diff --git a/doc/go1.20.html b/doc/go1.20.html deleted file mode 100644 index 1fef45204e..0000000000 --- a/doc/go1.20.html +++ /dev/null @@ -1,1246 +0,0 @@ - - - - - - -

DRAFT RELEASE NOTES — Introduction to Go 1.20

- -

- - Go 1.20 is not yet released. These are work-in-progress - release notes. Go 1.20 is expected to be released in February 2023. - -

- -

Changes to the language

- -

- Go 1.20 includes four changes to the language. -

- -

- Go 1.17 added conversions from slice to an array pointer. - Go 1.20 extends this to allow conversions from a slice to an array: - given a slice x, [4]byte(x) can now be written - instead of *(*[4]byte)(x). -

- -

- The unsafe package defines - three new functions SliceData, String, and StringData. - Along with Go 1.17's Slice, these functions now provide the complete ability to - construct and deconstruct slice and string values, without depending on their exact representation. -

- -

- The specification now defines that struct values are compared one field at a time, - considering fields in the order they appear in the struct type definition, - and stopping at the first mismatch. - The specification could previously have been read as if - all fields needed to be compared beyond the first mismatch. - Similarly, the specification now defines that array values are compared - one element at a time, in increasing index order. - In both cases, the difference affects whether certain comparisons must panic. - Existing programs are unchanged: the new spec wording describes - what the implementations have always done. -

- -

- Comparable types (such as ordinary interfaces) - may now satisfy comparable constraints, even if the type arguments - are not strictly comparable (comparison may panic at runtime). - This makes it possible to instantiate a type parameter constrained by comparable - (e.g., a type parameter for a user-defined generic map key) with a non-strictly comparable type argument - such as an interface type, or a composite type containing an interface type. -

- -

Ports

- -

Windows

- -

- Go 1.20 is the last release that will run on any release of Windows 7, 8, Server 2008 and Server 2012. - Go 1.21 will require at least Windows 10 or Server 2016. -

- -

Darwin and iOS

- -

- Go 1.20 is the last release that will run on macOS 10.13 High Sierra or 10.14 Mojave. - Go 1.21 will require macOS 10.15 Catalina or later. -

- -

FreeBSD/RISC-V

- -

- Go 1.20 adds experimental support for FreeBSD on RISC-V (GOOS=freebsd, GOARCH=riscv64). -

- -

Tools

- -

Go command

- -

- The directory $GOROOT/pkg no longer stores - pre-compiled package archives for the standard library: - go install no longer writes them, - the go build no longer checks for them, - and the Go distribution no longer ships them. - Instead, packages in the standard library are built as needed - and cached in the build cache, just like packages outside GOROOT. - This change reduces the size of the Go distribution and also - avoids C toolchain skew for packages that use cgo. -

- -

- The implementation of go test -json - has been improved to make it more robust. - Programs that run go test -json - do not need any updates. - Programs that invoke go tool test2json - directly should now run the test binary with -v=test2json - (for example, go test -v=test2json - or ./pkg.test -test.v=test2json) - instead of plain -v. -

- -

- A related change to go test -json - is the addition of an event with Action set to start - at the beginning of each test program's execution. - When running multiple tests using the go command, - these start events are guaranteed to be emitted in the same order as - the packages named on the command line. -

- -

- The go command now defines - architecture feature build tags, such as amd64.v2, - to allow selecting a package implementation file based on the presence - or absence of a particular architecture feature. - See go help buildconstraint for details. -

- -

- The go subcommands now accept - -C <dir> to change directory to <dir> - before performing the command, which may be useful for scripts that need to - execute commands in multiple different modules. -

- -

- The go build and go test - commands no longer accept the -i flag, - which has been deprecated since Go 1.16. -

- -

- The go generate command now accepts - -skip <pattern> to skip //go:generate directives - matching <pattern>. -

- -

- The go test command now accepts - -skip <pattern> to skip tests, subtests, or examples - matching <pattern>. -

- -

- When the main module is located within GOPATH/src, - go install no longer installs libraries for - non-main packages to GOPATH/pkg, - and go list no longer reports a Target - field for such packages. (In module mode, compiled packages are stored in the - build cache - only, but a bug had caused - the GOPATH install targets to unexpectedly remain in effect.) -

