The latest Go release, version 1.11, arrives six months after Go 1.10. 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. We expect almost all Go programs to continue to compile and run as before.
There are no changes to the language specification.
As announced in the Go 1.10 release notes, Go 1.11 now requires OpenBSD 6.2 or later, macOS 10.10 Yosemite or later, or Windows 7 or later; support for previous versions of these operating systems has been removed.
Go 1.11 supports the upcoming OpenBSD 6.4 release. Due to changes in the OpenBSD kernel, older versions of Go will not work on OpenBSD 6.4.
There are known issues with NetBSD on i386 hardware.
The race detector is now supported on linux/ppc64le
and, to a lesser extent, on netbsd/amd64. The NetBSD race detector support
has known issues.
The memory sanitizer (-msan) is now supported on linux/arm64.
The build modes c-shared and c-archive are now supported on
freebsd/amd64.
On 64-bit MIPS systems, the new environment variable settings
GOMIPS64=hardfloat (the default) and
GOMIPS64=softfloat select whether to use
hardware instructions or software emulation for floating-point computations.
For 32-bit systems, the environment variable is still GOMIPS,
as added in Go 1.10.
On soft-float ARM systems (GOARM=5), Go now uses a more
efficient software floating point interface. This is transparent to
Go code, but ARM assembly that uses floating-point instructions not
guarded on GOARM will break and must be ported to
the new interface.
Go 1.11 on ARMv7 no longer requires a Linux kernel configured
with KUSER_HELPERS. This setting is enabled in default
kernel configurations, but is sometimes disabled in stripped-down
configurations.
Go 1.11 adds an experimental port to WebAssembly
(js/wasm).
Go programs currently compile to one WebAssembly module that
includes the Go runtime for goroutine scheduling, garbage
collection, maps, etc.
As a result, the resulting size is at minimum around
2 MB, or 500 KB compressed. Go programs can call into JavaScript
using the new experimental
syscall/js package.
Binary size and interop with other languages has not yet been a
priority but may be addressed in future releases.
As a result of the addition of the new GOOS value
"js" and GOARCH value "wasm",
Go files named *_js.go or *_wasm.go will
now be ignored by Go
tools except when those GOOS/GOARCH values are being used.
If you have existing filenames matching those patterns, you will need to rename them.
More information can be found on the WebAssembly wiki page.
The main Go compiler does not yet support the RISC-V architecture
but we've reserved the GOARCH values
"riscv" and "riscv64", as used by Gccgo,
which does support RISC-V. This means that Go files
named *_riscv.go will now also
be ignored by Go
tools except when those GOOS/GOARCH values are being used.
Go 1.11 adds preliminary support for a new concept called “modules,” an alternative to GOPATH with integrated support for versioning and package distribution. Using modules, developers are no longer confined to working inside GOPATH, version dependency information is explicit yet lightweight, and builds are more reliable and reproducible.
Module support is considered experimental.
Details are likely to change in response to feedback from Go 1.11 users,
and we have more tools planned.
Although the details of module support may change, projects that convert
to modules using Go 1.11 will continue to work with Go 1.12 and later.
If you encounter bugs using modules,
please file issues
so we can fix them. For more information, see the
go command documentation.
Because Go module support assigns special meaning to the
@ symbol in command line operations,
the go command now disallows the use of
import paths containing @ symbols.
Such import paths were never allowed by go get,
so this restriction can only affect users building
custom GOPATH trees by other means.
The new package
golang.org/x/tools/go/packages
provides a simple API for locating and loading packages of Go source code.
Although not yet part of the standard library, for many tasks it
effectively replaces the go/build
package, whose API is unable to fully support modules.
Because it runs an external query command such as
go list
to obtain information about Go packages, it enables the construction of
analysis tools that work equally well with alternative build systems
such as Bazel
and Buck.
Go 1.11 will be the last release to support setting the environment
variable GOCACHE=off to disable the
build cache,
introduced in Go 1.10.
Starting in Go 1.12, the build cache will be required,
as a step toward eliminating $GOPATH/pkg.
The module and package loading support described above
already require that the build cache be enabled.
If you have disabled the build cache to avoid problems you encountered,
please file an issue to let us know about them.
