[feature] Handle retractions of domain permission subscription entries (#4261)

# Description

> If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.
>
> If this is a documentation change, please briefly describe what you've changed and why.

This pull request adds logic for nicely handling retractions of entries from domain permission subscriptions.

See docs for how this works but basically retracted entries will either be removed (and possibly picked up by a lower-prio subscription), or orphaned (and then possibly adopted), depending on the config of the domain permission subscription.

closes https://codeberg.org/superseriousbusiness/gotosocial/issues/4101

## Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: `[ ]` -> `[x]`

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [ ] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4261
Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Co-committed-by: tobi <tobi.smethurst@protonmail.com>

4 files changed, 152 insertions, 0 deletions

diff --git a/internal/db/bundb/domain.go b/internal/db/bundb/domain.go
index 3d9ab41d0..4e3058de1 100644
--- a/internal/db/bundb/domain.go
+++ b/internal/db/bundb/domain.go
@@ -97,6 +97,20 @@ func (d *domainDB) GetDomainAllows(ctx context.Context) ([]*gtsmodel.DomainAllow
 	return allows, nil
 }
 
+func (d *domainDB) GetDomainAllowsBySubscriptionID(ctx context.Context, subscriptionID string) ([]*gtsmodel.DomainAllow, error) {
+	allows := []*gtsmodel.DomainAllow{}
+
+	if err := d.db.
+		NewSelect().
+		Model(&allows).
+		Where("? = ?", bun.Ident("subscription_id"), subscriptionID).
+		Scan(ctx); err != nil {
+		return nil, err
+	}
+
+	return allows, nil
+}
+
 func (d *domainDB) GetDomainAllowByID(ctx context.Context, id string) (*gtsmodel.DomainAllow, error) {
 	var allow gtsmodel.DomainAllow
 
@@ -225,6 +239,20 @@ func (d *domainDB) GetDomainBlocks(ctx context.Context) ([]*gtsmodel.DomainBlock
 	return blocks, nil
 }
 
+func (d *domainDB) GetDomainBlocksBySubscriptionID(ctx context.Context, subscriptionID string) ([]*gtsmodel.DomainBlock, error) {
+	blocks := []*gtsmodel.DomainBlock{}
+
+	if err := d.db.
+		NewSelect().
+		Model(&blocks).
+		Where("? = ?", bun.Ident("subscription_id"), subscriptionID).
+		Scan(ctx); err != nil {
+		return nil, err
+	}
+
+	return blocks, nil
+}
+
 func (d *domainDB) GetDomainBlockByID(ctx context.Context, id string) (*gtsmodel.DomainBlock, error) {
 	var block gtsmodel.DomainBlock
 
