cmd/yacc: move to subrepo

[rsc]

For Go 1.6 I intend to replace the use of cmd/yacc in the compiler with a hand-written recursive descent parser, as much a line-by-line translation of the current go.y as is possible. I've already done the conversion once, a month ago, although I'll have to redo it due to recent compiler changes.

After that's done, there will be no uses of cmd/yacc in the main repo. A recent mail to golang-dev points out that cmd/yacc has never shipped with gccgo.

Perhaps for Go 1.6 we should think about moving cmd/yacc out of the main distribution and into a subrepo. It will be easier for people to 'go get' and stay up to date, and there will no longer be any compelling reason for keeping it in the main repo (if there ever was).

[rsc]

Didn't happen for Go 1.6.

[mdempsky]

Is this something to consider for Go 1.7?

[bradfitz]

Yes, let's do it.

[mdempsky]

Should cmd/go still install it into $GOTOOLDIR so "go tool yacc" continues to work? Or do we demote it to a normal external command? If a normal command, should we rename it "goyacc" or something to avoid conflicting with the standard yacc command?

Also, I'm assuming we want to move it to the x/tools subdirectory?

[bradfitz]

Demoting to regular as "goyacc" in x/tools SGTM.

[minux]

Have we announced this plan publicly? I think removing it without prior notice will break a lot of //go:generate lines. I propose that we make a copy of cmd/yacc to x/tools/cmd/goyacc at the start of the Go 1.7 freeze, but we release cmd/yacc one more time in Go 1.7 and call out in the release docs that Go 1.7 is the last release containing `go tool yacc` and prompt users to switch to x/tools/cmd/goyacc.

[minux]

Alternatively, we can make go tool yacc print out an error message and prompt the user to use x/tools/cmd/goyacc instead.

[cznic]

Please note that, for years, there is an existing goyacc project. If the x/tools/goyacc will overwrite the goyacc binary, it will break things for users of, for example, ql, cc, pl0, gc(WIP), ...

[bradfitz]

Please note that, for years, there is an existing goyacc project.

Maybe yc. :)

Have we announced this plan publicly?

This bug has been open for a year. That doesn't mean everybody would see it, but not everybody always does.

I think removing it without prior notice will break a lot of //go:generate lines.

That's okay.

1. we don't guarantee stability of tools. Only API.
2. this doesn't break building of programs or end users. It only breaks developers updating their programs. They're by definition already changing stuff, so they can change their go:generate line too.