Go: Implement ContentSet

Author: owen-mc

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

@@ -230,6 +230,34 @@ class SyntheticFieldContent extends Content, TSyntheticFieldContent {
   override string toString() { result = s.toString() }
 }
 
+/**
+ * An entity that represents a set of `Content`s.
+ *
+ * The set may be interpreted differently depending on whether it is
+ * stored into (`getAStoreContent`) or read from (`getAReadContent`).
+ */
+class ContentSet instanceof Content {
+  /** Gets a content that may be stored into when storing into this set. */
+  Content getAStoreContent() { result = this }
+
+  /** Gets a content that may be read from when reading from this set. */
+  Content getAReadContent() { result = this }
+
+  /** Gets a textual representation of this content set. */
+  string toString() { result = super.toString() }
+
+  /**
+   * Holds if this element is at the specified location.
+   * The location spans column `startcolumn` of line `startline` to
+   * column `endcolumn` of line `endline` in file `filepath`.
+   * For more information, see
+   * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+   */
+  predicate hasLocationInfo(string path, int sl, int sc, int el, int ec) {
+    super.hasLocationInfo(path, sl, sc, el, ec)
+  }
+}
+
 /**
  * Holds if the guard `g` validates the expression `e` upon evaluating to `branch`.
  *