The new [unique] package provides facilities for
canonicalizing values (like "interning" or "hash-consing").

Any value of comparable type may be canonicalized with the new
`Make[T]` function, which produces a reference to a canonical copy of
the value in the form of a `Handle[T]`.
Two `Handle[T]` are equal if and only if the values used to produce the
handles are equal, allowing programs to deduplicate values and reduce
their memory footprint.

# Issue #7573
# cmd/cgo: undefined reference when linking a C-library using gccgo

[!cgo] skip
[!exec:gccgo] skip
[cross] skip  # gccgo can't necessarily cross-compile, so don't assume it will reach the step where we expect it to fail

! go build -x -compiler gccgo
stderr 'gccgo.*\-L [^ ]*alibpath \-lalib' # make sure that Go-inline "#cgo LDFLAGS:" ("-L alibpath -lalib") passed to gccgo linking stage

go list -json=EmbedPatterns,TestEmbedPatterns,XTestEmbedPatterns
stdout '"EmbedPatterns": \['
stdout '"TestEmbedPatterns": \['
stdout '"XTestEmbedPatterns": \['
# Test -json=<field> with *EmbedFiles fails due to broken file reference.
! go list -json=EmbedFiles
stderr 'no matching files found'
! go list -json=TestEmbedFiles
stderr 'no matching files found'
! go list -json=XTestEmbedFiles
stderr 'no matching files found'
cd ..

[!git] skip

analyzer, which flags references to symbols that are too new for the version
of Go in effect in the referring file. (The effective version is determined
by the `go` directive in the file's enclosing `go.mod` file, and
by any [`//go:build` constraints](https://pkg.go.dev/cmd/go#hdr-Build_constraints)
in the file.)

For example, it will report a diagnostic for a reference to the

are not marked with `//go:linkname` on their definitions.
Similarly, the linker disallows references to such symbols from assembly
code.
For backward compatibility, existing usages of `//go:linkname` found in
a large open-source code corpus remain supported.
Any new references to standard library internal symbols will be disallowed.

A linker command line flag `-checklinkname=0` can be used to disable

# Test that we can use the external linker with a host syso file that is
# embedded in a package, that is referenced by a Go assembly function.
# See issue 33139.

[!compiler:gc] skip
[!cgo] skip
[short] skip 'invokes system C compiler'

# External linking is not supported on linux/ppc64.
# See: https://github.com/golang/go/issues/8912
[GOOS:linux] [GOARCH:ppc64] skip

cc -c -o syso/objTestImpl.syso syso/src/objTestImpl.c

# Go should refuse to build code that is too new according to go.mod.

# go.mod too new
env GOTOOLCHAIN=local
! go build .
stderr '^go: go.mod requires go >= 1.99999 \(running go 1\..+\)$'

# go.mod referenced from go.work too new
cp go.work.old go.work
! go build .
stderr '^go: module . listed in go.work file requires go >= 1.99999, but go.work lists go 1.10; to update it:\n\tgo work use$'

! go work sync