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Code Coverage Analysis

Code coverage tells you which lines of script (or set of scripts) have been executed during a request. With this information you can for example find out how good your unit tests are.

Xdebug's code coverage functionality is often used in combination with PHP_CodeCoverage as part of PHPUnit runs. PHPUnit delegates the code coverage collection to Xdebug. It starts and stops code coverage through xdebug_start_code_coverage() and xdebug_stop_code_coverage() for every test, and uses xdebug_get_code_coverage() to retrieve the results.

Code coverage's main output is an array detailing which lines in which files have been "hit" while running the code with code coverage collection active. But the code coverage functionality can also, with an additional performance impact, analyse which lines of code have executable code on it, which lines of code can actually be hit (dead code analysis), and also can it do instrumentation to find out which branches and paths in functions and methods have been followed. The various options are documented with the xdebug_start_code_coverage() function.

Filtering

Xdebug 2.6 introduces filtering capabilities for code coverage. With a filter you can include, or exclude, paths or class name prefixes (namespaces) from being analysed during code coverage collection. A typyical use case would be to configure the filter to only include your src/ folder, so that Xdebug's code coverage analysis does not try to analyse tests, Composer dependencies, or PHPUnit/PHP_CodeCoverage itself. If you configure the filter correctly, you can expect a 2-fold speed increase for code coverage runs [1, 2, 3].

The filter works by tagging each executable unit (function, method, file) according to the configured filter. Xdebug can only do that the first time a specific executable unit is included/required, as the filtering happens when PHP parses and compiles a file for the first time. Xdebug needs to do it as this point, as this is also when it analyses which paths can run, and which lines of an executable unit can not be executed. Tagging executable units at this point, also means that the filter does not have to run every time Xdebug wants to count a line to be included in code coverage for example. It is therefore important to set-up the filter before the code is included/required. This currently can be best done through an auto-prepended file through PHP's auto_prepend_file setting.

To set-up a filter that only does code coverage analysis for the src/ folder, you would call xdebug_set_filter() with:

Example:

<?php
xdebug_set_filter(
	XDEBUG_FILTER_CODE_COVERAGE,
	XDEBUG_PATH_INCLUDE,
	[ __DIR__ . DIRECTORY_SEPARATOR . "src" . DIRECTORY_SEPARATOR ]
);
?>

With this filter set up, the code coverage information will only include functions, methods and files which are located in the src/ sub-directory of the file in which this file resides. You can tell PHP to add this prepend file by calling:

php -dauto_prepend_file=xdebug_filter.php yourscript.php

Or in combination with PHPUnit, when installed through Composer, with:

php -dauto_prepend_file=xdebug_filter.php vendor/bin/phpunit

The full documentation for the arguments to xdebug_set_filter() are described on its own documentation page.

Related Settings and Functions

Settings


string xdebug.log = #

Configures Xdebug's log file.

Xdebug will log to this file all file creations issues, Step Debugging connection attempts, failures, and debug communication.

Enable this functionality by setting the value to a absolute path. Make sure that the system user that PHP runs at (such as www-data if you are running with Apache) can create and write to the file.

The file is opened in append-mode, and will therefore not be overwritten by default. There is no concurrency protection available.

The log file will include any attempt that Xdebug makes to connect to an IDE:

[2693358] Log opened at 2020-09-02 07:19:09.616195
[2693358] [Step Debug] INFO: Connecting to configured address/port: localhost:9003.
[2693358] [Step Debug] ERR: Could not connect to debugging client. Tried: localhost:9003 (through xdebug.client_host/xdebug.client_port) :-(
[2693358] [Profiler] ERR: File '/foo/cachegrind.out.2693358' could not be opened.
[2693358] [Profiler] WARN: /foo: No such file or directory
[2693358] [Tracing] ERR: File '/foo/trace.1485761369' could not be opened.
[2693358] [Tracing] WARN: /foo: No such file or directory
[2693358] Log closed at 2020-09-02 07:19:09.617510

It includes the opening time (2020-09-02 07:19:09.616195), the IP/Hostname and port Xdebug is trying to connect to (localhost:9003), and whether it succeeded (Connected to client :-)). The number in brackets ([2693358]) is the Process ID.

