Forward-port data query source guard (#7985)

* issue#7809: stop reading a missing source key on output-only data query fields

query_snmp_host() tested $field_array['source'] as the left-most term of the
method-fix guard, so PHP raised "Undefined array key source" for every
output-only field before the direction test could short-circuit. Testing
direction first reads source only for input fields, which always define it.
The boolean result is unchanged.

Signed-off-by: Thomas Vincent <thomasvincent@gmail.com>
(cherry picked from commit 5f25145ba0)

* docs: restore changelog issue ordering

* Tighten data query regression error handling

* Clarify data query regression comment

---------

Signed-off-by: Thomas Vincent <thomasvincent@gmail.com>

tests/Unit/DataCollection/DataQuery/DataQuerySourceKeyTest.php

@@ -0,0 +1,93 @@
+<?php
+/*
+ +-------------------------------------------------------------------------+
+ | Copyright (C) 2004-2026 The Cacti Group                                 |
+ +-------------------------------------------------------------------------+
+ | Cacti: The Complete RRDtool-based Graphing Solution                     |
+ +-------------------------------------------------------------------------+
+*/
+
+/*
+ * Regression test for #7809.
+ *
+ * query_snmp_host() iterates every data query field, including output-only
+ * fields that carry no 'source' key. Before the fix, the pre-processing guard read
+ * $field_array['source'] as its left-most term, so PHP raised
+ * "Undefined array key source" for every output field before the direction
+ * test could short-circuit. Testing the direction first reads 'source' only
+ * for input fields, which always define it.
+ */
+
+function _data_query_source_7809() {
+	$path = dirname(__DIR__, 4) . '/lib/data_query.php';
+	$src  = file_get_contents($path);
+
+	expect($src)->not->toBeFalse('Failed to read lib/data_query.php');
+
+	return $src;
+}
+
+test('#7809: the method-fix guard tests direction before reading source', function () {
+	$src = _data_query_source_7809();
+
+	$needle = 'if ((' . '$field_array' . "['direction'] == 'input' || " . '$field_array' . "['direction'] == 'input-output') && " . '$field_array' . "['source'] != 'index'";
+	$start  = strpos($src, $needle);
+
+	expect($start)->not->toBeFalse(
+		"query_snmp_host() must test direction before reading \$field_array['source'] so output-only fields short-circuit"
+	);
+
+	// The old ordering (source first) must be gone.
+	$oldNeedle = 'if (' . '$field_array' . "['source'] != 'index' && (" . '$field_array' . "['direction'] == 'input'";
+	$old       = strpos($src, $oldNeedle);
+	expect($old)->toBeFalse('the source-first ordering must not remain');
+});
+
+test('#7809: an output-only field does not read a missing source key', function () {
+	// Mirrors the real guard. An output field carries direction=output and no source.
+	$field_array = [
+		'direction' => 'output',
+		'method'    => 'walk',
+	];
+
+	$warned = false;
+	set_error_handler(function ($errno, $errstr) use (&$warned) {
+		if ($errno === E_WARNING && stripos($errstr, 'source') !== false) {
+			$warned = true;
+
+			return true;
+		}
+
+		return false;
+	}, E_WARNING);
+
+	try {
+		$hit =
+			($field_array['direction'] == 'input' || $field_array['direction'] == 'input-output') &&
+			$field_array['source'] != 'index' &&
+			$field_array['method'] != 'get' &&
+			(isset($field_array['rewrite_index']) || isset($field_array['oid_suffix']));
+	} finally {
+		restore_error_handler();
+	}
+
+	expect($warned)->toBeFalse('output-only field must not trigger an undefined source-key warning');
+	expect($hit)->toBeFalse('output-only field must not enter the input method-fix branch');
+});
+
+test('#7809: an input field still enters the branch when it should', function () {
+	$field_array = [
+		'direction'     => 'input',
+		'source'        => 'value',
+		'method'        => 'walk',
+		'rewrite_index' => '.1',
+	];
+
+	$hit =
+		($field_array['direction'] == 'input' || $field_array['direction'] == 'input-output') &&
+		$field_array['source'] != 'index' &&
+		$field_array['method'] != 'get' &&
+		(isset($field_array['rewrite_index']) || isset($field_array['oid_suffix']));
+
+	expect($hit)->toBeTrue('input field with rewrite_index must still be corrected to method=get');
+});