…n' and 'go install' flags"

This caused other problems, and for the purposes of the Go 1.22
release, we can just roll back to the Go 1.21 behavior and then
decide in January what the correct path forward is.

Revert of CL 546635.

Unfixes #64282.
Fixes #64738.
For #57001.

This reverts commit e44b8b1.

Change-Id: I78753c76dcd0bc6dbc90caa17f73248c42e5f64a
Reviewed-on: https://go-review.googlesource.com/c/go/+/551215
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Than McIntosh <thanm@google.com>

…erw flag when downloading a module to determine what toolchain it needs

Fixes #64282.

Change-Id: I3f211c599ee70cb58254d0bc07eeb3c135124e58
Reviewed-on: https://go-review.googlesource.com/c/go/+/555436
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
(cherry picked from commit cc38c68)
Reviewed-on: https://go-review.googlesource.com/c/go/+/559218
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

…erw flag when downloading a module to determine what toolchain it needs

Fixes #64497.
Updates #64282.

Change-Id: I3f211c599ee70cb58254d0bc07eeb3c135124e58
Reviewed-on: https://go-review.googlesource.com/c/go/+/555436
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
(cherry picked from commit cc38c68)
Reviewed-on: https://go-review.googlesource.com/c/go/+/559198
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

…go install' flags

When the argument to 'go install' or 'go run' looks like a versioned
package, we make a best effort to switch to a toolchain compatible
with the module containing that package, by fetching its go.mod file
and checking the go version it specifies.

At this point in the code, we have not yet parsed the arguments given
on the command line: instead, we just make a best effort to find one
we can use to select a toolchain version. Since that toolchain may be
newer, the command to install it may also include flags that are only
supported by that Go version — and we don't want to fail due to an
error that would be resolved by switching to a more appropriate
toolchain.

So at this point in the code we can't parse the flags in a way that
will surface errors, but we want to make a best effort to parse the
ones that we know about. It turns out that “parse the flags we know
about” is already a familiar problem: that's also what we do in
'go test', so we can reuse the cmdflag library from that to do the
best-effort pass of parsing.

If it turns out that we don't need to switch toolchains after all,
cmd/go's main function will parse the flags again, and will report any
errors at that point.

This fixes a regression, introduced in CL 497879, which caused
'go install -modcacherw pkg@version' to unset the write bit for
directories created while selecting the toolchain to use.

Fixes golang#64282.
Updates golang#57001.

Change-Id: Icc409c57858aa15c7d58a97a61964b4bc2560547
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/546635
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

…n' and 'go install' flags"

This caused other problems, and for the purposes of the Go 1.22
release, we can just roll back to the Go 1.21 behavior and then
decide in January what the correct path forward is.

Revert of CL 546635.

Unfixes golang#64282.
Fixes golang#64738.
For golang#57001.

This reverts commit e44b8b1.

Change-Id: I78753c76dcd0bc6dbc90caa17f73248c42e5f64a
Reviewed-on: https://go-review.googlesource.com/c/go/+/551215
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Than McIntosh <thanm@google.com>

…g a module to determine what toolchain it needs

Fixes golang#64282.

Change-Id: I3f211c599ee70cb58254d0bc07eeb3c135124e58
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Reviewed-on: https://go-review.googlesource.com/c/go/+/555436
Auto-Submit: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Russ Cox <rsc@golang.org>