- -

- The go build, go install, - and other build-related commands now support a -pgo flag that enables - profile-guided optimization, which is described in more detail in the - Compiler section below. - The -pgo flag specifies the file path of the profile. - Specifying -pgo=auto causes the go command to search - for a file named default.pgo in the main package's directory and - use it if present. - This mode currently requires a single main package to be specified on the - command line, but we plan to lift this restriction in a future release. - Specifying -pgo=off turns off profile-guided optimization. -

- -

- The go build, go install, - and other build-related commands now support a -cover - flag that builds the specified target with code coverage instrumentation. - This is described in more detail in the - Cover section below. -

- -

go version

- -

- The go version -m command - now supports reading more types of Go binaries, most notably, Windows DLLs - built with go build -buildmode=c-shared - and Linux binaries without execute permission. -

- -

Cgo

- -

- The go command now disables cgo by default - on systems without a C toolchain. - More specifically, when the CGO_ENABLED environment variable is unset, - the CC environment variable is unset, - and the default C compiler (typically clang or gcc) - is not found in the path, - CGO_ENABLED defaults to 0. - As always, you can override the default by setting CGO_ENABLED explicitly. -

- -

- The most important effect of the default change is that when Go is installed - on a system without a C compiler, it will now use pure Go builds for packages - in the standard library that use cgo, instead of using pre-distributed package archives - (which have been removed, as noted above) - or attempting to use cgo and failing. - This makes Go work better in some minimal container environments - as well as on macOS, where pre-distributed package archives have - not been used for cgo-based packages since Go 1.16. -

- -

- The packages in the standard library that use cgo are net, - os/user, and - plugin. - On macOS, the net and os/user packages have been rewritten not to use cgo: - the same code is now used for cgo and non-cgo builds as well as cross-compiled builds. - On Windows, the net and os/user packages have never used cgo. - On other systems, builds with cgo disabled will use a pure Go version of these packages. -

- -

- On macOS, the race detector has been rewritten not to use cgo: - race-detector-enabled programs can be built and run without Xcode. - On Linux and other Unix systems, and on Windows, a host C toolchain - is required to use the race detector. -

- -

Cover

- -

- Go 1.20 supports collecting code coverage profiles for programs - (applications and integration tests), as opposed to just unit tests. -

- -

- To collect coverage data for a program, build it with go - build's -cover flag, then run the resulting - binary with the environment variable GOCOVERDIR set - to an output directory for coverage profiles. - See the - 'coverage for integration tests' landing page for more on how to get started. - For details on the design and implementation, see the - proposal. -

- -

Vet

- -

Improved detection of loop variable capture by nested functions

- -

- The vet tool now reports references to loop variables following - a call to T.Parallel() - within subtest function bodies. Such references may observe the value of the - variable from a different iteration (typically causing test cases to be - skipped) or an invalid state due to unsynchronized concurrent access. -

- -

- The tool also detects reference mistakes in more places. Previously it would - only consider the last statement of the loop body, but now it recursively - inspects the last statements within if, switch, and select statements. -

- -

New diagnostic for incorrect time formats

- -

- The vet tool now reports use of the time format 2006-02-01 (yyyy-dd-mm) - with Time.Format and - time.Parse. - This format does not appear in common date standards, but is frequently - used by mistake when attempting to use the ISO 8601 date format - (yyyy-mm-dd). -

- -

Runtime

- -

- Some of the garbage collector's internal data structures were reorganized to - be both more space and CPU efficient. - This change reduces memory overheads and improves overall CPU performance by - up to 2%. -

- -

- The garbage collector behaves less erratically with respect to goroutine - assists in some circumstances. -

- -

- Go 1.20 adds a new runtime/coverage package - containing APIs for writing coverage profile data at - runtime from long-running and/or server programs that - do not terminate via os.Exit(). -

