Fix testing methods with 2-qualifier or deeper input specifications

For example, an identity function on lists-of-maps, which might convey MapValue of Element of Argument[0] to MapValue of Element of ReturnValue, requiring `newWithElement(newWithMapValue(source())` on the input side but `getMapValue(getElement(out))` on the output side.

Author: smowton

java/ql/src/utils/GenerateFlowTestCase.qll

@@ -271,10 +271,26 @@ class RowTestSnippet extends TRowTestSnippet {
    */
   string getInputTypeString() { result = getShortNameIfPossible(this.getInputType()) }
 
+  /**
+   * Returns the next-highest stack item in `input`, treating the list as circular, so
+   * the top item's successor is `baseInput`, the bottom of the stack.
+   */
+  SummaryComponentStack nextInput(SummaryComponentStack prev) {
+    exists(SummaryComponentStack next | next.tail() = prev and next = input.drop(_) | result = next)
+    or
+    not exists(SummaryComponentStack next | next.tail() = prev and next = input.drop(_)) and
+    result = baseInput
+  }
+
   /**
    * Returns a call to `source()` wrapped in `newWith` methods as needed according to `input`.
    * For example, if the input specification is `ArrayElement of MapValue of Argument[0]`, this
-   * will return `newWithArrayElement(newWithMapValue(source()))`.
+   * will return `newWithMapValue(newWithArrayElement(source()))`.
+   *
+   * This requires a slightly awkward walk, out from the element above the root (`Argument[0]` above)
+   * climbing up towards the outer `ArrayElement of...`. This is implemented by treating the stack as
+   * a circular list, walking it backwards and treating the root as a sentinel indicating we should
+   * emit `source()`.
    */
   string getInput(SummaryComponentStack componentStack) {
     componentStack = input.drop(_) and
@@ -284,7 +300,7 @@ class RowTestSnippet extends TRowTestSnippet {
       else
         result =
           "newWith" + contentToken(getContent(componentStack.head())) + "(" +
-            this.getInput(componentStack.tail()) + ")"
+            this.getInput(nextInput(componentStack)) + ")"
     )
   }
 
@@ -364,8 +380,9 @@ class RowTestSnippet extends TRowTestSnippet {
     result =
       "\t\t{\n\t\t\t// \"" + row + "\"\n\t\t\t" + getShortNameIfPossible(this.getOutputType()) +
         " out = null;\n\t\t\t" + this.getInputTypeString() + " in = (" + this.getInputTypeString() +
-        ")" + this.getInput(input) + ";\n\t\t\t" + this.getInstancePrefix() + this.makeCall() +
-        ";\n\t\t\t" + "sink(" + this.getOutput(output) + "); " + this.getExpectation() + "\n\t\t}\n"
+        ")" + this.getInput(this.nextInput(baseInput)) + ";\n\t\t\t" + this.getInstancePrefix() +
+        this.makeCall() + ";\n\t\t\t" + "sink(" + this.getOutput(output) + "); " +
+        this.getExpectation() + "\n\t\t}\n"
   }
 }