The latest Go release, version 1.13, arrives six months after Go 1.12. 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.
As of Go 1.13, the go command by default downloads and authenticates modules using the Go module mirror and Go checksum database run by Google. See https://proxy.golang.org/privacy for privacy information about these services and the go command documentation for configuration details including how to disable the use of these servers or use different ones. If you depend on non-public modules, see the documentation for configuring your environment.
Per the number literal proposal, Go 1.13 supports a more uniform and modernized set of number literal prefixes.
0b or 0B indicates a binary integer literal
such as 0b1011.
0o or 0O indicates an octal integer literal
such as 0o660.
The existing octal notation indicated by a leading 0 followed by
octal digits remains valid.
0x or 0X may now be used to express the mantissa of a
floating-point number in hexadecimal format such as 0x1.0p-1021.
A hexadecimal floating-point number must always have an exponent, written as the letter
p or P followed by an exponent in decimal. The exponent scales
the mantissa by 2 to the power of the exponent.
i may now be used with any (binary, decimal, hexadecimal)
integer or floating-point literal.
1_000_000, 0b_1010_0110, or 3.1415_9265.
An underscore may appear between any two digits or the literal prefix and the first digit.
Per the signed shift counts proposal
Go 1.13 removes the restriction that a shift count
must be unsigned. This change eliminates the need for many artificial uint conversions,
solely introduced to satisfy this (now removed) restriction of the << and >> operators.
These language changes were implemented by changes to the compiler, and corresponding internal changes to the library
packages go/scanner and
text/scanner (number literals),
and go/types (signed shift counts).
If your code uses modules and your go.mod files specifies a language version, be sure
it is set to at least 1.13 to get access to these language changes.
You can do this by editing the go.mod file directly, or you can run
go mod edit -go=1.13.
Go 1.13 is the last release that will run on Native Client (NaCl).
For GOARCH=wasm, the new environment variable GOWASM takes a comma-separated list of experimental features that the binary gets compiled with.
The valid values are documented here.
AIX on PPC64 (aix/ppc64) now supports cgo, external
linking, and the c-archive and pie build
modes.
Go programs are now compatible with Android 10.
As announced in the Go 1.12 release notes, Go 1.13 now requires macOS 10.11 El Capitan or later; support for previous versions has been discontinued.
As announced in the Go 1.12 release notes,
Go 1.13 now requires FreeBSD 11.2 or later;
support for previous versions has been discontinued.
FreeBSD 12.0 or later requires a kernel with the COMPAT_FREEBSD11
option set (this is the default).
Go now supports Illumos with GOOS=illumos.
The illumos build tag implies the solaris
build tag.
The Windows version specified by internally-linked Windows binaries is now Windows 7 rather than NT 4.0. This was already the minimum required version for Go, but can affect the behavior of system calls that have a backwards-compatibility mode. These will now behave as documented. Externally-linked binaries (any program using cgo) have always specified a more recent Windows version.
The GO111MODULE
environment variable continues to default to auto, but
the auto setting now activates the module-aware mode of
the go command whenever the current working directory contains,
or is below a directory containing, a go.mod file — even if the
current directory is within GOPATH/src. This change simplifies
the migration of existing code within GOPATH/src and the ongoing
maintenance of module-aware packages alongside non-module-aware importers.
The new
GOPRIVATE
environment variable indicates module paths that are not publicly available.
It serves as the default value for the lower-level GONOPROXY
and GONOSUMDB variables, which provide finer-grained control over
which modules are fetched via proxy and verified using the checksum database.
The GOPROXY
environment variable may now be set to a comma-separated list of proxy
URLs or the special token direct, and
its default value is
now https://proxy.golang.org,direct. When resolving a package
path to its containing module, the go command will try all
candidate module paths on each proxy in the list in succession. An unreachable
proxy or HTTP status code other than 404 or 410 terminates the search without
consulting the remaining proxies.
The new
GOSUMDB
environment variable identifies the name, and optionally the public key and
server URL, of the database to consult for checksums of modules that are not
yet listed in the main module's go.sum file.
