framework/base/View.php
protected function findViewFile($view, $context = null)
    {
        if (strncmp($view, '@', 1) === 0) {
            // e.g. "@app/views/main"
            $file = Yii::getAlias($view);
        } elseif (strncmp($view, '//', 2) === 0) {
            // e.g. "//layouts/main"
            $file = Yii::$app->getViewPath() . DIRECTORY_SEPARATOR . ltrim($view, '/');
        } elseif (strncmp($view, '/', 1) === 0) {
            // e.g. "/site/index"
            if (Yii::$app->controller !== null) {
                $file = Yii::$app->controller->module->getViewPath() . DIRECTORY_SEPARATOR . ltrim($view, '/');
            } else {
                throw new InvalidCallException("Unable to locate view file for view '$view': no active controller.");
            }
        } elseif ($context instanceof ViewContextInterface) {
            $file = $context->getViewPath() . DIRECTORY_SEPARATOR . $view;
        } elseif (($currentViewFile = $this->getRequestedViewFile()) !== false) {
            $file = dirname($currentViewFile) . DIRECTORY_SEPARATOR . $view;
        } else {
            throw new InvalidCallException("Unable to resolve view file for view '$view': no active view context.");
        }

        if (pathinfo($file, PATHINFO_EXTENSION) !== '') {
            return $file;
        }
        $path = $file . '.' . $this->defaultExtension;
        if ($this->defaultExtension !== 'php' && !is_file($path)) {
            $path = $file . '.php';
        }

        return $path;
    }
protected function findViewFile($view, $context = null)
    {
        if (strncmp($view, '@', 1) === 0) {
            // e.g. "@app/views/main"
            $file = Yii::getAlias($view);
        } elseif (strncmp($view, '//', 2) === 0) {
            // e.g. "//layouts/main"
            $file = Yii::$app->getViewPath() . DIRECTORY_SEPARATOR . ltrim($view, '/');
        } elseif (strncmp($view, '/', 1) === 0) {
            // e.g. "/site/index"
            if (Yii::$app->controller !== null) {
                $file = Yii::$app->controller->module->getViewPath() . DIRECTORY_SEPARATOR . ltrim($view, '/');
            } else {
                throw new InvalidCallException("Unable to locate view file for view '$view': no active controller.");
            }
        } elseif ($context instanceof ViewContextInterface) {
            $file = $context->getViewPath() . DIRECTORY_SEPARATOR . $view;
        } elseif (($currentViewFile = $this->getRequestedViewFile()) !== false) {
            $file = dirname($currentViewFile) . DIRECTORY_SEPARATOR . $view;
        } else {
            throw new InvalidCallException("Unable to resolve view file for view '$view': no active view context.");
        }

        if (pathinfo($file, PATHINFO_EXTENSION) !== '') {
            return $file;
        }
        $path = $file . '.' . $this->defaultExtension;
        if ($this->defaultExtension !== 'php' && !is_file($path)) {
            $path = $file . '.php';
        }

        return $path;
    }
Finds the view file based on the given view name.
@param string $view the view name or the [path alias](guide:concept-aliases) of the view file. Please refer to [[render()]]
on how to specify this parameter.
@param object $context the context to be assigned to the view and can later be accessed via [[context]]
in the view. If the context implements [[ViewContextInterface]], it may also be used to locate
the view file corresponding to a relative view name.
@return string the view file path. Note that the file may not exist.
@throws InvalidCallException if a relative view name is given while there is no active context to
determine the corresponding view file.