More functions are now eligible for inlining by default, including
functions that call panic.
The compiler toolchain now supports column information in line directives.
A new package export data format has been introduced.
This should be transparent to end users, except for speeding up
build times for large Go projects.
If it does cause problems, it can be turned off again by
passing -gcflags=all=-iexport=false to
the go tool when building a binary.
The compiler now rejects unused variables declared in a type switch
guard, such as x in the following example:
func f(v interface{}) {
switch x := v.(type) {
}
}
This was already rejected by both gccgo
and go/types.
The assembler for amd64 now accepts AVX512 instructions.
The compiler now produces significantly more accurate debug
information for optimized binaries, including variable location
information, line numbers, and breakpoint locations.
This should make it possible to debug binaries
compiled without -N -l.
There are still limitations to the quality of the debug information,
some of which are fundamental, and some of which will continue to
improve with future releases.
DWARF sections are now compressed by default because of the expanded
and more accurate debug information produced by the compiler.
This is transparent to most ELF tools (such as debuggers on Linux
and *BSD) and is supported by the Delve debugger on all platforms,
but has limited support in the native tools on macOS and Windows.
To disable DWARF compression,
pass -ldflags=-compressdwarf=false to
the go tool when building a binary.
Go 1.11 adds experimental support for calling Go functions from
within a debugger.
This is useful, for example, to call String methods
when paused at a breakpoint.
This is currently only supported by Delve (version 1.1.0 and up).
Since Go 1.10, the go test command runs
go vet on the package being tested,
to identify problems before running the test. Since vet
typechecks the code with go/types
before running, tests that do not typecheck will now fail.
In particular, tests that contain an unused variable inside a
closure compiled with Go 1.10, because the Go compiler incorrectly
accepted them (Issue #3059),
but will now fail, since go/types correctly reports an
"unused variable" error in this case.
The -memprofile flag
to go test now defaults to the
"allocs" profile, which records the total bytes allocated since the
test began (including garbage-collected bytes).
The go vet
command now reports a fatal error when the package under analysis
does not typecheck. Previously, a type checking error simply caused
a warning to be printed, and vet to exit with status 1.
Additionally, go vet
has become more robust when format-checking printf wrappers.
Vet now detects the mistake in this example:
func wrapper(s string, args ...interface{}) {
fmt.Printf(s, args...)
}
func main() {
wrapper("%s", 42)
}
With the new runtime/trace
package's user
annotation API, users can record application-level information
in execution traces and create groups of related goroutines.
The go tool trace
command visualizes this information in the trace view and the new
user task/region analysis page.
Since Go 1.10, cgo has translated some C pointer types to the Go
type uintptr. These types include
the CFTypeRef hierarchy in Darwin's CoreFoundation
framework and the jobject hierarchy in Java's JNI
interface. In Go 1.11, several improvements have been made to the code
that detects these types. Code that uses these types may need some
updating. See the Go 1.10 release notes for
details.
The environment variable GOFLAGS may now be used
to set default flags for the go command.
This is useful in certain situations.
Linking can be noticeably slower on underpowered systems due to DWARF,
and users may want to set -ldflags=-w by default.
For modules, some users and CI systems will want vendoring always,
so they should set -mod=vendor by default.
For more information, see the go
command documentation.
Go 1.11 will be the last release to support godoc's command-line interface.
In future releases, godoc will only be a web server. Users should use
go doc for command-line help output instead.
The godoc web server now shows which version of Go introduced
new API features. The initial Go version of types, funcs, and methods are shown
right-aligned. For example, see UserCacheDir, with "1.11"
on the right side. For struct fields, inline comments are added when the struct field was
added in a Go version other than when the type itself was introduced.
For a struct field example, see
ClientTrace.Got1xxResponse.
One minor detail of the default formatting of Go source code has changed. When formatting expression lists with inline comments, the comments were aligned according to a heuristic. However, in some cases the alignment would be split up too easily, or introduce too much whitespace. The heuristic has been changed to behave better for human-written code.
Note that these kinds of minor updates to gofmt are expected from time to
time.
In general, systems that need consistent formatting of Go source code should
use a specific version of the gofmt binary.
See the go/format package documentation for more
information.
The go run
command now allows a single import path, a directory name or a
pattern matching a single package.
