[bugfix] Rework MultiError to wrap + unwrap errors properly (#2057)

* rework multierror a bit

* test multierror

cmd/gotosocial/action/admin/media/prune/common.go

@@ -75,14 +75,14 @@ func setupPrune(ctx context.Context) (*prune, error) {
 }
 
 func (p *prune) shutdown(ctx context.Context) error {
-	var errs gtserror.MultiError
+	errs := gtserror.NewMultiError(2)
 
 	if err := p.storage.Close(); err != nil {
-		errs.Appendf("error closing storage backend: %v", err)
+		errs.Appendf("error closing storage backend: %w", err)
 	}
 
 	if err := p.dbService.Stop(ctx); err != nil {
-		errs.Appendf("error stopping database: %v", err)
+		errs.Appendf("error stopping database: %w", err)
 	}
 
 	p.state.Workers.Stop()

internal/api/activitypub/users/inboxpost_test.go

@@ -22,7 +22,6 @@
 	"context"
 	"encoding/json"
 	"errors"
-	"fmt"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -105,16 +104,16 @@ func (suite *InboxPostTestSuite) inboxPost(
 		suite.FailNow(err.Error())
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	// Check expected code + body.
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// If we got an expected body, return early.
 	if expectedBody != "" && string(b) != expectedBody {
-		errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+		errs.Appendf("expected %s got %s", expectedBody, string(b))
 	}
 
 	if err := errs.Combine(); err != nil {

internal/api/client/accounts/accountupdate_test.go

@@ -90,16 +90,16 @@ func (suite *AccountUpdateTestSuite) updateAccount(
 		return nil, err
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	// Check expected code + body.
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// If we got an expected body, return early.
 	if expectedBody != "" && string(b) != expectedBody {
-		errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+		errs.Appendf("expected %s got %s", expectedBody, string(b))
 	}
 
 	if err := errs.Combine(); err != nil {

internal/api/client/accounts/lists_test.go

@@ -19,7 +19,6 @@
 
 import (
 	"encoding/json"
-	"fmt"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -63,16 +62,16 @@ func (suite *ListsTestSuite) getLists(targetAccountID string, expectedHTTPStatus
 		suite.FailNow(err.Error())
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	// Check expected code + body.
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// If we got an expected body, return early.
 	if expectedBody != "" && string(b) != expectedBody {
-		errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+		errs.Appendf("expected %s got %s", expectedBody, string(b))
 	}
 
 	if err := errs.Combine(); err != nil {

internal/api/client/accounts/search_test.go

@@ -19,7 +19,6 @@
 
 import (
 	"encoding/json"
-	"fmt"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -99,16 +98,16 @@ func (suite *AccountSearchTestSuite) getSearch(
 		suite.FailNow(err.Error())
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	// Check expected code + body.
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// If we got an expected body, return early.
 	if expectedBody != "" && string(b) != expectedBody {
-		errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+		errs.Appendf("expected %s got %s", expectedBody, string(b))
 	}
 
 	if err := errs.Combine(); err != nil {

internal/api/client/admin/reportresolve_test.go

@@ -19,7 +19,6 @@
 
 import (
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -84,16 +83,16 @@ func (suite *ReportResolveTestSuite) resolveReport(
 		return nil, err
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// if we got an expected body, return early
 	if expectedBody != "" {
 		if string(b) != expectedBody {
-			errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+			errs.Appendf("expected %s got %s", expectedBody, string(b))
 		}
 		return nil, errs.Combine()
 	}

internal/api/client/admin/reportsget_test.go

@@ -19,7 +19,6 @@
 
 import (
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -101,16 +100,16 @@ func (suite *ReportsGetTestSuite) getReports(
 		return nil, "", err
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// if we got an expected body, return early
 	if expectedBody != "" {
 		if string(b) != expectedBody {
-			errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+			errs.Appendf("expected %s got %s", expectedBody, string(b))
 		}
 		return nil, "", errs.Combine()
 	}

internal/api/client/lists/listaccounts_test.go

@@ -19,7 +19,6 @@
 
 import (
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -103,17 +102,17 @@ func (suite *ListAccountsTestSuite) getListAccounts(
 		return nil, "", err
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	// check code + body
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// if we got an expected body, return early
 	if expectedBody != "" {
 		if string(b) != expectedBody {
-			errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+			errs.Appendf("expected %s got %s", expectedBody, string(b))
 		}
 		return nil, "", errs.Combine()
 	}

internal/api/client/reports/reportcreate_test.go

@@ -19,7 +19,6 @@
 
 import (
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -77,17 +76,17 @@ func (suite *ReportCreateTestSuite) createReport(expectedHTTPStatus int, expecte
 		return nil, err
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	// check code + body
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// if we got an expected body, return early
 	if expectedBody != "" {
 		if string(b) != expectedBody {
-			errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+			errs.Appendf("expected %s got %s", expectedBody, string(b))
 		}
 		return nil, errs.Combine()
 	}