- -

Compiler

- -

- Go 1.20 adds preview support for profile-guided optimization (PGO). - PGO enables the toolchain to perform application- and workload-specific - optimizations based on run-time profile information. - Currently, the compiler supports pprof CPU profiles, which can be collected - through usual means, such as the runtime/pprof or - net/http/pprof packages. - To enable PGO, pass the path of a pprof profile file via the - -pgo flag to go build, - as mentioned above. - Go 1.20 uses PGO to more aggressively inline functions at hot call sites. - Benchmarks for a representative set of Go programs show enabling - profile-guided inlining optimization improves performance about 3–4%. - We plan to add more profile-guided optimizations in future releases. - Note that profile-guided optimization is a preview, so please use it - with appropriate caution. -

- -

- The Go 1.20 compiler upgraded its front-end to use a new way of handling the - compiler's internal data, which fixes several generic-types bugs and enables - local types in generic functions and methods. -

- -

- The compiler now disallows anonymous interface cycles. -

- -

- Go 1.18 and 1.19 saw regressions in build speed, largely due to the addition - of support for generics and follow-on work. Go 1.20 improves build speeds by - up to 10%, bringing it back in line with Go 1.17. - Relative to Go 1.19, generated code performance is also generally slightly improved. -

- -

Linker

- -

- On Linux, the linker now selects the dynamic interpreter for glibc - or musl at link time. -

- -

- On Windows, the Go linker now supports modern LLVM-based C toolchains. -

- -

- Go 1.20 uses go: and type: prefixes for compiler-generated - symbols rather than go. and type.. - This avoids confusion for user packages whose name starts with go.. - The debug/gosym package understands - this new naming convention for binaries built with Go 1.20 and newer. -

- -

Bootstrap

- -

- When building a Go release from source and GOROOT_BOOTSTRAP is not set, - previous versions of Go looked for a Go 1.4 or later bootstrap toolchain in the directory - $HOME/go1.4 (%HOMEDRIVE%%HOMEPATH%\go1.4 on Windows). - Go 1.18 and Go 1.19 looked first for $HOME/go1.17 or $HOME/sdk/go1.17 - before falling back to $HOME/go1.4, - in anticipation of requiring Go 1.17 for use when bootstrapping Go 1.20. - Go 1.20 does require a Go 1.17 release for bootstrapping, but we realized that we should - adopt the latest point release of the bootstrap toolchain, so it requires Go 1.17.13. - Go 1.20 looks for $HOME/go1.17.13 or $HOME/sdk/go1.17.13 - before falling back to $HOME/go1.4 - (to support systems that hard-coded the path $HOME/go1.4 but have installed - a newer Go toolchain there). - In the future, we plan to move the bootstrap toolchain forward approximately once a year, - and in particular we expect that Go 1.22 will require the final point release of Go 1.20 for bootstrap. -

- -

Core library

- -

New crypto/ecdh package

- -

- Go 1.20 adds a new crypto/ecdh package - to provide explicit support for Elliptic Curve Diffie-Hellman key exchanges - over NIST curves and Curve25519. -

-

- Programs should use crypto/ecdh instead of the lower-level functionality in - crypto/elliptic for ECDH, and - third-party modules for more advanced use cases. -

- -

Wrapping multiple errors

- -

- Go 1.20 expands support for error wrapping to permit an error to - wrap multiple other errors. -

-

- An error e can wrap more than one error by providing - an Unwrap method that returns a []error. -

-

- The errors.Is and - errors.As functions - have been updated to inspect multiply wrapped errors. -

-

- The fmt.Errorf function - now supports multiple occurrences of the %w format verb, - which will cause it to return an error that wraps all of those error operands. -

-

- The new function errors.Join - returns an error wrapping a list of errors. -

- -

HTTP ResponseController

- -

- The new - "net/http".ResponseController - type provides access to extended per-request functionality not handled by the - "net/http".ResponseWriter interface. -

- -

- Previously, we have added new per-request functionality by defining optional - interfaces which a ResponseWriter can implement, such as - Flusher. These interfaces - are not discoverable and clumsy to use. -

- -

- The ResponseController type provides a clearer, more discoverable way - to add per-handler controls. Two such controls also added in Go 1.20 are - SetReadDeadline and SetWriteDeadline, which allow setting - per-request read and write deadlines. For example: -

