Summary:
When accessing a field or array offset of a pure variable (`Exp.Var`) that does not resolve to an access expression, `HilExp.of_sil` will create an extraneous dereference that causes `HilExp.get_typ` to fail. This pull request wraps variables that are the bases of Lfield or Lindex expressions with AddressOf before they're dereferenced (this is already done for Lvar inside `AccessExpression.of_pvar`) and adds a couple of unit tests that make sure it behaves as expected.
**More details on the bug:**
Given the following code:
```
if (!event_obj->dict)
```
and SIL:
```
n$6=_fun_gdb::ref_ptr<event_object,gdbpy_ref_policy<event_object>>::operator->(&event_obj:gdb::ref_ptr<event_object,gdbpy_ref_policy<event_object>>&) [line 38, column 8];
n$7=*n$6.dict:_object* [line 38, column 8];
PRUNE(!n$7, true); [line 38, column 8];
```
`operator->` has return type `event_object*`, but `n$6.dict` only has access to the type of the struct, `event_object`. `of_sil` [calls](9f98368e49/infer/src/absint/HilExp.ml (L567)) `access_expr_of_lhs_exp` with that type, which [calls](9f98368e49/infer/src/absint/HilExp.ml (L498)) `access_exprs_of_exp` (note that `add_deref` is always true). The Lfield case will then [recurse](9f98368e49/infer/src/absint/HilExp.ml (L469)) to process the Exp.Var, and `AccessExpression.of_id` will return an `AccessPath.base` that is then [dereferenced](9f98368e49/infer/src/absint/HilExp.ml (L440)). When resolving types, `get_typ` will find a non-pointer type wrapped by a `Dereference` and return [None](9f98368e49/infer/src/absint/HilExp.ml (L286)). To fix this, we match what [of_pvar](9f98368e49/infer/src/absint/HilExp.ml (L295)) does and wrap the base in an AddressOf, which is removed by the dereference.
Pull Request resolved: https://github.com/facebook/infer/pull/1372
Reviewed By: ngorogiannis
Differential Revision: D25803049
Pulled By: jvillard
fbshipit-source-id: ceadc8cad
Kevin Higgs
afc9666e15
