cmd/vet: add hostport analyzer

+ test, release note

Fixes #28308

Change-Id: I190e2fe513eeb6b90b0398841f67bf52510b5f59
Reviewed-on: https://go-review.googlesource.com/c/go/+/667596
Auto-Submit: Alan Donovan <[email protected]>
Commit-Queue: Alan Donovan <[email protected]>
Reviewed-by: Jonathan Amsterdam <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: adonovan

doc/next/3-tools.md

@@ -26,10 +26,17 @@ specifying the command's current version.
 
 ### Vet {#vet}
 
+The `go vet` command includes new analyzers:
+
 <!-- go.dev/issue/18022 -->
 
-The `go vet` command now includes the
-[waitgroup](https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/waitgroup)
-analyzer, which reports misplaced calls to [sync.WaitGroup.Add].
+- [waitgroup](https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/waitgroup),
+  which reports misplaced calls to [sync.WaitGroup.Add]; and
+
+<!-- go.dev/issue/28308 -->
 
+- [hostport](https://pkg.go.dev/golang.org/x/tools/go/analysis/passes/hostport),
+  which reports uses of `fmt.Sprintf("%s:%d", host, port)` to
+  construct addresses for [net.Dial], as these will not work with
+  IPv6; instead it suggests using [net.JoinHostPort].
 

src/cmd/go/internal/test/flagdefs.go

@@ -18,6 +18,9 @@ func TestMain(m *testing.M) {
 	os.Exit(m.Run())
 }
 
+// TestPassFlagToTest ensures that the generated table of flags is
+// consistent with output of "go tool vet -flags", using the installed
+// go command---so if it fails, you may need to re-run make.bash.
 func TestPassFlagToTest(t *testing.T) {
 	wantNames := genflags.ShortTestFlags()