// psiBased
        (symbol.psi?.containingFile as? KtFile)?.let { ktFile ->
            with(analysisSession) {
                return ktFile.getFileSymbol()
            }
        }
        // descriptorBased
        val descriptor = symbol.containingSymbolOrSelf.getDescriptor()
        val ktFile = descriptor?.let(DescriptorToSourceUtils::getContainingFile) ?: return null
        with(analysisSession) {

## Use Case

Let's start with an example **use case** and then see how to solve it with this.

Let's imagine that you have some **machine learning models** that you want to use to handle requests. 🤖

The same models are shared among requests, so, it's not one model per request, or one per user or something similar.

     */
    private inline fun <reified T : FirCallableDeclaration> T.unwrapSubstitutionOverrideIfNeeded(): T? {
        unwrapUseSiteSubstitutionOverride()?.let { return it }

        unwrapInheritanceSubstitutionOverrideIfNeeded()?.let { return it }

        return null
    }

    /**
     * Use-site substitution override happens in situations like this:
     *
     * ```

Вот некоторые варианты, которые вы можете использовать в качестве такого прокси-сервера:

* Traefik (может обновлять сертификаты)
* Caddy (может обновлять сертификаты)
* Nginx
* HAProxy

## Let's Encrypt (центр сертификации)

До появления Let's Encrypt **сертификаты HTTPS** приходилось покупать у третьих сторон.

Процесс получения такого сертификата был трудоёмким, требовал предоставления подтверждающих документов и сертификаты стоили дорого.

            substitutor.substitute(returnType),
            receiverType?.let { substitutor.substitute(it) },
            valueParameters.map { valueParameter ->
                KtFe10VariableLikeSignature<KtValueParameterSymbol>(
                    valueParameter.symbol,
                    substitutor.substitute(valueParameter.returnType),
                    valueParameter.receiverType?.let { substitutor.substitute(it) }
                )
            }

## Testing: extended example

Now let's extend this example and add more details to see how to test different parts.

### Extended **FastAPI** app file

Let's continue with the same file structure as before:

```
.
├── app
│   ├── __init__.py
│   ├── main.py
│   └── test_main.py
```

* Nginx
* HAProxy

## Let's Encrypt

Before Let's Encrypt, these **HTTPS certificates** were sold by trusted third parties.

The process to acquire one of these certificates used to be cumbersome, require quite some paperwork and the certificates were quite expensive.

But then **<a href="https://letsencrypt.org/" class="external-link" target="_blank">Let's Encrypt</a>** was created.

    pass


@app.post("/invoices/", callbacks=invoices_callback_router.routes)
def create_invoice(invoice: Invoice, callback_url: Union[HttpUrl, None] = None):
    """
    Create an invoice.

    This will (let's imagine) let the API user (some external developer) create an
    invoice.

    And this path operation will:

    * Send the invoice to the client.
    * Collect the money from the client.

        Disposer.newDisposable().let { disposable ->
            ParsedKotlinFiles(disposable.parseKotlinFiles(sourceRoots, compilationClasspath), disposable)
        }

    private
    fun <T : Any?> withParsedKotlinSource(sourceRoots: List<File>, block: (List<KtFile>) -> T) =
        Disposer.newDisposable().use {
            parseKotlinFiles(sourceRoots, emptyList()).let(block)
        }

    private

    System.setErr(object : PrintStream(OutputStream.nullOutputStream()) {})
  }

  fun uninstall() {
    originalSystemOut.let {
      System.setOut(it)
    }
    originalSystemErr.let {
      System.setErr(it)
    }
  }