If GOSUMDB does not include an explicit URL, the URL is chosen by
probing the GOPROXY URLs for an endpoint indicating support for
the checksum database, falling back to a direct connection to the named
database if it is not supported by any proxy. If GOSUMDB is set
to off, the checksum database is not consulted and only the
existing checksums in the go.sum file are verified.
Users who cannot reach the default proxy and checksum database (for example,
due to a firewalled or sandboxed configuration) may disable their use by
setting GOPROXY to direct, and/or
GOSUMDB to off.
go env -w
can be used to set the default values for these variables independent of
platform:
go env -w GOPROXY=direct go env -w GOSUMDB=off
go get
In module-aware mode,
go get
with the -u flag now updates a smaller set of modules that is
more consistent with the set of packages updated by
go get -u in GOPATH mode.
go get -u continues to update the
modules and packages named on the command line, but additionally updates only
the modules containing the packages imported by the named packages,
rather than the transitive module requirements of the modules containing the
named packages.
Note in particular that go get -u
(without additional arguments) now updates only the transitive imports of the
package in the current directory. To instead update all of the packages
transitively imported by the main module (including test dependencies), use
go get -u all.
As a result of the above changes to
go get -u, the
go get subcommand no longer supports
the -m flag, which caused go get to
stop before loading packages. The -d flag remains supported, and
continues to cause go get to stop after downloading
the source code needed to build dependencies of the named packages.
By default, go get -u in module mode
upgrades only non-test dependencies, as in GOPATH mode. It now also accepts
the -t flag, which (as in GOPATH mode)
causes go get to include the packages imported
by tests of the packages named on the command line.
In module-aware mode, the go get subcommand now
supports the version suffix @patch. The @patch
suffix indicates that the named module, or module containing the named
package, should be updated to the highest patch release with the same
major and minor versions as the version found in the build list.
If a module passed as an argument to go get
without a version suffix is already required at a newer version than the
latest released version, it will remain at the newer version. This is
consistent with the behavior of the -u flag for module
dependencies. This prevents unexpected downgrades from pre-release versions.
The new version suffix @upgrade explicitly requests this
behavior. @latest explicitly requests the latest version
regardless of the current version.
When extracting a module from a version control system, the go
command now performs additional validation on the requested version string.
The +incompatible version annotation bypasses the requirement
of semantic
import versioning for repositories that predate the introduction of
modules. The go command now verifies that such a version does not
include an explicit go.mod file.
The go command now verifies the mapping
between pseudo-versions and
version-control metadata. Specifically:
vX.0.0, or derived
from a tag on an ancestor of the named revision, or derived from a tag that
includes build metadata on
the named revision itself.go command would generate. (For SHA-1 hashes as used
by git, a 12-digit prefix.)
If a require directive in the
main module uses
an invalid pseudo-version, it can usually be corrected by redacting the
version to just the commit hash and re-running a go command, such
as go list -m all
or go mod tidy. For example,
require github.com/docker/docker v1.14.0-0.20190319215453-e7b5f7dbe98c
can be redacted to
require github.com/docker/docker e7b5f7dbe98c
which currently resolves to
require github.com/docker/docker v0.7.3-0.20190319215453-e7b5f7dbe98c
If one of the transitive dependencies of the main module requires an invalid
version or pseudo-version, the invalid version can be replaced with a valid
one using a
replace directive in
the go.mod file of the main module. If the replacement is a
commit hash, it will be resolved to the appropriate pseudo-version as above.
For example,
replace github.com/docker/docker v1.14.0-0.20190319215453-e7b5f7dbe98c => github.com/docker/docker e7b5f7dbe98c
currently resolves to
replace github.com/docker/docker v1.14.0-0.20190319215453-e7b5f7dbe98c => github.com/docker/docker v0.7.3-0.20190319215453-e7b5f7dbe98c
The go env
command now accepts a -w flag to set the per-user default value
of an environment variable recognized by the
go command, and a corresponding -u flag to unset a
previously-set default. Defaults set via
go env -w are stored in the
go/env file within
os.UserConfigDir().
The
go version command now accepts arguments naming
executables and directories. When invoked on an executable,
go version prints the version of Go used to build
the executable. If the -m flag is used,
go version prints the executable's embedded module
version information, if available. When invoked on a directory,
go version prints information about executables
contained in the directory and its subdirectories.
