Better error reporting for PopStyleColor()/PopStyleVar() + easier to recover. (#1651)

docs/CHANGELOG.txt

@@ -83,6 +83,7 @@ Other Changes:
 - Nav: Pressing Space/GamepadFaceDown on a repeating button uses the same repeating rate as a mouse hold.
 - Platform IME: [Windows] Removed call to ImmAssociateContextEx() leading to freeze on some setups.
   (#2589, #5535, #5264, #4972)
+- Misc: better error reporting for PopStyleColor()/PopStyleVar() + easier to recover. (#1651)
 - Misc: io.Framerate moving average now converge in 60 frames instead of 120. (#5236, #4138)
 - Debug Tools: Debug Log: Added 'IO' and 'Clipper' events logging.
 - Debug Tools: Item Picker: Mouse button can be changed by holding Ctrl+Shift, making it easier

imgui.cpp

@@ -2860,6 +2860,11 @@ void ImGui::PushStyleColor(ImGuiCol idx, const ImVec4& col)
 void ImGui::PopStyleColor(int count)
 {
     ImGuiContext& g = *GImGui;
+    if (g.ColorStack.Size < count)
+    {
+        IM_ASSERT_USER_ERROR(g.ColorStack.Size > count, "Calling PopStyleColor() too many times: stack underflow.");
+        count = g.ColorStack.Size;
+    }
     while (count > 0)
     {
         ImGuiColorMod& backup = g.ColorStack.back();
@@ -2944,6 +2949,11 @@ void ImGui::PushStyleVar(ImGuiStyleVar idx, const ImVec2& val)
 void ImGui::PopStyleVar(int count)
 {
     ImGuiContext& g = *GImGui;
+    if (g.StyleVarStack.Size < count)
+    {
+        IM_ASSERT_USER_ERROR(g.StyleVarStack.Size > count, "Calling PopStyleVar() too many times: stack underflow.");
+        count = g.StyleVarStack.Size;
+    }
     while (count > 0)
     {
         // We avoid a generic memcpy(data, &backup.Backup.., GDataTypeSize[info->Type] * info->Count), the overhead in Debug is not worth it.