[LyX/master] #6401 improve doc iterator to allow easy backward navigation

[Stephan Witt]

commit ba21c946a1583d0b1f68f34f2ea378887ed502f9
Author: Stephan Witt <switt at lyx.org>
Date:   Sun Aug 16 16:54:03 2020 +0200

    #6401 improve doc iterator to allow easy backward navigation
---
 src/DocIterator.cpp |   12 ++++++++++++
 src/DocIterator.h   |    4 ++++
 2 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/src/DocIterator.cpp b/src/DocIterator.cpp
index 0f4bc10..6eba5a7 100644
--- a/src/DocIterator.cpp
+++ b/src/DocIterator.cpp
@@ -500,6 +500,18 @@ void DocIterator::backwardPos()
 }
 
 
+void DocIterator::backwardPosIgnoreCollapsed()
+{
+	backwardPos();
+	if (inTexted()) {
+		Inset const * ins = realInset();
+		if (ins && !ins->editable()) {
+			pop_back(); // move out of collapsed inset
+		}
+	}
+}
+
+
 #if 0
 // works, but currently not needed
 void DocIterator::backwardInset()
diff --git a/src/DocIterator.h b/src/DocIterator.h
index 8ee4d4e..69930fc 100644
--- a/src/DocIterator.h
+++ b/src/DocIterator.h
@@ -69,6 +69,8 @@ public:
 
 	/// does this iterator have any content?
 	bool empty() const { return slices_.empty(); }
+	/// is this the begin position?
+	bool atBegin() const { return depth() == 1 && pit() == 0 && pos() == 0; }
 	/// is this the end position?
 	bool atEnd() const { return slices_.empty(); }
 
@@ -210,6 +212,8 @@ public:
 	void forwardInset();
 	/// move backward one logical position
 	void backwardPos();
+	/// move backward one logical position, skip collapsed insets
+	void backwardPosIgnoreCollapsed();
 	/// move backward one physical character or inset
 	void backwardChar();
 	/// move backward one paragraph