Modernize Go code per use-modern-go guidelines (#61)

Apply the gopls modernize analyzer (-fix -test) across all workspace
modules, then a hand-reviewed sweep for guideline idioms the analyzer
misses. All rewrites are mechanical and behavior-preserving; no public
API changes.

Analyzer: errors.AsType, range-over-int, slices.Contains/ContainsFunc/
Backward, atomic.Int32, reflect.TypeFor, new(bool) inline.
Manual: sync.WaitGroup.Go, min/max clamp in BackoffDelay, strings.
CutPrefix in decodeThreadID, strings.FieldsFuncSeq, json omitzero on
bool/int wire fields.

Validated: mise run vet + GOFLAGS=-race mise run test across all
modules; burst/admission suites stressed with -race -count=5.

Author: ThomasK33

adapters/linear/harden_capability_test.go

@@ -205,8 +205,7 @@ func TestRateLimitDeadlineReturnsTypedRateLimited(t *testing.T) {
 
 	select {
 	case err := <-done:
-		var rl *linear.RateLimited
-		if !errors.As(err, &rl) {
+		if _, ok := errors.AsType[*linear.RateLimited](err); !ok {
 			t.Fatalf("err = %v, want *linear.RateLimited (deadline-bounded, not slept off)", err)
 		}
 		if elapsed := time.Since(start); elapsed > time.Second {

adapters/linear/history.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"slices"
 
 	"github.com/coder/chat"
 )
@@ -119,8 +120,7 @@ func (a *Adapter) readAgentSessionHistory(ctx context.Context, thread threadPayl
 	nodes := resp.Data.AgentSession.Activities.Nodes
 	messages := make([]chat.Message, 0, len(nodes))
 	// Linear returns the page createdAt-ascending; reverse for newest-first.
-	for i := len(nodes) - 1; i >= 0; i-- {
-		node := nodes[i]
+	for _, node := range slices.Backward(nodes) {
 		messages = append(messages, chat.Message{
 			ID:     node.ID,
 			Text:   node.Content.Body,
@@ -164,8 +164,8 @@ func (a *Adapter) readCommentThreadHistory(ctx context.Context, thread threadPay
 	children := resp.Data.Thread.Children.Nodes
 	messages := make([]chat.Message, 0, len(children)+1)
 	// Linear returns the page createdAt-ascending; reverse for newest-first.
-	for i := len(children) - 1; i >= 0; i-- {
-		messages = append(messages, historyCommentMessage(thread.Organization, children[i]))
+	for _, c := range slices.Backward(children) {
+		messages = append(messages, historyCommentMessage(thread.Organization, c))
 	}
 	// No older replies remain, so the root comment closes the oldest page.
 	if !resp.Data.Thread.Children.PageInfo.HasPreviousPage {

adapters/linear/history_test.go

@@ -623,8 +623,7 @@ func TestLinearReadHistoryRateLimitObservedAndErrors(t *testing.T) {
 
 	id := linear.EncodeAgentSessionThreadIDForTest("ORG1", "ISSUE1", "S1")
 	msgs, err := hr.ReadHistory(context.Background(), id, chat.HistoryQuery{})
-	var limited *linear.RateLimited
-	if !errors.As(err, &limited) {
+	if _, ok := errors.AsType[*linear.RateLimited](err); !ok {
 		t.Fatalf("err = %v, want *linear.RateLimited on a throttled read", err)
 	}
 	if msgs != nil {

adapters/linear/linear.go

@@ -246,8 +246,7 @@ func (a *Adapter) Webhook(dispatch chat.DispatchFunc) http.Handler {
 		}
 		body, err := io.ReadAll(http.MaxBytesReader(w, r.Body, maxWebhookBodyBytes))
 		if err != nil {
-			var maxBytesErr *http.MaxBytesError
-			if errors.As(err, &maxBytesErr) {
+			if _, ok := errors.AsType[*http.MaxBytesError](err); ok {
 				http.Error(w, "linear webhook too large", http.StatusRequestEntityTooLarge)
 				return
 			}
@@ -926,10 +925,11 @@ func encodeThreadID(payload threadPayload) (chat.ThreadID, error) {
 
