feat(dotenv): Adding support for dotenv files

Cargo.toml

@@ -127,6 +127,7 @@ yaml = ["yaml-rust2"]
 ini = ["rust-ini"]
 json5 = ["json5_rs", "dep:serde-untagged"]
 corn = ["dep:corn"]
+dotenv = ["dep:dotenvy"]
 convert-case = ["convert_case"]
 preserve_order = ["indexmap", "toml?/preserve_order", "serde_json?/preserve_order", "ron?/indexmap"]
 async = ["async-trait"]
@@ -143,6 +144,7 @@ rust-ini = { version = "0.21.3", optional = true }
 ron = { version = "0.8.1", optional = true }
 json5_rs = { version = "0.4.1", optional = true, package = "json5" }
 corn = { version = "0.10.0", optional = true, package = "libcorn" }
+dotenvy = { version = "0.15.7", optional = true }
 indexmap = { version = "2.11.4", features = ["serde"], optional = true }
 convert_case = { version = "0.6.0", optional = true }
 pathdiff = "0.2.3"

src/file/format/dotenv.rs

@@ -0,0 +1,31 @@
+use std::error::Error;
+use std::io::Cursor;
+
+use dotenvy::from_read_iter;
+
+use crate::map::Map;
+use crate::value::{Value, ValueKind};
+
+pub(crate) fn parse(
+    uri: Option<&String>,
+    text: &str,
+) -> Result<Map<String, Value>, Box<dyn Error + Send + Sync>> {
+    let mut map: Map<String, Value> = Map::new();
+    let cursor = Cursor::new(text);
+
+    for item in from_read_iter(cursor) {
+        let (key, mut value) = item?;
+
+        let os_env_vars = std::env::vars_os();
+        for (os_string_key, os_string_value) in os_env_vars {
+            let string_key: String = os_string_key.to_string_lossy().into_owned();
+            if string_key == key {
+                value = os_string_value.to_string_lossy().into_owned();
+            }
+        }
+
+        map.insert(key, Value::new(uri, ValueKind::String(value)));
+    }
+
+    Ok(map)
+}

src/file/format/mod.rs

@@ -24,6 +24,9 @@ mod json5;
 #[cfg(feature = "corn")]
 mod corn;
 
+#[cfg(feature = "dotenv")]
+mod dotenv;
+
 /// File formats provided by the library.
 ///
 /// Although it is possible to define custom formats using [`Format`] trait it is recommended to use `FileFormat` if possible.
@@ -57,6 +60,10 @@ pub enum FileFormat {
     /// Corn (parsed with `libcorn`)
     #[cfg(feature = "corn")]
     Corn,
+
+    /// Dotenv (parsed with `dotenvy`)
+    #[cfg(feature = "dotenv")]
+    Dotenv,
 }
 
 impl FileFormat {
@@ -76,6 +83,8 @@ impl FileFormat {
             FileFormat::Json5,
             #[cfg(feature = "corn")]
             FileFormat::Corn,
+            #[cfg(feature = "dotenv")]
+            FileFormat::Dotenv,
         ]
     }
 
@@ -102,13 +111,17 @@ impl FileFormat {
             #[cfg(feature = "corn")]
             FileFormat::Corn => &["corn"],
 
+            #[cfg(feature = "dotenv")]
+            FileFormat::Dotenv => &["dotenv"],
+
             #[cfg(all(
                 not(feature = "toml"),
                 not(feature = "json"),
                 not(feature = "yaml"),
                 not(feature = "ini"),
                 not(feature = "ron"),
                 not(feature = "json5"),
+                not(feature = "dotenv"),
             ))]
             _ => unreachable!("No features are enabled, this library won't work without features"),
         }
@@ -141,13 +154,17 @@ impl FileFormat {
             #[cfg(feature = "corn")]
             FileFormat::Corn => corn::parse(uri, text),
 
+            #[cfg(feature = "dotenv")]
+            FileFormat::Dotenv => dotenv::parse(uri, text),
+
             #[cfg(all(
                 not(feature = "toml"),
                 not(feature = "json"),
                 not(feature = "yaml"),
                 not(feature = "ini"),
                 not(feature = "ron"),
                 not(feature = "json5"),
+                not(feature = "dotenv"),
             ))]
             _ => unreachable!("No features are enabled, this library won't work without features"),
         }

tests/testsuite/file_dotenv.rs

@@ -0,0 +1,78 @@
+#![cfg(feature = "dotenv")]
+
+use config::Config;
+use std::env;
+
+#[test]
+fn basic_dotenv() {
+    let s = Config::builder()
+        .add_source(config::File::from_str(
+            r#"
+                FOO=bar
+                BAZ=qux
+            "#,
+            config::FileFormat::Dotenv,
+        ))
+        .build()
+        .unwrap();
+
+    assert_eq!(s.get::<String>("FOO").unwrap(), "bar");
+    assert_eq!(s.get::<String>("BAZ").unwrap(), "qux");
+}
+
+#[test]
+fn optional_variables() {
+    let s = Config::builder()
+        .add_source(config::File::from_str(
+            r#"
+                FOO=bar
+                BAZ=${FOO}
+                BAR=${UNDEFINED:-}
+            "#,
+            config::FileFormat::Dotenv,
+        ))
+        .build()
+        .unwrap();
+
+    assert_eq!(s.get::<String>("BAR").unwrap(), "");
+}
+
+#[test]
+fn multiple_files() {
+    let s = Config::builder()
+        .add_source(config::File::from_str(
+            r#"
+                FOO=bar
+            "#,
+            config::FileFormat::Dotenv,
+        ))
+        .add_source(config::File::from_str(
+            r#"
+                BAZ=qux
+            "#,
+            config::FileFormat::Dotenv,
+        ))
+        .build()
+        .unwrap();
+
+    assert_eq!(s.get::<String>("FOO").unwrap(), "bar");
+    assert_eq!(s.get::<String>("BAZ").unwrap(), "qux");
+}
+
+#[test]
+fn environment_overrides() {
+    env::set_var("FOOBAR", "env_value");
+
+    let s = Config::builder()
+        .add_source(config::File::from_str(
+            r#"
+                FOOBAR=file_value
+            "#,
+            config::FileFormat::Dotenv,
+        ))
+        .add_source(config::Environment::with_prefix("env").separator("_"))
+        .build()
+        .unwrap();
+
+    assert_eq!(s.get::<String>("FOOBAR").unwrap(), "env_value");
+}

tests/testsuite/main.rs

@@ -9,6 +9,7 @@ pub mod env;
 pub mod errors;
 pub mod file;
 pub mod file_corn;
+pub mod file_dotenv;
 pub mod file_ini;
 pub mod file_json;
 pub mod file_json5;