A lot of [-Wincompatible-pointer-types] compiler warnings
I just checked a build log  of the 0.12.2 release and it shows a lot of compiler warnings about
incompatible-pointer-types, specifically mixing
GtkSourceBuffer (from those I've spot).
I do not know which of the two types is correct, but it should be relative simple to fix this and verify that correct functions are used with the expected types (unless really bad things can happen in runtime).
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