[erlang-bugs] Compiler/linter bug breaking unused variable warnings
Anders.Ramsell@REDACTED
Anders.Ramsell@REDACTED
Wed May 29 20:02:23 CEST 2013
When a function creates a record and more than one field is bound to the value of a list comprehension the compiler/linter fails to generate warnings for unused variables in that function. I just tested this on R16B and the problem is still there.
I use the following module to test this:
--8<----------------------------------------------------------
-module(missing_warning).
-export([test_missing_warning/2,
test_with_warning1/2,
test_with_warning2/2
]).
-record(data, {aList, bList}).
test_missing_warning(Data, KeyList) -> %% Data never used - no warning.
KeyList2 = filter(KeyList), %% KeyList2 never used - no warning.
#data{aList = [Key || Key <- KeyList],
bList = [Key || Key <- KeyList]}.
test_with_warning1(Data, KeyList) -> %% Data never used - get warning.
KeyList2 = filter(KeyList), %% KeyList2 never used - get warning.
#data{aList = [Key || Key <- KeyList]}. %% Only one LC in the record.
test_with_warning2(Data, KeyList) -> %% Data never used - get warning.
KeyList2 = filter(KeyList), %% KeyList2 never used - get warning.
{data,
[Key || Key <- KeyList], %% Not in a record.
[Key || Key <- KeyList]}.
filter(L) -> L.
--8<----------------------------------------------------------
In all three test functions the variables Data (in the function head) and KeyList2 (in the function body) are unused.
Compiling the module should produce six warnings but I only get four.
You get the same result with other "advanced" calls like
lists:map(fun(Key) -> Key end, KeyList)
so it's not limited to list comprehensions.
If the fields are bound to e.g. the variable KeyList directly the warnings work just fine.
/Anders
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