threadbuilder: allow threading by subject

If no match were found in the References and In-Reply-To headers,
allow threading by looking at subjects.

This behaviour is disabled by default. Add a setting to enable it.

Changelog-added: Allow fallback to threading by subject with
 `[ui].threading-by-subject`.
Signed-off-by: Robin Jarry <robin@jarry.cc>
Tested-by: Matěj Cepl <mcepl@cepl.eu>

2 files changed, 28 insertions, 10 deletions

diff --git a/lib/msgstore.go b/lib/msgstore.go
index b4790735..45b9cfd7 100644
--- a/lib/msgstore.go
+++ b/lib/msgstore.go
@@ -51,6 +51,7 @@ type MessageStore struct {
 	selectLast         bool
 	reverseThreadOrder bool
 	threadContext      bool
+	threadBySubject    bool
 	sortThreadSiblings bool
 	buildThreads       bool
 	builder            *ThreadBuilder
@@ -90,7 +91,7 @@ const MagicUid = 0xFFFFFFFF
 func NewMessageStore(worker *types.Worker,
 	defaultSortCriteria []*types.SortCriterion,
 	thread bool, clientThreads bool, clientThreadsDelay time.Duration,
-	selectLast bool,
+	selectLast bool, threadBySubject bool,
 	reverseOrder bool, reverseThreadOrder bool, sortThreadSiblings bool,
 	triggerNewEmail func(*models.MessageInfo),
 	triggerDirectoryChange func(), triggerMailDeleted func(),
@@ -118,6 +119,7 @@ func NewMessageStore(worker *types.Worker,
 		threadedView:       thread,
 		buildThreads:       clientThreads,
 		threadContext:      threadContext,
+		threadBySubject:    threadBySubject,
 		selectLast:         selectLast,
 		reverseThreadOrder: reverseThreadOrder,
 		sortThreadSiblings: sortThreadSiblings,
@@ -280,7 +282,7 @@ func (store *MessageStore) Update(msg types.WorkerMessage) {
 		}
 	case *types.DirectoryThreaded:
 		if store.builder == nil {
-			store.builder = NewThreadBuilder(store.iterFactory)
+			store.builder = NewThreadBuilder(store.iterFactory, store.threadBySubject)
 		}
 		store.builder.RebuildUids(msg.Threads, store.reverseThreadOrder)
 		store.uids = store.builder.Uids()
@@ -424,7 +426,7 @@ func (store *MessageStore) update(threads bool) {
 			store.runThreadBuilder()
 		default:
 			if store.builder == nil {
-				store.builder = NewThreadBuilder(store.iterFactory)
+				store.builder = NewThreadBuilder(store.iterFactory, store.threadBySubject)
 			}
 			store.threadsMutex.Lock()
 			store.builder.RebuildUids(store.threads, store.reverseThreadOrder)
@@ -478,7 +480,7 @@ func (store *MessageStore) BuildThreads() bool {
 
 func (store *MessageStore) runThreadBuilder() {
 	if store.builder == nil {
-		store.builder = NewThreadBuilder(store.iterFactory)
+		store.builder = NewThreadBuilder(store.iterFactory, store.threadBySubject)
 		for _, msg := range store.Messages {
 			store.builder.Update(msg)
 		}
@@ -495,7 +497,7 @@ func (store *MessageStore) runThreadBuilder() {
 // runThreadBuilderNow runs the threadbuilder without any debounce logic
 func (store *MessageStore) runThreadBuilderNow() {
 	if store.builder == nil {
-		store.builder = NewThreadBuilder(store.iterFactory)
+		store.builder = NewThreadBuilder(store.iterFactory, store.threadBySubject)
 		for _, msg := range store.Messages {
 			store.builder.Update(msg)
 		}
diff --git a/lib/threadbuilder.go b/lib/threadbuilder.go
index b7dae431..abfbadb7 100644
--- a/lib/threadbuilder.go
+++ b/lib/threadbuilder.go
@@ -9,6 +9,7 @@ import (
 	"git.sr.ht/~rjarry/aerc/lib/log"
 	"git.sr.ht/~rjarry/aerc/models"
 	"git.sr.ht/~rjarry/aerc/worker/types"
+	sortthread "github.com/emersion/go-imap-sortthread"
 	"github.com/gatherstars-com/jwz"
 )
 
@@ -18,13 +19,15 @@ type ThreadBuilder struct {
 	threadedUids []uint32
 	threadMap    map[uint32]*types.Thread
 	iterFactory  iterator.Factory
+	bySubject    bool
 }
 
-func NewThreadBuilder(i iterator.Factory) *ThreadBuilder {
+func NewThreadBuilder(i iterator.Factory, bySubject bool) *ThreadBuilder {
 	tb := &ThreadBuilder{
 		threadBlocks: make(map[uint32]jwz.Threadable),
 		iterFactory:  i,
 		threadMap:    make(map[uint32]*types.Thread),
+		bySubject:    bySubject,
 	}
 	return tb
 }
@@ -57,7 +60,8 @@ func (builder *ThreadBuilder) Update(msg *models.MessageInfo) {
 	defer builder.Unlock()
 
 	if msg != nil {
-		if threadable := newThreadable(msg); threadable != nil {
+		threadable := newThreadable(msg, builder.bySubject)
+		if threadable != nil {
 			builder.threadBlocks[msg.Uid] = threadable
 		}
 	}
@@ -244,9 +248,10 @@ type threadable struct {
 	Parent    jwz.Threadable
 	Child     jwz.Threadable
 	Dummy     bool
+	bySubject bool
 }
 
-func newThreadable(msg *models.MessageInfo) *threadable {
+func newThreadable(msg *models.MessageInfo, bySubject bool) *threadable {
 	msgid, err := msg.MsgId()
 	if err != nil {
 		return nil
@@ -258,6 +263,7 @@ func newThreadable(msg *models.MessageInfo) *threadable {
 		Parent:    nil,
 		Child:     nil,
 		Dummy:     false,
+		bySubject: bySubject,
 	}
 }
 
@@ -312,15 +318,25 @@ func (t *threadable) UID() uint32 {
 }
 
 func (t *threadable) Subject() string {
-	// deactivate threading by subject for now
-	return ""
+	if !t.bySubject || t.MsgInfo == nil || t.MsgInfo.Envelope == nil {
+		return ""
+	}
+	return t.MsgInfo.Envelope.Subject
 }
 
 func (t *threadable) SimplifiedSubject() string {
+	if t.bySubject {
+		subject, _ := sortthread.GetBaseSubject(t.Subject())
+		return subject
+	}
 	return ""
 }
 
 func (t *threadable) SubjectIsReply() bool {
+	if t.bySubject {
+		_, replyOrForward := sortthread.GetBaseSubject(t.Subject())
+		return replyOrForward
+	}
 	return false
 }