Some tests break with ppx_deriving.6.1.2 - #87
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ppx_deriving generated code used to have a dummy location, which is a loc_ghost. Thus, its content was not tracked by the analyzer. Since ocaml-ppx/ppx_deriving#297, it holds more coherent locations (the one of the ppx-ed type_decl). Because the generated code is basically an `include (struct ... end)` in .ml and `include (sig ... end)` in .mli, the included content appears inlined in cmi, and indistinguishable from user-written content at this place. I don't think we need to worry too much about ppx generated code that gets reported (for now). I think its locations should always be loc_ghosts but it is not enforced, and, as a result, any ppx may lead to false positives. The best we can do is, when such a false positive appears, try and fix the concerned ppx to generate loc_ghosts.
sim642
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Following #297, some generated code now have proper locations attached by using the type_decl's location by default instead of a dummy one. However, because the location is used as-is, the generated code is indistinguishable from user code. This leads to false positives in the dead_code_analyzer (LexiFi/dead_code_analyzer#87). According to [`Location`'s documentation](https://ocaml.org/manual/5.5/api/compilerlibref/Location.html#TYPEt), > loc_ghost=false whenever the AST described by the location can be > parsed from the location. In all other cases, loc_ghost must be true. > Most locations produced by the parser have loc_ghost=false. > When loc_ghost=true, the location is usually a best effort approximation. The dead_code_analyzer actually relies on this property to decide if an element of code should be tracked or not. Marking the generated code's default location with `loc_ghost=true` fixes the false positives, without breaking the expected merlin behavior mentioned in #297.
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ppx_deriving generated code used to have a dummy location, which is a loc_ghost. Thus, its content was not tracked by the analyzer.
Since ocaml-ppx/ppx_deriving#297, it holds more coherent locations (the one of the ppx-ed type_decl). Because the generated code is basically an
include (struct ... end)in .ml andinclude (sig ... end)in .mli, the included content appears inlined in cmi, and indistinguishable from user-written content at this place.I don't think we need to worry too much about ppx generated code that gets reported (for now). I think its locations should always be loc_ghosts but it is not enforced, and, as a result, any ppx may lead to false positives. The best we can do is, when such a false positive appears, try and fix the concerned ppx to generate loc_ghosts.