internal/api/client/reports/reportget_test.go

@@ -19,7 +19,6 @@
 
 import (
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -64,17 +63,17 @@ func (suite *ReportGetTestSuite) getReport(expectedHTTPStatus int, expectedBody
 		return nil, err
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	// check code + body
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// if we got an expected body, return early
 	if expectedBody != "" {
 		if string(b) != expectedBody {
-			errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+			errs.Appendf("expected %s got %s", expectedBody, string(b))
 		}
 		return nil, errs.Combine()
 	}

internal/api/client/search/searchget_test.go

@@ -22,7 +22,6 @@
 	"crypto/rand"
 	"crypto/rsa"
 	"encoding/json"
-	"fmt"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -122,16 +121,16 @@ func (suite *SearchGetTestSuite) getSearch(
 		suite.FailNow(err.Error())
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
 	// Check expected code + body.
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d: %v", expectedHTTPStatus, resultCode, ctx.Errors.JSON()))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
 	// If we got an expected body, return early.
 	if expectedBody != "" && string(b) != expectedBody {
-		errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+		errs.Appendf("expected %s got %s", expectedBody, string(b))
 	}
 
 	if err := errs.Combine(); err != nil {

internal/api/client/statuses/statuspin_test.go

@@ -20,7 +20,6 @@
 import (
 	"context"
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -74,20 +73,20 @@ func (suite *StatusPinTestSuite) createPin(
 		return nil, err
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
-	// check code + body
+	// Check expected code + body.
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
-	// if we got an expected body, return early
+	// If we got an expected body, return early.
 	if expectedBody != "" && string(b) != expectedBody {
-		errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+		errs.Appendf("expected %s got %s", expectedBody, string(b))
 	}
 
-	if len(errs) > 0 {
+	if err := errs.Combine(); err != nil {
-		return nil, errs.Combine()
+		suite.FailNow("", "%v (body %s)", err, string(b))
 	}
 
 	resp := &apimodel.Status{}

internal/api/client/statuses/statusunpin_test.go

@@ -19,7 +19,6 @@
 
 import (
 	"encoding/json"
-	"fmt"
 	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
@@ -68,20 +67,20 @@ func (suite *StatusUnpinTestSuite) createUnpin(
 		return nil, err
 	}
 
-	errs := gtserror.MultiError{}
+	errs := gtserror.NewMultiError(2)
 
-	// check code + body
+	// Check expected code + body.
 	if resultCode := recorder.Code; expectedHTTPStatus != resultCode {
-		errs = append(errs, fmt.Sprintf("expected %d got %d", expectedHTTPStatus, resultCode))
+		errs.Appendf("expected %d got %d", expectedHTTPStatus, resultCode)
 	}
 
-	// if we got an expected body, return early
+	// If we got an expected body, return early.
 	if expectedBody != "" && string(b) != expectedBody {
-		errs = append(errs, fmt.Sprintf("expected %s got %s", expectedBody, string(b)))
+		errs.Appendf("expected %s got %s", expectedBody, string(b))
 	}
 
-	if len(errs) > 0 {
+	if err := errs.Combine(); err != nil {
-		return nil, errs.Combine()
+		suite.FailNow("", "%v (body %s)", err, string(b))
 	}
 
 	resp := &apimodel.Status{}

internal/cleaner/cleaner.go

@@ -83,19 +83,23 @@ func (c *Cleaner) removeFiles(ctx context.Context, files ...string) (int, error)
 		return len(files), nil
 	}
 
-	var errs gtserror.MultiError
+	var (
+		errs     gtserror.MultiError
+		errCount int
+	)
 
 	for _, path := range files {
 		// Remove each provided storage path.
 		log.Debugf(ctx, "removing file: %s", path)
 		err := c.state.Storage.Delete(ctx, path)
 		if err != nil && !errors.Is(err, storage.ErrNotFound) {
-			errs.Appendf("error removing %s: %v", path, err)
+			errs.Appendf("error removing %s: %w", path, err)
+			errCount++
 		}
 	}
 
 	// Calculate no. files removed.
-	diff := len(files) - len(errs)
+	diff := len(files) - errCount
 
 	// Wrap the combined error slice.
 	if err := errs.Combine(); err != nil {

internal/db/bundb/account.go

@@ -20,7 +20,6 @@
 import (
 	"context"
 	"errors"
-	"fmt"
 	"strings"
 	"time"
 
