private function determineMissingVersions($supportedPhpByTravis, $travisVersions, $constraintsComposer)
    {
        $versionParser   = new VersionParser();
        $missingVersions = array();
        foreach (array_diff($supportedPhpByTravis, $travisVersions) as $version) {
            if ('nightly' === $version) {
                continue;
            }

            // Travis only allows major.minor specification.
            $constraintsTravis = $versionParser->parseConstraints($version . '.9999999.9999999');
            if ($constraintsComposer->matches($constraintsTravis)) {
                $missingVersions[] = $version;
            }
        }

        return $missingVersions;
    }