bug” starts a bug report on GitHub, prefilled
with information about the current system.
The
“go
doc” command
now groups constants and variables with their type,
following the behavior of
godoc.
In order to improve the readability of doc's
output, each summary of the first-level items is guaranteed to
occupy a single line.
Documentation for a specific method in an interface definition can
now be requested, as in
“go doc net.Conn.SetDeadline”.
Go now supports a “plugin” build mode for generating
plugins written in Go, and a
new plugin package for
loading such plugins at run time. Plugin support is only currently
available on Linux and macOS.
The garbage collector no longer considers
arguments live throughout the entirety of a function. For more
information, and for how to force a variable to remain live, see
the runtime.KeepAlive
function added in Go 1.7.
Updating:
Code that sets a finalizer on an allocated object may need to add
calls to runtime.KeepAlive in functions or methods
using that object.
Read the
KeepAlive
documentation and its example for more details.
The runtime's MemStats
type has been more thoroughly documented.
As always, the changes are so general and varied that precise statements about performance are difficult to make. Most programs should run a bit faster, due to speedups in the garbage collector and optimizations in the standard library.
There have been significant optimizations bringing more than 10% improvements
to implementations in the
TODO TODO:
foo,
bar,
and
quux
packages.
Garbage collection pauses should be significantly shorter than they were in Go 1.7, usually under 100 microseconds and often as low as 10 microseconds. See the document on eliminating stop-the-world stack re-scanning for details. More work remains for Go 1.9.
The overhead of deferred function calls has been reduced by about half.
The overhead of calls from Go into C has been reduced by about half.
Examples have been added to the documentation across many packages.
The sort package
now includes a convenience function
Slice to sort a
slice given a less function.
In many cases this means that writing a new sorter type is not
necessary.
Also new are
SliceStable and
SliceIsSorted.
The net/http package now includes a
mechanism to
send HTTP/2 server pushes from a
Handler.
Similar to the existing Flusher and Hijacker
interfaces, an HTTP/2
ResponseWriter
now implements the new
Pusher interface.
The HTTP Server now has support for graceful shutdown using the new
Server.Shutdown
method and abrupt shutdown using the new
Server.Close
method.
Continuing Go 1.7's adoption
of context.Context
into the standard library, Go 1.8 adds more context support
to existing packages:
Server.Shutdown
takes a context argument.T.Context
method in the testing package now returns a context for
the active test or benchmark.Lookup methods on the new
net.Resolver now
take a context.As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibility in mind.
The tar implementation corrects many bugs in corner cases of the file format.
The Reader
is now able to process tar files in the PAX format with entries larger than 8GB.
The Writer
no longer produces invalid tar files in some situations involving long pathnames.
The zip Reader now supports modification times in
the NTFS, UNIX, and Extended Time Stamp metadata fields.
When writing zip files, the Extended Time Stamp field is written
if TODO: validate implementation.
There have been some minor fixes to the encoder to improve the
compression ratio in certain situations. As a result, the exact
encoded output of DEFLATE may be different from Go 1.7. Since
DEFLATE is the underlying compression of gzip, png, zlib, and zip,
those formats may have changed outputs.
The encoder, when operating in
NoCompression
mode, now produces a consistent output that is not dependent on
the size of the slices passed to the
Write
method.
The decoder, upon encountering an error, now returns any buffered data it had uncompressed along with the error.
The Writer
now encodes a zero MTIME field when
the Header.ModTime
field is the zero value.
In previous releases of Go, the Writer would encode
a nonsensical value.
Similarly,
the Reader
now reports a zero encoded MTIME field as a zero
Header.ModTime.
The DeadlineExceeded
error now implements
net.Error
and reports true for both the Timeout and
Temporary methods.
The package now supports context.Context. There are new methods
ending in Context such as
DB.QueryContext and
DB.PrepareContext
that take context arguments. Using the new Context methods ensures that
connections are closed and returned to the connection pool when the
request is done; enables canceling in-progress queries
should the driver support that; and allows the database
pool to cancel waiting for the next available connection.