The new go
build flag -trimpath removes all file system paths
from the compiled executable, to improve build reproducibility.
If the -o flag passed to go build
refers to an existing directory, go build will now
write executable files within that directory for main packages
matching its package arguments.
go
generate now sets the generate build tag so that
files may be searched for directives but ignored during build.
As announced in the Go 1.12 release
notes, binary-only packages are no longer supported. Building a binary-only
package (marked with a //go:binary-only-package comment) now
results in an error.
The compiler has a new implementation of escape analysis that is
more precise. For most Go code should be an improvement (in other
words, more Go variables and expressions allocated on the stack
instead of heap). However, this increased precision may also break
invalid code that happened to work before (for example, code that
violates
the unsafe.Pointer
safety rules). If you notice any regressions that appear
related, the old escape analysis pass can be re-enabled
with go build -gcflags=all=-newescape=false.
The option to use the old escape analysis will be removed in a
future release.
The compiler no longer emits floating point or complex constants
to go_asm.h files. These have always been emitted in a
form that could not be used as numeric constant in assembly code.
The assembler now supports many of the atomic instructions introduced in ARM v8.1.
gofmt (and with that go fmt) now canonicalizes
number literal prefixes and exponents to use lower-case letters, but
leaves hexadecimal digits alone. This improves readability when using the new octal prefix
(0O becomes 0o), and the rewrite is applied consistently.
gofmt now also removes unnecessary leading zeroes from a decimal integer
imaginary literal. (For backwards-compatibility, an integer imaginary literal
starting with 0 is considered a decimal, not an octal number.
Removing superfluous leading zeroes avoids potential confusion.)
For instance, 0B1010, 0XabcDEF, 0O660,
1.2E3, and 01i become 0b1010, 0xabcDEF,
0o660, 1.2e3, and 1i after applying gofmt.
godoc and go doc
The godoc webserver is no longer included in the main binary distribution.
To run the godoc webserver locally, manually install it first:
go get golang.org/x/tools/cmd/godoc godoc
The
go doc
command now always includes the package clause in its output, except for
commands. This replaces the previous behavior where a heuristic was used,
causing the package clause to be omitted under certain conditions.
Out of range panic messages now include the index that was out of
bounds and the length (or capacity) of the slice. For
example, s[3] on a slice of length 1 will panic with
"runtime error: index out of range [3] with length 1".
This release improves performance of most uses of defer
by 30%.
The runtime is now more aggressive at returning memory to the operating system to make it available to co-tenant applications. Previously, the runtime could retain memory for five or more minutes following a spike in the heap size. It will now begin returning it promptly after the heap shrinks. However, on many OSes, including Linux, the OS itself reclaims memory lazily, so process RSS will not decrease until the system is under memory pressure.
As announced in Go 1.12, Go 1.13 enables support for TLS 1.3 in the
crypto/tls package by default. It can be disabled by adding the
value tls13=0 to the GODEBUG
environment variable. The opt-out will be removed in Go 1.14.
See the Go 1.12 release notes for important compatibility information.
The new crypto/ed25519
package implements the Ed25519 signature
scheme. This functionality was previously provided by the
golang.org/x/crypto/ed25519
package, which becomes a wrapper for
crypto/ed25519 when used with Go 1.13+.
Go 1.13 contains support for error wrapping, as first proposed in the Error Values proposal and discussed on the associated issue.
An error e can wrap another error w by providing
an Unwrap method that returns w. Both e
and w are available to programs, allowing e to provide
additional context to w or to reinterpret it while still allowing
programs to make decisions based on w.
To support wrapping, fmt.Errorf now has a %w
verb for creating wrapped errors, and three new functions in
the errors package (
errors.Unwrap,
errors.Is and
errors.As) simplify unwrapping
and inspecting wrapped errors.
For more information, read the errors package
documentation, or see
the Error Value FAQ.
There will soon be a blog post as well.
As always, there are various minor changes and updates to the library, made with the Go 1 promise of compatibility in mind.
The new ToValidUTF8 function returns a
copy of a given byte slice with each run of invalid UTF-8 byte sequences replaced by a given slice.
