fix(taint): a guard validates only the value it tests

p14 showed PMPro's functions.php:906 discharged by `elseif (in_array('E', $levels))`.
That checks whether a constant is in `$levels`; it says nothing about `$levels`. The
guard counted a carried variable in any argument. Only argument 1, the tested value
(`in_array`'s needle, the URL given to `url_has_allowed_host_and_scheme`), is
validated now. The allowlist test gains the haystack shape as a reported control.
The test fails when any argument counts.

The other p14 removals were right: WP Statistics export_data x2
(`if (!in_array($table, $allow_tbl)) $table = false;`) and PMPro memberorder.php:1633.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

src/openultrasast/cpg/queries/taint.sc

@@ -710,8 +710,11 @@
   def guardsIn(root: io.shiftleft.codepropertygraph.generated.nodes.AstNode, names: Set[String]): List[io.shiftleft.codepropertygraph.generated.nodes.Call] =
     if (guardNames.isEmpty) Nil
     else
+      // Only the TESTED value is validated -- the first argument: `in_array`'s needle, the URL a redirect check is
+      // given. PMPro's `in_array( 'E', $levels )` asks whether a constant is in `$levels`; with any argument
+      // counted, it discharged a flow through `$levels` itself.
       root.ast.isCall.l.filter(g => guardNames.contains(g.name)).filter { g =>
-        g.argument.l.exists(_.ast.exists {
+        g.argument.l.filter(_.argumentIndex == 1).exists(_.ast.exists {
           case i: io.shiftleft.codepropertygraph.generated.nodes.Identifier                       => names(i.name) || names(i.code.trim)
           case c: io.shiftleft.codepropertygraph.generated.nodes.Call if c.name == FIELD_ACCESS => names(c.code.trim)
           case _                                                                                 => false

tests/test_cpg_queries_compile.py

@@ -1400,8 +1400,11 @@ def test_an_allowlist_check_guards_its_branch_and_its_ternary_arm(tmp_path: Path
         '  else { $o = " ORDER BY u.{$s} "; }\n'
         "  $o = apply_filters( 'sort', $o, $s );\n"
         '  return $wpdb->query( "SELECT 1 FROM t {$o}" ); }\n'
+        "function haystack() { global $wpdb; $l = $_POST['l'];\n"
+        "  if ( in_array( 'E', $l, true ) ) { return $wpdb->query( \"SELECT 1 FROM t WHERE u = {$l[0]}\" ); }\n"
+        "  return null; }\n"
     )
-    names = ("ternary", "wrong_arm", "branch", "else_branch", "stored_in_branch", "stored_in_else")
+    names = ("ternary", "wrong_arm", "branch", "else_branch", "stored_in_branch", "stored_in_else", "haystack")
     common = {
         "sources": ",".join(spec.sources),
         "sinks": ",".join(spec.sinks),
@@ -1413,4 +1416,4 @@ def test_an_allowlist_check_guards_its_branch_and_its_ternary_arm(tmp_path: Path
     }
     payload = _taint_rows(tmp_path, "php2cpg", {"app.php": app}, {n: {**common, "function": n} for n in names})
     reported = {n for n in names if _unsanitized(payload, n)}
-    assert reported == {"wrong_arm", "else_branch", "stored_in_else"}, {n: payload[n] for n in names}
+    assert reported == {"wrong_arm", "else_branch", "stored_in_else", "haystack"}, {n: payload[n] for n in names}