Go 1.12 is not yet released. These are work-in-progress release notes. Go 1.12 is expected to be released in February 2019.
The latest Go release, version 1.12, arrives six months after Go 1.11. Most of its changes are in TODO. 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.
Go 1.12 is the last release that is supported on FreeBSD 10.x, which has already reached end-of-life. Go 1.13 will require FreeBSD 11.2+ or FreeBSD 12.0+.
Go 1.12 is the last release that will run on macOS 10.10 Yosemite. Go 1.13 will require macOS 10.11 El Capitan or later.
TODO: status of ARM32 port?
TODO: status of AIX port?
hurd is now a recognized value for GOOS, reserved
for the GNU/Hurd system for use with gccgo.
go tool vet no longer supported
The go vet command has been rewritten to serve as the
base for a range of different source code analysis tools. See
the golang.org/x/tools/go/analysis
package for details. A side-effect is that go tool vet
is no longer supported. External tools that use go tool
vet must be changed to use go
vet. Using go vet instead of go tool
vet should work with all supported versions of Go.
The build cache is now
required as a step toward eliminating
$GOPATH/pkg. Setting the environment variable
GOCACHE=off will cause go commands that write to the
cache to fail.
Go 1.12 is the last release that will support binary-only packages.
When GO111MODULE is set to on, the go
command now supports module-aware operations outside of a module directory,
provided that those operations do not need to resolve import paths relative to
the current directory or explicitly edit the go.mod file.
Commands such as go get,
go list, and
go mod download behave as if in a
module with initially-empty requirements.
In this mode, go env GOMOD reports
the system's null device (/dev/null or NUL).
go commands that download and extract modules are now safe to
invoke concurrently.
The module cache (GOPATH/pkg/mod) must reside in a filesystem that
supports file locking.
The go directive in a go.mod file now indicates the
version of the language used by the files within that module, and
go mod tidy sets it to the
current release (go 1.12) if no existing
version is present.
If the go directive for a module specifies a
version newer than the toolchain in use, the go command
will attempt to build the packages regardless, and will note the mismatch only if
that build fails.
When an import cannot be resolved using the active modules,
the go command will now try to use the modules mentioned in the
main module's replace directives before consulting the module
cache and the usual network sources.
If a matching replacement is found but the replace directive does
not specify a version, the go command uses a pseudo-version
derived from the zero time.Time (such
as v0.0.0-00010101000000-000000000000).
The compiler's live variable analysis has improved. This may mean that
finalizers will be executed sooner in this release than in previous
releases. If that is a problem, consider the appropriate addition of a
runtime.KeepAlive call.
More functions are now eligible for inlining by default, including
functions that do nothing but call another function.
This extra inlining makes it additionally important to use
runtime.CallersFrames
instead of iterating over the result of
runtime.Callers directly.
// Old code which no longer works correctly (it will miss inlined call frames).
var pcs [10]uintptr
n := runtime.Callers(1, pcs[:])
for _, pc := range pcs[:n] {
f := runtime.FuncForPC(pc)
if f != nil {
fmt.Println(f.Name())
}
}
// New code which will work correctly.
var pcs [10]uintptr
n := runtime.Callers(1, pcs[:])
frames := runtime.CallersFrames(pcs[:n])
for {
frame, more := frames.Next()
fmt.Println(frame.Function)
if !more {
break
}
}
The compiler now accepts a -lang flag to set the Go language
version to use. For example, -lang=go1.8 causes the compiler to
emit an error if the program uses type aliases, which were added in Go 1.9.
Language changes made before Go 1.12 are not consistently enforced.
In Go 1.12, godoc no longer has a command-line interface and
is only a web server. Users should use go doc
for command-line help output instead.
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.
TODO: https://golang.org/cl/149297: make Reader.Peek invalidate Unreads
TODO: https://golang.org/cl/61511: support frame-pointer for arm64
The new function ReplaceAll returns a copy of
a byte slice with all non-overlapping instances of a value replaced by another.
A pointer to a zero-value Reader is now
functionally equivalent to NewReader(nil).
Prior to Go 1.12, the former could not be used as a substitute for the latter in all cases.
TODO: https://golang.org/cl/138675: enable race detector on arm64
TODO: https://golang.org/cl/120055: use the new getrandom syscall on FreeBSD
TODO: https://golang.org/cl/139419: warn to stderr if blocked 60+ sec on first Reader.Read call
TODO: https://golang.org/cl/130397: remove assembler implementations
Maps are now printed in key-sorted order to ease testing. The ordering rules are:
reflect.Type describing the concrete type
and then by concrete value as described in the previous rules.
When printing maps, non-reflexive key values like NaN were previously
displayed as <nil>. As of this release, the correct values are printed.
To address some outstanding issues in cmd/doc,
this package has a new Mode bit,
PreserveAST, which controls whether AST data is cleared.