The formatting of contexts returned by WithValue no longer depends on fmt and will not stringify in the same way. Code that depends on the exact previous stringification might be affected.
Support for SSL version 3.0 (SSLv3) is now deprecated and will be removed in Go 1.14. Note that SSLv3 is the cryptographically broken protocol predating TLS.
SSLv3 was always disabled by default, other than in Go 1.12, when it was mistakenly enabled by default server-side. It is now again disabled by default. (SSLv3 was never supported client-side.)
Ed25519 certificates are now supported in TLS versions 1.2 and 1.3.
Ed25519 keys are now supported in certificates and certificate requests
according to RFC 8410, as well as by the
ParsePKCS8PrivateKey,
MarshalPKCS8PrivateKey,
and ParsePKIXPublicKey functions.
The paths searched for system roots now include /etc/ssl/cert.pem
to support the default location in Alpine Linux 3.7+.
The new NullTime type represents a time.Time that may be null.
The new NullInt32 type represents an int32 that may be null.
The Data.Type
method no longer panics if it encounters an unknown DWARF tag in
the type graph. Instead, it represents that component of the
type with
an UnsupportedType
object.
The new function As finds the first
error in a given error’s chain (sequence of wrapped errors)
that matches a given target’s type, and if so, sets the target to that error value.
The new function Is reports whether a given error value matches an
error in another’s chain.
The new function Unwrap returns the result of calling
Unwrap on a given error, if one exists.
The printing verbs %x and %X now format floating-point and
complex numbers in hexadecimal notation, in lower-case and upper-case respectively.
The new printing verb %O formats integers in base 8, emitting the 0o prefix.
The scanner now accepts hexadecimal floating-point values, digit-separating underscores
and leading 0b and 0o prefixes.
See the Changes to the language for details.
The Errorf function
has a new verb, %w, whose operand must be an error.
The error returned from Errorf will have an
Unwrap method which returns the operand of %w.
The scanner has been updated to recognize the new Go number literals, specifically
binary literals with 0b/0B prefix, octal literals with 0o/0O prefix,
and floating-point numbers with hexadecimal mantissa. The imaginary suffix i may now be used with any number
literal, and underscores may used as digit separators for grouping.
See the Changes to the language for details.
The type-checker has been updated to follow the new rules for integer shifts. See the Changes to the language for details.
When using a <script> tag with "module" set as the
type attribute, code will now be interpreted as JavaScript module script.
The new Writer function returns the output destination for the standard logger.
The new Rat.SetUint64 method sets the Rat to a uint64 value.
For Float.Parse, if base is 0, underscores
may be used between digits for readability.
See the Changes to the language for details.
For Int.SetString, if base is 0, underscores
may be used between digits for readability.
See the Changes to the language for details.
Rat.SetString now accepts non-decimal floating point representations.
The execution time of Add,
Sub,
Mul,
RotateLeft, and
ReverseBytes is now
guaranteed to be independent of the inputs.
On Unix systems where use-vc is set in resolv.conf, TCP is used for DNS resolution.
The new field ListenConfig.KeepAlive
specifies the keep-alive period for network connections accepted by the listener.
If this field is 0 (the default) TCP keep-alives will be enabled.
To disable them, set it to a negative value.
Note that the error returned from I/O on a connection that was
closed by a keep-alive timeout will have a
Timeout method that returns true if called.
This can make a keep-alive error difficult to distinguish from
an error returned due to a missed deadline as set by the
SetDeadline
method and similar methods.
Code that uses deadlines and checks for them with
the Timeout method or
with os.IsTimeout
may want to disable keep-alives, or
use errors.Is(syscall.ETIMEDOUT) (on Unix systems)
which will return true for a keep-alive timeout and false for a
deadline timeout.
The new fields Transport.WriteBufferSize
and Transport.ReadBufferSize
allow one to specify the sizes of the write and read buffers for a Transport.
If either field is zero, a default size of 4KB is used.
The new field Transport.ForceAttemptHTTP2
controls whether HTTP/2 is enabled when a non-zero Dial, DialTLS, or DialContext
func or TLSClientConfig is provided.
