DRAFT RELEASE NOTES — Introduction to Go 1.16

Go 1.16 is not yet released. These are work-in-progress release notes. Go 1.16 is expected to be released in February 2021.

Changes to the language

TODO

Ports

NetBSD

Go now supports the 64-bit ARM architecture on NetBSD (the netbsd/arm64 port).

Tools

TODO

Go command

Modules

go install now accepts arguments with version suffixes (for example, go install example.com/cmd@v1.0.0). This causes go install to build and install packages in module-aware mode, ignoring the go.mod file in the current directory or any parent directory, if there is one. This is useful for installing executables without affecting the dependencies of the main module.
TODO: write and link to section in golang.org/ref/mod
TODO: write and link to blog post

retract directives may now be used in a go.mod file to indicate that certain published versions of the module should not be used by other modules. A module author may retract a version after a severe problem is discovered or if the version was published unintentionally.
TODO: write and link to section in golang.org/ref/mod
TODO: write and link to tutorial or blog post

The go mod vendor and go mod tidy subcommands now accept the -e flag, which instructs them to proceed despite errors in resolving missing packages.

go test

When using go test, a test that calls os.Exit(0) during execution of a test function will now be considered to fail. This will help catch cases in which a test calls code that calls os.Exit(0) and thereby stops running all future tests. If a TestMain function calls os.Exit(0) that is still considered to be a passing test.

The go get -insecure flag is deprecated and will be removed in a future version. This flag permits fetching from repositories and resolving custom domains using insecure schemes such as HTTP, and also bypassess module sum validation using the checksum database. To permit the use of insecure schemes, use the GOINSECURE environment variable instead. To bypass module sum validation, use GOPRIVATE or GONOSUMDB. See go help environment for details.

The all pattern

When the main module's go.mod file declares go 1.16 or higher, the all package pattern now matches only those packages that are transitively imported by a package or test found in the main module. (Packages imported by tests of packages imported by the main module are no longer included.) This is the same set of packages retained by go mod vendor since Go 1.11.

Cgo

The cgo tool will no longer try to translate C struct bitfields into Go struct fields, even if their size can be represented in Go. The order in which C bitfields appear in memory is implementation dependent, so in some cases the cgo tool produced results that were silently incorrect.

TODO

Runtime

TODO

Compiler

TODO

Linker

This release includes additional improvements to the Go linker, reducing linker resource usage (both time and memory) and improving code robustness/maintainability. These changes form the second half of a two-release project to modernize the Go linker.

The linker changes in 1.16 extend the 1.15 improvements to all supported architecture/OS combinations (the 1.15 performance improvements were primarily focused on ELF-based OSes and amd64 architectures). For a representative set of large Go programs, linking is 20-35% faster than 1.15 and requires 5-15% less memory on average for linux/amd64, with larger improvements for other architectures and OSes.

TODO: update with final numbers later in the release.

Core library

TODO

crypto/tls

I/O operations on closing or closed TLS connections can now be detected using the new ErrClosed error. A typical use would be errors.Is(err, net.ErrClosed). In earlier releases the only way to reliably detect this case was to match the string returned by the Error method with "tls: use of closed connection".

crypto/x509

ParseCertificate and CreateCertificate both now enforce string encoding restrictions for the fields DNSNames, EmailAddresses, and URIs. These fields can only contain strings with characters within the ASCII range.

net

The case of I/O on a closed network connection, or I/O on a network connection that is closed before any of the I/O completes, can now be detected using the new ErrClosed error. A typical use would be errors.Is(err, net.ErrClosed). In earlier releases the only way to reliably detect this case was to match the string returned by the Error method with "use of closed network connection".

text/template/parse

A new CommentNode was added to the parse tree. The Mode field in the parse.Tree enables access to it.

unicode

The unicode package and associated support throughout the system has been upgraded from Unicode 12.0.0 to Unicode 13.0.0, which adds 5,930 new characters, including four new scripts, and 55 new emoji. Unicode 13.0.0 also designates plane 3 (U+30000-U+3FFFF) as the tertiary ideographic plane.

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.

TODO

crypto/dsa

The crypto/dsa package is now deprecated. See issue #40337.

crypto/x509

DSA signature verification is no longer supported. Note that DSA signature generation was never supported. See issue #40337.

net/http

In the net/http package, the behavior of StripPrefix has been changed to strip the prefix from the request URL's RawPath field in addition to its Path field. In past releases, only the Path field was trimmed, and so if the request URL contained any escaped characters the URL would be modified to have mismatched Path and RawPath fields. In Go 1.16, StripPrefix trims both fields. If there are escaped characters in the prefix part of the request URL the handler serves a 404 instead of its previous behavior of invoking the underlying handler with a mismatched Path/RawPath pair.

The net/http package now rejects HTTP range requests of the form "Range": "bytes=--N" where "-N" is a negative suffix length, for example "Range": "bytes=--2". It now replies with a 416 "Range Not Satisfiable" response.