Bryan C. Mills 02e5505858 [release-branch.go1.16] cmd/go: avoid +incompatible major versions if a go.mod file exists in a subdirectory for that version
Previous versions of the 'go' command would reject a pseudo-version
passed to 'go get' if that pseudo-version had a mismatched major
version and lacked a "+incompatible" suffix. However, they would
erroneously accept a version *with* a "+incompatible" suffix even if
the repo contained a vN/go.mod file for the same major version, and
would generate a "+incompatible" pseudo-version or version if the user
requested a tag, branch, or commit hash.

This change uniformly rejects "vN.…" without "+incompatible", and also
avoids resolving to "vN.…+incompatible", when vN/go.mod exists.
To maintain compatibility with existing go.mod files, it still accepts
"vN.…+incompatible" if the version is requested explicitly as such
and the repo root lacks a go.mod file.

Fixes #51331
Updates #51324
Updates #36438

Change-Id: I2b16150c73fc2abe4d0a1cd34cb1600635db7139
Reviewed-on: https://go-review.googlesource.com/c/go/+/387675
Trust: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
(cherry picked from commit 5a9fc946b42cc987db41eabcfcbaffd2fb310d94)
Reviewed-on: https://go-review.googlesource.com/c/go/+/387923
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
2022-03-03 14:29:55 +00:00
..
2020-11-04 21:02:29 +00:00

Vendoring in std and cmd
========================

The Go command maintains copies of external packages needed by the
standard library in the src/vendor and src/cmd/vendor directories.

In GOPATH mode, imports of vendored packages are resolved to these
directories following normal vendor directory logic
(see golang.org/s/go15vendor).

In module mode, std and cmd are modules (defined in src/go.mod and
src/cmd/go.mod). When a package outside std or cmd is imported
by a package inside std or cmd, the import path is interpreted
as if it had a "vendor/" prefix. For example, within "crypto/tls",
an import of "golang.org/x/crypto/cryptobyte" resolves to
"vendor/golang.org/x/crypto/cryptobyte". When a package with the
same path is imported from a package outside std or cmd, it will
be resolved normally. Consequently, a binary may be built with two
copies of a package at different versions if the package is
imported normally and vendored by the standard library.

Vendored packages are internally renamed with a "vendor/" prefix
to preserve the invariant that all packages have distinct paths.
This is necessary to avoid compiler and linker conflicts. Adding
a "vendor/" prefix also maintains the invariant that standard
library packages begin with a dotless path element.

The module requirements of std and cmd do not influence version
selection in other modules. They are only considered when running
module commands like 'go get' and 'go mod vendor' from a directory
in GOROOT/src.

Maintaining vendor directories
==============================

Before updating vendor directories, ensure that module mode is enabled.
Make sure GO111MODULE=off is not set ('on' or 'auto' should work).

Requirements may be added, updated, and removed with 'go get'.
The vendor directory may be updated with 'go mod vendor'.
A typical sequence might be:

    cd src
    go get -d golang.org/x/net@latest
    go mod tidy
    go mod vendor

Use caution when passing '-u' to 'go get'. The '-u' flag updates
modules providing all transitively imported packages, not only
the module providing the target package.

Note that 'go mod vendor' only copies packages that are transitively
imported by packages in the current module. If a new package is needed,
it should be imported before running 'go mod vendor'.