Fix researching cache population (#358)

GameEngine/Database/DatabaseTroopQueries.php

@@ -354,8 +354,8 @@ trait DatabaseTroopQueries {
 
 		$q = "SELECT * FROM " . TB_PREFIX . "research where vref = $vid ORDER BY timestamp ASC";
 		$result = mysqli_query($this->dblink,$q);
-        $researchingCache[$vid] = $this->mysqli_fetch_all($result);
+        self::$researchingCache[$vid] = $this->mysqli_fetch_all($result);
-        return $researchingCache[$vid];
+        return self::$researchingCache[$vid];
 	}
 
 	function checkIfResearched($vref, $unit, $use_cache = true) {

tests/regression/GetResearchingCacheTest.php

@@ -0,0 +1,70 @@
+<?php
+
+if (function_exists('mysqli_query')) {
+    $command = escapeshellarg(PHP_BINARY)
+        . ' -d disable_functions=mysqli_query '
+        . escapeshellarg(__FILE__);
+
+    passthru($command, $status);
+    exit($status);
+}
+
+if (!function_exists('mysqli_query')) {
+    function mysqli_query($connection, $query)
+    {
+        $GLOBALS['queryCount']++;
+
+        return $query;
+    }
+}
+
+define('TB_PREFIX', 'test_');
+
+require_once __DIR__ . '/../../GameEngine/Database/DatabaseTroopQueries.php';
+
+final class ResearchingCacheHarness
+{
+    use DatabaseTroopQueries;
+
+    public $dblink;
+    public $rows = [];
+
+    private static $researchingCache = [];
+
+    private static function returnCachedContent(&$cache, $key)
+    {
+        return isset($cache[$key]) && !empty($cache[$key])
+            ? $cache[$key]
+            : null;
+    }
+
+    public function mysqli_fetch_all($result)
+    {
+        return $this->rows;
+    }
+}
+
+$GLOBALS['queryCount'] = 0;
+
+$database = new ResearchingCacheHarness();
+$database->rows = [
+    ['id' => 1, 'vref' => 42, 'tech' => 't2', 'timestamp' => 1234],
+];
+
+$first = $database->getResearching(42);
+$second = $database->getResearching(42);
+
+if ($first !== $database->rows || $second !== $database->rows) {
+    fwrite(STDERR, "getResearching() did not return the fetched research rows.\n");
+    exit(1);
+}
+
+if ($GLOBALS['queryCount'] !== 1) {
+    fwrite(
+        STDERR,
+        "Expected one query across two cached reads; got {$GLOBALS['queryCount']}.\n"
+    );
+    exit(1);
+}
+
+fwrite(STDOUT, "getResearching cache regression test passed.\n");