chore(federation): re-enable nilnil lint (#11253)

First round of patches to re-enable some lints from my side.

This PR also refactors the general key fetching code quite a bit due to the way it currently worked
with relying on some values being nil sometimes.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11253
Reviewed-by: elle <0xllx0@noreply.codeberg.org>
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: famfo <famfo@famfo.xyz>
Co-committed-by: famfo <famfo@famfo.xyz>

models/forgefed/error.go

@@ -0,0 +1,22 @@
+// Copyright 2026 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+package forgefed
+
+import (
+	"fmt"
+)
+
+type ErrFederationHostNotFound struct {
+	SearchKey   string
+	SearchValue string
+}
+
+func (err ErrFederationHostNotFound) Error() string {
+	return fmt.Sprintf("ErrFederationHostNotFound: search key: %s, search value: %s", err.SearchKey, err.SearchValue)
+}
+
+func IsErrFederationHostNotFound(err error) bool {
+	_, ok := err.(ErrFederationHostNotFound)
+	return ok
+}

models/forgefed/federationhost_repository.go

@@ -57,13 +57,13 @@ func GetFederationHost(ctx context.Context, ID int64) (*FederationHost, error) {
 	return host, nil
 }
 
-func findFederationHostFromDB(ctx context.Context, searchKey, searchValue string) (*FederationHost, error) {
+func findFederationHostFromDB(ctx context.Context, searchKey string, searchValue ...any) (*FederationHost, error) {
 	host := new(FederationHost)
-	has, err := db.GetEngine(ctx).Where(searchKey, searchValue).Get(host)
+	has, err := db.GetEngine(ctx).Where(searchKey, searchValue...).Get(host)
 	if err != nil {
 		return nil, err
 	} else if !has {
-		return nil, nil
+		return nil, ErrFederationHostNotFound{SearchKey: searchKey, SearchValue: fmt.Sprintf("%v", searchValue)}
 	}
 	if res, err := validation.IsValid(host); !res {
 		return nil, err
@@ -72,17 +72,7 @@ func findFederationHostFromDB(ctx context.Context, searchKey, searchValue string
 }
 
 func FindFederationHostByFqdnAndPort(ctx context.Context, fqdn string, port uint16) (*FederationHost, error) {
-	host := new(FederationHost)
-	has, err := db.GetEngine(ctx).Where("host_fqdn=? AND host_port=?", fqdn, port).Get(host)
-	if err != nil {
-		return nil, err
-	} else if !has {
-		return nil, nil
-	}
-	if res, err := validation.IsValid(host); !res {
-		return nil, err
-	}
-	return host, nil
+	return findFederationHostFromDB(ctx, "host_fqdn=? AND host_port=?", fqdn, port)
 }
 
 func FindFederationHostByKeyID(ctx context.Context, keyID string) (*FederationHost, error) {

models/user/error.go

@@ -105,3 +105,16 @@ func IsErrUserIsNotLocal(err error) bool {
 	_, ok := err.(ErrUserIsNotLocal)
 	return ok
 }
+
+type ErrFederatedUserNotExists struct {
+	Identifier string
+}
+
+func (err ErrFederatedUserNotExists) Error() string {
+	return fmt.Sprintf("No cached federated user found for identifier %s", err.Identifier)
+}
+
+func IsErrFederatedUserNotExists(err error) bool {
+	_, ok := err.(ErrFederatedUserNotExists)
+	return ok
+}

models/user/user_repository.go

@@ -65,7 +65,7 @@ func FindFederatedUser(ctx context.Context, externalID string, federationHostID
 	if err != nil {
 		return nil, nil, err
 	} else if !has {
-		return nil, nil, nil
+		return nil, nil, ErrFederatedUserNotExists{Identifier: externalID}
 	}
 	has, err = db.GetEngine(ctx).ID(federatedUser.UserID).Get(user)
 	if err != nil {
@@ -134,16 +134,6 @@ func FindFederatedUsersByHostID(ctx context.Context, federationHostID int64, opt
 	return users, nil
 }
 
-func GetFederatedUser(ctx context.Context, externalID string, federationHostID int64) (*User, *FederatedUser, error) {
-	user, federatedUser, err := FindFederatedUser(ctx, externalID, federationHostID)
-	if err != nil {
-		return nil, nil, err
-	} else if federatedUser == nil {
-		return nil, nil, fmt.Errorf("FederatedUser not found (given externalId: %v, federationHostId: %v)", externalID, federationHostID)
-	}
-	return user, federatedUser, nil
-}
-
 func GetFederatedUserByUserID(ctx context.Context, userID int64) (*User, *FederatedUser, error) {
 	federatedUser := new(FederatedUser)
 	user := new(User)
@@ -177,7 +167,7 @@ func FindFederatedUserByKeyID(ctx context.Context, keyID string) (*User, *Federa
 	if err != nil {
 		return nil, nil, err
 	} else if !has {
-		return nil, nil, nil
+		return nil, nil, ErrFederatedUserNotExists{Identifier: keyID}
 	}
 	has, err = db.GetEngine(ctx).ID(federatedUser.UserID).Get(user)
 	if err != nil {