Fix YAML dump incorrectly handling zero values

In PHP, empty(0) and empty("0") return true, which caused the YAML
dumper to incorrectly treat zero values as empty. This resulted in:
- Arrays containing 0 being serialized without the zero value
- Scalar zero values being omitted from YAML output

Changes:
- dump(): Replace 'if ($array)' with explicit null/empty checks to
  properly handle arrays that may contain zero values
- _yamlize(): Replace 'empty($value)' with 'count($value) === 0' to
  only treat actually empty arrays as empty, not zero values

Added test cases:
- testDumpIntegerZero: Verify integer 0 is correctly dumped
- testDumpStringZero: Verify string '0' is correctly dumped
- testDumpAssociativeZero: Verify zero values in associative arrays
- testDumpMixedWithZero: Verify mixed arrays containing zero

Fixes wp-cli/wp-cli#6188

Author: AdityaS62

src/Spyc.php

@@ -211,7 +211,9 @@ public function dump($array,$indent = false,$wordwrap = false, $no_opening_dashe
     if (!$no_opening_dashes) $string = "---\n";
 
     // Start at the base of the array and move through it.
-    if ($array) {
+    // Note: We use !== null check to properly handle arrays containing zero values
+    // since `if ($array)` would incorrectly skip processing for falsey values like 0.
+    if ($array !== null && $array !== '' && (!is_array($array) || count($array) > 0)) {
       $array = (array)$array;
       $previous_key = -1;
       foreach ($array as $key => $value) {
@@ -234,7 +236,9 @@ public function dump($array,$indent = false,$wordwrap = false, $no_opening_dashe
   private function _yamlize($key,$value,$indent, $previous_key = -1, $first_key = 0, $source_array = null) {
     if(is_object($value)) $value = (array)$value;
     if (is_array($value)) {
-      if (empty ($value))
+      // Note: We use explicit count check instead of empty() because empty(0) and empty("0")
+      // return true in PHP, which would incorrectly treat zero values as empty arrays.
+      if (count($value) === 0)
         return $this->_dumpNode($key, array(), $indent, $previous_key, $first_key, $source_array);
       // It has children.  What to do?
       // Make it the right kind of item

tests/DumpTest.php

@@ -193,4 +193,43 @@ public function testPerCentAndDoubleQuote() {
       $this->assertEquals ($awaiting, $dump);
     }
 
+    /**
+     * Test that integer zero values are correctly dumped.
+     * This is a regression test for the issue where empty(0) returns true in PHP,
+     * causing zero values to be incorrectly treated as empty.
+     */
+    public function testDumpIntegerZero() {
+      $dump = Spyc::YAMLDump(array(0));
+      $awaiting = "---\n- 0\n";
+      $this->assertEquals($awaiting, $dump);
+    }
+
+    /**
+     * Test that string zero values are correctly dumped.
+     * This is a regression test for the issue where empty("0") returns true in PHP.
+     */
+    public function testDumpStringZero() {
+      $dump = Spyc::YAMLDump(array('0'));
+      $awaiting = "---\n- \"0\"\n";
+      $this->assertEquals($awaiting, $dump);
+    }
+
+    /**
+     * Test that associative arrays with zero values are correctly dumped.
+     */
+    public function testDumpAssociativeZero() {
+      $dump = Spyc::YAMLDump(array('key' => 0));
+      $awaiting = "---\nkey: 0\n";
+      $this->assertEquals($awaiting, $dump);
+    }
+
+    /**
+     * Test that mixed arrays containing zero values are correctly dumped.
+     */
+    public function testDumpMixedWithZero() {
+      $dump = Spyc::YAMLDump(array(1, 0, 2));
+      $awaiting = "---\n- 1\n- 0\n- 2\n";
+      $this->assertEquals($awaiting, $dump);
+    }
+
 }