Dumper.php

@@ -67,9 +67,7 @@ public function dump(mixed $input, int $inline = 0, int $indent = 0, int $flags
                 }
 
                 if (Yaml::DUMP_MULTI_LINE_LITERAL_BLOCK & $flags && \is_string($value) && str_contains($value, "\n") && !str_contains($value, "\r")) {
-                    // If the first line starts with a space character, the spec requires a blockIndicationIndicator
-                    // http://www.yaml.org/spec/1.2/spec.html#id2793979
-                    $blockIndentationIndicator = str_starts_with($value, ' ') ? (string) $this->indentation : '';
+                    $blockIndentationIndicator = $this->getBlockIndentationIndicator($value);
 
                     if (isset($value[-2]) && "\n" === $value[-2] && "\n" === $value[-1]) {
                         $blockChompingIndicator = '+';
@@ -96,9 +94,7 @@ public function dump(mixed $input, int $inline = 0, int $indent = 0, int $flags
                     $output .= sprintf('%s%s !%s', $prefix, $dumpAsMap ? Inline::dump($key, $flags).':' : '-', $value->getTag());
 
                     if (Yaml::DUMP_MULTI_LINE_LITERAL_BLOCK & $flags && \is_string($value->getValue()) && str_contains($value->getValue(), "\n") && !str_contains($value->getValue(), "\r\n")) {
-                        // If the first line starts with a space character, the spec requires a blockIndicationIndicator
-                        // http://www.yaml.org/spec/1.2/spec.html#id2793979
-                        $blockIndentationIndicator = str_starts_with($value->getValue(), ' ') ? (string) $this->indentation : '';
+                        $blockIndentationIndicator = $this->getBlockIndentationIndicator($value->getValue());
                         $output .= sprintf(' |%s', $blockIndentationIndicator);
 
                         foreach (explode("\n", $value->getValue()) as $row) {
@@ -143,9 +139,7 @@ private function dumpTaggedValue(TaggedValue $value, int $inline, int $indent, i
         $output = sprintf('%s!%s', $prefix ? $prefix.' ' : '', $value->getTag());
 
         if (Yaml::DUMP_MULTI_LINE_LITERAL_BLOCK & $flags && \is_string($value->getValue()) && str_contains($value->getValue(), "\n") && !str_contains($value->getValue(), "\r\n")) {
-            // If the first line starts with a space character, the spec requires a blockIndicationIndicator
-            // http://www.yaml.org/spec/1.2/spec.html#id2793979
-            $blockIndentationIndicator = (' ' === substr($value->getValue(), 0, 1)) ? (string) $this->indentation : '';
+            $blockIndentationIndicator = $this->getBlockIndentationIndicator($value->getValue());
             $output .= sprintf(' |%s', $blockIndentationIndicator);
 
             foreach (explode("\n", $value->getValue()) as $row) {
@@ -161,4 +155,20 @@ private function dumpTaggedValue(TaggedValue $value, int $inline, int $indent, i
 
         return $output."\n".$this->dump($value->getValue(), $inline - 1, $indent, $flags);
     }
+
+    private function getBlockIndentationIndicator(string $value): string
+    {
+        $lines = explode("\n", $value);
+
+        // If the first line (that is neither empty nor contains only spaces)
+        // starts with a space character, the spec requires a block indentation indicator
+        // http://www.yaml.org/spec/1.2/spec.html#id2793979
+        foreach ($lines as $line) {
+            if ('' !== trim($line, ' ')) {
+                return (' ' === substr($line, 0, 1)) ? (string) $this->indentation : '';
+            }
+        }
+
+        return '';
+    }
 }

Tests/DumperTest.php

@@ -710,6 +710,42 @@ public function testDumpMultiLineStringAsScalarBlockWhenFirstLineHasLeadingSpace
         $this->assertSame($data, $this->parser->parse($yml));
     }
 
+    public function testDumpMultiLineStringAsScalarBlockWhenFirstLineIsEmptyAndSecondLineHasLeadingSpace()
+    {
+        $data = [
+            'data' => [
+                'multi_line' => "\n    the second line has leading spaces\nThe third line does not.",
+            ],
+        ];
+
+        $expected = "data:\n    multi_line: |4-\n\n            the second line has leading spaces\n        The third line does not.";
+
+        $yml = $this->dumper->dump($data, 2, 0, Yaml::DUMP_MULTI_LINE_LITERAL_BLOCK);
+        $this->assertSame($expected, $yml);
+        $this->assertSame($data, $this->parser->parse($yml));
+    }
+
+    public function testDumpMultiLineStringAsScalarBlockWhenFirstLineHasOnlySpaces()
+    {
+        $data = [
+            'data' => [
+                'multi_line' => "    \nthe second line\nThe third line.",
+            ],
+        ];
+
+        $expectedData = [
+            'data' => [
+                'multi_line' => "\nthe second line\nThe third line.",
+            ],
+        ];
+
+        $expectedYml = "data:\n    multi_line: |-\n            \n        the second line\n        The third line.";
+
+        $yml = $this->dumper->dump($data, 2, 0, Yaml::DUMP_MULTI_LINE_LITERAL_BLOCK);
+        $this->assertSame($expectedYml, $yml);
+        $this->assertSame($expectedData, $this->parser->parse($yml));
+    }
+
     public function testCarriageReturnFollowedByNewlineIsMaintainedWhenDumpingAsMultiLineLiteralBlock()
     {
         $data = ["a\r\nb\nc"];