Make selection undo skip over entries that are nop after buffer change

After buffer modification - in particular after deletion - adjacent
selection history entries may correspond to the same effective
selection when applied to the current buffer. This means that we
sometimes need to press <c-h> multiple times to make one visible
change. This is not what the user expects, so let's keep walking the
selection history until we hit an actual change.

Alternatively, we could minimize the selection history after buffer
changes but I think that would make the it worse after content
undo+redo.

5 files changed, 31 insertions, 16 deletions

diff --git a/src/context.cc b/src/context.cc
index 3a0aadb4..0c1b8aad 100644
--- a/src/context.cc
+++ b/src/context.cc
@@ -225,24 +225,29 @@ void Context::SelectionHistory::undo()
     if (in_edition())
         throw runtime_error("selection undo is only supported at top-level");
     kak_assert(not empty());
+    SelectionList old_selections = selections();
     HistoryId next;
-    if constexpr (backward)
-        next = current_history_node().parent;
-    else
-        next = current_history_node().redo_child;
-    if (next == HistoryId::Invalid)
-        throw runtime_error(backward ? "no selection change to undo" : "no selection change to redo");
-    auto select_next = [&, next] {
-        HistoryId previous_id = m_history_id;
-        m_history_id = next;
+    do
+    {
         if constexpr (backward)
-            current_history_node().redo_child = previous_id;
-    };
-    Buffer& destination_buffer = history_node(next).selections.buffer();
-    if (&destination_buffer == &m_context.buffer())
-        select_next();
-    else
-        m_context.change_buffer(destination_buffer, { std::move(select_next) });
+            next = current_history_node().parent;
+        else
+            next = current_history_node().redo_child;
+        if (next == HistoryId::Invalid)
+            throw runtime_error(backward ? "no selection change to undo" : "no selection change to redo");
+        auto select_next = [&, next] {
+            HistoryId previous_id = m_history_id;
+            m_history_id = next;
+            if constexpr (backward)
+                current_history_node().redo_child = previous_id;
+        };
+        Buffer& destination_buffer = history_node(next).selections.buffer();
+        if (&destination_buffer == &m_context.buffer())
+            select_next();
+        else
+            m_context.change_buffer(destination_buffer, { std::move(select_next) });
+    }
+    while (selections() == old_selections);
 }
 
 void Context::SelectionHistory::forget_buffer(Buffer& buffer)
diff --git a/test/normal/selection-undo/fold-redundant-entries/cmd b/test/normal/selection-undo/fold-redundant-entries/cmd
new file mode 100644
index 00000000..8b137891
--- /dev/null
+++ b/test/normal/selection-undo/fold-redundant-entries/cmd
@@ -0,0 +1 @@
+
diff --git a/test/normal/selection-undo/fold-redundant-entries/in b/test/normal/selection-undo/fold-redundant-entries/in
new file mode 100644
index 00000000..94ebaf90
--- /dev/null
+++ b/test/normal/selection-undo/fold-redundant-entries/in
@@ -0,0 +1,4 @@
+1
+2
+3
+4
diff --git a/test/normal/selection-undo/fold-redundant-entries/out b/test/normal/selection-undo/fold-redundant-entries/out
new file mode 100644
index 00000000..239c8675
--- /dev/null
+++ b/test/normal/selection-undo/fold-redundant-entries/out
@@ -0,0 +1,3 @@
+2
+3
+here4
diff --git a/test/normal/selection-undo/fold-redundant-entries/script b/test/normal/selection-undo/fold-redundant-entries/script
new file mode 100644
index 00000000..456f92f2
--- /dev/null
+++ b/test/normal/selection-undo/fold-redundant-entries/script
@@ -0,0 +1,2 @@
+ui_out -ignore 4
+ui_in '{ "jsonrpc": "2.0", "method": "keys", "params": [ "gjgkxd<c-h>ihere<esc>" ] }'