@@ -255,7 +254,7 @@ func (a *accountDB) getAccount(ctx context.Context, lookup string, dbQuery func(
 func (a *accountDB) PopulateAccount(ctx context.Context, account *gtsmodel.Account) error {
 	var (
 		err  error
-		errs = make(gtserror.MultiError, 0, 3)
+		errs = gtserror.NewMultiError(3)
 	)
 
 	if account.AvatarMediaAttachment == nil && account.AvatarMediaAttachmentID != "" {
@@ -265,7 +264,7 @@ func (a *accountDB) PopulateAccount(ctx context.Context, account *gtsmodel.Accou
 			account.AvatarMediaAttachmentID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating account avatar: %w", err))
+			errs.Appendf("error populating account avatar: %w", err)
 		}
 	}
 
@@ -276,7 +275,7 @@ func (a *accountDB) PopulateAccount(ctx context.Context, account *gtsmodel.Accou
 			account.HeaderMediaAttachmentID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating account header: %w", err))
+			errs.Appendf("error populating account header: %w", err)
 		}
 	}
 
@@ -287,11 +286,15 @@ func (a *accountDB) PopulateAccount(ctx context.Context, account *gtsmodel.Accou
 			account.EmojiIDs,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating account emojis: %w", err))
+			errs.Appendf("error populating account emojis: %w", err)
 		}
 	}
 
-	return errs.Combine()
+	if err := errs.Combine(); err != nil {
+		return gtserror.Newf("%w", err)
+	}
+
+	return nil
 }
 
 func (a *accountDB) PutAccount(ctx context.Context, account *gtsmodel.Account) error {

internal/db/bundb/instance.go

@@ -173,7 +173,7 @@ func (i *instanceDB) getInstance(ctx context.Context, lookup string, dbQuery fun
 func (i *instanceDB) populateInstance(ctx context.Context, instance *gtsmodel.Instance) error {
 	var (
 		err  error
-		errs = make(gtserror.MultiError, 0, 2)
+		errs = gtserror.NewMultiError(2)
 	)
 
 	if instance.DomainBlockID != "" && instance.DomainBlock == nil {
@@ -183,7 +183,7 @@ func (i *instanceDB) populateInstance(ctx context.Context, instance *gtsmodel.In
 			instance.Domain,
 		)
 		if err != nil {
-			errs.Append(gtserror.Newf("error populating instance domain block: %w", err))
+			errs.Appendf("error populating instance domain block: %w", err)
 		}
 	}
 
@@ -194,11 +194,15 @@ func (i *instanceDB) populateInstance(ctx context.Context, instance *gtsmodel.In
 			instance.ContactAccountID,
 		)
 		if err != nil {
-			errs.Append(gtserror.Newf("error populating instance contact account: %w", err))
+			errs.Appendf("error populating instance contact account: %w", err)
 		}
 	}
 
-	return errs.Combine()
+	if err := errs.Combine(); err != nil {
+		return gtserror.Newf("%w", err)
+	}
+
+	return nil
 }
 
 func (i *instanceDB) PutInstance(ctx context.Context, instance *gtsmodel.Instance) error {

internal/db/bundb/list.go

@@ -117,7 +117,7 @@ func (l *listDB) GetListsForAccountID(ctx context.Context, accountID string) ([]
 func (l *listDB) PopulateList(ctx context.Context, list *gtsmodel.List) error {
 	var (
 		err  error
-		errs = make(gtserror.MultiError, 0, 2)
+		errs = gtserror.NewMultiError(2)
 	)
 
 	if list.Account == nil {
@@ -127,7 +127,7 @@ func (l *listDB) PopulateList(ctx context.Context, list *gtsmodel.List) error {
 			list.AccountID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating list account: %w", err))
+			errs.Appendf("error populating list account: %w", err)
 		}
 	}
 
@@ -139,11 +139,15 @@ func (l *listDB) PopulateList(ctx context.Context, list *gtsmodel.List) error {
 			"", "", "", 0,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating list entries: %w", err))
+			errs.Appendf("error populating list entries: %w", err)
 		}
 	}
 
-	return errs.Combine()
+	if err := errs.Combine(); err != nil {
+		return gtserror.Newf("%w", err)
+	}
+
+	return nil
 }
 
 func (l *listDB) PutList(ctx context.Context, list *gtsmodel.List) error {

internal/db/bundb/relationship_follow.go

@@ -160,7 +160,7 @@ func (r *relationshipDB) getFollow(ctx context.Context, lookup string, dbQuery f
 func (r *relationshipDB) PopulateFollow(ctx context.Context, follow *gtsmodel.Follow) error {
 	var (
 		err  error
-		errs = make(gtserror.MultiError, 0, 2)
+		errs = gtserror.NewMultiError(2)
 	)
 
 	if follow.Account == nil {
@@ -170,7 +170,7 @@ func (r *relationshipDB) PopulateFollow(ctx context.Context, follow *gtsmodel.Fo
 			follow.AccountID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating follow account: %w", err))
+			errs.Appendf("error populating follow account: %w", err)
 		}
 	}
 
