bug #19288 [VarDumper] Fix indentation trimming in ExceptionCaster (nicolas-grekas)

This PR was merged into the 2.8 branch.

Discussion
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[VarDumper] Fix indentation trimming in ExceptionCaster

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Blank lines prevent left-trimming of source code excerpts currently.

Commits
-------

ab9daeb [VarDumper] Fix indentation trimming in ExceptionCaster

src/Symfony/Component/VarDumper/Caster/ExceptionCaster.php

@@ -253,19 +253,24 @@ class ExceptionCaster
         }
 
         $ltrim = 0;
-        while (' ' === $src[0][$ltrim] || "\t" === $src[0][$ltrim]) {
-            $i = $srcContext << 1;
-            while ($i > 0 && $src[0][$ltrim] === $src[$i][$ltrim]) {
-                --$i;
+        do {
+            $pad = null;
+            for ($i = $srcContext << 1; $i >= 0; --$i) {
+                if (isset($src[$i][$ltrim]) && "\r" !== ($c = $src[$i][$ltrim]) && "\n" !== $c) {
+                    if (null === $pad) {
+                        $pad = $c;
                     }
-            if ($i) {
+                    if ((' ' !== $c && "\t" !== $c) || $pad !== $c) {
                         break;
                     }
-            ++$ltrim;
                 }
-        if ($ltrim) {
+            }
+            ++$ltrim;
+        } while (0 > $i && null !== $pad);
+
+        if (--$ltrim) {
             foreach ($src as $i => $line) {
-                $src[$i] = substr($line, $ltrim);
+                $src[$i] = isset($line[$ltrim]) && "\r" !== $line[$ltrim] ? substr($line, $ltrim) : ltrim($line, " \t");
             }
         }