Multi-Select: disable MultiSelectAddSetRange() attempt at merging consecutive requests submitted from box-selection.

Essentially reverts 79b77d91c, f904a6646c which did the initial span merging.
Amend and disable change done for f08b33f.

docs/CHANGELOG.txt

@@ -67,6 +67,11 @@ Other Changes:
     enough to overlap multiple rows during a frame. (#7994, #1861, #6518)
   - Box-Select: fixed an issue using ImGuiMultiSelectFlags_BoxSelect2d mode in a Table
     while relying on the TableNextColumn() return value to perform coarse clipping. (#7994)
+  - Box-Select: disabled merging consecutive selection requests as we have no reliable
+    way of detecting if user has submitted all consecutives items without clipping gaps,
+    and ImGuiSelectionUserData is technically opaque storage. (#7994, #1861)
+    (we will probably bring this back as a minor optimization if we have a way to for
+    user to tell us ImGuiSelectionUserData are indices)
 - Fonts:
   - imgui_freetype: add FreeType headers & compiled version in 'About Dear ImGui' details.
 - Clipper:

imgui_internal.h

@@ -1915,8 +1915,8 @@ struct IMGUI_API ImGuiMultiSelectTempData
     ImGuiMultiSelectFlags   Flags;
     ImVec2                  ScopeRectMin;
     ImVec2                  BackupCursorMaxPos;
-    ImGuiSelectionUserData  CurrSubmittedItem;  // Copy of last submitted item data, used to merge output ranges.
+    //ImGuiSelectionUserData CurrSubmittedItem; // Copy of last submitted item data, used to merge output ranges.
-    ImGuiSelectionUserData  PrevSubmittedItem;  // Copy of previous submitted item data, used to merge output ranges.
+    //ImGuiSelectionUserData PrevSubmittedItem; // Copy of previous submitted item data, used to merge output ranges.
     ImGuiID                 BoxSelectId;
     ImGuiKeyChord           KeyMods;
     ImS8                    LoopRequestSetAll;  // -1: no operation, 0: clear all, 1: select all.

imgui_widgets.cpp

@@ -8050,7 +8050,7 @@ ImGuiMultiSelectIO* ImGui::BeginMultiSelect(ImGuiMultiSelectFlags flags, int sel
             storage->LastSelectionSize = 0;
     }
     ms->LoopRequestSetAll = request_select_all ? 1 : request_clear ? 0 : -1;
-    ms->PrevSubmittedItem = ImGuiSelectionUserData_Invalid;
+    //ms->PrevSubmittedItem = ImGuiSelectionUserData_Invalid;
 
     if (g.DebugLogFlags & ImGuiDebugLogFlags_EventSelection)
         DebugLogMultiSelectRequests("BeginMultiSelect", &ms->IO);
@@ -8153,8 +8153,8 @@ void ImGui::SetNextItemSelectionUserData(ImGuiSelectionUserData selection_user_d
         g.NextItemData.ItemFlags |= ImGuiItemFlags_HasSelectionUserData | ImGuiItemFlags_IsMultiSelect;
         if (ms->IO.RangeSrcItem == selection_user_data)
             ms->RangeSrcPassedBy = true;
-        ms->PrevSubmittedItem = ms->CurrSubmittedItem; // Can't rely on previous g.NextItemData.SelectionUserData because NextItemData is not restored on nested multi-select.
+        //ms->PrevSubmittedItem = ms->CurrSubmittedItem; // Can't rely on previous g.NextItemData.SelectionUserData because NextItemData is not restored on nested multi-select.
-        ms->CurrSubmittedItem = selection_user_data;
+        //ms->CurrSubmittedItem = selection_user_data;
     }
     else
     {
@@ -8447,6 +8447,10 @@ void ImGui::MultiSelectAddSetAll(ImGuiMultiSelectTempData* ms, bool selected)
 void ImGui::MultiSelectAddSetRange(ImGuiMultiSelectTempData* ms, bool selected, int range_dir, ImGuiSelectionUserData first_item, ImGuiSelectionUserData last_item)
 {
     // Merge contiguous spans into same request (unless NoRangeSelect is set which guarantees single-item ranges)
+    // FIXME-OPT: Disabled on 2026/04/09 as this would break with any form of coarse clipping that we don't know about (e.g. TableNextColumn() return value).
+    // The low-hanging fruit would be to know that ImGuiSelectionUserData are sequential indices, in which case we can trivially compare PrevSubmittedItem + RangeDir == FirstItem.
+    // User can always perform this merge if required.
+#if 0
     if (ms->IO.Requests.Size > 0 && first_item == last_item && (ms->Flags & ImGuiMultiSelectFlags_NoRangeSelect) == 0)
     {
         ImGuiSelectionRequest* prev = &ms->IO.Requests.Data[ms->IO.Requests.Size - 1];
@@ -8456,6 +8460,7 @@ void ImGui::MultiSelectAddSetRange(ImGuiMultiSelectTempData* ms, bool selected,
             return;
         }
     }
+#endif
 
     ImGuiSelectionRequest req = { ImGuiSelectionRequestType_SetRange, selected, (ImS8)range_dir, (range_dir > 0) ? first_item : last_item, (range_dir > 0) ? last_item : first_item };
     ms->IO.Requests.push_back(req); // Add new request