@@ -181,11 +181,15 @@ func (r *relationshipDB) PopulateFollow(ctx context.Context, follow *gtsmodel.Fo
 			follow.TargetAccountID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating follow target account: %w", err))
+			errs.Appendf("error populating follow target account: %w", err)
 		}
 	}
 
-	return errs.Combine()
+	if err := errs.Combine(); err != nil {
+		return gtserror.Newf("%w", err)
+	}
+
+	return nil
 }
 
 func (r *relationshipDB) PutFollow(ctx context.Context, follow *gtsmodel.Follow) error {

internal/db/bundb/status.go

@@ -22,7 +22,6 @@
 	"context"
 	"database/sql"
 	"errors"
-	"fmt"
 	"time"
 
 	"github.com/superseriousbusiness/gotosocial/internal/db"
@@ -129,7 +128,7 @@ func (s *statusDB) getStatus(ctx context.Context, lookup string, dbQuery func(*g
 func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status) error {
 	var (
 		err  error
-		errs = make(gtserror.MultiError, 0, 9)
+		errs = gtserror.NewMultiError(9)
 	)
 
 	if status.Account == nil {
@@ -139,7 +138,7 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 			status.AccountID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating status author: %w", err))
+			errs.Appendf("error populating status author: %w", err)
 		}
 	}
 
@@ -150,7 +149,7 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 			status.InReplyToID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating status parent: %w", err))
+			errs.Appendf("error populating status parent: %w", err)
 		}
 	}
 
@@ -162,7 +161,7 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 				status.InReplyToID,
 			)
 			if err != nil {
-				errs.Append(fmt.Errorf("error populating status parent: %w", err))
+				errs.Appendf("error populating status parent: %w", err)
 			}
 		}
 
@@ -173,7 +172,7 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 				status.InReplyToAccountID,
 			)
 			if err != nil {
-				errs.Append(fmt.Errorf("error populating status parent author: %w", err))
+				errs.Appendf("error populating status parent author: %w", err)
 			}
 		}
 	}
@@ -186,7 +185,7 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 				status.BoostOfID,
 			)
 			if err != nil {
-				errs.Append(fmt.Errorf("error populating status boost: %w", err))
+				errs.Appendf("error populating status boost: %w", err)
 			}
 		}
 
@@ -197,7 +196,7 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 				status.BoostOfAccountID,
 			)
 			if err != nil {
-				errs.Append(fmt.Errorf("error populating status boost author: %w", err))
+				errs.Appendf("error populating status boost author: %w", err)
 			}
 		}
 	}
@@ -209,7 +208,7 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 			status.AttachmentIDs,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating status attachments: %w", err))
+			errs.Appendf("error populating status attachments: %w", err)
 		}
 	}
 
@@ -220,7 +219,7 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 			status.TagIDs,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating status tags: %w", err))
+			errs.Appendf("error populating status tags: %w", err)
 		}
 	}
 
@@ -231,7 +230,7 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 			status.MentionIDs,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating status mentions: %w", err))
+			errs.Appendf("error populating status mentions: %w", err)
 		}
 	}
 
@@ -242,11 +241,15 @@ func (s *statusDB) PopulateStatus(ctx context.Context, status *gtsmodel.Status)
 			status.EmojiIDs,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating status emojis: %w", err))
+			errs.Appendf("error populating status emojis: %w", err)
 		}
 	}
 
-	return errs.Combine()
+	if err := errs.Combine(); err != nil {
+		return gtserror.Newf("%w", err)
+	}
+
+	return nil
 }
 
 func (s *statusDB) PutStatus(ctx context.Context, status *gtsmodel.Status) error {

internal/db/bundb/statusfave.go

@@ -149,7 +149,7 @@ func (s *statusFaveDB) GetStatusFavesForStatus(ctx context.Context, statusID str
 func (s *statusFaveDB) PopulateStatusFave(ctx context.Context, statusFave *gtsmodel.StatusFave) error {
 	var (
 		err  error
-		errs = make(gtserror.MultiError, 0, 3)
+		errs = gtserror.NewMultiError(3)
 	)
 
 	if statusFave.Account == nil {
@@ -159,7 +159,7 @@ func (s *statusFaveDB) PopulateStatusFave(ctx context.Context, statusFave *gtsmo
 			statusFave.AccountID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating status fave author: %w", err))
+			errs.Appendf("error populating status fave author: %w", err)
 		}
 	}
 
@@ -170,7 +170,7 @@ func (s *statusFaveDB) PopulateStatusFave(ctx context.Context, statusFave *gtsmo
 			statusFave.TargetAccountID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating status fave target account: %w", err))
+			errs.Appendf("error populating status fave target account: %w", err)
 		}
 	}
 
@@ -181,11 +181,15 @@ func (s *statusFaveDB) PopulateStatusFave(ctx context.Context, statusFave *gtsmo
 			statusFave.StatusID,
 		)
 		if err != nil {
-			errs.Append(fmt.Errorf("error populating status fave status: %w", err))
+			errs.Appendf("error populating status fave status: %w", err)
 		}
 	}
 
