P: SDK: folder:getParent() raises error instead of returning nil on root folder

[johnrellis]

The SDK call folder:getParent() raises the error "?:0: attempt to index field 'parent' (a nil value)" when called on the root folder of some catalogs on Windows -- it should return nil instead. To reproduce on LR 15.0.1 / Windows 11 ARM and Windows 11 Intel:

1. Download and uncompress this catalog folder:

https://www.dropbox.com/scl/fi/t1gksh5hw2ov8g48tcca6/folder-getparent-bug.2025-11-20.zip?rlkey=kxqi5...

2. Move the file "folder-getparent-bug.lua" from the catalog folder to the LR Scripts folder.

3. Start LR and open the catalog.

4. In the Scripts menu, invoke "folder-getparent-bug".  Observe this output:

When tested on Mac OS 15.7.1, no error occurs:

 Note that on Mac, the call to folder:getParent() returns 0 results rather than nil (though in most contexts, there's no difference).

[Eugene Tyson]

No idea! But I'll give a guess!

I'm guessing it's platform related. Maybe the root folder raises the error cos the internal parent field is nil. 

Try checking if a folder parent exists before callniiig the get parent. 

Something like

local parent = nil
if folder.parent then
parent = folder:getParent()
end

Maybe this will help with root folders and maintain compatibility across Windows and Mac.

If this works let us know - we can move the discussion to the bugs section and get traction there.

[johnrellis]

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"local parent = nil
if folder.parent then
parent = folder:getParent()"

The field "parent" isn't defined for LrFolder objects.  Accessing any undefined field always returns nil, as this example shows:

[johnrellis]

"we can move the discussion to the bugs section and get traction there."

@Rikk Flohr: Photography can correct me, but I believe he moved this from Bugs to Discussions until/if the developers confirm they can reproduce this bug.

[Eugene Tyson]

Oh right - sorry I'm no expert in this stuff but I'm trying to learn and help out 

Can you test this and see if it's working? 

local function safeGetParent(folder)
    local ok, parent = pcall(function()
        return folder:getParent()
    end)

    if ok then
        return parent  -- either a folder object or nil
    else
        return nil     -- getParent exploded so we treat it as no parent
    end
end

-- Example usage
local folder = catalog:getActiveSources()[1]
local parent = safeGetParent(folder)

if parent then
    LrLogger("debug"):trace("Parent is " .. parent:getPath())
else
    LrLogger("debug"):trace("No parent folder")
end

[johnrellis]

I use LrTasks.pcall() to catch the erroneous error.  You have to use LrTasks.pcall() rather than the built-in Lua pcall() because of LR's task architecture.  LrTasks.pcall() is about 4 times as expensive as pcall(), which can be noticeable in some circumstances, e.g. traversing very large folder hierarchies.