On this Makefile: https://github.com/GrapheneOS/platform_frameworks_base/blob/11/Android.mk I found
SDK_METADATA_DIR :=$= $(call intermediates-dir-for,PACKAGING,framework-doc-stubs-metadata,,COMMON)
What does :=$= means?
I found nothing here: What's the difference between := and = in Makefile? neither on the links provided
From the book thegnumakebook, page 126, The Twilight Zone:
It’s possible to take definitions like $( ) and $(\n) and go much further, defining variables with names like =, # or :
I think, = is just some other variable. Here, $= implies, expanding the variable =.
And := is used for simple assignment (Evaluated only once).