It includes:

[2693358]
process ID in brackets
2020-09-02 07:19:09.616195
opening time

For Step Debugging:

INFO: Connecting to configured address/port: localhost:9003.
ERR: Could not connect to debugging client. Tried: localhost:9003 (through xdebug.client_host/xdebug.client_port) :-(

For Profiling:

ERR: File '/foo/cachegrind.out.2693358' could not be opened.
WARN: /foo: No such file or directory

For Function Trace:

ERR: File '/foo/trace.1485761369' could not be opened.
WARN: /foo: No such file or directory

All warnings and errors are described on the Description of errors page, with detailed instructions on how to resolve the problem, if possible. All errors are always logged through PHP's internal logging mechanism (configured with error_log in php.ini). All warnings and errors also show up in the diagnostics log that you can view by calling xdebug_info().

Step Debugger Communication

The debugging log can also log the communication between Xdebug and an IDE. This communication is in XML, and starts with the <init XML element:

<init
    xmlns="urn:debugger_protocol_v1" xmlns:xdebug="https://xdebug.org/dbgp/xdebug"
    fileuri="file:///home/httpd/www.xdebug.org/html/router.php"
    language="PHP" xdebug:language_version="7.4.11-dev"
    protocol_version="1.0" appid="2693358" idekey="XDEBUG_ECLIPSE">
        <engine version="3.0.0-dev"><![CDATA[Xdebug]]></engine>
        <author><![CDATA[Derick Rethans]]></author>
        <url><![CDATA[https://xdebug.org]]></url>
        <copyright><![CDATA[Copyright (c) 2002-2020 by Derick Rethans]]></copyright>
</init>

The fileuri attribute lists the entry point of your application, which can be useful to compare to breakpoint_set commands to see if path mappings are set-up correctly.

Beyond the <init element, you will find the configuration of features:

<- feature_set -i 4 -n extended_properties -v 1
-> <response
       xmlns="urn:debugger_protocol_v1" xmlns:xdebug="https://xdebug.org/dbgp/xdebug"
       command="feature_set" transaction_id="4" feature="extended_properties" success="1">
   </response>

And continuation commands:

<- step_into -i 9
-> <response
       xmlns="urn:debugger_protocol_v1" xmlns:xdebug="https://xdebug.org/dbgp/xdebug"
       command="step_into" transaction_id="9"
       status="break" reason="ok">
           <xdebug:message filename="file:///home/httpd/www.xdebug.org/html/router.php" lineno="3">
           </xdebug:message>
   </response>

You can read about DBGP - A common debugger protocol specification at its dedicated documation page.

The xdebug.log_level setting controls how much information is logged.

Note: Many Linux distributions now use systemd, which implements private tmp directories. This means that when PHP is run through a web server or as PHP-FPM, the /tmp directory is prefixed with something akin to:

/tmp/systemd-private-ea3cfa882b4e478993e1994033fc5feb-apache.service-FfWZRg

integer xdebug.log_level = 7 #

Configures which logging messages should be emitted.

The following levels are supported:

LevelNameExample
1ErrorsConnection errors
3WarningsConnection warnings
5CommunicationProtocol messages
7InformationInformation while connecting
10DebugBreakpoint resolving information

Errors are also logged through PHP's internal logging mechanism (configured with error_log in php.ini).

Warnings and errors show up in the diagnostics log that you can view by calling xdebug_info().


string xdebug.mode = display #

This setting controls which Xdebug features are enabled.

The following values are accepted:

off
Nothing is enabled. Xdebug does no work besides checking whether functionality is enabled. Use this setting if you want close to 0 overhead.
develop
Enables Development Aids including the overloaded var_dump().
coverage
Enables Code Coverage Analysis to generate code coverage reports, mainly in combination with PHPUnit.
debug
Enables Step Debugging. This can be used to step through your code while it is running, and analyse values of variables.
gcstats
Enables Garbage Collection Statistics to collect statistics about PHP's Garbage Collection Mechanism.
profile
Enables Profiling, with which you can analyse performance bottlenecks with tools like KCacheGrind.
trace
Enables the Function Trace feature, which allows you record every function call, including arguments, variable assignment, and return value that is made during a request to a file.