-	return errs.Combine()
+	if err := errs.Combine(); err != nil {
+		return gtserror.Newf("%w", err)
+	}
+
+	return nil
 }
 
 func (s *statusFaveDB) PutStatusFave(ctx context.Context, fave *gtsmodel.StatusFave) error {

internal/gtserror/multi.go

@@ -20,25 +20,48 @@
 import (
 	"errors"
 	"fmt"
-	"strings"
 )
 
-// MultiError allows encapsulating multiple errors under a singular instance,
+// MultiError allows encapsulating multiple
-// which is useful when you only want to log on errors, not return early / bubble up.
+// errors under a singular instance, which
-type MultiError []string
+// is useful when you only want to log on
-
+// errors, not return early / bubble up.
-func (e *MultiError) Append(err error) {
+type MultiError struct {
-	*e = append(*e, err.Error())
+	e []error
 }
 
-func (e *MultiError) Appendf(format string, args ...any) {
+// NewMultiError returns a *MultiError with
-	*e = append(*e, fmt.Sprintf(format, args...))
+// the capacity of its underlying error slice
+// set to the provided value.
+//
+// This capacity can be exceeded if necessary,
+// but it saves a teeny tiny bit of memory if
+// callers set it correctly.
+//
+// If you don't know in advance what the capacity
+// must be, just use new(MultiError) instead.
+func NewMultiError(capacity int) *MultiError {
+	return &MultiError{
+		e: make([]error, 0, capacity),
+	}
 }
 
-// Combine converts this multiError to a singular error instance, returning nil if empty.
+// Append the given error to the MultiError.
-func (e MultiError) Combine() error {
+func (m *MultiError) Append(err error) {
-	if len(e) == 0 {
+	m.e = append(m.e, err)
-		return nil
 }
-	return errors.New(`"` + strings.Join(e, `","`) + `"`)
+
+// Append the given format string to the MultiError.
+//
+// It is valid to use %w in the format string
+// to wrap any other errors.
+func (m *MultiError) Appendf(format string, args ...any) {
+	m.e = append(m.e, fmt.Errorf(format, args...))
+}
+
+// Combine the MultiError into a single error.
+//
+// Unwrap will work on the returned error as expected.
+func (m MultiError) Combine() error {
+	return errors.Join(m.e...)
 }

internal/gtserror/multi_test.go

@@ -0,0 +1,64 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package gtserror
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/superseriousbusiness/gotosocial/internal/db"
+)
+
+func TestMultiError(t *testing.T) {
+	errs := MultiError{
+		e: []error{
+			db.ErrNoEntries,
+			errors.New("oopsie woopsie we did a fucky wucky etc"),
+		},
+	}
+	errs.Appendf("appended + wrapped error: %w", db.ErrAlreadyExists)
+
+	err := errs.Combine()
+
+	if !errors.Is(err, db.ErrNoEntries) {
+		t.Error("should be db.ErrNoEntries")
+	}
+
+	if !errors.Is(err, db.ErrAlreadyExists) {
+		t.Error("should be db.ErrAlreadyExists")
+	}
+
+	if errors.Is(err, db.ErrBusyTimeout) {
+		t.Error("should not be db.ErrBusyTimeout")
+	}
+
+	errString := err.Error()
+	expected := `sql: no rows in result set
+oopsie woopsie we did a fucky wucky etc
+appended + wrapped error: already exists`
+	if errString != expected {
+		t.Errorf("errString '%s' should be '%s'", errString, expected)
+	}
+}
+
+func TestMultiErrorEmpty(t *testing.T) {
+	err := new(MultiError).Combine()
+	if err != nil {
+		t.Errorf("should be nil")
+	}
+}

internal/processing/fromcommon.go

@@ -20,7 +20,6 @@
 import (
 	"context"
 	"errors"
-	"fmt"
 
 	"github.com/superseriousbusiness/gotosocial/internal/config"
 	"github.com/superseriousbusiness/gotosocial/internal/db"
@@ -42,13 +41,13 @@
 func (p *Processor) timelineAndNotifyStatus(ctx context.Context, status *gtsmodel.Status) error {
 	// Ensure status fully populated; including account, mentions, etc.
 	if err := p.state.DB.PopulateStatus(ctx, status); err != nil {
-		return fmt.Errorf("timelineAndNotifyStatus: error populating status with id %s: %w", status.ID, err)
+		return gtserror.Newf("error populating status with id %s: %w", status.ID, err)
 	}
 
 	// Get local followers of the account that posted the status.
 	follows, err := p.state.DB.GetAccountLocalFollowers(ctx, status.AccountID)
 	if err != nil {
-		return fmt.Errorf("timelineAndNotifyStatus: error getting local followers for account id %s: %w", status.AccountID, err)
+		return gtserror.Newf("error getting local followers for account id %s: %w", status.AccountID, err)
 	}
 
