[ruby] Fixed Paramater without method issue (#5159)

* Fixed issue where InstanceFieldIdentifier was wrongly mapped to SimpleIdentifier

* Instance Field Assignment made more type safe

joern-cli/frontends/rubysrc2cpg/src/main/scala/io/joern/rubysrc2cpg/parser/RubyJsonToNodeCreator.scala

@@ -1045,8 +1045,12 @@ class RubyJsonToNodeCreator(
       case Some(rhs) =>
         SingleAssignment(lhs, "=", rhs)(obj.toTextSpan)
       case None =>
-        // `lvasgn` is used in exec_var for rescueExpr, which only has LHS
-        MandatoryParameter(lhs.span.text)(lhs.span)
+        if (AstType.fromString(obj(ParserKeys.Type).str) == AstType.LocalVariableAssign) {
+          // `lvasgn` is used in exec_var for rescueExpr, which only has LHS
+          MandatoryParameter(lhs.span.text)(lhs.span)
+        } else {
+          lhs
+        }
     }
   }
 

joern-cli/frontends/rubysrc2cpg/src/test/scala/io/joern/rubysrc2cpg/querying/ClassTests.scala

@@ -1311,4 +1311,27 @@ class ClassTests extends RubyCode2CpgFixture {
 
     cpg.typeDecl("Foo").astChildren.whereNot(_.or(_.isMethod, _.isModifier, _.isTypeDecl, _.isMember)).size shouldBe 0
   }
+
+  "Proc-param in method with instance field assignment and instance field argument" in {
+    val cpg = code("""
+        |class Batches
+        |  def as_batches(query, &)
+        |     records.each(&)
+        |     @limit -= 100
+        |     return if @limit.zero?
+        |  end
+        |end
+        |""".stripMargin)
+
+    inside(cpg.method.name("as_batches").l) {
+      case batchesMethod :: Nil =>
+        inside(batchesMethod.parameter.l) {
+          case _ :: _ :: procParam :: Nil =>
+            procParam.code shouldBe "&"
+            procParam.name shouldBe "<proc-param-0>"
+          case xs => fail(s"Expected three parameters, got (${xs.size}) [${xs.code.mkString(",")}]")
+        }
+      case xs =>
+    }
+  }
 }