cmd/go: go install should warn or error if none of its arguments have install targets

[zamicol]

(I'm on go version go1.19.5 linux/amd64)

go test reports a warning if there's nothing to do:

$ go test -run test_that_doesn't_exist
testing: warning: no tests to run

The commands go test, go run, go build, and go install will also warn if there are no Go files in the given directory.

$ go test
no Go files in /directory

(In the case of go run, the warning is go: no go files listed)

However, unlike go test and go run, go build and go install will not warn when a Go file is present in the current directory but no binary is produced.

For example, in a directory with file helloWorld.go with the contents of the following:

package hello

import "fmt"

func talk() {
    fmt.Println("Hello World!")
}

go run warns

$ go run helloWorld.go 
package command-line-arguments is not a main package

go test warns

$ go test
?   	/helloWorldDir	[no test files]
$ go test helloWorld.go 
?   	command-line-arguments	[no test files]

But go install and go build reports nothing.

$ go install helloWorld.go
$

$ go build helloWorld.go
$

And simply doing go install and go build also reports nothing.

$ go install
$

$ go build
$

What I would expect to see is the same warning as go run

$ go install
package is not a main package

$ go build
package is not a main package

[thanm]

The fact that the Go command prints nothing when you run "go build helloWorld.go" doesn't mean that nothing's happening, it just means that there was nothing to report at the end of the build action. Try running "go build -x" to see what's happening.

In addition, developers run "go build" on non-main packages all the time without any expectation that a binary is going to be produced-- they just want to see if the code still compiles after a change to the source.

People also run builds of non-main packages to gather more info. For example in your hello package perhaps you might want to do a build with "-gcflags=-m" to see what decisions are made by the compiler regarding inlining or escape analysis.

[zamicol]

Perhaps go install should be considered independently. What use is go install on packages without func main()?

[ianlancetaylor]

When using GOPATH mode, go install will install a non-main package .a file in $GOPATH/src. Also, before 1.20, go install of a standard library package would install it in $GOROOT/src. That said, it's true that not many people use GOPATH mode any more, and presumably people are starting to use 1.20. A warning from go install for a non-main package might make sense now.

CC @bcmills

[bcmills]

go install cmd is useful even though that pattern matches a mix of main and non-main packages. I think the same is true for other patterns.

On the other hand, I think it would make sense for go install to error out completely (not just warn!) if it doesn't actually have anything to install — that is: if the arguments don't match any main packages and the remaining arguments don't have a (GOPATH or GODEBUG=installgoroot=all) install target.

[anthoturc]

@bcmills would you recommend this as a good first issue for someone looking to contribute?

[bcmills]

@anthoturc, I'm honestly not sure. 😅

But if you want to take a look, the entry point for the go install command is the function runInstall in src/cmd/go/internal/work/build.go.