minor symfony#60808 [HttpFoundation] Handle error when expected directory is a file (afiestas)

This PR was merged into the 7.4 branch.

Discussion
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[HttpFoundation] Handle error when expected directory is a file

| Q             | A
| ------------- | ---
| Branch?       | 7.4
| Bug fix?      | kinda
| New feature?  | no
| Deprecations? | no
| License       | MIT

[HttpFoundation] In File::getTargetFile the directory is recursively created if it does not exists. If directory creation fails a FileException is thrown.

This commit improves error clarity by adding  a new FileException for the relatively common case where the path exists but instead of a directory it is a file.

Since errors from `@mkdir` are being suppressed we don't really know why the operation has failed.

There are many ways of doing this depending on the warranties that Symfony gives on retro-compatibility for the thrown exceptions. I Haven't been able to find documentation about that so I've decided to open a PR with the easiest to read change to get the conversation started.

Depending on your preferences we could:

- Manage the mkdir errors similar to how  is done in [Filesystem::box](https://github.com/symfony/filesystem/blob/7.3/Filesystem.php#L753). Perhaps add that extra information after the current message like "Unable to create the %s directory (error goes here).
- Same thing as the PR but as part of the if/elseif block.
- Move the is_file check within the error handling code path to prevent another I/O operation (so we do not affect the happy path)
- Others?

Also since I haven't been able to find the compatibility guidelines I'm doing this to the 7.4 branch.

Commits
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b1a9d58 [HttpFoundation] Handle error when directory is a file

Author: nicolas-grekas

src/Symfony/Component/HttpFoundation/File/File.php

@@ -114,10 +114,11 @@ public function getContent(): string
 
     protected function getTargetFile(string $directory, ?string $name = null): self
     {
-        if (!is_dir($directory)) {
-            if (false === @mkdir($directory, 0o777, true) && !is_dir($directory)) {
-                throw new FileException(\sprintf('Unable to create the "%s" directory.', $directory));
+        if (!is_dir($directory) && !@mkdir($directory, 0o777, true) && !is_dir($directory)) {
+            if (is_file($directory)) {
+                throw new FileException(\sprintf('Unable to create the "%s" directory: a similarly-named file exists.', $directory));
             }
+            throw new FileException(\sprintf('Unable to create the "%s" directory.', $directory));
         } elseif (!is_writable($directory)) {
             throw new FileException(\sprintf('Unable to write in the "%s" directory.', $directory));
         }