- -
-func RequestHandler(w ResponseWriter, r *Request) {
-  rc := http.NewResponseController(w)
-  rc.SetWriteDeadline(time.Time{}) // disable Server.WriteTimeout when sending a large response
-  io.Copy(w, bigData)
-}
-
- -

New ReverseProxy Rewrite hook

- -

- The httputil.ReverseProxy - forwarding proxy includes a new - Rewrite - hook function, superseding the - previous Director hook. -

- -

- The Rewrite hook accepts a - ProxyRequest parameter, - which includes both the inbound request received by the proxy and the outbound - request that it will send. - Unlike Director hooks, which only operate on the outbound request, - this permits Rewrite hooks to avoid certain scenarios where - a malicious inbound request may cause headers added by the hook - to be removed before forwarding. - See issue #50580. -

- -

- The ProxyRequest.SetURL - method routes the outbound request to a provided destination - and supersedes the NewSingleHostReverseProxy function. - Unlike NewSingleHostReverseProxy, SetURL - also sets the Host header of the outbound request. -

- -

- The - ProxyRequest.SetXForwarded - method sets the X-Forwarded-For, X-Forwarded-Host, - and X-Forwarded-Proto headers of the outbound request. - When using a Rewrite, these headers are not added by default. -

- -

- An example of a Rewrite hook using these features is: -

- -
-proxyHandler := &httputil.ReverseProxy{
-  Rewrite: func(r *httputil.ProxyRequest) {
-    r.SetURL(outboundURL) // Forward request to outboundURL.
-    r.SetXForwarded()     // Set X-Forwarded-* headers.
-    r.Out.Header.Set("X-Additional-Header", "header set by the proxy")
-  },
-}
-
- -

- ReverseProxy no longer adds a User-Agent header - to forwarded requests when the incoming request does not have one. -

- -

Minor changes to the library

- -

- As always, there are various minor changes and updates to the library, - made with the Go 1 promise of compatibility - in mind. - There are also various performance improvements, not enumerated here. -

- -
archive/tar
-
-

- When the GODEBUG=tarinsecurepath=0 environment variable is set, - Reader.Next method - will now return the error ErrInsecurePath - for an entry with a file name that is an absolute path, - refers to a location outside the current directory, contains invalid - characters, or (on Windows) is a reserved name such as NUL. - A future version of Go may disable insecure paths by default. -

-
-
- -
archive/zip
-
-

- When the GODEBUG=zipinsecurepath=0 environment variable is set, - NewReader will now return the error - ErrInsecurePath - when opening an archive which contains any file name that is an absolute path, - refers to a location outside the current directory, contains invalid - characters, or (on Windows) is a reserved names such as NUL. - A future version of Go may disable insecure paths by default. -

-

- Reading from a directory file that contains file data will now return an error. - The zip specification does not permit directory files to contain file data, - so this change only affects reading from invalid archives. -

-
-
- -
bytes
-
-

- The new - CutPrefix and - CutSuffix functions - are like TrimPrefix - and TrimSuffix - but also report whether the string was trimmed. -

- -

- The new Clone function - allocates a copy of a byte slice. -

-
-
- -
context
-
-

- The new WithCancelCause function - provides a way to cancel a context with a given error. - That error can be retrieved by calling the new Cause function. -

-
-
- -
crypto/ecdsa
-
-

- When using supported curves, all operations are now implemented in constant time. - This led to an increase in CPU time between 5% and 30%, mostly affecting P-384 and P-521. -

- -

- The new PrivateKey.ECDH method - converts an ecdsa.PrivateKey to an ecdh.PrivateKey. -

-
-
- -
crypto/ed25519
-
-

- The PrivateKey.Sign method - and the - VerifyWithOptions function - now support signing pre-hashed messages with Ed25519ph, - indicated by an - Options.HashFunc - that returns - crypto.SHA512. - They also now support Ed25519ctx and Ed25519ph with context, - indicated by setting the new - Options.Context - field. -

-
-
- -
crypto/rsa
-
-

- The new field OAEPOptions.MGFHash - allows configuring the MGF1 hash separately for OAEP decryption. -

