[pulse] do not destroy `this` even if asked to

Summary:
Some code calls `this->~Obj()` then proceeds to use fields in the current
object, which previously we would report as invalid uses. Assume people know
what they are doing and ignore destructor calls to `this`.

Reviewed By: mbouaziz

Differential Revision: D13401145

fbshipit-source-id: f6b0fb6ec

infer/src/IR/Var.ml

@@ -42,6 +42,8 @@ let is_global = function ProgramVar pvar -> Pvar.is_global pvar | LogicalVar _ -
 
 let is_return = function ProgramVar pvar -> Pvar.is_return pvar | LogicalVar _ -> false
 
+let is_this = function ProgramVar pvar -> Pvar.is_this pvar | LogicalVar _ -> false
+
 let is_footprint = function ProgramVar _ -> false | LogicalVar id -> Ident.is_footprint id
 
 let is_none = function LogicalVar id -> Ident.is_none id | _ -> false

infer/src/IR/Var.mli

@@ -37,6 +37,9 @@ val is_global : t -> bool
 
 val is_return : t -> bool
 
+val is_this : t -> bool
+(** return whether the var is the special "this" var *)
+
 val is_footprint : t -> bool
 
 val is_none : t -> bool

infer/src/checkers/Pulse.ml

@@ -61,6 +61,9 @@ module TransferFunctions (CFG : ProcCfg.S) = struct
     match call with
     | Direct callee_pname when is_destructor callee_pname -> (
       match actuals with
+      | [AccessExpression (Base (destroyed_var, _))] when Var.is_this destroyed_var ->
+          (* do not invalidate [this] when it is destroyed by calls to [this->~Obj()] *)
+          Ok astate
       | [AccessExpression destroyed_access] ->
           let destroyed_object = HilExp.AccessExpression.dereference destroyed_access in
           PulseDomain.invalidate

infer/tests/codetoanalyze/cpp/pulse/basics.cpp

@@ -100,3 +100,18 @@ int struct_inside_loop_ok(std::vector<int> numbers) {
   }
   return sum;
 }
+
+struct UseAfterSelfDestruct {
+  A a_;
+  int x_;
+  ~UseAfterSelfDestruct() {
+    if (x_ == 0) {
+      a_ = getA();
+    }
+  }
+
+  void reset_ok() {
+    this->~UseAfterSelfDestruct();
+    x_ = a_.f(x_);
+  }
+};