loopvarcapture linter should check interface methods

[srosenberg]

The existing implementation of the loopvarcapture linter [1] incorrectly omits all checks inside Monitor.Go [2]. This was a fairly random discovery. I was performing a manual inspection of the output of the go compiler, using -gcflags="-m=2". Surprisingly, I noticed the following diagnostic message. Upon closer inspection, it's indeed a bug which was supposed to be flagged by the loopvarcapture linter.

pkg/cmd/roachtest/tests/kv.go:759:7: registerKVScalability.func1 capturing by ref: i (addr=false assign=true width=8)

The root cause is restricting callees (of Go variants) to be non-interface methods. The callee in [2] happens to be an interface method.

[1] #80803
[2]

cockroach/pkg/testutils/lint/passes/loopvarcapture/loopvarcapture.go

Line 68 in ede4f45

{Pkg: "github.com/cockroachdb/cockroach/pkg/cmd/roachtest/cluster", Type: "Monitor", Name: "Go"},

Jira issue: CRDB-27587

[blathers-crl]

cc @cockroachdb/test-eng

[srosenberg]

After instrumenting the linter to print matched Go variants (inside isGoRoutineFunction), we can confirm the missing checks as follows.

Build roachvet

./dev build //pkg/cmd/roachvet

roachvet analysis results (before fix)

go vet -vettool _bazel/bin/pkg/cmd/roachvet/roachvet_/roachvet -tags stdmalloc ./... >/tmp/loopvarcapture.out 2>&1

grep isGoRoutineFunction /tmp/loopvarcapture.out |sed -E "s|^.+call=([^,]+).+$|\1|g"|sort |uniq -c |sort -rn
  78 golang.org/x/sync/errgroup.Group.Go
  57 github.com/cockroachdb/cockroach/pkg/util/ctxgroup.Group.GoCtx
   5 github.com/cockroachdb/cockroach/pkg/util/ctxgroup.Group.Go

roachvet analysis results (after fix)

go vet -vettool _bazel/bin/pkg/cmd/roachvet/roachvet_/roachvet -tags stdmalloc ./... >/tmp/loopvarcapture.out 2>&1

grep isGoRoutineFunction /tmp/loopvarcapture.out |sed -E "s|^.+call=([^,]+).+$|\1|g"|sort |uniq -c |sort -rn
  78 golang.org/x/sync/errgroup.Group.Go
  57 github.com/cockroachdb/cockroach/pkg/util/ctxgroup.Group.GoCtx
  28 github.com/cockroachdb/cockroach/pkg/cmd/roachtest/cluster.Monitor.Go
   5 github.com/cockroachdb/cockroach/pkg/util/ctxgroup.Group.Go

Thus, we were missing 28 occurrences inside Monitor.Go, one of which contains a bug, introduced ~5 years ago:

cockroach/pkg/cmd/roachtest/tests/kv.go

Lines 759 to 767 in ede4f45

	for i := nodes; i <= nodes*maxPerNodeConcurrency; i += nodes {
	c.Wipe(ctx, c.Range(1, nodes))
	c.Start(ctx, t.L(), option.DefaultStartOpts(), install.MakeClusterSettings(), c.Range(1, nodes))
	t.Status("running workload")
	m := c.NewMonitor(ctx, c.Range(1, nodes))
	m.Go(func(ctx context.Context) error {
	cmd := fmt.Sprintf("./workload run kv --init --read-percent=%d "+
	"--splits=1000 --duration=1m "+fmt.Sprintf("--concurrency=%d", i)+