[erlang] Add field about first usage in variable scope

Summary: During scope pre-analysis, mark first usages of a variable. This way, later we'll know if in a pattern it needs to be translated as an equality check or an assignment.

Reviewed By: rgrig

Differential Revision: D62127340

fbshipit-source-id: 90a705a16547ad0f1bbdefdb47fbd5a8c9d0944b

infer/src/erlang/ErlangAst.ml

@@ -71,6 +71,8 @@ type literal = Atom of string | Char of string | Float of float | Int of string
 
 (** {2 S8.4: Expressions} *)
 
+type scope = {procname: (Procname.t[@sexp.opaque]); is_first_use: bool} [@@deriving sexp_of]
+
 type body = expression list
 
 and simple_expression =
@@ -104,7 +106,7 @@ and simple_expression =
   | TryCatch of {body: body; ok_cases: case_clause list; catch_cases: catch_clause list; after: body}
   | Tuple of expression list
   | UnaryOperator of unary_operator * expression
-  | Variable of {vname: string; mutable scope: (Procname.t option[@sexp.opaque])}
+  | Variable of {vname: string; mutable scope: scope option}
 
 and expression = {location: location; simple_expression: simple_expression}
 

infer/src/erlang/ErlangScopes.ml

@@ -172,20 +172,24 @@ let rec annotate_expression (env : (_, _) Env.t) lambda_cntr (scopes : scope lis
   | Variable v -> (
     match scopes with
     | hd :: tl -> (
-        if String.Set.mem hd.locals v.vname then (
+        if String.equal "_" v.vname then (
+          (* The anonymus variable is always fresh in the local scope *)
+          v.scope <- Some {procname= hd.procname; is_first_use= true} ;
+          scopes )
+        else if String.Set.mem hd.locals v.vname then (
           (* Known local var *)
-          v.scope <- Some hd.procname ;
+          v.scope <- Some {procname= hd.procname; is_first_use= false} ;
           scopes )
         else
           (* Check if it's captured from outside *)
           match lookup_var tl v.vname with
           | Some procname ->
               let pvar = Pvar.mk (Mangled.from_string v.vname) procname in
-              v.scope <- Some procname ;
+              v.scope <- Some {procname; is_first_use= false} ;
               {hd with captured= Pvar.Set.add pvar hd.captured} :: tl
           | None ->
               (* It's a local we see here first *)
-              v.scope <- Some hd.procname ;
+              v.scope <- Some {procname= hd.procname; is_first_use= true} ;
               {hd with locals= String.Set.add hd.locals v.vname} :: tl )
     | [] ->
         L.die InternalError "No scope found during variable annotation." )

infer/src/erlang/ErlangTranslator.ml

@@ -179,10 +179,10 @@ let unbox_integer env expr : Exp.t * Block.t =
   (unboxed_expr, {start; exit_success= unbox_block.exit_success; exit_failure= Node.make_nop env})
 
 
-let procname_exn scope =
+let scope_exn (scope : Ast.scope option) =
   match scope with
-  | Some name ->
-      name
+  | Some scope ->
+      scope
   | None ->
       (* Can happen e.g. if we have the _ variable in record field initializers (T134336886) *)
       L.die InternalError "Scope not found for variable, probably missing annotation."
@@ -210,7 +210,7 @@ let vars_of_pattern p =
     | UnaryOperator (_, e) ->
         f acc e
     | Variable {vname; scope} ->
-        let procname = procname_exn scope in
+        let procname = (scope_exn scope).procname in
         Pvar.Set.add (Pvar.mk (Mangled.from_string vname) procname) acc
     | Literal _ | Nil | RecordIndex _ ->
         acc
@@ -523,7 +523,7 @@ and translate_pattern_number_expression (env : (_, _) Env.t) value location simp
 and translate_pattern_variable (env : (_, _) Env.t) value vname scope : Block.t =
   (* We also assign to _ so that stuff like f()->_=1. works. But if we start checking for
      re-binding, we should exclude _ from such checks. *)
-  let procname = procname_exn scope in
+  let procname = (scope_exn scope).procname in
   let store : Sil.instr =
     let e1 : Exp.t = Lvar (Pvar.mk (Mangled.from_string vname) procname) in
     let e2 : Exp.t = Var value in
@@ -1486,7 +1486,7 @@ and translate_expression_unary_operator (env : (_, _) Env.t) ret_var (op : Ast.u
 
 
 and translate_expression_variable (env : (_, _) Env.t) ret_var vname scope : Block.t =
-  let procname = procname_exn scope in
+  let procname = (scope_exn scope).procname in
   let e = Exp.Lvar (Pvar.mk (Mangled.from_string vname) procname) in
   let load_instr = Sil.Load {id= ret_var; e; typ= any_typ; loc= env.location} in
   Block.make_instruction env [load_instr]