The IsolationLevel
can now be set when starting a transaction by setting the isolation level
on the Context then passing that Context to
DB.BeginContext.
An error will be returned if an isolation level is selected that the driver
does not support. A read-only attribute may also be set on the transaction
with ReadOnlyContext
Queries now expose the SQL column type information for drivers that support it.
Rows can return ColumnTypes
which can include SQL type information, column type lengths, and the Go type.
A Rows
can now represent multiple result sets. After
Rows.Next returns false,
Rows.NextResultSet
may be called to advance to the next result set. The existing Rows
should be continued to be used after it advances to the next result set.
NamedParam may be used
as query arguments. The new function Param
helps create a NamedParam
more succinctly.
If a driver supports the new
Pinger
interface, the DB's
DB.Ping
and
DB.PingContext
methods will use that interface to check whether a
database connection is still valid.
The new Context query methods work for all drivers, but
Context cancelation is not responsive unless the driver has been
updated to used them. The other features require driver support in
database/sql/driver.
Driver authors should review the new interfaces. Users of existing
driver should review the driver documentation to see what
it supports and any system specific documentation on each feature.
TODO: describe Issue 15345 and CL 22181, CL 22332, CL 22336
pkg debug/pe, method (*COFFSymbol) FullName(StringTable) (string, error) pkg debug/pe, method (StringTable) String(uint32) (string, error) pkg debug/pe, type File struct, COFFSymbols []COFFSymbol pkg debug/pe, type File struct, StringTable StringTable pkg debug/pe, type Reloc struct pkg debug/pe, type Reloc struct, SymbolTableIndex uint32 pkg debug/pe, type Reloc struct, Type uint16 pkg debug/pe, type Reloc struct, VirtualAddress uint32 pkg debug/pe, type Section struct, Relocs []Reloc pkg debug/pe, type StringTable []uint8
The new
Encoding.Strict
method returns an Encoding that causes the decoder
to return an error when the trailing padding bits are not zero.
The package now supports boolean values. TODO: add docs in encoding/binary package, then link to package docs here.
UnmarshalTypeError
now includes the struct and field name.
A nil Marshaler
now marshals as a JSON null value.
A RawMessage value now
marshals the same as its pointer type.
Marshal
encodes floating-point numbers using the same format as in ES6,
preferring decimal (not exponential) notation for a wider range of values.
In particular, all floating-point integers up to 264 format the
same as the equivalent int64 representation.
In previous versions of Go, unmarshaling a JSON null into an
of Unmarshaler
was considered a no-op; now the Unmarshaler's
UnmarshalJSON method is called with the JSON literal
null and can define the semantics of that case.
Decode
is now strict about the format of the ending line.
The new methods
Int.Value,
String.Value,
Float.Value, and
Func.Value
report the current value of an exported variable.
The new
function Handler
returns the package's HTTP handler, to enable installing it in
non-standard locations.
Decode
(and DecodeConfig)
now supports True Color and grayscale transparency.
Encoder
is now faster and creates smaller output
when encoding paletted images.
The new Rand.Uint64
method returns uint64 values. The
new Source64
interface describes sources capable of generating such values
directly; otherwise the Rand.Uint64 method
constructs a uint64 from two calls
to Source's
Int63 method.
The
Reader's
parsing has been relaxed in two ways to accept
more input seen in the wild.
First, it accepts an equals sign (=) not followed
by two hex digits as a literal equal sign.
Second, it silently ignores a trailing equals sign at the end of
an encoded input.
The Conn documentation
has been updated to clarify expectations of an interface
implementation. Updates in the net/http packages
depend on implementations obeying the documentation.
Updating: implementations of the Conn interface should verify
they implement the documented semantics. TODO: https://golang.org/cl/18097
TODO: many other net changes
Server changes:
Server
adds configuration options
ReadHeaderTimeout and IdleTimeout
and documents WriteTimeout.
