1 Vendoring in std and cmd
2 ========================
3 4 The Go command maintains copies of external packages needed by the
5 standard library in the src/vendor and src/cmd/vendor directories.
6 7 There are two modules, std and cmd, defined in src/go.mod and
8 src/cmd/go.mod. When a package outside std or cmd is imported
9 by a package inside std or cmd, the import path is interpreted
10 as if it had a "vendor/" prefix. For example, within "crypto/tls",
11 an import of "golang.org/x/crypto/cryptobyte" resolves to
12 "vendor/golang.org/x/crypto/cryptobyte". When a package with the
13 same path is imported from a package outside std or cmd, it will
14 be resolved normally. Consequently, a binary may be built with two
15 copies of a package at different versions if the package is
16 imported normally and vendored by the standard library.
17 18 Vendored packages are internally renamed with a "vendor/" prefix
19 to preserve the invariant that all packages have distinct paths.
20 This is necessary to avoid compiler and linker conflicts. Adding
21 a "vendor/" prefix also maintains the invariant that standard
22 library packages begin with a dotless path element.
23 24 The module requirements of std and cmd do not influence version
25 selection in other modules. They are only considered when running
26 module commands like 'go get' and 'go mod vendor' from a directory
27 in GOROOT/src.
28 29 Maintaining vendor directories
30 ==============================
31 32 Before updating vendor directories, ensure that module mode is enabled.
33 Make sure that GO111MODULE is not set in the environment, or that it is
34 set to 'on' or 'auto', and if you use a go.work file, set GOWORK=off.
35 36 Also, ensure that 'go env GOROOT' shows the root of this Go source
37 tree. Otherwise, the results are undefined. It's recommended to build
38 Go from source and use that 'go' binary to update its source tree.
39 40 Requirements may be added, updated, and removed with 'go get'.
41 The vendor directory may be updated with 'go mod vendor'.
42 A typical sequence might be:
43 44 cd src # or src/cmd
45 go get golang.org/x/net@master
46 go mod tidy
47 go mod vendor
48 49 Use caution when passing '-u' to 'go get'. The '-u' flag updates
50 modules providing all transitively imported packages, not only
51 the module providing the target package.
52 53 Note that 'go mod vendor' only copies packages that are transitively
54 imported by packages in the current module. If a new package is needed,
55 it should be imported before running 'go mod vendor'.
56