diff --git a/internal/db/bundb/migrations/20250603125942_domain_perm_sub_retractions.go b/internal/db/bundb/migrations/20250603125942_domain_perm_sub_retractions.go
new file mode 100644
index 000000000..83237a614
--- /dev/null
+++ b/internal/db/bundb/migrations/20250603125942_domain_perm_sub_retractions.go
@@ -0,0 +1,76 @@
+// 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 migrations
+
+import (
+	"context"
+	"fmt"
+	"reflect"
+
+	"code.superseriousbusiness.org/gotosocial/internal/db/bundb/migrations/20250603125942_domain_perm_sub_retractions"
+	"code.superseriousbusiness.org/gotosocial/internal/log"
+	"github.com/uptrace/bun"
+)
+
+func init() {
+	up := func(ctx context.Context, db *bun.DB) error {
+		return db.RunInTx(ctx, nil, func(ctx context.Context, tx bun.Tx) error {
+			// Bail if "remove_retracted"
+			// column already created.
+			if exists, err := doesColumnExist(
+				ctx,
+				tx,
+				"domain_permission_subscriptions",
+				"remove_retracted",
+			); err != nil {
+				return err
+			} else if exists {
+				return nil
+			}
+
+			// Derive column definition.
+			var permSub *gtsmodel.DomainPermissionSubscription
+			permSubType := reflect.TypeOf(permSub)
+			colDef, err := getBunColumnDef(tx, permSubType, "RemoveRetracted")
+			if err != nil {
+				return fmt.Errorf("error making column def: %w", err)
+			}
+
+			log.Info(ctx, "adding domain_permission_subscriptions.remove_retracted column...")
+			if _, err := tx.
+				NewAddColumn().
+				Model(permSub).
+				ColumnExpr(colDef).
+				Exec(ctx); err != nil {
+				return fmt.Errorf("error adding column: %w", err)
+			}
+
+			return nil
+		})
+	}
+
+	down := func(ctx context.Context, db *bun.DB) error {
+		return db.RunInTx(ctx, nil, func(ctx context.Context, tx bun.Tx) error {
+			return nil
+		})
+	}
+
+	if err := Migrations.Register(up, down); err != nil {
+		panic(err)
+	}
+}
diff --git a/internal/db/bundb/migrations/20250603125942_domain_perm_sub_retractions/domainpermissionsubscription.go b/internal/db/bundb/migrations/20250603125942_domain_perm_sub_retractions/domainpermissionsubscription.go
new file mode 100644
index 000000000..a8d00cb06
--- /dev/null
+++ b/internal/db/bundb/migrations/20250603125942_domain_perm_sub_retractions/domainpermissionsubscription.go
@@ -0,0 +1,42 @@
+// 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 gtsmodel
+
+import "time"
+
+type DomainPermissionSubscription struct {
+	ID                    string    `bun:"type:CHAR(26),pk,nullzero,notnull,unique"`
+	Priority              uint8     `bun:""`
+	Title                 string    `bun:",nullzero,unique"`
+	PermissionType        uint8     `bun:",nullzero,notnull"`
+	AsDraft               *bool     `bun:",nullzero,notnull,default:true"`
+	AdoptOrphans          *bool     `bun:",nullzero,notnull,default:false"`
+	CreatedByAccountID    string    `bun:"type:CHAR(26),nullzero,notnull"`
+	URI                   string    `bun:",nullzero,notnull,unique"`
+	ContentType           int16     `bun:",nullzero,notnull"`
+	FetchUsername         string    `bun:",nullzero"`
+	FetchPassword         string    `bun:",nullzero"`
+	FetchedAt             time.Time `bun:"type:timestamptz,nullzero"`
+	SuccessfullyFetchedAt time.Time `bun:"type:timestamptz,nullzero"`
+	LastModified          time.Time `bun:"type:timestamptz,nullzero"`
+	ETag                  string    `bun:"etag,nullzero"`
+	Error                 string    `bun:",nullzero"`
+
+	// This is the field added by this migration.
+	RemoveRetracted *bool `bun:",nullzero,notnull,default:true"`
+}
diff --git a/internal/db/domain.go b/internal/db/domain.go
index 0c1fb97b3..466fb0a4f 100644
--- a/internal/db/domain.go
+++ b/internal/db/domain.go
@@ -43,6 +43,9 @@ type Domain interface {
 	// GetDomainAllows returns all instance-level domain allows currently enforced by this instance.
 	GetDomainAllows(ctx context.Context) ([]*gtsmodel.DomainAllow, error)
 
+	// GetDomainAllowsBySubscriptionID gets all domain allows that have the given subscription ID.
+	GetDomainAllowsBySubscriptionID(ctx context.Context, subscriptionID string) ([]*gtsmodel.DomainAllow, error)
+
 	// UpdateDomainAllow updates the given domain allow, setting the provided columns (empty for all).
 	UpdateDomainAllow(ctx context.Context, allow *gtsmodel.DomainAllow, columns ...string) error
 
@@ -58,6 +61,9 @@ type Domain interface {
 	// GetDomainBlockByID returns one instance-level domain block with the given id, if it exists.
 	GetDomainBlockByID(ctx context.Context, id string) (*gtsmodel.DomainBlock, error)
 
+	// GetDomainBlocksBySubscriptionID gets all domain blocks that have the given subscription ID.
+	GetDomainBlocksBySubscriptionID(ctx context.Context, subscriptionID string) ([]*gtsmodel.DomainBlock, error)
+
 	// GetDomainBlocks returns all instance-level domain blocks currently enforced by this instance.
 	GetDomainBlocks(ctx context.Context) ([]*gtsmodel.DomainBlock, error)