1Vendoring in std and cmd
2========================
3
4The Go command maintains copies of external packages needed by the
5standard library in the src/vendor and src/cmd/vendor directories.
6
7There are two modules, std and cmd, defined in src/go.mod and
8src/cmd/go.mod. When a package outside std or cmd is imported
9by a package inside std or cmd, the import path is interpreted
10as if it had a "vendor/" prefix. For example, within "crypto/tls",
11an import of "golang.org/x/crypto/cryptobyte" resolves to
12"vendor/golang.org/x/crypto/cryptobyte". When a package with the
13same path is imported from a package outside std or cmd, it will
14be resolved normally. Consequently, a binary may be built with two
15copies of a package at different versions if the package is
16imported normally and vendored by the standard library.
17
18Vendored packages are internally renamed with a "vendor/" prefix
19to preserve the invariant that all packages have distinct paths.
20This is necessary to avoid compiler and linker conflicts. Adding
21a "vendor/" prefix also maintains the invariant that standard
22library packages begin with a dotless path element.
23
24The module requirements of std and cmd do not influence version
25selection in other modules. They are only considered when running
26module commands like 'go get' and 'go mod vendor' from a directory
27in GOROOT/src.
28
29Maintaining vendor directories
30==============================
31
32Before updating vendor directories, ensure that module mode is enabled.
33Make sure that GO111MODULE is not set in the environment, or that it is
34set to 'on' or 'auto', and if you use a go.work file, set GOWORK=off.
35
36Requirements may be added, updated, and removed with 'go get'.
37The vendor directory may be updated with 'go mod vendor'.
38A typical sequence might be:
39
40    cd src  # or src/cmd
41    go get golang.org/x/net@master
42    go mod tidy
43    go mod vendor
44
45Use caution when passing '-u' to 'go get'. The '-u' flag updates
46modules providing all transitively imported packages, not only
47the module providing the target package.
48
49Note that 'go mod vendor' only copies packages that are transitively
50imported by packages in the current module. If a new package is needed,
51it should be imported before running 'go mod vendor'.
52