 func decodeThreadID(id chat.ThreadID) (threadPayload, error) {
 	const prefix = "linear:v1:"
-	if !strings.HasPrefix(string(id), prefix) {
+	rest, ok := strings.CutPrefix(string(id), prefix)
+	if !ok {
 		return threadPayload{}, fmt.Errorf("linear: malformed thread id %q", id)
 	}
-	body, err := base64.RawURLEncoding.DecodeString(strings.TrimPrefix(string(id), prefix))
+	body, err := base64.RawURLEncoding.DecodeString(rest)
 	if err != nil {
 		return threadPayload{}, fmt.Errorf("linear: decode thread id: %w", err)
 	}
@@ -1179,7 +1179,7 @@ func verifyGrantedScopes(requested []string, granted string) error {
 
 func parseGrantedScopes(value string) map[string]struct{} {
 	out := map[string]struct{}{}
-	for _, scope := range strings.FieldsFunc(value, func(r rune) bool { return r == ',' || r == ' ' || r == '\t' || r == '\n' || r == '\r' }) {
+	for scope := range strings.FieldsFuncSeq(value, func(r rune) bool { return r == ',' || r == ' ' || r == '\t' || r == '\n' || r == '\r' }) {
 		scope = strings.TrimSpace(scope)
 		if scope != "" {
 			out[scope] = struct{}{}

adapters/linear/linear_test.go

@@ -11,6 +11,7 @@ import (
 	"io"
 	"net/http"
 	"net/http/httptest"
+	"slices"
 	"strings"
 	"sync"
 	"testing"
@@ -684,10 +685,8 @@ func containsToken(v any) bool {
 			}
 		}
 	case []any:
-		for _, val := range t {
-			if containsToken(val) {
-				return true
-			}
+		if slices.ContainsFunc(t, containsToken) {
+			return true
 		}
 	}
 	return false

adapters/slack/history.go

@@ -112,9 +112,9 @@ func (a *Adapter) ReadHistory(ctx context.Context, id chat.ThreadID, q chat.Hist
 type conversationsReadPayload struct {
 	Channel   string `json:"channel"`
 	TS        string `json:"ts,omitempty"`
-	Limit     int    `json:"limit,omitempty"`
+	Limit     int    `json:"limit,omitzero"`
 	Latest    string `json:"latest,omitempty"`
-	Inclusive bool   `json:"inclusive,omitempty"`
+	Inclusive bool   `json:"inclusive,omitzero"`
 }
 
 type conversationsHistoryResponse struct {

adapters/slack/history_hardening_test.go

@@ -123,8 +123,7 @@ func TestSlackReadHistoryRateLimitObservedAndErrors(t *testing.T) {
 
 	id := slack.EncodeThreadReplyThreadIDForTest("T1", "C1", "111.000")
 	msgs, err := hr.ReadHistory(context.Background(), id, chat.HistoryQuery{Limit: 5})
-	var limited *slack.RateLimited
-	if !errors.As(err, &limited) {
+	if _, ok := errors.AsType[*slack.RateLimited](err); !ok {
 		t.Fatalf("err = %v, want *slack.RateLimited on a throttled read", err)
 	}
 	if msgs != nil {

adapters/slack/interactive_hardening_test.go

@@ -57,7 +57,7 @@ func TestSlackCommandDedupedByEventIdentity(t *testing.T) {
 	}
 