 	// If the poster is also local, add a fake entry for them
@@ -66,12 +65,12 @@ func (p *Processor) timelineAndNotifyStatus(ctx context.Context, status *gtsmode
 	// This will also handle notifying any followers with notify
 	// set to true on their follow.
 	if err := p.timelineAndNotifyStatusForFollowers(ctx, status, follows); err != nil {
-		return fmt.Errorf("timelineAndNotifyStatus: error timelining status %s for followers: %w", status.ID, err)
+		return gtserror.Newf("error timelining status %s for followers: %w", status.ID, err)
 	}
 
 	// Notify each local account that's mentioned by this status.
 	if err := p.notifyStatusMentions(ctx, status); err != nil {
-		return fmt.Errorf("timelineAndNotifyStatus: error notifying status mentions for status %s: %w", status.ID, err)
+		return gtserror.Newf("error notifying status mentions for status %s: %w", status.ID, err)
 	}
 
 	return nil
@@ -79,7 +78,7 @@ func (p *Processor) timelineAndNotifyStatus(ctx context.Context, status *gtsmode
 
 func (p *Processor) timelineAndNotifyStatusForFollowers(ctx context.Context, status *gtsmodel.Status, follows []*gtsmodel.Follow) error {
 	var (
-		errs  = make(gtserror.MultiError, 0, len(follows))
+		errs  = gtserror.NewMultiError(len(follows))
 		boost = status.BoostOfID != ""
 		reply = status.InReplyToURI != ""
 	)
@@ -100,7 +99,7 @@ func (p *Processor) timelineAndNotifyStatusForFollowers(ctx context.Context, sta
 			follow.ID,
 		)
 		if err != nil && !errors.Is(err, db.ErrNoEntries) {
-			errs.Append(fmt.Errorf("timelineAndNotifyStatusForFollowers: error list timelining status: %w", err))
+			errs.Appendf("error list timelining status: %w", err)
 			continue
 		}
 
@@ -113,7 +112,7 @@ func (p *Processor) timelineAndNotifyStatusForFollowers(ctx context.Context, sta
 				status,
 				stream.TimelineList+":"+listEntry.ListID, // key streamType to this specific list
 			); err != nil {
-				errs.Append(fmt.Errorf("timelineAndNotifyStatusForFollowers: error list timelining status: %w", err))
+				errs.Appendf("error list timelining status: %w", err)
 				continue
 			}
 		}
@@ -128,7 +127,7 @@ func (p *Processor) timelineAndNotifyStatusForFollowers(ctx context.Context, sta
 			status,
 			stream.TimelineHome,
 		); err != nil {
-			errs.Append(fmt.Errorf("timelineAndNotifyStatusForFollowers: error home timelining status: %w", err))
+			errs.Appendf("error home timelining status: %w", err)
 			continue
 		} else if !timelined {
 			// Status wasn't added to home tomeline,
@@ -162,11 +161,15 @@ func (p *Processor) timelineAndNotifyStatusForFollowers(ctx context.Context, sta
 			status.AccountID,
 			status.ID,
 		); err != nil {
-			errs.Append(fmt.Errorf("timelineAndNotifyStatusForFollowers: error notifying account %s about new status: %w", follow.AccountID, err))
+			errs.Appendf("error notifying account %s about new status: %w", follow.AccountID, err)
 		}
 	}
 
-	return errs.Combine()
+	if err := errs.Combine(); err != nil {
+		return gtserror.Newf("%w", err)
+	}
+
+	return nil
 }
 
 // timelineStatus uses the provided ingest function to put the given
@@ -185,7 +188,7 @@ func (p *Processor) timelineStatus(
 	// Make sure the status is timelineable.
 	// This works for both home and list timelines.
 	if timelineable, err := p.filter.StatusHomeTimelineable(ctx, account, status); err != nil {
-		err = fmt.Errorf("timelineStatusForAccount: error getting timelineability for status for timeline with id %s: %w", account.ID, err)
+		err = gtserror.Newf("error getting timelineability for status for timeline with id %s: %w", account.ID, err)
 		return false, err
 	} else if !timelineable {
 		// Nothing to do.
@@ -194,7 +197,7 @@ func (p *Processor) timelineStatus(
 