Functions


xdebug_code_coverage_started() : bool #

Returns whether code coverage is active

Returns whether code coverage has been started.

Example:

<?php
    var_dump
(xdebug_code_coverage_started());

    
xdebug_start_code_coverage();

    
var_dump(xdebug_code_coverage_started());
?>

Returns:

bool(false)
bool(true)

xdebug_get_code_coverage() : array #

Returns code coverage information

Returns a structure which contains information about which lines were executed in your script (including include files). The following example shows code coverage for one specific file:

Example:

<?php
xdebug_start_code_coverage
(XDEBUG_CC_UNUSED XDEBUG_CC_DEAD_CODE);

function 
a($a) {
    return;
    echo 
$a 2.5;
}

function 
b($count) {
    if (
$count 25) {
        echo 
"too much\n";
    }
    for (
$i 0$i $count$i++) {
        
a($i 0.17);
    }
}

b(6);
b(10);

var_dump(xdebug_get_code_coverage());
?>

Returns:

array
  '/home/httpd/html/test/xdebug/docs/xdebug_get_code_coverage.php' =>
    array (size=11)
      5 => int 1
      6 => int -2
      7 => int -2
      10 => int 1
      11 => int -1
      13 => int 1
      14 => int 1
      16 => int 1
      18 => int 1
      19 => int 1
      21 => int 1

The information that is collected consists of an two dimensional array with as primary index the executed filename and as secondary key the line number. The value in the elements represents whether the line has been executed or whether it has unreachable lines.

The returned values for each line are:

  • 1: this line was executed
  • -1: this line was not executed
  • -2: this line did not have executable code on it
Value -1 is only returned when the XDEBUG_CC_UNUSED is enabled and value -2 is only returned when both XDEBUG_CC_UNUSED and XDEBUG_CC_DEAD_CODE are enabled when starting Code Coverage Analysis through xdebug_start_code_coverage().

If path and branch checking has been enabled with the XDEBUG_CC_BRANCH_CHECK flag to xdebug_start_code_coverage() then the returned format is different. The lines array is returned in a sub-array element lines, and separate information is returned for each function in the functions element.

The following example illustrates that.

Example:

<?php
xdebug_start_code_coverage
(XDEBUG_CC_UNUSED XDEBUG_CC_DEAD_CODE);

function 
c($count) {
    for (
$i 0$i $count$i++) {
        
$i += 0.17;
    }
}

c(10);

var_dump(xdebug_get_code_coverage());
?>

Returns:

array (size=1)
  '/tmp/foo2.php' =>
    array (size=2)
      'lines' =>
        array (size=5)
          5 => int 1
          6 => int 1
          8 => int 1
          10 => int 1
          12 => int 1
      'functions' =>
        array (size=1)
          'c' =>
            array (size=2)
              'branches' =>
                array (size=4)
                  0 =>
                    array (size=7)
                      'op_start' => int 0
                      'op_end' => int 4
                      'line_start' => int 4
                      'line_end' => int 5
                      'hit' => int 1
                      'out' =>
                        array (size=1)
                          0 => int 9
                      'out_hit' =>
                        array (size=1)
                          0 => int 1
                  5 =>
                    array (size=7)
                      'op_start' => int 5
                      'op_end' => int 8
                      'line_start' => int 6
                      'line_end' => int 5
                      'hit' => int 1
                      'out' =>
                        array (size=1)
                          0 => int 9
                      'out_hit' =>
                        array (size=1)
                          0 => int 1
                  9 =>
                    array (size=7)
                      'op_start' => int 9
                      'op_end' => int 11
                      'line_start' => int 5
                      'line_end' => int 5
                      'hit' => int 1
                      'out' =>
                        array (size=2)
                          0 => int 12
                          1 => int 5
                      'out_hit' =>
                        array (size=2)
                          0 => int 1
                          1 => int 1
                  12 =>
                    array (size=7)
                      'op_start' => int 12
                      'op_end' => int 13
                      'line_start' => int 8
                      'line_end' => int 8
                      'hit' => int 1
                      'out' =>
                        array (size=1)
                          0 => int 2147483645
                      'out_hit' =>
                        array (size=1)
                          0 => int 0
              'paths' =>
                array (size=2)
                  0 =>
                    array (size=2)
                      'path' =>
                        array (size=3)
                          0 => int 0
                          1 => int 9
                          2 => int 12
                      'hit' => int 0
                  1 =>
                    array (size=2)
                      'path' =>
                        array (size=5)
                          0 => int 0
                          1 => int 9
                          2 => int 5
                          3 => int 9
                          4 => int 12
                      'hit' => int 1

