[erlang-questions] Understanding dialyzer errors better

[Alex S.]

The general approach I use in these cases is to slap specs on EVERYTHING and see which stuff Dialyzer complains about.
> 2 марта 2017 г., в 12:39, Raghav Karol <raghav.karol@REDACTED> написал(а):
> 
> I spent a bit of time yesterday on some dialyzer warnings resulting from the singleton type 'undefined' no longer automatically to record fields types OTP-19. What threw me off were several related but hard to decipher warnings. 
> 
> Using OTP-19, `rebar3 dialyzer` on this commit https://github.com/basho/bitcask/commit/cd74f59bfe47a39878d7a56a55ce0ae723723677 <https://github.com/basho/bitcask/commit/cd74f59bfe47a39878d7a56a55ce0ae723723677> produces: 
> 
> ```
> src/bitcask.erl
>  197: The call bitcask_fileops:close_for_writing(WriteFile::#filestate{mode::'read_only' | 'read_write' | 'undefined',filename::string(),tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::integer(),ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()}) will never return since it differs in the 1st argument from the success typing arguments: ('fresh' | 'undefined')
>  219: The call bitcask_fileops:close_for_writing(WriteFile::#filestate{mode::'read_only' | 'read_write' | 'undefined',filename::string(),tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::integer(),ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()}) will never return since it differs in the 1st argument from the success typing arguments: ('fresh' | 'undefined')
>  520: The created fun has no local return
>  529: The call bitcask_fileops:close(FD::{_,_,_,_,_,_,_,_,_,_,_}) will never return since it differs in the 1st argument from the success typing arguments: ('fresh' | 'undefined')
>  717: The call bitcask_fileops:close(Outfile::#filestate{mode::'read_write',filename::string(),tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::integer(),ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()}) will never return since it differs in the 1st argument from the success typing arguments: ('fresh' | 'undefined')
>  722: The call bitcask_fileops:close(TFile::#filestate{mode::'read_write',filename::string(),tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::integer(),ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()}) will never return since it differs in the 1st argument from the success typing arguments: ('fresh' | 'undefined')
>  774: The call bitcask_fileops:close(F::#filestate{mode::'read_only' | 'read_write' | 'undefined',filename::[any()],tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::integer(),ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()}) will never return since it differs in the 1st argument from the success typing arguments: ('fresh' | 'undefined')
> 1224: The call bitcask_fileops:close(File::#filestate{mode::'read_write',filename::string(),tstamp::integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::non_neg_integer(),ofs::'undefined' | non_neg_integer(),l_ofs::0,l_hbytes::0,l_hintcrc::0}) will never return since it differs in the 1st argument from the success typing arguments: ('fresh' | 'undefined')
> 1719: The pattern <_Key, _Value, State, 0, LastErr> can never match the type <_,_,#bc_state{dirname::string(),write_file::'fresh' | 'undefined' | #filestate{mode::'read_only' | 'read_write' | 'undefined',filename::[any()],tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::integer(),ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()},write_lock::'undefined' | reference(),read_files::'undefined' | [{_,_,_,_,_,_,_,_,_,_,_}],max_file_size::'undefined' | integer(),opts::'undefined' | [any()],key_transform::'undefined' | fun(),keydir::reference(),read_write_p::'undefined' | integer(),tombstone_version::0 | 2},100,'undefined'>
> 1870: Function wrap_write_file/1 has no local return
> 1924: Record construction #filestate{filename::[any()],hintfd::'undefined',hintcrc::0,l_ofs::0,l_hbytes::0,l_hintcrc::0} violates the declared type of field hintfd::port()
> 
> src/bitcask_fileops.erl
>  166: Record construction #filestate{mode::'read_only',filename::string() | #filestate{mode::'read_only' | 'read_write' | 'undefined',filename::string(),tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::integer(),ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()},tstamp::integer(),hintfd::'undefined',hintcrc::0,ofs::0,l_ofs::0,l_hbytes::0,l_hintcrc::0} violates the declared type of field hintfd::port()
>  240: Function close_hintfile/1 has no local return
>  240: Matching of pattern {'filestate', _, _, _, _, 'undefined', _, _, _, _, _} tagged with a record name violates the declared type of #filestate{mode::'read_only' | 'read_write' | 'undefined',filename::string(),tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::integer(),ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()}
>  251: Record construction #filestate{mode::'read_only' | 'read_write' | 'undefined',filename::string(),tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::'undefined',hintcrc::0,ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()} violates the declared type of field hintfd::port()
>  314: The pattern 'undefined' can never match the type port()
> 
> src/bitcask_merge_delete.erl
>  151: Record construction #filestate{hintfd::'undefined',hintcrc::0,l_ofs::0,l_hbytes::0,l_hintcrc::0} violates the declared type of field hintfd::port()
> ===> Warnings written to /Users/raghav/github/riak_kv/deps/bitcask/_build/default/19.2.dialyzer_warnings
> ===> Warnings occured running dialyzer: 17
> ```
> 
> Particularly confusing, are errors like the first one 
> 
> ```
>  197: The call bitcask_fileops:close_for_writing(WriteFile::#filestate{mode::'read_only' | 'read_write' | 'undefined',filename::string(),tstamp::'undefined' | integer(),fd::'undefined' | port(),hintfd::port(),hintcrc::integer(),ofs::'undefined' | non_neg_integer(),l_ofs::non_neg_integer(),l_hbytes::non_neg_integer(),l_hintcrc::non_neg_integer()}) will never return since it differs in the 1st argument from the success typing arguments: ('fresh' | 'undefined')
> ```
> 
> I _think_ dialyzer is saying that the call `bitcask_fileops:close_for_writing(WriteFile#filestate{}, ...)` is not possible because of type violations when creating `#filestate{}` lower down the call stack.
> 
> Would appreciate if someone could help understand this better and also suggest how one separates noise from real warnings with dialyzer.
> 
> Best,
> Raghav
> 
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