Default platform setting for multi-target applications

[ealmloff]

Feature Request

In multi-target fullstack setups like the template with fullstack enabled the Cargo.toml must have features for each platform like this:

[features]
desktop = ["dioxus/desktop"]
web = ["dioxus/web"]
mobile = ["dioxus/mobile"]

server = ["dioxus/server"]

During a web build, two binaries are built: the server with the server feature enabled and the client with the web feature enabled.

web should not be a default feature flag because that would enable the web feature during the server build. That could cause issues with user code with web-only logic gated behind that flag.

Implement Suggestion

The CLI could read from a default_platform config with either web, desktop, or mobile to determine what platform to serve if --platform argument is set

Restore the default_platform setting that was removed in #2975

[ealmloff]

There is some interaction here with the default features and rust analyzer. Whatever features we have enabled by default are used by default by rust analyzer. It sounds like the intention in #2975 was to enable a feature by default for rust analyzer. We could enable all features by default for rust analyzer and disable default features in the CLI when we serve, but it makes it more difficult to reason about what features are enabled when you build:

[features]
default = ["desktop", "web", "mobile", "server"]
desktop = ["dioxus/desktop"]
web = ["dioxus/web"]
mobile = ["dioxus/mobile"]
server = ["dioxus/server"]