serde-with-expand-env

Parse environment variables in serde crate using deserialize_with.

Example:

```rust use std::env; use serdejson; use serde::Deserialize; use serdewithexpandenv::withexpandenvs;

[derive(Deserialize, Debug)]

struct Test { #[serde(deserializewith="withexpandenvs")] number: usize, #[serde(deserializewith="withexpandenvs")] string: String, #[serde(deserializewith="withexpand_envs")] default: usize, }

fn main() { let serialized = r#"{"number": "$NUMBER", "string": "my string: $STRING", "default": "${DEFAULT:-42}" }"#;

// No envs set will fail with enviroment variable not found
assert_eq!(serde_json::from_str::<Test>(&serialized).is_err(), true);

env::set_var("NUMBER", "42");
env::set_var("STRING", "hacker");
let deserialized: Test = serde_json::from_str(&serialized).unwrap();

assert_eq!(deserialized.number, 42);
assert_eq!(deserialized.string, "my string: hacker");
assert_eq!(deserialized.default, 42);

env::set_var("DEFAULT", "4200");
let deserialized: Test = serde_json::from_str(&serialized).unwrap();
assert_eq!(deserialized.default, 4200);

// Invalid number
env::set_var("NUMBER", "cuarentaydos");
env::set_var("STRING", "42");
assert_eq!(serde_json::from_str::<Test>(&serialized).is_err(), true);

} ```

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