lint: switch to new staticcheck

Replace the TestMegacheck and TestUnused tests with a call to the new
`staticcheck`.

Our custom checkers will need to be rewritten using the new
interfaces; disable the old code until then (this will be tracked
by cockroachdb#33669).

Fixes cockroachdb#37061.

Release note: None

Gopkg.toml

@@ -16,6 +16,7 @@ required = [
  "golang.org/x/tools/cmd/goyacc",
  "golang.org/x/tools/cmd/stringer",
  "golang.org/x/tools/go/analysis/passes/shadow/cmd/shadow",
+ "honnef.co/go/tools/cmd/staticcheck",
 ]
 
 ignored = [
@@ -98,7 +99,9 @@ ignored = [
 # Pin to 2017.2.2 because of https://github.com/cockroachdb/cockroach/issues/33669.
 [[constraint]]
   name = "honnef.co/go/tools"
-  version = "=2017.2.2"
+  # This revision is not yet on master (as of 05-12-2019); when it is, we can
+  # switch to just using the master branch.
+  revision = "4187a5ff696fcfe80ef2204f78a3ae8262b2d54d"
 
 # Test util - don't need to pin.
 [[constraint]]

Makefile

@@ -313,7 +313,8 @@ bin/.bootstrap: $(GITHOOKS) Gopkg.lock | bin/.submodules-initialized
 		./vendor/golang.org/x/perf/cmd/benchstat \
 		./vendor/golang.org/x/tools/cmd/goyacc \
 		./vendor/golang.org/x/tools/cmd/stringer \
-		./vendor/golang.org/x/tools/go/analysis/passes/shadow/cmd/shadow
+		./vendor/golang.org/x/tools/go/analysis/passes/shadow/cmd/shadow \
+		./vendor/honnef.co/go/tools/cmd/staticcheck
 	touch $@
 
 .SECONDARY: bin/.submodules-initialized

pkg/cli/flags_util.go

@@ -31,10 +31,13 @@ import (
 	humanize "github.com/dustin/go-humanize"
 	"github.com/elastic/gosigar"
 	"github.com/pkg/errors"
+	"github.com/spf13/pflag"
 )
 
 type localityList []roachpb.LocalityAddress
 
+var _ pflag.Value = &localityList{}
+
 // Type implements the pflag.Value interface.
 func (l *localityList) Type() string { return "localityList" }
 

pkg/roachpb/span_group.go

@@ -68,6 +68,8 @@ func (g *SpanGroup) Len() int {
 	return g.rg.Len()
 }
 
+var _ = (*SpanGroup).Len
+
 // Slice will return the contents of the SpanGroup as a slice of Spans.
 func (g *SpanGroup) Slice() []Span {
 	rg := g.rg

pkg/storage/engine/batch.go

@@ -135,6 +135,8 @@ func (b *RocksDBBatchBuilder) Len() int {
 	return len(b.repr)
 }
 
+var _ = (*RocksDBBatchBuilder).Len
+
 // getRepr constructs the batch representation and returns it.
 func (b *RocksDBBatchBuilder) getRepr() []byte {
 	b.maybeInit()

pkg/testutils/lint/checker_float.go

@@ -12,7 +12,8 @@
 // implied. See the License for the specific language governing
 // permissions and limitations under the License.
 
-// +build lint
+// TODO(radu): re-enable the checkers using the new staticcheck interfaces.
+// +build lint_todo
 
 package lint
 

pkg/testutils/lint/checker_hash.go

@@ -12,7 +12,8 @@
 // implied. See the License for the specific language governing
 // permissions and limitations under the License.
 
-// +build lint
+// TODO(radu): re-enable the checkers using the new staticcheck interfaces.
+// +build lint_todo
 
 package lint
 

pkg/testutils/lint/checker_misc.go

@@ -12,7 +12,8 @@
 // implied. See the License for the specific language governing
 // permissions and limitations under the License.
 
-// +build lint
+// TODO(radu): re-enable the checkers using the new staticcheck interfaces.
+// +build lint_todo
 
 package lint
 

pkg/testutils/lint/checker_timer.go

@@ -12,7 +12,8 @@
 // implied. See the License for the specific language governing
 // permissions and limitations under the License.
 
-// +build lint
+// TODO(radu): re-enable the checkers using the new staticcheck interfaces.
+// +build lint_todo
 
 package lint
 

pkg/testutils/lint/checker_unconvert.go

@@ -12,7 +12,8 @@
 // implied. See the License for the specific language governing
 // permissions and limitations under the License.
 
-// +build lint
+// TODO(radu): re-enable the checkers using the new staticcheck interfaces.
+// +build lint_todo
 
 package lint