Macros Key Cannot Utilize Colons.

This means /function can't with an item component.

Valid SNBT key is not valid in a macro.

To reproduce

Create a new test.mcfunction, enter a command:

$say $(minecraft:custom_name)

Rename any item to foo with an anvil and hold it.

Execute in chat:

/function test:test with entity @s SelectedItem.components

Expected to happen:

Game Output: "foo"

Actually happen:

Game Output: Unknown function test:test

 
Even if the key is put in quotation marks (test2.mcfunction):

$say $("minecraft:custom_name")

The issue persists.