Inside each function the branches element describes each branch.

Returns:

9 =>
  array (size=7)
    'op_start' => int 9
    'op_end' => int 11
    'line_start' => int 5
    'line_end' => int 5
    'hit' => int 1
    'out' =>
      array (size=2)
        0 => int 12
        1 => int 5
    'out_hit' =>
      array (size=2)
        0 => int 1
        1 => int 1

The index is the starting opcode, and the fields mean:

op_start
The starting opcode. This is the same number as the array index.
op_end
The last opcode in the branch
line_start
The line number of the op_start opcode.
line_end
The line number of the op_end opcode. This can potentially be a number that is lower than line_start due to the way the PHP compiler generates opcodes.
hit
Whether the opcodes in this branch have been executed or not.
out
An array containing the op_start opcodes for branches that can follow this one.
out_hit
Each element matches the same index as in out and indicates whether this branch exit has been reached.

Each function also contains a paths element, which shows all the possible paths through the function, and whether they have been hit.

Returns:

1 =>
  array (size=2)
    'path' =>
      array (size=5)
        0 => int 0
        1 => int 9
        2 => int 5
        3 => int 9
        4 => int 12
    'hit' => int 1

The index is a normal PHP array index, and the fields mean:

path
An array containing the op_start opcodes indicating the branches that make up this path. In the example, 9 features twice because this path (the loop) has after branch 9 an exit to opcode 5 (the start of the loop), and opcode 12 (the next branch after the loop).
hit
Whether this specific path has been followed.

The Xdebug source contains a file containing a dump_branch_coverage function, which you can use the show the information in a more concise way. The above array would instead be shown as:

Returns:

c
- branches
  - 00; OP: 00-04; line: 06-07 HIT; out1: 09 HIT
  - 05; OP: 05-08; line: 08-07 HIT; out1: 09 HIT
  - 09; OP: 09-11; line: 07-07 HIT; out1: 12 HIT; out2: 05 HIT
  - 12; OP: 12-13; line: 10-10 HIT; out1: EX  X
- paths
  - 0 9 12:  X
  - 0 9 5 9 12: HIT

The function also generates a file /tmp/paths.dot, which can be processed with the dot tool of the Graphviz software to create an image.

Example:

dot -Tpng /tmp/paths.dot > /tmp/paths.png

This generates an image where a solid line means that the path has been followed, and a dashed line means that that path has not been followed.


xdebug_info() : void #

Show diagnostic information

This function returns an HTML page which shows diagnostic information. It is analogous to PHP's phpinfo() function.

The HTML output includes which mode is active, what the settings are, and diagnostic information in case there are problems with debugging connections, opening of files, etc.

Each warning and error in the diagnostics log also links through to the Description of errors documentation page.


xdebug_set_filter( int $group, int $listType, array $configuration ) : void #

Set filter

This function configures a filter that Xdebug employs when displaying stack traces or recording function traces, or when gathering code coverage. Filter configurations are applied to each execution unit (function, method, script body) independently.

The first argument, $group selects for which feature you want to set up a filter. Currently there are two groups:

XDEBUG_FILTER_TRACING
The filter group used for filtering a Development Aids upon errors, as well as for elements in a Function Trace.
XDEBUG_FILTER_CODE_COVERAGE
The filter group used for restricting the file paths which Xdebug would use for Code Coverage Analysis.
Each group can be configured independently.

