fix warnings by ineffassign, with a one actual issue

In store/search.go, we would make a copy of a byte array, but then still use
the original instead of the copy. Could result in search operations not finding
messages that do have the content, but under very unlikely conditions only.

We'll keep running ineffassign with "make check", useful enough.

Makefile

@@ -42,6 +42,9 @@ test-upgrade: build
 install-staticcheck:
 	CGO_ENABLED=0 go install honnef.co/go/tools/cmd/staticcheck@latest
 
+install-ineffassign:
+	CGO_ENABLED=0 go install github.com/gordonklaus/ineffassign@v0.1.0
+
 check:
 	CGO_ENABLED=0 go vet -tags integration
 	CGO_ENABLED=0 go vet -tags website website/website.go
@@ -55,6 +58,7 @@ check:
 	CGO_ENABLED=0 staticcheck -tags link rfc/link.go
 	CGO_ENABLED=0 staticcheck -tags errata rfc/errata.go
 	CGO_ENABLED=0 staticcheck -tags xr rfc/xr.go
+	CGO_ENABLED=0 ineffassign ./...
 
 # needed for check-shadow
 install-shadow:

backup.go

@@ -512,7 +512,6 @@ func backupctl(ctx context.Context, ctl *ctl) {
 			backupDB(db, jfpath)
 			bloompath := filepath.Join("accounts", acc.Name, "junkfilter.bloom")
 			backupFile(bloompath)
-			db = nil
 			err := jf.Close()
 			ctl.log.Check(err, "closing junkfilter")
 		}

develop.txt

@@ -13,11 +13,12 @@ code paths are reachable/testable with mox localserve, but some use cases will
 require a full setup.
 
 Before committing, run at least "make fmt" and "make check" (which requires
-staticcheck, run "make install-staticcheck" once). Also run "make check-shadow"
-and fix any shadowed variables other than "err" (which are filtered out, but
-causes the command to always exit with an error code; run "make install-shadow"
-once to install the shadow command). If you've updated RFC references, run
-"make" in rfc/, it verifies the referenced files exist.
+staticcheck and ineffassign, run "make install-staticcheck install-ineffassign"
+once). Also run "make check-shadow" and fix any shadowed variables other than
+"err" (which are filtered out, but causes the command to always exit with an
+error code; run "make install-shadow" once to install the shadow command). If
+you've updated RFC references, run "make" in rfc/, it verifies the referenced
+files exist.
 
 When making changes to the public API of a package listed in
 apidiff/packages.txt, run "make genapidiff" to update the list of changes in

main.go

@@ -1960,11 +1960,12 @@ sharing most of its code.
 
 	resolver := dns.StrictResolver{}
 	var haveMX bool
-	var origNextHopAuthentic, expandedNextHopAuthentic bool
+	var expandedNextHopAuthentic bool
 	var expandedNextHop dns.Domain
 	var hosts []dns.IPDomain
 	if len(args) == 1 {
 		var permanent bool
+		var origNextHopAuthentic bool
 		var err error
 		haveMX, origNextHopAuthentic, expandedNextHopAuthentic, expandedNextHop, hosts, permanent, err = smtpclient.GatherDestinations(ctxbg, c.log.Logger, resolver, dns.IPDomain{Domain: origNextHop})
 		status := "temporary"
@@ -1998,7 +1999,6 @@ sharing most of its code.
 		d := xparseDomain(args[1], "destination host")
 		log.Printf("skipping domain mx/cname lookups, assuming domain is dnssec-protected")
 
-		origNextHopAuthentic = true
 		expandedNextHopAuthentic = true
 		expandedNextHop = d
 		hosts = []dns.IPDomain{{Domain: d}}

queue/hook_test.go

@@ -656,7 +656,6 @@ func TestHookListFilterSort(t *testing.T) {
 	var lr []HookRetired
 	lastID = 0
 	last = ""
-	l = nil
 	for {
 		nl, err := HookRetiredList(ctxbg, HookRetiredFilter{Max: 1}, HookRetiredSort{LastID: lastID, Last: last})
 		tcheck(t, err, "list paginated")

queue/queue_test.go

@@ -1435,7 +1435,6 @@ func TestListFilterSort(t *testing.T) {
 	var lr []MsgRetired
 	lastID = 0
 	last = ""
-	l = nil
 	for {
 		nl, err := RetiredList(ctxbg, RetiredFilter{Max: 1}, RetiredSort{LastID: lastID, Last: last})
 		tcheck(t, err, "list paginated")

smtpserver/server.go

@@ -3424,18 +3424,16 @@ func (c *conn) deliver(ctx context.Context, recvHdrFor func(string) string, msgW
 							return fmt.Errorf("finding rejects mailbox: %v", err)
 						}
 
-						hasSpace := true
 						if !conf.KeepRejects && mbrej != nil {
-							var chl []store.Change
-							chl, hasSpace, err = a.d.acc.TidyRejectsMailbox(c.log, tx, mbrej)
+							chl, hasSpace, err := a.d.acc.TidyRejectsMailbox(c.log, tx, mbrej)
 							if err != nil {
 								return fmt.Errorf("tidying rejects mailbox: %v", err)
 							}
+							changes = append(changes, chl...)
 							if !hasSpace {
 								log.Info("not storing spammy mail to full rejects mailbox")
 								return nil
 							}
-							changes = append(changes, chl...)
 						}
 						if mbrej == nil {
 							nmb, chl, _, _, err := a.d.acc.MailboxCreate(tx, conf.RejectsMailbox, store.SpecialUse{})

store/search.go

@@ -187,7 +187,7 @@ func toLower(buf []byte) []byte {
 			copied = true
 			nr := make([]byte, len(r), len(r)+nsize+len(buf)-i)
 			copy(nr, r)
-			nr = r
+			r = nr
 		}
 		r = utf8.AppendRune(r, nc)
 	}