Transport.MaxConnsPerHost now works
properly with HTTP/2.
TimeoutHandler's
ResponseWriter now implements the
Pusher and Flusher interfaces.
The StatusCode 103 "Early Hints" has been added.
Transport now uses the Request.Body's
io.ReaderFrom implementation if available, to optimize writing the body.
On encountering unsupported transfer-encodings, http.Server now
returns a "501 Unimplemented" status as mandated by the HTTP specification RFC 7230 Section 3.3.1.
The new Server fields
BaseContext and
ConnContext
allow finer control over the Context values provided to requests and connections.
http.DetectContentType now correctly detects RAR signatures, and can now also detect RAR v5 signatures.
The new Header method
Clone returns a copy of the receiver.
A new function NewRequestWithContext has been added and it
accepts a Context that controls the entire lifetime of
the created outgoing Request, suitable for use with
Client.Do and Transport.RoundTrip.
The Transport no longer logs errors when servers
gracefully shut down idle connections using a "408 Request Timeout" response.
The new UserConfigDir function
returns the default directory to use for user-specific configuration data.
If a File is opened using the O_APPEND flag, its
WriteAt method will always return an error.
On Windows, the environment for a Cmd always inherits the
%SYSTEMROOT% value of the parent process unless the
Cmd.Env field includes an explicit value for it.
The new Value.IsZero method reports whether a Value is the zero value for its type.
The MakeFunc function now allows assignment conversions on returned values, instead of requiring exact type match. This is particularly useful when the type being returned is an interface type, but the value actually returned is a concrete value implementing that type.
Tracebacks, runtime.Caller,
and runtime.Callers now refer to the function that
initializes the global variables of PKG
as PKG.init instead of PKG.init.ializers.
For strconv.ParseFloat,
strconv.ParseInt
and strconv.ParseUint,
if base is 0, underscores may be used between digits for readability.
See the Changes to the language for details.
The new ToValidUTF8 function returns a
copy of a given string with each run of invalid UTF-8 byte sequences replaced by a given string.
The fast paths of Mutex.Lock, Mutex.Unlock,
RWMutex.Lock, RWMutex.RUnlock, and
Once.Do are now inlined in their callers.
For the uncontended cases on amd64, these changes make Once.Do twice as fast, and the
Mutex/RWMutex methods up to 10% faster.
Large Pool no longer increase stop-the-world pause times.
Pool no longer needs to be completely repopulated after every GC. It now retains some objects across GCs,
as opposed to releasing all objects, reducing load spikes for heavy users of Pool.
Uses of _getdirentries64 have been removed from
Darwin builds, to allow Go binaries to be uploaded to the macOS
App Store.
The new ProcessAttributes and ThreadAttributes fields in
SysProcAttr have been introduced for Windows,
exposing security settings when creating new processes.
EINVAL is no longer returned in zero
Chmod mode on Windows.
Values of type Errno can be tested against error values in
the os package,
like ErrExist, using
errors.Is.
TypedArrayOf has been replaced by
CopyBytesToGo and
CopyBytesToJS for copying bytes
between a byte slice and a Uint8Array.
When running benchmarks, B.N is no longer rounded.
The new method B.ReportMetric lets users report
custom benchmark metrics and override built-in metrics.
Testing flags are now registered in the new Init function,
which is invoked by the generated main function for the test.
As a result, testing flags are now only registered when running a test binary,
and packages that call flag.Parse during package initialization may cause tests to fail.
The scanner has been updated to recognize the new Go number literals, specifically
binary literals with 0b/0B prefix, octal literals with 0o/0O prefix,
and floating-point numbers with hexadecimal mantissa.
Also, the new AllowDigitSeparators
mode allows number literals to contain underscores as digit separators (off by default for backwards-compatibility).
See the Changes to the language for details.
The new slice function returns the result of slicing its first argument by the following arguments.
Day-of-year is now supported by Format
and Parse.
The new Duration methods
Microseconds and
Milliseconds return
the duration as an integer count of their respectively named units.
The unicode package and associated
support throughout the system has been upgraded from Unicode 10.0 to
Unicode 11.0,
which adds 684 new characters, including seven new scripts, and 66 new emoji.