This allows go run pkg or go run dir, most importantly go run .
The runtime now uses a sparse heap layout so there is no longer a
limit to the size of the Go heap (previously, the limit was 512GiB).
This also fixes rare "address space conflict" failures in mixed Go/C
binaries or binaries compiled with -race.
On macOS and iOS, the runtime now uses libSystem.dylib instead of
calling the kernel directly. This should make Go binaries more
compatible with future versions of macOS and iOS.
The syscall package still makes direct
system calls; fixing this is planned for a future release.
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 better generated code and optimizations in the core library.
There were multiple performance changes to the math/big
package as well as many changes across the tree specific to GOARCH=arm64.
The compiler now optimizes map clearing operations of the form:
for k := range m {
delete(m, k)
}
The compiler now optimizes slice extension of the form
append(s, make([]T, n)...).
The compiler now performs significantly more aggressive bounds-check
and branch elimination. Notably, it now recognizes transitive
relations, so if i<j and j<len(s),
it can use these facts to eliminate the bounds check
for s[i]. It also understands simple arithmetic such
as s[i-10] and can recognize more inductive cases in
loops. Furthermore, the compiler now uses bounds information to more
aggressively optimize shift operations.
All of the changes to the standard library are minor.
As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibility in mind.
Certain crypto operations, including
ecdsa.Sign,
rsa.EncryptPKCS1v15 and
rsa.GenerateKey,
now randomly read an extra byte of randomness to ensure tests don't rely on internal behavior.
The new function NewGCMWithTagSize
implements Galois Counter Mode with non-standard tag lengths for compatibility with existing cryptosystems.
ConnectionState's new
ExportKeyingMaterial
method allows exporting keying material bound to the
connection according to RFC 5705.
The deprecated, legacy behavior of treating the CommonName field as
a hostname when no Subject Alternative Names are present is now disabled when the CN is not a
valid hostname.
The CommonName can be completely ignored by adding the experimental value
x509ignoreCN=1 to the GODEBUG environment variable.
When the CN is ignored, certificates without SANs validate under chains with name constraints
instead of returning NameConstraintsWithoutSANs.
Extended key usage restrictions are again checked only if they appear in the KeyUsages
field of VerifyOptions, instead of always being checked.
This matches the behavior of Go 1.9 and earlier.
The value returned by SystemCertPool
is now cached and might not reflect system changes between invocations.
Marshal and Unmarshal
now support "private" class annotations for fields.
The decoder now consistently
returns io.ErrUnexpectedEOF for an incomplete
chunk. Previously it would return io.EOF in some
cases.
The Reader now rejects attempts to set
the Comma
field to a double-quote character, as double-quote characters
already have a special meaning in CSV.
The package has changed its behavior when a typed interface
value is passed to an implicit escaper function. Previously such
a value was written out as (an escaped form)
of <nil>. Now such values are ignored, just
as an untyped nil value is (and always has been)
ignored.
Non-looping animated GIFs are now supported. They are denoted by having a
LoopCount of -1.
The TempFile
function now supports specifying where the random characters in
the filename are placed. If the prefix argument
includes a "*", the random string replaces the
"*". For example, a prefix argument of "myname.*.bat" will
result in a random filename such as
"myname.123456.bat". If no "*" is
included the old behavior is retained, and the random digits are
appended to the end.
ModInverse now returns nil when g and n are not relatively prime. The result was previously undefined.
The handling of form-data with missing/empty file names has been
restored to the behavior in Go 1.9: in the
Form for
the form-data part the value is available in
the Value field rather than the File
field. In Go releases 1.10 through 1.10.3 a form-data part with
a missing/empty file name and a non-empty "Content-Type" field
was stored in the File field. This change was a
mistake in 1.10 and has been reverted to the 1.9 behavior.
To support invalid input found in the wild, the package now permits non-ASCII bytes but does not validate their encoding.
The new ListenConfig type and the new
Dialer.Control field permit
setting socket options before accepting and creating connections, respectively.
The syscall.RawConn Read
and Write methods now work correctly on Windows.
The net package now automatically uses the
splice system call
on Linux when copying data between TCP connections in
TCPConn.ReadFrom, as called by
io.Copy. The result is faster, more efficient TCP proxying.
