cmd/go: reject list -export -find more clearly

[rsc]

cmd/go/internal/list/list.go says

// These pairings make no sense.
if *listFind && *listDeps {
	base.Fatalf("go list -deps cannot be used with -find")
}
if *listFind && *listTest {
	base.Fatalf("go list -test cannot be used with -find")
}

but the same is true of *listExports.

% go list -export -f '{{.Export}}' strconv
/Users/rsc/go/pkg/darwin_amd64/strconv.a
% go list -export -find -f '{{.Export}}' strconv
# strconv
../../strconv/atof.go:13:8: could not import math (open : no such file or directory)
../../strconv/atoi.go:7:8: could not import errors (open : no such file or directory)
../../strconv/bytealg.go:10:8: could not import internal/bytealg (open : no such file or directory)
../../strconv/eisel_lemire.go:22:2: could not import math/bits (open : no such file or directory)
../../strconv/quote.go:10:2: could not import unicode/utf8 (open : no such file or directory)
% 

This should probably be fixed in cmd/go and possibly also in the docs, which say nothing about -find being incompatible with other flags.

[gopherbot]

Change https://go.dev/cl/396074 mentions this issue: internal/cmd: update to reject list when -find and -export are specified

[ianlancetaylor]

@bcmills @matloob This issue is marked for 1.19. It's just been rolling forward in milestones. Should it move to Backlog? Thanks.

[bcmills]

Looks like a contributor sent a fix CL that we missed. I've reviewed it (it's small, self-contained, and low-risk), so I think this can indeed make Go 1.19.