src/Composer/Repository/BaseRepository.php
public function getDependents($needle, $constraint = null, $invert = false, $recurse = true, $packagesFound = null)
    {
        $needles = array_map('strtolower', (array) $needle);
        $results = array();

        // initialize the array with the needles before any recursion occurs
        if (null === $packagesFound) {
            $packagesFound = $needles;
        }

        // locate root package for use below
        $rootPackage = null;
        foreach ($this->getPackages() as $package) {
            if ($package instanceof RootPackageInterface) {
                $rootPackage = $package;
                break;
            }
        }

        // Loop over all currently installed packages.
        foreach ($this->getPackages() as $package) {
            $links = $package->getRequires();

            // each loop needs its own "tree" as we want to show the complete dependent set of every needle
            // without warning all the time about finding circular deps
            $packagesInTree = $packagesFound;

            // Replacements are considered valid reasons for a package to be installed during forward resolution
            if (!$invert) {
                $links += $package->getReplaces();
            }

            // Require-dev is only relevant for the root package
            if ($package instanceof RootPackageInterface) {
                $links += $package->getDevRequires();
            }

            // Cross-reference all discovered links to the needles
            foreach ($links as $link) {
                foreach ($needles as $needle) {
                    if ($link->getTarget() === $needle) {
                        if ($constraint === null || ($link->getConstraint()->matches($constraint) === !$invert)) {
                            // already displayed this node's dependencies, cutting short
                            if (in_array($link->getSource(), $packagesInTree)) {
                                $results[$link->getSource()] = array($package, $link, false);
                                continue;
                            }
                            $packagesInTree[] = $link->getSource();
                            $dependents = $recurse ? $this->getDependents($link->getSource(), null, false, true, $packagesInTree) : array();
                            $results[$link->getSource()] = array($package, $link, $dependents);
                        }
                    }
                }
            }

            // When inverting, we need to check for conflicts of the needles against installed packages
            if ($invert && in_array($package->getName(), $needles)) {
                foreach ($package->getConflicts() as $link) {
                    foreach ($this->findPackages($link->getTarget()) as $pkg) {
                        $version = new Constraint('=', $pkg->getVersion());
                        if ($link->getConstraint()->matches($version) === $invert) {
                            $results[] = array($package, $link, false);
                        }
                    }
                }
            }

            // When inverting, we need to check for conflicts of the needles' requirements against installed packages
            if ($invert && $constraint && in_array($package->getName(), $needles) && $constraint->matches(new Constraint('=', $package->getVersion()))) {
                foreach ($package->getRequires() as $link) {
                    if (preg_match(PlatformRepository::PLATFORM_PACKAGE_REGEX, $link->getTarget())) {
                        if ($this->findPackage($link->getTarget(), $link->getConstraint())) {
                            continue;
                        }

                        $platformPkg = $this->findPackage($link->getTarget(), '*');
                        $description = $platformPkg ? 'but '.$platformPkg->getPrettyVersion().' is installed' : 'but it is missing';
                        $results[] = array($package, new Link($package->getName(), $link->getTarget(), null, 'requires', $link->getPrettyConstraint().' '.$description), false);

                        continue;
                    }

                    foreach ($this->getPackages() as $pkg) {
                        if (!in_array($link->getTarget(), $pkg->getNames())) {
                            continue;
                        }

                        $version = new Constraint('=', $pkg->getVersion());
                        if (!$link->getConstraint()->matches($version)) {
                            // if we have a root package (we should but can not guarantee..) we show
                            // the root requires as well to perhaps allow to find an issue there
                            if ($rootPackage) {
                                foreach (array_merge($rootPackage->getRequires(), $rootPackage->getDevRequires()) as $rootReq) {
                                    if (in_array($rootReq->getTarget(), $pkg->getNames()) && !$rootReq->getConstraint()->matches($link->getConstraint())) {
                                        $results[] = array($package, $link, false);
                                        $results[] = array($rootPackage, $rootReq, false);
                                        continue 3;
                                    }
                                }
                                $results[] = array($package, $link, false);
                                $results[] = array($rootPackage, new Link($rootPackage->getName(), $link->getTarget(), null, 'does not require', 'but ' . $pkg->getPrettyVersion() . ' is installed'), false);
                            } else {
                                // no root so let's just print whatever we found
                                $results[] = array($package, $link, false);
                            }
                        }

                        continue 2;
                    }
                }
            }
        }

        ksort($results);

        return $results;
    }
public function getDependents($needle, $constraint = null, $invert = false, $recurse = true, $packagesFound = null)
    {
        $needles = array_map('strtolower', (array) $needle);
        $results = array();

        // initialize the array with the needles before any recursion occurs
        if (null === $packagesFound) {
            $packagesFound = $needles;
        }