 	// Ingest status into given timeline using provided function.
 	if inserted, err := ingest(ctx, timelineID, status); err != nil {
-		err = fmt.Errorf("timelineStatusForAccount: error ingesting status %s: %w", status.ID, err)
+		err = gtserror.Newf("error ingesting status %s: %w", status.ID, err)
 		return false, err
 	} else if !inserted {
 		// Nothing more to do.
@@ -204,12 +207,12 @@ func (p *Processor) timelineStatus(
 	// The status was inserted so stream it to the user.
 	apiStatus, err := p.tc.StatusToAPIStatus(ctx, status, account)
 	if err != nil {
-		err = fmt.Errorf("timelineStatusForAccount: error converting status %s to frontend representation: %w", status.ID, err)
+		err = gtserror.Newf("error converting status %s to frontend representation: %w", status.ID, err)
 		return true, err
 	}
 
 	if err := p.stream.Update(apiStatus, account, []string{streamType}); err != nil {
-		err = fmt.Errorf("timelineStatusForAccount: error streaming update for status %s: %w", status.ID, err)
+		err = gtserror.Newf("error streaming update for status %s: %w", status.ID, err)
 		return true, err
 	}
 
@@ -217,7 +220,7 @@ func (p *Processor) timelineStatus(
 }
 
 func (p *Processor) notifyStatusMentions(ctx context.Context, status *gtsmodel.Status) error {
-	errs := make(gtserror.MultiError, 0, len(status.Mentions))
+	errs := gtserror.NewMultiError(len(status.Mentions))
 
 	for _, m := range status.Mentions {
 		if err := p.notify(
@@ -231,7 +234,11 @@ func (p *Processor) notifyStatusMentions(ctx context.Context, status *gtsmodel.S
 		}
 	}
 
-	return errs.Combine()
+	if err := errs.Combine(); err != nil {
+		return gtserror.Newf("%w", err)
+	}
+
+	return nil
 }
 
 func (p *Processor) notifyFollowRequest(ctx context.Context, followRequest *gtsmodel.FollowRequest) error {
@@ -255,13 +262,13 @@ func (p *Processor) notifyFollow(ctx context.Context, follow *gtsmodel.Follow, t
 	)
 	if err != nil && !errors.Is(err, db.ErrNoEntries) {
 		// Proper error while checking.
-		return fmt.Errorf("notifyFollow: db error checking for previous follow request notification: %w", err)
+		return gtserror.Newf("db error checking for previous follow request notification: %w", err)
 	}
 
 	if prevNotif != nil {
 		// Previous notification existed, delete.
 		if err := p.state.DB.DeleteNotificationByID(ctx, prevNotif.ID); err != nil {
-			return fmt.Errorf("notifyFollow: db error removing previous follow request notification %s: %w", prevNotif.ID, err)
+			return gtserror.Newf("db error removing previous follow request notification %s: %w", prevNotif.ID, err)
 		}
 	}
 
@@ -319,7 +326,7 @@ func (p *Processor) notify(
 ) error {
 	targetAccount, err := p.state.DB.GetAccountByID(ctx, targetAccountID)
 	if err != nil {
-		return fmt.Errorf("notify: error getting target account %s: %w", targetAccountID, err)
+		return gtserror.Newf("error getting target account %s: %w", targetAccountID, err)
 	}
 
 	if !targetAccount.IsLocal() {
@@ -340,7 +347,7 @@ func (p *Processor) notify(
 		return nil
 	} else if !errors.Is(err, db.ErrNoEntries) {
 		// Real error.
-		return fmt.Errorf("notify: error checking existence of notification: %w", err)
+		return gtserror.Newf("error checking existence of notification: %w", err)
 	}
 
 	// Notification doesn't yet exist, so
@@ -354,17 +361,17 @@ func (p *Processor) notify(
 	}
 
 	if err := p.state.DB.PutNotification(ctx, notif); err != nil {
-		return fmt.Errorf("notify: error putting notification in database: %w", err)
+		return gtserror.Newf("error putting notification in database: %w", err)
 	}
 
 	// Stream notification to the user.
 	apiNotif, err := p.tc.NotificationToAPINotification(ctx, notif)
 	if err != nil {
-		return fmt.Errorf("notify: error converting notification to api representation: %w", err)
+		return gtserror.Newf("error converting notification to api representation: %w", err)
 	}
 
 	if err := p.stream.Notify(apiNotif, targetAccount); err != nil {
-		return fmt.Errorf("notify: error streaming notification to account: %w", err)
+		return gtserror.Newf("error streaming notification to account: %w", err)
 	}
 
 	return nil
@@ -479,7 +486,7 @@ func (p *Processor) invalidateStatusFromTimelines(ctx context.Context, statusID
 func (p *Processor) emailReport(ctx context.Context, report *gtsmodel.Report) error {
 	instance, err := p.state.DB.GetInstance(ctx, config.GetHost())
 	if err != nil {
-		return fmt.Errorf("emailReport: error getting instance: %w", err)
+		return gtserror.Newf("error getting instance: %w", err)
 	}
 
 	toAddresses, err := p.state.DB.GetInstanceModeratorAddresses(ctx)
@@ -488,20 +495,20 @@ func (p *Processor) emailReport(ctx context.Context, report *gtsmodel.Report) er
 			// No registered moderator addresses.
 			return nil
 		}
-		return fmt.Errorf("emailReport: error getting instance moderator addresses: %w", err)
+		return gtserror.Newf("error getting instance moderator addresses: %w", err)
 	}
 
