Constant propagation of this.field (semgrep#2283)

Fixes semgrep#2247

test plan:
test file included

CHANGELOG.md

@@ -11,6 +11,7 @@ This project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html
 - Support for '...' in chains of method calls in JS, e.g. `$O.foo() ... .bar()`
 - typed metavariables can now match field access when we can propagate
   the type of a field
+- Constant propagation for Java final fields (using this.field syntax)
 - Official Ruby GA support
 
 ### Fixed

semgrep-core/matching/Normalize_generic.ml

@@ -81,7 +81,11 @@ let normalize_import_opt is_pattern i =
 let rec eval x =
   match x with
   | L x -> Some x
-  | Id (_, { id_const_literal = {contents = Some x}; _}) -> Some x
+  | Id (_, { id_const_literal = {contents = Some x}; _})
+  (* todo: Java does not generate a special This! use Id *)
+  | DotAccess ((IdSpecial (This, _) | Id(("this", _), _)),
+               _, EId (_, {id_const_literal = {contents = Some x}; _})) ->
+      Some x
 
   | Call(IdSpecial((Op(Plus | Concat) | ConcatString _), _), args)->
       let literals = args |> unbracket |> Common.map_filter (fun (arg) ->

semgrep-core/tests/java/equivalence_constant_propagation_field.java

@@ -0,0 +1,11 @@
+class Foo {
+  private final String FIELD = "password";
+
+  void test() {
+    //ERROR: match
+    foo(FIELD);
+
+    //ERROR: match
+    foo(this.FIELD);
+  }
+}

semgrep-core/tests/java/equivalence_constant_propagation_field.sgrep

@@ -0,0 +1 @@
+foo("password")