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The "decoration" of opaque types works better than before when opaque
types are used by other opaque types.
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Parameterized modules are no longer supported, so module() can only be
an atom().
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Background
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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
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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
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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
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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.
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Comparing two operands for (in)equality is allowed if both operands
are of the same unknown opaque type. Since OTP 17, there is a warning
if the types of the operands have nothing in common (this cannot
happen before OTP 17). However, the warning says there is a test
between opaque types, which is wrong. The warning now states that the
comparison cannot evaluate to 'true', which is more consistent.
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In OTP 17 it is possible to mix types such as dict:dict() and
dict:dict(_, _) outside of the dict module (and similarly for some
other opaque types in STDLIB), but the results are unfortunately
possibly invalid warnings in users' code. In OTP 18 parameterized
opaque types with the same name but with different number of
parameters are no longer compatible when seen from outside of the
module where the types are declared.
The types in STDLIB have been updated accordingly; for instance
-opaque dict() :: dict(_, _).
has been replaced by
-type dict() :: dict(_, _).
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This ticket is about records in Erlang code, and when to check the
fields against the (optional) types given when defining records.
Dialyzer operates on the Erlang Core format, where there are no trace
of records. The fix implemented is a Real Hack:
Given the new option 'dialyzer' erl_expand_records marks the line
number of records in a way that is undone by v3_core, which in turn
inserts annotations that can be recognized by Dialyzer.
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The types array(), dict(), digraph(), gb_set(), gb_tree(), queue(),
set(), and tid() have been deprecated. They will be removed in OTP 18.0.
Instead the types array:array(), dict:dict(), digraph:graph(),
gb_set:set(), gb_tree:tree(), queue:queue(), sets:set(), and ets:tid()
can be used. (Note: it has always been necessary to use ets:tid().)
It is allowed in OTP 17.0 to locally re-define the types array(), dict(),
and so on.
New types array:array/1, dict:dict/2, gb_sets:set/1, gb_trees:tree/2,
queue:queue/1, and sets:set/1 have been added.
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It is now OK to inspect and modify the internals of opaque types within
the scope of the module.
The contracts are used for decorating types with opaqueness when it is
harmless to do so. The opaqueness is propagated by the typesig module
and also by the dataflow module.
A lot of details have been fixed or updated. In particular the modules
erl_types and erl_bif_types have been modified extensively.
The version in vsn.mk has been updated to 2.7. The reason is a
modification of #opaque{} in erl_types.
Dialyzer seems to be about five percent slower than it used to be.
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1. Sometimes the solver forgot that a list had entered the error
state. The bug has been fixed by storing the atom 'error' in
MapDict. An example where the bug occurred is
io_lib_pretty:printable_bin(). The returned spec was weaker than it
should have been, but the fix-point loop hid the bug (in this case).
2. lists:partition() has been substituted for lists:splitwith() in
enumerate_constraints(). This fix together with 3. solves a
problem with long execution times for deeply nested fun:s. An
example which is now much faster is
lib/compiler/test/lc_SUITE:deeply_nested/1
(included as dialyzer/test/small_SUITE_data/src/deep_lc.erl).
3. The calculation of components in enumerate_constraints() has been
simplified and optimized. The important thing here is that _all_ of
the simple constraints have been saturated before entering the
complex part.
4. The pretty printing of constraints has been improved.
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Dialyzer emits warnings like the following "The specification for _
states that the function might also return _ but the inferred return
is _", which are actually underspecifications and not wrong type
specifications. This patch makes sure that they are filed under the
appropriate category.
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