FileServer
and
ServeContent
now support HTTP If-Match conditional requests,
in addition to the previous If-None-Match
support.
There are several additions to what a server's Handler can do:
Context
returned
by Request.Context
is canceled if the underlying net.Conn
closes. For instance, if the user closes their browser in the
middle of a slow request, the Handler can now
detect that the user is gone. This complements the
existing CloseNotifier
support. This functionality requires that the underlying
net.Conn implements
recently-clarified interface documentation.
TrailerPrefix
mechanism.
Handler can now abort a response by panicking
with the error
ErrAbortHandler.
Write of zero bytes to a
ResponseWriter
is now defined as a
way to test whether a ResponseWriter has been hijacked:
if so, the Write returns
ErrHijacked
without printing an error
to the server's error log.
Client & Transport changes:
Client
now copies most request headers on redirect. Authentication-specific
headers are only sent to the same origin or subdomains thereof.
Cookies are not sent again, unless they were set explicitly.
TODO: verify this, and link to docs once https://golang.org/issue/18096
is fixed.
Transport
now supports international domain names. Consequently, so do
Get and other helpers.
Client now supports 307 and 308 redirects.
If the redirect requires resending the request body,
the request must have the new
Request.GetBody
field defined.
NewRequest
sets Request.GetBody automatically for common
body types.
Transport now rejects requests for URLs with
ports containing non-digit characters.
Transport will now retry non-idempotent
requests if no bytes were written before a network failure.
Transport.ProxyConnectHeader
allows configuration of header values to send to a proxy
during a CONNECT request.
DefaultTransport.Dialer
now enables DualStack ("Happy Eyeballs") support,
to use IPv4 as a backup if it looks like IPv6 might be
failing.
Empty quoted strings are once again allowed in the name part of
an address. That is, Go 1.4 and earlier accepted
"" <gopher@example.com>,
but Go 1.5 introduced a bug that rejected this address.
The address is recognized again.
The
Header.Date
method has always provided a way to parse
the Date: header.
A new function
ParseDate
allows parsing dates found in other
header lines, such as the Resent-Date: header.
If an implementation of
the Auth
interface's Start method returns an
empty toServer value, the package no longer sends
trailing whitespace in the SMTP AUTH command,
which some servers rejected.
The new functions
PathEscape
and
PathUnescape
are similar to the query escaping and unescaping functions but
for path elements.
The new methods
URL.Hostname
and
URL.Port
return the hostname and port fields of a URL,
correctly handling the case where the port may not be present.
The existing method
URL.ResolveReference
now properly handles paths with escaped bytes without losing
the escaping.
The URL type now implements
encoding.BinaryMarshaler and
encoding.BinaryUnmarshaler,
making it possible to process URLs in gob data.
Following RFC 3986,
Parse
now rejects URLs like this_that:other/thing instead of
interpreting them as relative paths (this_that is not a valid scheme).
To force interpretation as a relative path,
such URLs should be prefixed with "./".
The URL.String method now inserts this prefix as needed.
The new function
Executable returns
the path name of the running executable.
The new function
Swapper was
added to support sort.Slice.
The Unquote
function now strips carriage returns (\r) in
backquoted raw strings, following the
Go language semantics.
The new function
Until complements
the analogous Since function.
ParseDuration
now accepts long fractional parts.
Parse
now rejects dates before the start of a month, such as June 0;
it already rejected dates beyond the end of the month, such as
June 31 and July 32.
The tzdata database has been updated to version
2016i for systems that don't already have a local time zone
database.
The new method
T.Name
(and B.Name) returns the name of the current
test or benchmark.
The new method
T.Context
(and B.Context) returns
a Context for
the current running test or benchmark.
The new function
CoverMode
reports the test coverage mode.
Tests and benchmarks are now marked as failed if the race detector is enabled and a data race occurs during execution. Previously, individual test cases would appear to pass, and only the overall execution of the test binary would fail.
SimpleFold now returns its argument unchanged
if the provided input was an invalid rune.
Previously, the implementation failed with an index bounds check panic.