 	if report.Account == nil {
 		report.Account, err = p.state.DB.GetAccountByID(ctx, report.AccountID)
 		if err != nil {
-			return fmt.Errorf("emailReport: error getting report account: %w", err)
+			return gtserror.Newf("error getting report account: %w", err)
 		}
 	}
 
 	if report.TargetAccount == nil {
 		report.TargetAccount, err = p.state.DB.GetAccountByID(ctx, report.TargetAccountID)
 		if err != nil {
-			return fmt.Errorf("emailReport: error getting report target account: %w", err)
+			return gtserror.Newf("error getting report target account: %w", err)
 		}
 	}
 
@@ -514,7 +521,7 @@ func (p *Processor) emailReport(ctx context.Context, report *gtsmodel.Report) er
 	}
 
 	if err := p.emailSender.SendNewReportEmail(toAddresses, reportData); err != nil {
-		return fmt.Errorf("emailReport: error emailing instance moderators: %w", err)
+		return gtserror.Newf("error emailing instance moderators: %w", err)
 	}
 
 	return nil
@@ -523,7 +530,7 @@ func (p *Processor) emailReport(ctx context.Context, report *gtsmodel.Report) er
 func (p *Processor) emailReportClosed(ctx context.Context, report *gtsmodel.Report) error {
 	user, err := p.state.DB.GetUserByAccountID(ctx, report.Account.ID)
 	if err != nil {
-		return fmt.Errorf("emailReportClosed: db error getting user: %w", err)
+		return gtserror.Newf("db error getting user: %w", err)
 	}
 
 	if user.ConfirmedAt.IsZero() || !*user.Approved || *user.Disabled || user.Email == "" {
@@ -537,20 +544,20 @@ func (p *Processor) emailReportClosed(ctx context.Context, report *gtsmodel.Repo
 
 	instance, err := p.state.DB.GetInstance(ctx, config.GetHost())
 	if err != nil {
-		return fmt.Errorf("emailReportClosed: db error getting instance: %w", err)
+		return gtserror.Newf("db error getting instance: %w", err)
 	}
 
 	if report.Account == nil {
 		report.Account, err = p.state.DB.GetAccountByID(ctx, report.AccountID)
 		if err != nil {
-			return fmt.Errorf("emailReportClosed: error getting report account: %w", err)
+			return gtserror.Newf("error getting report account: %w", err)
 		}
 	}
 
 	if report.TargetAccount == nil {
 		report.TargetAccount, err = p.state.DB.GetAccountByID(ctx, report.TargetAccountID)
 		if err != nil {
-			return fmt.Errorf("emailReportClosed: error getting report target account: %w", err)
+			return gtserror.Newf("error getting report target account: %w", err)
 		}
 	}
 

internal/timeline/manager.go

@@ -190,18 +190,18 @@ func (m *manager) GetOldestIndexedID(ctx context.Context, timelineID string) str
 }
 
 func (m *manager) WipeItemFromAllTimelines(ctx context.Context, itemID string) error {
-	errors := gtserror.MultiError{}
+	errs := new(gtserror.MultiError)
 
 	m.timelines.Range(func(_ any, v any) bool {
 		if _, err := v.(Timeline).Remove(ctx, itemID); err != nil {
-			errors.Append(err)
+			errs.Append(err)
 		}
 
 		return true // always continue range
 	})
 
-	if len(errors) > 0 {
+	if err := errs.Combine(); err != nil {
-		return gtserror.Newf("error(s) wiping status %s: %w", itemID, errors.Combine())
+		return gtserror.Newf("error(s) wiping status %s: %w", itemID, errs.Combine())
 	}
 
 	return nil
@@ -213,21 +213,21 @@ func (m *manager) WipeItemsFromAccountID(ctx context.Context, timelineID string,
 }
 
 func (m *manager) UnprepareItemFromAllTimelines(ctx context.Context, itemID string) error {
-	errors := gtserror.MultiError{}
+	errs := new(gtserror.MultiError)
 
 	// Work through all timelines held by this
 	// manager, and call Unprepare for each.
 	m.timelines.Range(func(_ any, v any) bool {
 		// nolint:forcetypeassert
 		if err := v.(Timeline).Unprepare(ctx, itemID); err != nil {
-			errors.Append(err)
+			errs.Append(err)
 		}
 
 		return true // always continue range
 	})
 
-	if len(errors) > 0 {
+	if err := errs.Combine(); err != nil {
-		return gtserror.Newf("error(s) unpreparing status %s: %w", itemID, errors.Combine())
+		return gtserror.Newf("error(s) unpreparing status %s: %w", itemID, errs.Combine())
 	}
 
 	return nil