The File type has a new
LineStart field,
which returns the position of the start of a given line. This is especially useful
in programs that occassionally handle non-Go files, such as assembly, but wish to use
the token.Pos mechanism to identify file positions.
The RegisterFormat function is now safe for concurrent use.
Paletted images with fewer than 16 colors now encode to smaller outputs.
TODO: https://golang.org/cl/149578: move GODEBUGCPU options into GODEBUG
TODO: https://golang.org/cl/130676: use F_FULLFSYNC fcntl for FD.Fsync on OS X
The new StringWriter interface wraps the
WriteString function.
The time zone database in $GOROOT/lib/time/zoneinfo.zip has been updated to version 2018g. Note that this ZIP file is only used if a time zone database is not provided by the operating system.
New extended precision operations Add, Sub, Mul, and Div are available in int, int32, and int64 versions.
The
Dialer.DualStack setting is now ignored and deprecated;
RFC 6555 Fast Fallback ("Happy Eyeballs") is now enabled by default. To disable, set
Dialer.FallbackDelay to a negative value.
Similarly, TCP keep-alives are now enabled by default if
Dialer.KeepAlive is zero.
To disable, set it to a negative value.
On Linux, the splice system call is now used when copying from a
UnixConn to a
TCPConn.
The HTTP server now rejects misdirected HTTP requests to HTTPS servers with a plaintext "400 Bad Request" response.
The new Client.CloseIdleConnections
method calls the Client's underlying Transport's CloseIdleConnections
if it has one.
The Transport no longer rejects HTTP responses which declare
HTTP Trailers but don't use chunked encoding. Instead, the declared trailers are now just ignored.
The Transport no longer handles MAX_CONCURRENT_STREAMS values
advertised from HTTP/2 servers as strictly as it did during Go 1.10 and Go 1.11. The default behavior is now back
to how it was in Go 1.9: each connection to a server can have up to MAX_CONCURRENT_STREAMS requests
active and then new TCP connections are created as needed. In Go 1.10 and Go 1.11 the http2 package
would block and wait for requests to finish instead of creating new connections.
To get the stricter behavior back, import the
golang.org/x/net/http2 package
directly and set
Transport.StrictMaxConcurrentStreams to
true.
The ReverseProxy now automatically
proxies WebSocket requests.
The new ProcessState.ExitCode method
returns the process's exit code.
ModeCharDevice has been added to the ModeType bitmask, allowing for
ModeDevice | ModeCharDevice to be recovered when masking a
FileMode with ModeType.
The new function UserHomeDir returns the
current user's home directory.
RemoveAll now supports paths longer than 4096 characters
on most Unix systems.
The IsAbs function now returns true when passed
a reserved filename on Windows such as NUL.
List of reserved names.
A new MapIter type is
an iterator for ranging over a map. This type is exposed through the
Value type's new
MapRange method.
This follows the same iteration semantics as a range statment, with Next
to advance the iterator, and Key/Value to access each entry.
TODO: https://golang.org/cl/139783: add DeepEqual test
TODO: https://golang.org/cl/139784: add partial Deprecation comment to Copy
TODO: https://golang.org/cl/135395: use MADV_FREE on Linux if available
TODO: https://golang.org/cl/144220: add API to read module info in binary
The new function ReplaceAll returns a copy of
a string with all non-overlapping instances of a value replaced by another.
A pointer to a zero-value Reader is now
functionally equivalent to NewReader(nil).
Prior to Go 1.12, the former could not be used as a substitute for the latter in all cases.
The new Builder.Cap method returns the capacity of the builder's underlying byte slice.
The character mapping functions Map,
Title,
ToLower,
ToLowerSpecial,
ToTitle,
ToTitleSpecial,
ToUpper, and
ToUpperSpecial
now always guarantee to return valid UTF-8. In earlier releases, if the input was invalid UTF-8 but no character replacements
needed to be applied, these routines incorrectly returned the invalid UTF-8 unmodified.
TODO: https://golang.org/cl/125456: implement Unix Socket for Windows
TODO: https://golang.org/cl/138595: FreeBSD 12 ino64 support
TODO: https://golang.org/cl/141639: implement syscalls on Darwin using libSystem
TODO: https://golang.org/cl/147117: add Syscall18 on Windows
TODO: https://golang.org/cl/141644: add Wrapper interface to support external Value wrapper types
TODO: https://golang.org/cl/143137: make zero js.Value represent "undefined"
TODO: https://golang.org/cl/144384: add the Value.Truthy method
The -benchtime flag now supports setting an explicit iteration count instead of a time when the value ends with an "x". For example, -benchtime=100x runs the benchmark 100 times.
When executing a template, long context values are no longer truncated in errors.
executing "tmpl" at <.very.deep.context.v...>: map has no entry for key "notpresent"
is now
executing "tmpl" at <.very.deep.context.value.notpresent>: map has no entry for key "notpresent"