fix(context): tag selected segment after editing

call Context::BeginEditing when input is edited after selection.
move cursor also counts as edit.

the tag is used to tell if BackSpace should delete the last input
character or revert a recent selection.

the information was previously denoted by kConfirmed status which caused
the side-effect of breaking a user phrase into individual segments.

fixed #746, fixed #830

src/rime/context.cc

@@ -12,6 +12,8 @@
 
 namespace rime {
 
+const string kSelectedBeforeEditing = "selected_before_editing";
+
 bool Context::Commit() {
   if (!IsComposing())
     return false;
@@ -185,16 +187,20 @@ bool Context::ConfirmCurrentSelection() {
   return true;
 }
 
-bool Context::ConfirmPreviousSelection() {
+void Context::BeginEditing() {
   for (auto it = composition_.rbegin(); it != composition_.rend(); ++it) {
     if (it->status > Segment::kSelected) {
-      return false;
+      return;
     }
     if (it->status == Segment::kSelected) {
-      it->status = Segment::kConfirmed;
-      return true;
+      it->tags.insert(kSelectedBeforeEditing);
+      return;
     }
   }
+}
+
+bool Context::ConfirmPreviousSelection() {
+  BeginEditing();
   return false;
 }
 
@@ -225,6 +231,10 @@ bool Context::ReopenPreviousSelection() {
     if (it->status > Segment::kSelected)
       return false;
     if (it->status == Segment::kSelected) {
+      // do not reopen the previous selection after editing input.
+      if (it->tags.count(kSelectedBeforeEditing) != 0) {
+        return false;
+      }
       while (it != composition_.rbegin()) {
         composition_.pop_back();
       }

src/rime/context.h

@@ -50,8 +50,8 @@ class RIME_API Context {
   // return false if there's no candidate for current segment
   bool ConfirmCurrentSelection();
   bool DeleteCurrentSelection();
-
-  bool ConfirmPreviousSelection();
+  void BeginEditing();
+  bool ConfirmPreviousSelection();  // deprecated
   bool ReopenPreviousSegment();
   bool ClearPreviousSegment();
   bool ReopenPreviousSelection();

src/rime/gear/editor.cc

@@ -123,7 +123,8 @@ bool Editor::CommitComposition(Context* ctx) {
 }
 
 bool Editor::RevertLastEdit(Context* ctx) {
-  // different behavior in regard to previous operation type
+  // revert last selection or delete last input character
+  // depending on recent operation type
   ctx->ReopenPreviousSelection() ||
       (ctx->PopInput() && ctx->ReopenPreviousSegment());
   return true;
@@ -181,7 +182,7 @@ ProcessResult Editor::DirectCommit(Context* ctx, int ch) {
 
 ProcessResult Editor::AddToInput(Context* ctx, int ch) {
   ctx->PushInput(ch);
-  ctx->ConfirmPreviousSelection();
+  ctx->BeginEditing();
   return kAccepted;
 }
 

src/rime/gear/navigator.cc

@@ -123,7 +123,7 @@ bool Navigator::End(Context* ctx) {
 }
 
 void Navigator::BeginMove(Context* ctx) {
-  ctx->ConfirmPreviousSelection();
+  ctx->BeginEditing();
   // update spans
   if (input_ != ctx->input() || ctx->caret_pos() > spans_.end()) {
     input_ = ctx->input();

src/rime/gear/speller.cc

@@ -121,8 +121,7 @@ ProcessResult Speller::ProcessKeyEvent(const KeyEvent& key_event) {
   }
   DLOG(INFO) << "add to input: '" << (char)ch << "', " << key_event.repr();
   ctx->PushInput(ch);
-  ctx->ConfirmPreviousSelection();  // so that next BackSpace won't revert
-                                    // previous selection
+  ctx->BeginEditing();
   if (AutoSelectPreviousMatch(ctx, &previous_segment)) {
     DLOG(INFO) << "auto-select previous match.";
     // after auto-selecting, if only the current non-initial key is left,