- -

- crypto/rsa now uses a new, safer, constant-time backend. This causes a CPU - runtime increase for decryption operations between approximately 15% - (RSA-2048 on amd64) and 45% (RSA-4096 on arm64), and more on 32-bit architectures. - Encryption operations are approximately 20x slower than before (but still 5-10x faster than decryption). - Performance is expected to improve in future releases. - Programs must not modify or manually generate the fields of - PrecomputedValues. -

-
-
- -
crypto/subtle
-
-

- The new function XORBytes - XORs two byte slices together. -

-
-
- -
crypto/tls
-
-

- Parsed certificates are now shared across all clients actively using that certificate. - The memory savings can be significant in programs that make many concurrent connections to a - server or collection of servers sharing any part of their certificate chains. -

- -

- For a handshake failure due to a certificate verification failure, - the TLS client and server now return an error of the new type - CertificateVerificationError, - which includes the presented certificates. -

-
-
- -
crypto/x509
-
-

- ParsePKCS8PrivateKey - and - MarshalPKCS8PrivateKey - now support keys of type *crypto/ecdh.PrivateKey. - ParsePKIXPublicKey - and - MarshalPKIXPublicKey - now support keys of type *crypto/ecdh.PublicKey. - Parsing NIST curve keys still returns values of type - *ecdsa.PublicKey and *ecdsa.PrivateKey. - Use their new ECDH methods to convert to the crypto/ecdh types. -

-

- The new SetFallbackRoots - function allows a program to define a set of fallback root certificates in case an - operating system verifier or standard platform root bundle is unavailable at runtime. - It will most commonly be used with a new package, golang.org/x/crypto/x509roots/fallback, - which will provide an up to date root bundle. -

-
-
- -
debug/elf
-
-

- Attempts to read from a SHT_NOBITS section using - Section.Data - or the reader returned by Section.Open - now return an error. -

-

- Additional R_LARCH_* constants are defined for use with LoongArch systems. -

-

- Additional R_PPC64_* constants are defined for use with PPC64 ELFv2 relocations. -

-

- The constant value for R_PPC64_SECTOFF_LO_DS is corrected, from 61 to 62. -

-
-
- -
debug/gosym
-
-

- Due to a change of Go's symbol naming conventions, tools that - process Go binaries should use Go 1.20's debug/gosym package to - transparently handle both old and new binaries. -

-
-
- -
debug/pe
-
-

- Additional IMAGE_FILE_MACHINE_RISCV* constants are defined for use with RISC-V systems. -

-
-
- -
encoding/binary
-
-

- The ReadVarint and - ReadUvarint - functions will now return io.ErrUnexpectedEOF after reading a partial value, - rather than io.EOF. -

-
-
- -
encoding/xml
-
-

- The new Encoder.Close method - can be used to check for unclosed elements when finished encoding. -

- -

- The decoder now rejects element and attribute names with more than one colon, - such as <a:b:c>, - as well as namespaces that resolve to an empty string, such as xmlns:a="". -

- -

- The decoder now rejects elements that use different namespace prefixes in the opening and closing tag, - even if those prefixes both denote the same namespace. -

-
-
- -
errors
-
-

- The new Join function returns an error wrapping a list of errors. -

-
-
- -
fmt
-
-

- The Errorf function supports multiple occurrences of - the %w format verb, returning an error that unwraps to the list of all arguments to %w. -

-

- The new FormatString function recovers the - formatting directive corresponding to a State, - which can be useful in Formatter. - implementations. -

-
-
- -
go/ast
-
-

- The new RangeStmt.Range field - records the position of the range keyword in a range statement. -

-

- The new File.FileStart - and File.FileEnd fields - record the position of the start and end of the entire source file. -

-
-
- -
go/token
-
-

- The new FileSet.RemoveFile method - removes a file from a FileSet. - Long-running programs can use this to release memory associated - with files they no longer need. -

-
-
- -
go/types
-
-

- The new Satisfies function reports - whether a type satisfies a constraint. - This change aligns with the new language semantics - that distinguish satisfying a constraint from implementing an interface. -

