wip PHPC-2064: Change strategy for disabling SKIPIF caching

This complements php/php-src#8076

Author: jmikola

tests/utils/basic-skipif.inc

@@ -25,3 +25,5 @@ register_shutdown_function(function() {
         exit(sprintf('skip %s: %s', errno_as_string($lastError['type']), $lastError['message']));
     }
 });
+
+disable_skipif_caching_if_necessary();

tests/utils/skipif.php

@@ -10,15 +10,33 @@
 require_once __DIR__ . '/basic.inc';
 require_once __DIR__ . '/tools.php';
 
-/**
- * Disables SKIPIF caching (PHP 8.1+).
+/* Disable SKIPIF caching on PHP 8.1+ if the current script calls any functions
+ * that cannot be cached. SkipCache (from run-tests.php) requires that "nocache"
+ * be printed before all other SKIPIF output, so this function should be called
+ * from basic-skipif.inc before test-level skip code.
  */
-function disable_skipif_caching()
+function disable_skipif_caching_if_necessary()
 {
     if (PHP_VERSION_ID < 80100) {
         return;
     }
 
+    $skipif = file_get_contents($_SERVER['PATH_TRANSLATED']);
+
+    if (strpos($skipif, 'skip_if_not_clean') === false) {
+        return;
+    }
+
+    /* Earlier versions of PHP 8.1.x discard SKIPIF output after consuming a
+     * leading "nocache" tag, which could prevent a test from being skipped. To
+     * avoid that, only print "nocache" as the final output. In the event the
+     * test does skip, this trailing "nocache" tag will be ignored, but that is
+     * preferable to ignoring the skip entirely. */
+    if (PHP_VERSION_ID < 80103) {
+        register_shutdown_function(function() { echo "nocache\n"; });
+        return;
+    }
+
     echo "nocache\n";
 }
 
@@ -432,10 +450,6 @@ function skip_if_not_clean($databaseName = DATABASE_NAME, $collectionName = COLL
     } catch (RuntimeException $e) {
         exit("skip Could not drop '$databaseName.$collectionName': " . $e->getMessage());
     }
-
-    /* Since this function modifies the state of the database, we need it to run
-     * each time before a test. */
-    disable_skipif_caching();
 }
 
 function skip_if_no_getmore_failpoint()