(Refactor) Make lookThroughImplicitFieldRead public

Author: owen-mc

go/ql/lib/semmle/go/controlflow/IR.qll

@@ -1588,4 +1588,9 @@ module IR {
    * in a field/method access, element access, or slice expression.
    */
   EvalImplicitDerefInstruction implicitDerefInstruction(Expr e) { result = MkImplicitDeref(e) }
+
+  /** Gets the base of `insn`, if `insn` is an implicit field read. */
+  Instruction lookThroughImplicitFieldRead(Instruction insn) {
+    result = insn.(ImplicitFieldReadInstruction).getBaseInstruction()
+  }
 }

go/ql/lib/semmle/go/dataflow/internal/FlowSummaryImpl.qll

@@ -384,17 +384,13 @@ module SourceSinkInterpretationInput implements
   }
 
   private DataFlow::Node skipImplicitFieldReads(DataFlow::Node n) {
-    not exists(lookThroughImplicitFieldRead(n)) and result = n
+    not exists(IR::lookThroughImplicitFieldRead(n.asInstruction())) and result = n
     or
-    result = skipImplicitFieldReads(lookThroughImplicitFieldRead(n))
-  }
-
-  private DataFlow::Node lookThroughImplicitFieldRead(DataFlow::Node n) {
-    result.asInstruction() =
-      n.(DataFlow::InstructionNode)
-          .asInstruction()
-          .(IR::ImplicitFieldReadInstruction)
-          .getBaseInstruction()
+    exists(DataFlow::Node mid |
+      mid.asInstruction() = IR::lookThroughImplicitFieldRead(n.asInstruction())
+    |
+      result = skipImplicitFieldReads(mid)
+    )
   }
 
   /** Provides additional sink specification logic. */