 	form := signedCommandForm()
-	for i := 0; i < 3; i++ {
+	for i := range 3 {
 		rec := serveSignedSlackForm(t, handler, now, form)
 		if rec.Code != http.StatusOK {
 			t.Fatalf("delivery %d status = %d", i, rec.Code)
@@ -100,7 +100,7 @@ func TestSlackInteractionDedupedByEventIdentity(t *testing.T) {
 		"response_url":"https://hooks.slack.com/actions/T1/999",
 		"actions":[{"action_id":"approve","block_id":"b1","value":"yes","type":"button"}]
 	}`
-	for i := 0; i < 3; i++ {
+	for i := range 3 {
 		rec := serveSignedSlackInteractivity(t, handler, now, payload)
 		if rec.Code != http.StatusOK {
 			t.Fatalf("delivery %d status = %d", i, rec.Code)
@@ -154,7 +154,7 @@ func TestSlackRepeatInteractionsAreDistinctEvents(t *testing.T) {
 	for _, actionTS := range []string{"1700000001.000100", "1700000002.000200", "1700000003.000300"} {
 		payload := activation(actionTS)
 		// Deliver each activation twice: the original and a redelivery.
-		for delivery := 0; delivery < 2; delivery++ {
+		for delivery := range 2 {
 			rec := serveSignedSlackInteractivity(t, handler, now, payload)
 			if rec.Code != http.StatusOK {
 				t.Fatalf("activation %s delivery %d status = %d", actionTS, delivery, rec.Code)

adapters/slack/multitenant_test.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"slices"
 	"sync"
 	"testing"
 	"time"
@@ -57,12 +58,7 @@ func (s *fakeInstallStore) callCount() int {
 func (s *fakeInstallStore) lookedUp(tenant string) bool {
 	s.mu.Lock()
 	defer s.mu.Unlock()
-	for _, c := range s.calls {
-		if c == "slack:"+tenant {
-			return true
-		}
-	}
-	return false
+	return slices.Contains(s.calls, "slack:"+tenant)
 }
 
 func TestSlackConstructionModeSelection(t *testing.T) {
@@ -400,15 +396,13 @@ func TestSlackMultiTenantConcurrentTenantsDoNotCross(t *testing.T) {
 	}
 	var wg sync.WaitGroup
 	for _, team := range []string{"T1", "T2"} {
-		wg.Add(1)
-		go func(team string) {
-			defer wg.Done()
+		wg.Go(func() {
 			rec := serveSignedSlackWebhook(t, handler, now,
 				slackEventBody(team, "Ev"+team, "U"+team, "<@UBOT"+team[1:]+"> hi"), "", "")
 			if rec.Code != http.StatusOK {
 				t.Errorf("team %s status = %d", team, rec.Code)
 			}
-		}(team)
+		})
 	}
 	wg.Wait()
 

adapters/slack/ratelimit_hardening_test.go

@@ -258,8 +258,7 @@ func TestSlackPostNeverSleepsPastContextDeadline(t *testing.T) {
 
 	select {
 	case err := <-done:
-		var limited *slack.RateLimited
-		if !errors.As(err, &limited) {
+		if _, ok := errors.AsType[*slack.RateLimited](err); !ok {
 			t.Fatalf("err = %v, want *slack.RateLimited (deadline-bounded, not slept off)", err)
 		}
 	case <-time.After(5 * time.Second):
@@ -306,8 +305,7 @@ func TestSlackPostDoesNotRetryNonThrottlingError(t *testing.T) {
 	if postErr == nil {
 		t.Fatal("expected an error from a 401 auth failure")
 	}
-	var limited *slack.RateLimited
-	if errors.As(postErr, &limited) {
+	if _, ok := errors.AsType[*slack.RateLimited](postErr); ok {
 		t.Fatal("a non-throttling 401 must not surface as RateLimited")
 	}
 	mu.Lock()
@@ -337,8 +335,7 @@ func TestSlackDefaultPolicyCeilingUnderAckWindow(t *testing.T) {
 	_, err := adapter.PostMessage(context.Background(), ref, chat.Text("hi"))
 	elapsed := time.Since(start)
 
-	var limited *slack.RateLimited
-	if !errors.As(err, &limited) {
+	if _, ok := errors.AsType[*slack.RateLimited](err); !ok {
 		t.Fatalf("err = %v, want *slack.RateLimited", err)
 	}
 	if elapsed >= 3*time.Second {