git and hg diff views did not show empty context lines, a regression

from the commit(s) from issue 633. The diff parser assumed a properly
formatted diff that denotes empty context lines with a single space in
the first column. This single space however was missing, because the
hg and git backends got the diff through PHP's exec() function and
this returns already line-splitted output, but - and this is the actual
problem - removes trailing whitespace at the end of each line, essentially
making " \n" only "\n". When splitting this string now again with
PREG_SPLIT_NO_EMPTY the empty line was completely lost in the diff output.

To make it clear that an empty line does not mark a context line now, but
should stop the diff parsing, the Diff parser now also defaults to 'false'
as line type.

This commit fixes issue 688.

NEWS.mdtext

@@ -14,6 +14,7 @@
 - Timeline only displays filter options for items a user has actually access to (issue 655)
 - The log, tags and branches parsers for Mercurial are more robust now (issue 663)
 - Fix SSH public key parsing issues and improve the check for existing, uploaded keys (issue 679)
+- Diff views now show empty context lines for git and hg again (issue 688)
 - Let the SVN command line client not store the login credentials we give him as arguments
 
 ## Documentation

src/IDF/Diff.php

@@ -101,7 +101,7 @@ class IDF_Diff
                 $files[$current_file]['chunks'][] = array();
 
                 while ($i < $diffsize && ($addlines >= 0 || $dellines >= 0)) {
-                    $linetype = $this->lines[$i] != '' ? $this->lines[$i][0] : ' ';
+                    $linetype = $this->lines[$i] != '' ? $this->lines[$i][0] : false;
                     switch ($linetype) {
                         case ' ':
                             $files[$current_file]['chunks'][$current_chunk][] =

src/IDF/Scm.php

@@ -88,22 +88,37 @@ class IDF_Scm
     }
 
     /**
-     * Run exec and log some information.
+     * Runs the given command and log some information.
+     *
+     * A previous version used plain exec(), but this should not be used
+     * for various reasons, one being that this command does not preserve
+     * trailing whitespace, which is essential for proper diff parsing.
      *
      * @param $caller Calling method
      * @param $cmd Command to run
      * @param &$out Array of output
      * @param &$return Return value
-     * @return string Last line of the command
      */
     public static function exec($caller, $cmd, &$out=null, &$return=null)
     {
+        $return = 1;
         Pluf_Log::stime('timer');
-        $ret = exec($cmd, $out, $return);
+        $fp = popen($cmd, 'r');
+        $buf = '';
+        if ($fp !== false) {
+            $return = 0;
+            while (!feof($fp)) {
+                $buf .= fread($fp, 1024);
+            }
+            pclose($fp);
+        }
+        $out = preg_split('/\r\n|\r|\n/', $buf);
+        $elem = count($out);
+        if ($elem > 0 && $out[$elem-1] === '')
+            unset($out[$elem-1]);
         Pluf_Log::perf(array($caller, $cmd, Pluf_Log::etime('timer', 'total_exec')));
         Pluf_Log::debug(array($caller, $cmd, $out));
         Pluf_Log::inc('exec_calls');
-        return $ret;
     }
 
     /**