Error in go mode tidy go warning “all” matched no packages

Possible reasons found:
1. The local go compiler version
2. The go module build mode is not enabled
3. Is it in the directory where go.mod is located?Executed go mod tidy

Parse

When it was first released, there was no package management when go was released.
The go get command will obtain and save the corresponding module according to the path in $GOPATH/src
There is no concept of version,master represents the stable version
Later, the Go Module was introduced in GO1.11, and there is no longer only one version. Use go.mod to record the version of each package

So here comes the problem

Do you follow the rules of $GOPATH or follow the Go Module?

GO111MODULE is an environment variable used to change the way go imports packages

Go1.11 and Go1.12

• GO111MODULE=on
  This setting will force the use of Go modules, even if the project is in your GOPATH.Requires go.mod to work.
• GO111MOUDLE=off, use GOPATH way, even outside GOPATH
• GO111MODULE=auto, the default setting.

1. When you are not in the GOPATH, like GO111MODULE=on

2. When you are in GOPATH, even if there is go.mod, it is the effect of GO111MODULE=off

3. When you are in GOPATH and you need GO modules to do something (like go get a specific version), then do this:
   GO111MODULE=on go getxxxxx

Go 1.13, the meaning of auto has changed: if go.mod is found, or if there is no go.mod, but outside the GOPATH, then the effect is GO111MODULE=on (force to use go module).So you can keep all repositories in your GOPATH

why
When there is no go.mod, in the GOPATH, the effect is GO111MODULE=off (get the package and put it in $GOPATH/src/)

Check

1. Local go compiler version

Project version is 1.16, here go.mod defaults to GO111MODULE=on

2.go module build mode is not enabled

Just to be on the safe side
win

set GO111MODULE=auto

linux

export GO111MODULE=auto

It didn't work

go mod command

3. Whether to execute go mod tidy in the directory where go.mod is located

Finding is the third reason

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