make.bash: make default GOROOT_BOOTSTRAP more useful

[perillo]

There are currently two problems with default GOROOT_BOOTSTRAP handling in the make.bash script.

The first problem is that the default value set in make.bash ($HOME/go1.4) will not be used by the go dist tool, since the new GOROOT_BOOSTRAP environment variable is not exported. The code works only because the go dist tool uses the same default value.

The second problem is that $HOME/go1.4 will be an invalid GOROOT for the majority of users, thus forcing the user to explicitly set the GOROOT_BOOSTRAP environment variable.

I propose to change the default GOROOT_BOOTSTRAP value to the value returned by go env GOROOT, where the go command in PATH is used. The GOROOT_BOOSTRAP should be exported. As an example:

export GOROOT_BOOTSTRAP=${GOROOT_BOOTSTRAP:-$(go env GOROOT 2>/dev/null)}
export GOROOT="$(cd .. && pwd)"

[minux]

Changing the default GOROOT_BOOTSTRAP to $(go env GOROOT) will break users of go tip.

[perillo]

On Mon, Feb 15, 2016 at 8:57 PM, Minux Ma notifications@github.com wrote:

Changing the default GOROOT_BOOTSTRAP to $(go env GOROOT)
will break users of go tip.

But using $HOME/go1.4 will force everyone to explicitly set
GOROOT_BOOTSTRAP.
What is better: forcing "normal " users to explicitly set GOROOT_BOOTSTRAP
or forcing users of go tip to explicitly set GOROOT_BOOTSTRAP?

[minux]

I don't think it's unreasonable to rebuild Go with make.bash with the current $GOROOT/bin in $PATH. It's not necessarily specific to Go tip users.

[rsc]

I strongly disagree about using the current PATH's 'go', because many times that will be the Go distribution being rebuilt at that moment, and you'll get into weird circularity problems.

However, if you can filter out the current directory's go command, for example with appropriate processing of "which -a go", then using the next go in the path might be reasonable. That seems fine if someone wants to write the CL (and it's simple!), but it's not a release blocker.

[gopherbot]

Change https://golang.org/cl/57753 mentions this issue: make.bash: add go env GOROOT as default GOROOT_BOOTSTRAP value