Default env name

CHANGELOG.md

@@ -1,3 +1,7 @@
+#### Unreleased
+* [breaking] Nested config fields now needs to be marked with #[envconfig(nested = true)]
+* Environment variable can be automatically derived from a field name (e.g. `db_host` will be tried to loaded from `DB_HOST` env var)
+
 #### v0.9.1 - 2019-10-09
 * Get rid of thiserror dependency
 

envconfig/src/error.rs

@@ -21,6 +21,6 @@ impl fmt::Display for Error {
 
 impl StdError for Error {
     fn source(&self) -> Option<&(dyn StdError + 'static)> {
-        return None;
+        None
     }
 }

envconfig/src/lib.rs

@@ -20,18 +20,16 @@
 //!     pub http_port: u16,
 //! }
 //!
-//! fn main() {
-//!     // We assume that those environment variables are set somewhere outside
-//!     env::set_var("DB_HOST", "localhost");
-//!     env::set_var("DB_PORT", "5432");
+//! // We assume that those environment variables are set somewhere outside
+//! env::set_var("DB_HOST", "localhost");
+//! env::set_var("DB_PORT", "5432");
 //!
-//!     // Initialize config from environment variables
-//!     let config = Config::init().unwrap();
+//! // Initialize config from environment variables
+//! let config = Config::init().unwrap();
 //!
-//!     assert_eq!(config.db_host, "localhost");
-//!     assert_eq!(config.db_port, Some(5432));
-//!     assert_eq!(config.http_port, 8080);
-//! }
+//! assert_eq!(config.db_host, "localhost");
+//! assert_eq!(config.db_port, Some(5432));
+//! assert_eq!(config.http_port, 8080);
 //! ```
 //!
 //! The library uses `std::str::FromStr` trait to convert environment variables into custom

envconfig_derive/src/lib.rs

@@ -60,19 +60,46 @@ fn gen_field_assign(field: &Field) -> proc_macro2::TokenStream {
     let attr = fetch_envconfig_attr_from_field(field);
 
     if let Some(attr) = attr {
+        // if #[envconfig(...)] is there
         let list = fetch_list_from_attr(field, attr);
-        let from_value = find_item_in_list_or_panic(field, &list, "from");
+
+        // If nested attribute is present
+        let nested_value_opt = find_item_in_list(field, &list, "nested");
+        if nested_value_opt.is_some() {
+            return gen_field_assign_for_struct_type(field);
+        }
+
         let opt_default = find_item_in_list(field, &list, "default");
 
-        let field_type = &field.ty;
+        let from_opt = find_item_in_list(field, &list, "from");
+        let env_var = match from_opt {
+            Some(v) => quote! { #v },
+            None => field_to_env_var(field),
+        };
 
-        if to_s(field_type).starts_with("Option ") {
-            gen_field_assign_for_optional_type(field, from_value, opt_default)
-        } else {
-            gen_field_assign_for_non_optional_type(field, from_value, opt_default)
-        }
+        geen(field, env_var, opt_default)
+    } else {
+        // if #[envconfig(...)] is not present
+        let env_var = field_to_env_var(field);
+        geen(field, env_var, None)
+    }
+}
+
+fn field_to_env_var(field: &Field) -> proc_macro2::TokenStream {
+    let field_name = field.clone().ident.unwrap().to_string().to_uppercase();
+    quote! { #field_name }
+}
+
+fn geen(
+    field: &Field,
+    from: proc_macro2::TokenStream,
+    opt_default: Option<&Lit>,
+) -> proc_macro2::TokenStream {
+    let field_type = &field.ty;
+    if to_s(field_type).starts_with("Option ") {
+        gen_field_assign_for_optional_type(field, from, opt_default)
     } else {
-        gen_field_assign_for_struct_type(field)
+        gen_field_assign_for_non_optional_type(field, from, opt_default)
     }
 }
 
@@ -90,7 +117,7 @@ fn gen_field_assign_for_struct_type(field: &Field) -> proc_macro2::TokenStream {
 
 fn gen_field_assign_for_optional_type(
     field: &Field,
-    from: &Lit,
+    from: proc_macro2::TokenStream,
     opt_default: Option<&Lit>,
 ) -> proc_macro2::TokenStream {
     let ident = &field.ident;
@@ -106,7 +133,7 @@ fn gen_field_assign_for_optional_type(
 
 fn gen_field_assign_for_non_optional_type(
     field: &Field,
-    from: &Lit,
+    from: proc_macro2::TokenStream,
     opt_default: Option<&Lit>,
 ) -> proc_macro2::TokenStream {
     let ident = &field.ident;
@@ -148,20 +175,6 @@ fn fetch_list_from_attr(field: &Field, attr: &Attribute) -> Punctuated<NestedMet
     }
 }
 
-fn find_item_in_list_or_panic<'l, 'n>(
-    field: &Field,
-    list: &'l Punctuated<NestedMeta, Comma>,
-    item_name: &'n str,
-) -> &'l Lit {
-    find_item_in_list(field, list, item_name).unwrap_or_else(|| {
-        panic!(
-            "`envconfig` attribute on field `{}` must contain `{}` item",
-            field_name(field),
-            item_name
-        )
-    })
-}
-
 fn find_item_in_list<'l, 'n>(
     field: &Field,
     list: &'l Punctuated<NestedMeta, Comma>,

test_suite/src/main.rs

@@ -4,7 +4,6 @@ use envconfig::Envconfig;
 
 #[derive(Envconfig)]
 pub struct Config {
-    #[envconfig(from = "PORT")]
     pub port: u16,
 
     #[envconfig(from = "HOST")]

test_suite/tests/default_env_var.rs

@@ -0,0 +1,36 @@
+extern crate envconfig;
+
+use envconfig::{Envconfig, Error};
+use std::env;
+
+#[derive(Envconfig)]
+pub struct Config {
+    pub db_host: String,
+    pub db_port: Option<u16>,
+}
+
+fn setup() {
+    env::remove_var("DB_HOST");
+    env::remove_var("DB_PORT");
+}
+
+#[test]
+fn test_derives_env_variable_names_automatically() {
+    setup();
+
+    env::set_var("DB_HOST", "db.example.com");
+    env::set_var("DB_PORT", "5050");
+
+    let config = Config::init_from_env().unwrap();
+    assert_eq!(config.db_host, "db.example.com");
+    assert_eq!(config.db_port, Some(5050));
+}
+
+#[test]
+fn test_var_is_missing() {
+    setup();
+
+    let err = Config::init_from_env().err().unwrap();
+    let expected_err = Error::EnvVarMissing { name: "DB_HOST" };
+    assert_eq!(err, expected_err);
+}

test_suite/tests/nesting.rs → test_suite/tests/nested.rs

@@ -14,12 +14,16 @@ pub struct DBConfig {
 
 #[derive(Envconfig)]
 pub struct Config {
+    #[envconfig(nested = true)]
     pub db: DBConfig,
 }
 
 #[derive(Envconfig)]
 pub struct ConfigDouble {
+    #[envconfig(nested = true)]
     pub db1: DBConfig,
+
+    #[envconfig(nested = true)]
     pub db2: DBConfig,
 }