-
-
- -
io
-
-

- The new OffsetWriter wraps an underlying - WriterAt - and provides Seek, Write, and WriteAt methods - that adjust their effective file offset position by a fixed amount. -

-
-
- -
io/fs
-
-

- The new error SkipAll - terminates a WalkDir - immediately but successfully. -

-
-
- -
math/big
-
-

- The math/big package's wide scope and - input-dependent timing make it ill-suited for implementing cryptography. - The cryptography packages in the standard library no longer call non-trivial - Int methods on attacker-controlled inputs. - In the future, the determination of whether a bug in math/big is - considered a security vulnerability will depend on its wider impact on the - standard library. -

-
-
- -
math/rand
-
-

- The math/rand package now automatically seeds - the global random number generator - (used by top-level functions like Float64 and Int) with a random value, - and the top-level Seed function has been deprecated. - Programs that need a reproducible sequence of random numbers - should prefer to allocate their own random source, using rand.New(rand.NewSource(seed)). -

-

- Programs that need the earlier consistent global seeding behavior can set - GODEBUG=randautoseed=0 in their environment. -

-

- The top-level Read function has been deprecated. - In almost all cases, crypto/rand.Read is more appropriate. -

-
-
- -
mime
-
-

- The ParseMediaType function now allows duplicate parameter names, - so long as the values of the names are the same. -

-
-
- -
mime/multipart
-
-

- Methods of the Reader type now wrap errors - returned by the underlying io.Reader. -

-
-
- -
net
-
-

- The LookupCNAME - function now consistently returns the contents - of a CNAME record when one exists. Previously on Unix systems and - when using the pure Go resolver, LookupCNAME would return an error - if a CNAME record referred to a name that with no A, - AAAA, or CNAME record. This change modifies - LookupCNAME to match the previous behavior on Windows, - allowing LookupCNAME to succeed whenever a - CNAME exists. -

- -

- Interface.Flags now includes the new flag FlagRunning, - indicating an operationally active interface. An interface which is administratively - configured but not active (for example, because the network cable is not connected) - will have FlagUp set but not FlagRunning. -

- -

- The new Dialer.ControlContext field contains a callback function - similar to the existing Dialer.Control hook, that additionally - accepts the dial context as a parameter. - Control is ignored when ControlContext is not nil. -

- -

- The Go DNS resolver recognizes the trust-ad resolver option. - When options trust-ad is set in resolv.conf, - the Go resolver will set the AD bit in DNS queries. The resolver does not - make use of the AD bit in responses. -

- -

- DNS resolution will detect changes to /etc/nsswitch.conf - and reload the file when it changes. Checks are made at most once every - five seconds, matching the previous handling of /etc/hosts - and /etc/resolv.conf. -

-
-
- -
net/http
-
-

- The ResponseWriter.WriteHeader function now supports sending - 1xx status codes. -

- -

- The new Server.DisableGeneralOptionsHandler configuration setting - allows disabling the default OPTIONS * handler. -

- -

- The new Transport.OnProxyConnectResponse hook is called - when a Transport receives an HTTP response from a proxy - for a CONNECT request. -

- -

- The HTTP server now accepts HEAD requests containing a body, - rather than rejecting them as invalid. -

- -

- HTTP/2 stream errors returned by net/http functions may be converted - to a golang.org/x/net/http2.StreamError using - errors.As. -

- -

- Leading and trailing spaces are trimmed from cookie names, - rather than being rejected as invalid. - For example, a cookie setting of "name =value" - is now accepted as setting the cookie "name". -

-
-
- -
net/netip
-
-

- The new IPv6LinkLocalAllRouters - and IPv6Loopback functions - are the net/netip equivalents of - net.IPv6loopback and - net.IPv6linklocalallrouters. -

-
-
- -
os
-
-

- On Windows, the name NUL is no longer treated as a special case in - Mkdir and - Stat. -

-

- On Windows, File.Stat - now uses the file handle to retrieve attributes when the file is a directory. - Previously it would use the path passed to - Open, which may no longer be the file - represented by the file handle if the file has been moved or replaced. - This change modifies Open to open directories without the - FILE_SHARE_DELETE access, which match the behavior of regular files. -