The TCPConn.File,
UDPConn.File,
UnixConn.File,
and IPConn.File
methods no longer put the returned *os.File into
blocking mode.
The Transport type has a
new MaxConnsPerHost
option that permits limiting the maximum number of connections
per host.
The Cookie type has a new
SameSite field
(of new type also named
SameSite) to represent the new cookie attribute recently supported by most browsers.
The net/http's Transport does not use the SameSite
attribute itself, but the package supports parsing and serializing the
attribute for browsers to use.
It is no longer allowed to reuse a Server
after a call to
Shutdown or
Close. It was never officially supported
in the past and had often surprising behavior. Now, all future calls to the server's Serve
methods will return errors after a shutdown or close.
The constant StatusMisdirectedRequest is now defined for HTTP status code 421.
The HTTP server will no longer cancel contexts or send on
CloseNotifier
channels upon receiving pipelined HTTP/1.1 requests. Browsers do
not use HTTP pipelining, but some clients (such as
Debian's apt) may be configured to do so.
ProxyFromEnvironment, which is used by the
DefaultTransport, now
supports CIDR notation and ports in the NO_PROXY environment variable.
The
ReverseProxy
has a new
ErrorHandler
option to permit changing how errors are handled.
The ReverseProxy now also passes
"TE: trailers" request headers
through to the backend, as required by the gRPC protocol.
The new UserCacheDir function
returns the default root directory to use for user-specific cached data.
The new ModeIrregular
is a FileMode bit to represent
that a file is not a regular file, but nothing else is known about it, or that
it's not a socket, device, named pipe, symlink, or other file type for which
Go has a defined mode bit.
Symlink now works
for unprivileged users on Windows 10 on machines with Developer
Mode enabled.
When a non-blocking descriptor is passed
to NewFile, the
resulting *File will be kept in non-blocking
mode. This means that I/O for that *File will use
the runtime poller rather than a separate thread, and that
the SetDeadline
methods will work.
The new Ignored function reports
whether a signal is currently ignored.
The os/user package can now be built in pure Go
mode using the build tag "osusergo",
independent of the use of the environment
variable CGO_ENABLED=0. Previously the only way to use
the package's pure Go implementation was to disable cgo
support across the entire program.
Setting the GODEBUG=tracebackancestors=N
environment variable now extends tracebacks with the stacks at
which goroutines were created, where N limits the
number of ancestor goroutines to report.
This release adds a new "allocs" profile type that profiles
total number of bytes allocated since the program began
(including garbage-collected bytes). This is identical to the
existing "heap" profile viewed in -alloc_space mode.
Now go test -memprofile=... reports an "allocs" profile
instead of "heap" profile.
The mutex profile now includes reader/writer contention
for RWMutex.
Writer/writer contention was already included in the mutex
profile.
On Windows, several fields were changed from uintptr to a new
Pointer
type to avoid problems with Go's garbage collector. The same change was made
to the golang.org/x/sys/windows
package. For any code affected, users should first migrate away from the syscall
package to the golang.org/x/sys/windows package, and then change
to using the Pointer, while obeying the
unsafe.Pointer conversion rules.
On Linux, the flags parameter to
Faccessat
is now implemented just as in glibc. In earlier Go releases the
flags parameter was ignored.
On Linux, the flags parameter to
Fchmodat
is now validated. Linux's fchmodat doesn't support the flags parameter
so we now mimic glibc's behavior and return an error if it's non-zero.
The Scanner.Scan method now returns
the RawString token
instead of String
for raw string literals.
Modifying template variables via assignments is now permitted via the = token:
{{"{{"}} $v := "init" {{"}}"}}
{{"{{"}} if true {{"}}"}}
{{"{{"}} $v = "changed" {{"}}"}}
{{"{{"}} end {{"}}"}}
v: {{"{{"}} $v {{"}}"}} {{"{{"}}/* "changed" */{{"}}"}}
In previous versions untyped nil values passed to
template functions were ignored. They are now passed as normal
arguments.
Parsing of timezones denoted by sign and offset is now
supported. In previous versions, numeric timezone names
(such as +03) were not considered valid, and only
three-letter abbreviations (such as MST) were accepted
when expecting a timezone name.