How to get a backtrace in Drupal, without problems like out-of-memory when huge objects are in the trace?

Question

I often have problems with the standard backtracing functions when working with Drupal:

• debug_print_backtrace(); often seems to get lost between pages and never prints,
• Drupal's objects and classes are often so big that debug( debug_backtrace(), "Backtrace", true ); can kill my server with out of memory errors, and debug( debug_backtrace() ); almost always fails with a "Nested dependency" recursion error.

Is there any alternative to the above approaches that can be used reliably, ideally as a drop-in function without needing to set up any framework?

Answer 1

I find this useful as a less memory intensive Drupal-friendly way to backtrace PHP as a one-off code snippet to temporarily drop into a troublesome location without installing modules or server-side tools:

  $trace = debug_backtrace();
  $backtrace_lite = array();
  foreach( $trace as $call ) {
    $backtrace_lite[] = $call['function']."    ".$call['file']."    line ".$call['line'];
  }
  debug( $backtrace_lite, "TRACE", true );

It gets the backtrace into Drupal's debugging system, but strips it down to the essentials to avoid failures when massive objects are involved.

For handy reference, the other keys within each row of the debug_backtrace() object are:

• class
• object
• type
• args

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_{Note - this answer was first posted in the now-deleted too-broad question How do I debug Drupal?}

Answer 2

More compact variant:

  $backtrace_lite = array_map(function($call_item) {
    return "{$call_item['function']} -> {$call_item['file']} -> line {$call_item['line']}";
  }, debug_backtrace());