From 6e93fb788aebb9050da2166749b41ff54197e049 Mon Sep 17 00:00:00 2001 From: Kostis Sagonas Date: Thu, 7 May 2015 14:43:02 +0200 Subject: Take out automatic insertion of 'undefined' from typed record fields Background ----------- In record fields with a type declaration but without an initializer, the Erlang parser inserted automatically the singleton type 'undefined' to the list of declared types, if that value was not present there. I.e. the record declaration: -record(rec, {f1 :: float(), f2 = 42 :: integer(), f3 :: some_mod:some_typ()}). was translated by the parser to: -record(rec, {f1 :: float() | 'undefined', f2 = 42 :: integer(), f3 :: some_mod:some_typ() | 'undefined'}). The rationale for this was that creation of a "dummy" #rec{} record should not result in a warning from dialyzer that e.g. the implicit initialization of the #rec.f1 field violates its type declaration. Problems --------- This seemingly innocent action has some unforeseen consequences. For starters, there is no way for programmers to declare that e.g. only floats make sense for the f1 field of #rec{} records when there is no `obvious' default initializer for this field. (This also affects tools like PropEr that use these declarations produced by the Erlang parser to generate random instances of records for testing purposes.) It also means that dialyzer does not warn if e.g. an is_atom/1 test or something more exotic like an atom_to_list/1 call is performed on the value of the f1 field. Similarly, there is no way to extend dialyzer to warn if it finds record constructions where f1 is not initialized to some float. Last but not least, it is semantically problematic when the type of the field is an opaque type: creating a union of an opaque and a structured type is very problematic for analysis because it fundamentally breaks the opacity of the term at that point. Change ------- To solve these problems the parser will not automatically insert the 'undefined' value anymore; instead the user has the option to choose the places where this value makes sense (for the field) and where it does not and insert the | 'undefined' there manually. Consequences of this change ---------------------------- This change means that dialyzer will issue a warning for all places where records with uninitialized fields are created and those fields have a declared type that is incompatible with 'undefined' (e.g. float()). This warning can be suppressed easily by adding | 'undefined' to the type of this field. This also adds documentation that the user really intends to create records where this field is uninitialized. --- lib/hipe/cerl/erl_types.erl | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) (limited to 'lib/hipe/cerl') diff --git a/lib/hipe/cerl/erl_types.erl b/lib/hipe/cerl/erl_types.erl index cd2d2fe207..420d7e2a8f 100644 --- a/lib/hipe/cerl/erl_types.erl +++ b/lib/hipe/cerl/erl_types.erl @@ -3974,18 +3974,17 @@ record_to_string(Tag, [_|Fields], FieldNames, RecDict) -> FieldStrings = record_fields_to_string(Fields, FieldNames, RecDict, []), "#" ++ atom_to_string(Tag) ++ "{" ++ string:join(FieldStrings, ",") ++ "}". -record_fields_to_string([F|Fs], [{FName, _Abstr, _DefType}|FDefs], +record_fields_to_string([F|Fs], [{FName, _Abstr, DefType}|FDefs], RecDict, Acc) -> NewAcc = - case t_is_equal(F, t_any()) orelse t_is_any_atom('undefined', F) of + case + t_is_equal(F, t_any()) orelse + (t_is_any_atom('undefined', F) andalso + not t_is_none(t_inf(F, DefType))) + of true -> Acc; false -> StrFV = atom_to_string(FName) ++ "::" ++ t_to_string(F, RecDict), - %% ActualDefType = t_subtract(DefType, t_atom('undefined')), - %% Str = case t_is_any(ActualDefType) of - %% true -> StrFV; - %% false -> StrFV ++ "::" ++ t_to_string(ActualDefType, RecDict) - %% end, [StrFV|Acc] end, record_fields_to_string(Fs, FDefs, RecDict, NewAcc); -- cgit v1.2.3