Ignore null value in comparison validators
Fix empty process argument escaping on Windows
merged branch helmer/processutils_patch (PR #8691)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #8691).

Discussion
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[Process] Fix empty process argument escaping on Windows

PR #6796 introduced a regression on Windows platform (symfony 2.3.0+), forgetting to escape explicitly requested empty arguments to ```""``` and return an empty string instead.

This behaviour is imo unintended and renders the component unusable for corner-cases, where you indeed want to specify an empty argument. One good example of this is assetic and compass, which (up to this day) relies on existence of empty parameters on windows.

Some panic and related links on the topic:
https://github.com/kriswallsmith/assetic/issues/455
https://github.com/kriswallsmith/assetic/pull/471
http://stackoverflow.com/questions/17001517/symfony2-3-with-compass ([diff](http://marker.to/KrctHM))
http://stackoverflow.com/questions/17135219/symfony-2-compass-with-assetic-on-windows-xp

Please consider a merge to master and a backport to 2.3.x

Commits
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a91537a Fix empty process argument escaping on Windows
merged branch EmmanuelVella/validators (PR #8577)

This PR was merged into the 2.3 branch.

Discussion
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Validators

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

This PR avoid comparison validators to be executed if the compared value is null.

Commits
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48338fc Ignore null value in comparison validators
Make sure ContextErrorException is loaded during compile time errors
merged branch ShiraNai7/master (PR #8688)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #8688).

Discussion
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[Debug] Make sure ContextErrorException is loaded during compile time errors

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | no
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

### Description

When the `ErrorHandler->handle()` attempts to throw a `ContextErrorException` the script might die with a Fatal Error because the class is not found.

    FatalErrorException: Error: Class 'Symfony\Component\Debug\Exception\ContextErrorException' not found in ...

That effectively hides the original error and causes confusion.

### Cause

The cause is a bug/limitation of PHP that makes class autoloading completely inactive during "compiling".

Relevant PHP source code in `zend_execute_API.c`:

    /* The compiler is not-reentrant. Make sure we __autoload() only during run-time
     * (doesn't impact functionality of __autoload()
    */
    if (!use_autoload || zend_is_compiling(TSRMLS_C)) {

#### More information about the PHP bug/limitation:
- https://bugs.php.net/bug.php?id=65322
- many duplicates/relevant: https://www.google.com/search?btnG=1&pws=0&q=site%3Abugs.php.net+autoload+error+handling

### The fix

The most simple way to fix this is to manually ensure that `ContextErrorException` is loaded and if not, load it. This is what I did.

Another way is to detect if autoloading is available (possible by prepending a temporary autoloader) and act accordingly (how?).

### The test

I also added a test case that would fail with a fatal error if the error handler does not successfully throw an exception in case of a compile time error. But I'm not sure if this is the best way or if there should be a test case at all.

###

Commits
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b0082ab [Debug] Make sure ContextErrorException is loaded during compile time errors
Use strstr instead of strpos
merged branch larowlan/master (PR #8081)

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #8081).

Discussion
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Use strstr instead of strpos in ClassLoader (4% perf improvement)

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | [
| License       | MIT
| Doc PR        |

Using ClassLoader in Drupal 8, using strstr instead of strpos nets 4% perf improvement.
XHPROF diff https://dl.dropboxusercontent.com/u/10201421/diff.html

Commits
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25d7b90 [ClassLoader] Use strstr instead of strpos
[Form] Moved auto_initialize option to the BaseType
merged branch jakzal/2.3-form-button-fix (PR #8349)

This PR was squashed before being merged into the 2.3 branch (closes #8349).

Discussion
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[Form] Moved auto_initialize option to the BaseType

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8162
| License       | MIT
| Doc PR        | -

I'm not fully confident in this change, so let someone review it before mergin please. My thinking was - since "auto_initialized" option is always passed to a form factory, it should be required by the base type.

Commits
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6ed0fdf [Form] Moved auto_initialize option to the BaseType
[FrameworkBundle] made code more generic
Fix internal sub-request creation

Fixes the creation of internal sub-request in case of disabled trusted
client-ip header
merged branch lazyhammer/fix-inline-fragment (PR #7893)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #7893).

Discussion
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[HttpKernel] Fix internal sub-request creation

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Fixes the creation of internal sub-request in case of disabled trusted
client-ip header.

Commits
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85d5413 [HttpKernel] Fix internal sub-request creation
Created stopwatch tag
fixed CS
removed unneeded safeguard as it's already done during compilation
removed code that prevents the stopwatch to work properly
change the stopwatch argument to be any valid expression
[TwigBridge] Prevent code extension to display warning
[Process] Fix Process::checkTimeout docblock