This PR was squashed before being merged into the 4.1-dev branch (closes #23888).

Discussion
----------

[DI] Validate env vars in config

| Q             | A
| ------------- | ---
| Branch?       | 4.1/master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #22151, #25868
| License       | MIT
| Doc PR        | symfony/symfony-docs#8382

This PR registers the env placeholders in `Config\BaseNode` with its default value or an empty string. It doesnt request real env vars during compilation,

What it does is if a config value exactly matches a env placeholder, we validate/normalize the default value/empty string but we keep returning the env placeholder as usual. If a placeholder occurs in the middle of a string it also proceeds as usual.

The latter to me is OK as you need to expect any string value during runtime anyway,  including the empty string.

Commits
-------

2c74fbc [DI] Validate env vars in config

This PR was squashed before being merged into the 4.1-dev branch (closes #23888).

Discussion
----------

[DI] Validate env vars in config

| Q             | A
| ------------- | ---
| Branch?       | 4.1/master
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #22151, #25868
| License       | MIT
| Doc PR        | symfony/symfony-docs#8382

This PR registers the env placeholders in `Config\BaseNode` with its default value or an empty string. It doesnt request real env vars during compilation,

What it does is if a config value exactly matches a env placeholder, we validate/normalize the default value/empty string but we keep returning the env placeholder as usual. If a placeholder occurs in the middle of a string it also proceeds as usual.

The latter to me is OK as you need to expect any string value during runtime anyway,  including the empty string.

Commits
-------

2c74fbc [DI] Validate env vars in config

…guiluz)

This PR was merged into the master branch.

Discussion
----------

Document the built in env var processors

This is start at adding documentation for env var processors, e.g. `%env(int:FOO)%`

I would welcome some feedback, if this a appropriate way to go about this, I think it needs some more examples to show how its used.

It also would ideally add a description of how custom processors are added, although that might be a later request.

starts to fix #8382, #9094

Commits
-------

aed1607 Minor rewords and formatting fixes
e3fe5fe Example of customer env var processor
67227a6 Add examples for parameter processors
cd353c7 Add description of the built in envvar processors

…javiereguiluz)

This PR was merged into the 3.4 branch.

Discussion
----------

Document the built in env var processors

This is start at adding documentation for env var processors, e.g. `%env(int:FOO)%`

I would welcome some feedback, if this a appropriate way to go about this, I think it needs some more examples to show how its used.

It also would ideally add a description of how custom processors are added, although that might be a later request.

starts to fix symfony#8382, symfony#9094

Commits
-------

aed1607 Minor rewords and formatting fixes
e3fe5fe Example of customer env var processor
67227a6 Add examples for parameter processors
cd353c7 Add description of the built in envvar processors