About go get and go install from Go1.16

This article is a pinch hitter for the 16th day of Go Advent Calendar 2020. Strangely, I decided to talk about Go 1.16 on the 16th day.

Introduction

Go1.16 includes various updates for Modules. cf. https://tip.golang.org/doc/go1.16#tools

• New features have been added to go install to facilitate global installation of tools. In the future, the roles will be organized as " go install for building and installing binaries "and" go get for editing go.mod ". (The issue is here.)
• GO111MODULE is on by default, which means that Module mode is always enabled. Say goodbye to GOPATH mode.
• go build and go test no longer automatically update go.mod. Editing go.mod is done by go get, go mod tidy, or manually.

In this article, I will explain how to use go get / go install after Go1.16, and points to keep in mind. By the way, the following explanations are based on Module mode, not GOPATH mode. (Otherwise it would be too complicated)

Points to keep in mind

• Basically, use go install <package> @ <version> for global installation of tools.
• Example: go install golang.org/x/tools/gopls@latest
• I'm sorry if you wrote it in a script etc., I recommend you to correct it.
• The function of binary installation of go get will be removed in a future version.
• go get will be organized as a command only for adding dependencies to go.mod, but there are other ways to edit go.mod than go get. So, the chances of using go get are likely to decrease in the future.

Tool installation issues resolved in Go 1.16

Until now, the familiar go get command has been used to install tools globally ($ GOPATH/bin) in Go, but it had one problem. Since go get also has the role of editing go.mod, to install only the tool without touching go.mod," go through the directory with go.mod" " I needed to enable go.mod on the tool side and do go get. It is as follows when summarized in one.

$ cd $(mktemp -d); GO111MODULE=on go get golang.org/x/tools/gopls

I don't want to spend such a lot of time on installing it, and above all, I did go get without knowing about Modules and unwillingly updated go.mod. (Source is the author)

So, from Go 1.16 it looks like this:

$ go install golang.org/x/tools/gopls@latest

It was very refreshing.

** Actually, this format go install <package> @ <version> is newly introduced in Go 1.16 **. This format consistently installs the specified version in $ GOPATH/bin, whether under Module or not.

In Go1.16, GO111MODULE is on by default, and go install no longer edits go.mod, so you don't have to worry about accidents.

Note

• Only the main package can be installed with @version. Non-main packages are not subject to this format.

Note: About go install <package> without version specified

• You cannot do go install <package> without @ version outside the Module.
• Under Module, it is possible to install without @ version (the version of go.mod is reflected), but it takes a lot of work to describe the main package in go.mod. Since it is (https://qiita.com/nirasan/items/2bdbf0ada7b4182d56ce), I think it is simple to do go install <package> @ <version> even if it is under Module.
• For non-main package installation, see the following:

About other features of go install

Other features of go install, that is

• Ability to build a working directory and place it in $ GOPATH/bin
• Ability to build and cache non-main packages (under Module, go install <package> without specifying version)

As for, it is the same as before. These are things that you can live without, but it may be useful to remember them once in a while.

About go get, go.mod

On the other hand, go get transfers the role of binary installation to go install and is organized as a command only for editing go.mod. In releases after Go1.16 (scheduled for Go1.17), the function of binary installation by go get has been removed, and all go gets are equivalent to go get -d, and the source is downloaded and go. The behavior will be just to add to mod.

How to edit go.mod

Another change in Go1.16 was that go build and go test did not automatically edit go.mod. Based on these, the method of handling go.mod in Go1.16 is as follows.

A) How to write an import statement in your code and then reflect it in go.mod

• go get # no arguments
• Add new module only
• go mod tidy
• Removes unnecessary modules and adds new modules

B) How to add an unimported module to go.mod

• go get <package>[@<version>]
• Manually edit go.mod

I've listed four, but in reality, go mod tidy covers all of them, so it seems that you can go with just one go mod tidy.

Changes from Go 1.15

As mentioned earlier, the automatic editing feature of go.mod by go build etc. will be disabled from Go1.16, so users up to Go1.15 will have go.mod changed. But expecting go build, what? May be. Let's do go mod tidy.

Also, since Go1.17 or later will remove the function of binary installation of go get, it seems that various procedure manuals and scripts need to be modified by then.

gopls also has a change following Go1.16 from v0.6.0 that does not automatically edit go.mod. Regarding the sequential development flow, I think that it will be arranged for new Modules.

Summary

There are some incompatible changes around the tool, but Modules from Go 1.16 are much simpler and less addictive, so I think it's easier to recommend to beginners. As a writer who has a strong desire to spread Go, the less addictive you are, the easier it will be to do it, and the more motivated you will be to spread it.

Besides, I can't wait for Go 1.16, which is full of features such as embed and io/fs. The release is scheduled for February next year.