Dataflow: Add flowFrom predicates to mirror flowTo.

Author: aschackmull

shared/dataflow/codeql/dataflow/internal/DataFlowImpl.qll

@@ -207,6 +207,28 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
       flowLocal(source, sink) and Config::observeOverlayInformedIncrementalMode()
     }
 
+    /**
+     * Holds if data can flow from `source` to some sink.
+     * This is a local predicate that only has results local to the overlay/base database.
+     */
+    predicate flowFromLocal(Node source) = forceLocal(Flow::flowFrom/1)(source)
+
+    /**
+     * Holds if data can flow from `source` to some sink.
+     */
+    predicate flowFrom(Node source) {
+      Flow::flowFrom(source)
+      or
+      // If we are overlay informed (i.e. we are not diff-informed), we
+      // merge in the local results which includes the base database results.
+      flowFromLocal(source) and Config::observeOverlayInformedIncrementalMode()
+    }
+
+    /**
+     * Holds if data can flow from `source` to some sink.
+     */
+    predicate flowFromExpr(Lang::DataFlowExpr source) { flowFrom(exprNode(source)) }
+
     /**
      * Holds if data can flow from some source to `sink`.
      * This is a local predicate that only has results local to the overlay/base database.
@@ -3501,6 +3523,16 @@ module MakeImpl<LocationSig Location, InputSig<Location> Lang> {
       )
     }
 
+    /**
+     * Holds if data can flow from `source` to some sink.
+     */
+    predicate flowFrom(Node source) { exists(PathNode n | n.isSource() and n.getNode() = source) }
+
+    /**
+     * Holds if data can flow from `source` to some sink.
+     */
+    predicate flowFromExpr(Expr source) { flowFrom(exprNode(source)) }
+
     /**
      * Holds if data can flow from some source to `sink`.
      */