        // locate root package for use below
        $rootPackage = null;
        foreach ($this->getPackages() as $package) {
            if ($package instanceof RootPackageInterface) {
                $rootPackage = $package;
                break;
            }
        }

        // Loop over all currently installed packages.
        foreach ($this->getPackages() as $package) {
            $links = $package->getRequires();

            // each loop needs its own "tree" as we want to show the complete dependent set of every needle
            // without warning all the time about finding circular deps
            $packagesInTree = $packagesFound;

            // Replacements are considered valid reasons for a package to be installed during forward resolution
            if (!$invert) {
                $links += $package->getReplaces();
            }

            // Require-dev is only relevant for the root package
            if ($package instanceof RootPackageInterface) {
                $links += $package->getDevRequires();
            }

            // Cross-reference all discovered links to the needles
            foreach ($links as $link) {
                foreach ($needles as $needle) {
                    if ($link->getTarget() === $needle) {
                        if ($constraint === null || ($link->getConstraint()->matches($constraint) === !$invert)) {
                            // already displayed this node's dependencies, cutting short
                            if (in_array($link->getSource(), $packagesInTree)) {
                                $results[$link->getSource()] = array($package, $link, false);
                                continue;
                            }
                            $packagesInTree[] = $link->getSource();
                            $dependents = $recurse ? $this->getDependents($link->getSource(), null, false, true, $packagesInTree) : array();
                            $results[$link->getSource()] = array($package, $link, $dependents);
                        }
                    }
                }
            }

            // When inverting, we need to check for conflicts of the needles against installed packages
            if ($invert && in_array($package->getName(), $needles)) {
                foreach ($package->getConflicts() as $link) {
                    foreach ($this->findPackages($link->getTarget()) as $pkg) {
                        $version = new Constraint('=', $pkg->getVersion());
                        if ($link->getConstraint()->matches($version) === $invert) {
                            $results[] = array($package, $link, false);
                        }
                    }
                }
            }

            // When inverting, we need to check for conflicts of the needles' requirements against installed packages
            if ($invert && $constraint && in_array($package->getName(), $needles) && $constraint->matches(new Constraint('=', $package->getVersion()))) {
                foreach ($package->getRequires() as $link) {
                    if (preg_match(PlatformRepository::PLATFORM_PACKAGE_REGEX, $link->getTarget())) {
                        if ($this->findPackage($link->getTarget(), $link->getConstraint())) {
                            continue;
                        }

                        $platformPkg = $this->findPackage($link->getTarget(), '*');
                        $description = $platformPkg ? 'but '.$platformPkg->getPrettyVersion().' is installed' : 'but it is missing';
                        $results[] = array($package, new Link($package->getName(), $link->getTarget(), null, 'requires', $link->getPrettyConstraint().' '.$description), false);

                        continue;
                    }

                    foreach ($this->getPackages() as $pkg) {
                        if (!in_array($link->getTarget(), $pkg->getNames())) {
                            continue;
                        }

                        $version = new Constraint('=', $pkg->getVersion());
                        if (!$link->getConstraint()->matches($version)) {
                            // if we have a root package (we should but can not guarantee..) we show
                            // the root requires as well to perhaps allow to find an issue there
                            if ($rootPackage) {
                                foreach (array_merge($rootPackage->getRequires(), $rootPackage->getDevRequires()) as $rootReq) {
                                    if (in_array($rootReq->getTarget(), $pkg->getNames()) && !$rootReq->getConstraint()->matches($link->getConstraint())) {
                                        $results[] = array($package, $link, false);
                                        $results[] = array($rootPackage, $rootReq, false);
                                        continue 3;
                                    }
                                }
                                $results[] = array($package, $link, false);
                                $results[] = array($rootPackage, new Link($rootPackage->getName(), $link->getTarget(), null, 'does not require', 'but ' . $pkg->getPrettyVersion() . ' is installed'), false);
                            } else {
                                // no root so let's just print whatever we found
                                $results[] = array($package, $link, false);
                            }
                        }

                        continue 2;
                    }
                }
            }
        }

        ksort($results);

        return $results;
    }
Returns a list of links causing the requested needle packages to be installed, as an associative array with the
dependent's name as key, and an array containing in order the PackageInterface and Link describing the relationship
as values. If recursive lookup was requested a third value is returned containing an identically formed array up
to the root package. That third value will be false in case a circular recursion was detected.

@param  string|string[]          $needle        The package name(s) to inspect.
@param  ConstraintInterface|null $constraint    Optional constraint to filter by.
@param  bool                     $invert        Whether to invert matches to discover reasons for the package *NOT* to be installed.
@param  bool                     $recurse       Whether to recursively expand the requirement tree up to the root package.
@param  string[]                 $packagesFound Used internally when recurring
@return array                    An associative array of arrays as described above.