-

- On Windows, File.Seek now supports - seeking to the beginning of a directory. -

-
-
- -
os/exec
-
-

- The new Cmd fields - Cancel and - WaitDelay - specify the behavior of the Cmd when its associated - Context is canceled or its process exits with I/O pipes still - held open by a child process. -

-
-
- -
path/filepath
-
-

- The new error SkipAll - terminates a Walk - immediately but successfully. -

-

- The new IsLocal function reports whether a path is - lexically local to a directory. - For example, if IsLocal(p) is true, - then Open(p) will refer to a file that is lexically - within the subtree rooted at the current directory. -

-
-
- -
reflect
-
-

- The new Value.Comparable and - Value.Equal methods - can be used to compare two Values for equality. - Comparable reports whether Equal is a valid operation for a given Value receiver. -

- -

- The new Value.Grow method - extends a slice to guarantee space for another n elements. -

- -

- The new Value.SetZero method - sets a value to be the zero value for its type. -

- -

- Go 1.18 introduced Value.SetIterKey - and Value.SetIterValue methods. - These are optimizations: v.SetIterKey(it) is meant to be equivalent to v.Set(it.Key()). - The implementations incorrectly omitted a check for use of unexported fields that was present in the unoptimized forms. - Go 1.20 corrects these methods to include the unexported field check. -

-
-
- -
regexp
-
-

- Go 1.19.2 and Go 1.18.7 included a security fix to the regular expression parser, - making it reject very large expressions that would consume too much memory. - Because Go patch releases do not introduce new API, - the parser returned syntax.ErrInternalError in this case. - Go 1.20 adds a more specific error, syntax.ErrLarge, - which the parser now returns instead. -

-
-
- -
runtime/cgo
-
-

- Go 1.20 adds new Incomplete marker type. - Code generated by cgo will use cgo.Incomplete to mark an incomplete C type. -

-
-
- -
runtime/metrics
-
-

- Go 1.20 adds new supported metrics, - including the current GOMAXPROCS setting (/sched/gomaxprocs:threads), - the number of cgo calls executed (/cgo/go-to-c-calls:calls), - total mutex block time (/sync/mutex/wait/total), and various measures of time - spent in garbage collection. -

- -

- Time-based histogram metrics are now less precise, but take up much less memory. -

-
-
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runtime/pprof
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- Mutex profile samples are now pre-scaled, fixing an issue where old mutex profile - samples would be scaled incorrectly if the sampling rate changed during execution. -

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- Profiles collected on Windows now include memory mapping information that fixes - symbolization issues for position-independent binaries. -

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runtime/trace
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- The garbage collector's background sweeper now yields less frequently, - resulting in many fewer extraneous events in execution traces. -

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strings
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- The new - CutPrefix and - CutSuffix functions - are like TrimPrefix - and TrimSuffix - but also report whether the string was trimmed. -

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- The new Clone function - allocates a copy of a string. -

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sync
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- The new Map methods Swap, - CompareAndSwap, and - CompareAndDelete - allow existing map entries to be updated atomically. -

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syscall
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- On FreeBSD, compatibility shims needed for FreeBSD 11 and earlier have been removed. -

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- On Linux, additional CLONE_* constants - are defined for use with the SysProcAttr.Cloneflags field. -

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- On Linux, the new SysProcAttr.CgroupFD - and SysProcAttr.UseCgroupFD fields - provide a way to place a child process into a specific cgroup. -

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testing
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- The new method B.Elapsed - reports the current elapsed time of the benchmark, which may be useful for - calculating rates to report with ReportMetric. -

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time
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- The new time layout constants DateTime, - DateOnly, and - TimeOnly - provide names for three of the most common layout strings used in a survey of public Go source code. -

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- The new Time.Compare method - compares two times. -

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- Parse - now ignores sub-nanosecond precision in its input, - instead of reporting those digits as an error. -

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- The Time.MarshalJSON method - is now more strict about adherence to RFC 3339. -

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unicode/utf16
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- The new AppendRune - function appends the UTF-16 encoding of a given rune to a uint16 slice, - analogous to utf8.AppendRune. -

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