Inconsistent deserialization of Leptos' Env enum

[maeldroem]

Description

Deserialization of the Env enum (leptos_config::Env) is inconsistent depending on whether it is read from the Cargo.toml file or from the LEPTOS_ENV environment variable.

Normally, when cargo-leptos reads the Cargo.toml or if main.rs reads the same file via get_configuration, the Env is derived using env_from_str, which transforms the input as lowercase before detecting whether it is Env::PROD (allowed strings: "prod", "production") or Env::DEV (allowed strings: "dev", "development").

However, when get_configuration is used in main.rs with a valid path, the environment variable are handled by get_config_from_str instead of get_config_from_env, which is used when get_configuration is passed None.

Down the call stack, it uses serde to deserialize the values (here in get_config_from_str) from the environment variables.

Serde is strict when it comes to deserialization: it only accepts same-case values as the variants from the targetted enum, therefore it will only allow the strings "PROD" and "DEV" as valid strings. If those are not provided, running a leptos app with LEPTOS_ENV set to something that would normally be valid (e.g. lowercase "prod") will result in the following panic message:

thread 'main' (180029) panicked at src/main.rs:11:54:
called `Result::unwrap()` on an `Err` value: ConfigError("enum Env does not have variant constructor prod for key `env`")

Leptos Dependencies

leptos = { version = "0.8" }
leptos_axum = { version = "0.8", optional = true }
axum = { version = "0.8.0", optional = true }

Bug reproduction steps

1. Clone start-axum
2. Change line 11 of main.rs to be let conf = get_configuration(Some("Cargo.toml")).unwrap();
3. Run LEPTOS_ENV=prod cargo leptos serve
4. Observe panic message in console

Also possible with LEPTOS_ENV=production, LEPTOS_ENV=dev, etc. as described in the description.

Next steps

I would like to make a PR, but I also want to know which approach should be used. Should the implementation of serde::Deserialize be changed on the Env enum? Should the config sources be layered in a different way? (super unfamiliar with the crate config, so I'd appreciate if somebody knew if and how this could be done so we just replace the env layer with a call to get_config_from_env() or something of the kind).

I also don't mind if somebody wants to do the PR themselves, as this could be a good first issue for somebody looking to contribute to Leptos. (oc, i'm interested to contribute, but if somebody else wants to, I don't mind either)