bug symfony#13375 [YAML] Fix one-liners to work with multiple new lines (Alex Pott)

This PR was submitted for the 2.7 branch but it was merged into the 2.3 branch instead (closes symfony#13375).

Discussion
----------

[YAML] Fix one-liners to work with multiple new lines

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | none
| License       | MIT
| Doc PR        | n/a

Commits
-------

4d22bf7 [YAML] Fix one-liners to work with multiple new lines

Author: fabpot

src/Symfony/Component/Yaml/Parser.php

@@ -51,13 +51,13 @@ public function __construct($offset = 0)
      */
     public function parse($value, $exceptionOnInvalidType = false, $objectSupport = false)
     {
-        $this->currentLineNb = -1;
-        $this->currentLine = '';
-        $this->lines = explode("\n", $this->cleanup($value));
-
         if (!preg_match('//u', $value)) {
             throw new ParseException('The YAML value does not appear to be valid UTF-8.');
         }
+        $this->currentLineNb = -1;
+        $this->currentLine = '';
+        $value = $this->cleanup($value);
+        $this->lines = explode("\n", $value);
 
         if (function_exists('mb_internal_encoding') && ((int) ini_get('mbstring.func_overload')) & 2) {
             $mbEncoding = mb_internal_encoding();
@@ -197,9 +197,8 @@ public function parse($value, $exceptionOnInvalidType = false, $objectSupport =
                     throw new ParseException('Multiple documents are not supported.');
                 }
 
-                // 1-liner optionally followed by newline
-                $lineCount = count($this->lines);
-                if (1 === $lineCount || (2 === $lineCount && empty($this->lines[1]))) {
+                // 1-liner optionally followed by newline(s)
+                if ($this->lines[0] === trim($value)) {
                     try {
                         $value = Inline::parse($this->lines[0], $exceptionOnInvalidType, $objectSupport, $this->refs);
                     } catch (ParseException $e) {

src/Symfony/Component/Yaml/Tests/ParserTest.php

@@ -135,6 +135,14 @@ public function getBlockChompingTests()
         );
         $tests['Literal block chomping strip with multiple trailing newlines'] = array($expected, $yaml);
 
+        $yaml = <<<'EOF'
+{}
+
+
+EOF;
+        $expected = array();
+        $tests['Literal block chomping strip with multiple trailing newlines after a 1-liner'] = array($expected, $yaml);
+
         $yaml = <<<'EOF'
 foo: |-
     one