Provide SSR mode in conditional config

[Kingdutch]

Description

As a developer I want to be able to adjust my Vite config based on whether I'm building the client bundle or the SSR bundle.

Suggested solution

Extend the conditional config to also provide the SSR mode (the documentation currently encourages to set this as a command line flag so the info should be available at config build time?)

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[bluwy]

The SSR config is currently shared with the main config as they can work together. Can you show a usecase where this feature is needed?

[Kingdutch]

One use-case was to make it easier to work around e.g. #8836

Vite SSR causes vite build to be run twice for two different purposes. There's currently no good way to discern between the two when building a config, adding the ssr flag would help.

Another scenario can be seen internally in Vite 2 where the inlineDynamicImports was set to TRUE only for SSR builds. Users of Vite may want to make similar configuration changes or perhaps change the plugins that they run (e.g. run some plugin only for SSR or only for the client bundle).

[patak-dev]

We discussed at one point in a team meeting about this option, PR implementing it here:

• feat: ssrBuild flag in config env #8863