There are different kinds of filters that you can set. You can filter on either file path prefix, or fully qualified class name prefix (i.e. namespace). For each filter type you can a list of paths/namespaces to include or exclude. All matches are done in a case-insensitive way.

The XDEBUG_FILTER_CODE_COVERAGE group only supports XDEBUG_PATH_INCLUDE, XDEBUG_PATH_EXCLUDE, and XDEBUG_FILTER_NONE. All matches are done in a case-insensitive way.

The constants to use as second "$list_type" argument are:

XDEBUG_PATH_INCLUDE

Configures a list of file paths to include. An execution unit is included in the output if its file path is prefixed by any of the prefixes in the array passed as third $configuration argument.

Please note that a prefix of /home/derick would also match files in /home/derickrethans, so it is recommended that you add the trailing slash to the prefix in order to prevent this.

XDEBUG_PATH_EXCLUDE

Sets up a list of paths to exclude. An execution unit will be excluded from the output if its file path is prefixed by any of the prefixes from the $configuration array.

XDEBUG_NAMESPACE_INCLUDE

Configures a list of class name prefixes to include. An execution unit is included in the output if the class name, after namespace expansion, matches one of the prefixes in the $configuration array. An empty string value is special, and means functions that do not belong to a class. These are either user-defined, or built-in PHP functions (e.g. strlen()).

Name space expansion happens automatically in PHP, and its engine will always see the full qualified class name. In the code below, the fully qualified class name DramIO\Whisky:

Example:

<?php
namespace DramIO;

class 
Whisky {
}

In order to match for all clases within a namespace, it is recommended to specify the prefix with the namespace separator

XDEBUG_NAMESPACE_EXCLUDE
Sets up a list of namespaces to exclude. Execution units are excluded only if their prefix matches one of the prefixes in the $configuration array.
XDEBUG_FILTER_NONE
Turns off the filter for the selected $group.

It is not possible to configure a filter for paths/namespaces at the same time, and neither is it possible to configure which paths to exclude and include at the same time. Only one of the four list types can be active at any one time. It is possible however, to turn off the filter altogether by using XDEBUG_FILTER_NONE.

To exclude all files in the vendor sub-directory in traces:

Example:

<?php
xdebug_set_filter
XDEBUG_FILTER_TRACINGXDEBUG_PATH_EXCLUDE, [ __DIR__ "/vendor/" ] );
?>

To include only function calls (without class name), and methods calls for the ezc and DramIO\ classes in traces:

Example:

<?php
xdebug_set_filter
XDEBUG_FILTER_TRACINGXDEBUG_NAMESPACE_INCLUDE, [ """ezc""DramIO\" ] );
?>

To only perform code-coverage analysis for files in the src sub-directory:

Example:

<?php
xdebug_set_filter
XDEBUG_FILTER_CODE_COVERAGEXDEBUG_PATH_INCLUDE, [ __DIR__ "/src/" ] );
?>

xdebug_start_code_coverage( int $options = 0 ) : void #

Starts code coverage

This function starts gathering the information for code coverage. The information can be retrieved with the xdebug_get_code_coverage() function.

This function has three options, which act as a bitfield:

XDEBUG_CC_UNUSED
Enables scanning of code to figure out which line has executable code. Without this option the returned array will only have lines in them that were actually executed.
XDEBUG_CC_DEAD_CODE
Enables branch analyzes to figure out whether code can be executed.
XDEBUG_CC_BRANCH_CHECK
Enables path execution analysis.
Enabling those options make code coverage drastically slower.

You can use the options as shown in the following example.

Example:

<?php
xdebug_start_code_coverage
XDEBUG_CC_UNUSED XDEBUG_CC_DEAD_CODE );
?>

xdebug_stop_code_coverage( bool $cleanUp = true ) : void #

Stops code coverage

This function stops collecting information, the information in memory will be destroyed. If you pass 0 as an argument, then the code coverage information will not be destroyed so that you can resume the gathering of information with the xdebug_start_code_coverage() function again.