Introduce #[structopt(rename_all_env)]

src/lib.rs

@@ -475,7 +475,7 @@
 //! #[derive(StructOpt)]
 //! struct Foo {
 //!   #[structopt(short, long, env = "PARAMETER_VALUE")]
-//!   param: String
+//!   parameter_value: String
 //! }
 //! # fn main() {}
 //! ```
@@ -487,7 +487,7 @@
 //! $ cargo run -- --help
 //! ...
 //! OPTIONS:
-//!   -p, --param <param>     [env: PARAMETER_VALUE=env_value]
+//!   -p, --parameter-value <parameter-value>     [env: PARAMETER_VALUE=env_value]
 //! ```
 //!
 //! In some cases this may be undesirable, for example when being used for passing
@@ -499,11 +499,36 @@
 //! #[derive(StructOpt)]
 //! struct Foo {
 //!   #[structopt(long = "secret", env = "SECRET_VALUE", hide_env_values = true)]
-//!   param: String
+//!   secret_value: String
+//! }
+//! ```
+//!
+//! ### Auto-deriving environment variables
+//!
+//! Environment variables tend to be called after the corresponding `struct`'s field,
+//! as in example above. The field is `secret_value` and the env var is "SECRET_VALUE";
+//! the name is the same, except casing is different.
+//!
+//! It's pretty tedious and error-prone to type the same name twice,
+//! so you can ask `structopt` to do that for you.
+//!
+//! ```
+//! # use structopt::StructOpt;
+//!
+//! #[derive(StructOpt)]
+//! struct Foo {
+//!   #[structopt(long = "secret", env)]
+//!   secret_value: String
 //! }
-//! # fn main() {}
 //! ```
 //!
+//! It works just like `#[structopt(short/long)]`: if `env` is not set to some concrete
+//! value the value will be derived from the field's name. This is controlled by
+//! `#[structopt(rename_all_env)]`.
+//!
+//! `rename_all_env` works exactly as `rename_all` (including overriding)
+//! except default casing is `SCREAMING_SNAKE_CASE` instead of `kebab-case`.
+//!
 //! ## Skipping fields
 //!
 //! Sometimes you may want to add a field to your `Opt` struct that is not

structopt-derive/src/attrs.rs

@@ -73,6 +73,7 @@ pub enum Name {
 pub struct Attrs {
     name: Name,
     casing: Sp<CasingStyle>,
+    env_casing: Sp<CasingStyle>,
     methods: Vec<Method>,
     parser: Sp<Parser>,
     author: Option<Method>,
@@ -208,10 +209,16 @@ impl Name {
 }
 
 impl Attrs {
-    fn new(default_span: Span, name: Name, casing: Sp<CasingStyle>) -> Self {
+    fn new(
+        default_span: Span,
+        name: Name,
+        casing: Sp<CasingStyle>,
+        env_casing: Sp<CasingStyle>,
+    ) -> Self {
         Self {
             name,
             casing,
+            env_casing,
             methods: vec![],
             parser: Parser::default_spanned(default_span),
             about: None,
@@ -248,6 +255,13 @@ impl Attrs {
                     );
                 }
 
+                Env(ident) => {
+                    self.push_str_method(
+                        ident.into(),
+                        self.name.clone().translate(*self.env_casing).into(),
+                    );
+                }
+
                 Subcommand(ident) => {
                     let ty = Sp::call_site(Ty::Other);
                     let kind = Sp::new(Kind::Subcommand(ty), ident.span());
@@ -290,6 +304,10 @@ impl Attrs {
                     self.casing = CasingStyle::from_lit(casing_lit);
                 }
 
+                RenameAllEnv(_, casing_lit) => {
+                    self.env_casing = CasingStyle::from_lit(casing_lit);
+                }
+
                 Parse(ident, spec) => {
                     self.has_custom_parser = true;
                     self.parser = Parser::from_spec(ident, spec);
@@ -387,8 +405,9 @@ impl Attrs {
         attrs: &[Attribute],
         name: Name,
         argument_casing: Sp<CasingStyle>,
+        env_casing: Sp<CasingStyle>,
     ) -> Self {
-        let mut res = Self::new(span, name, argument_casing);
+        let mut res = Self::new(span, name, argument_casing, env_casing);
         res.push_attrs(attrs);
         res.push_doc_comment(attrs, "about");
 
@@ -406,9 +425,18 @@ impl Attrs {
         }
     }
 
-    pub fn from_field(field: &syn::Field, struct_casing: Sp<CasingStyle>) -> Self {
+    pub fn from_field(
+        field: &syn::Field,
+        struct_casing: Sp<CasingStyle>,
+        env_casing: Sp<CasingStyle>,
+    ) -> Self {
         let name = field.ident.clone().unwrap();
-        let mut res = Self::new(field.span(), Name::Derived(name.clone()), struct_casing);
+        let mut res = Self::new(
+            field.span(),
+            Name::Derived(name.clone()),
+            struct_casing,
+            env_casing,
+        );
         res.push_doc_comment(&field.attrs, "help");
         res.push_attrs(&field.attrs);
 
@@ -594,6 +622,10 @@ impl Attrs {
         self.casing.clone()
     }
 
+    pub fn env_casing(&self) -> Sp<CasingStyle> {
+        self.env_casing.clone()
+    }
+
     pub fn is_positional(&self) -> bool {
         self.methods
             .iter()

structopt-derive/src/lib.rs

@@ -33,6 +33,9 @@ use syn::{punctuated::Punctuated, spanned::Spanned, token::Comma, *};
 /// Default casing style for generated arguments.
 const DEFAULT_CASING: CasingStyle = CasingStyle::Kebab;
 
+/// Default casing style for environment variables
+const DEFAULT_ENV_CASING: CasingStyle = CasingStyle::ScreamingSnake;
+
 /// Output for the `gen_xxx()` methods were we need more than a simple stream of tokens.
 ///
 /// The output of a generation method is not only the stream of new tokens but also the attribute
@@ -60,7 +63,11 @@ fn gen_augmentation(
     parent_attribute: &Attrs,
 ) -> TokenStream {
     let mut subcmds = fields.iter().filter_map(|field| {
-        let attrs = Attrs::from_field(field, parent_attribute.casing());
+        let attrs = Attrs::from_field(
+            field,
+            parent_attribute.casing(),
+            parent_attribute.env_casing(),
+        );
         let kind = attrs.kind();
         if let Kind::Subcommand(ty) = &*kind {
             let subcmd_type = match (**ty, sub_type(&field.ty)) {
@@ -97,7 +104,11 @@ fn gen_augmentation(
     }
 
     let args = fields.iter().filter_map(|field| {
-        let attrs = Attrs::from_field(field, parent_attribute.casing());
+        let attrs = Attrs::from_field(
+            field,
+            parent_attribute.casing(),
+            parent_attribute.env_casing(),
+        );
         let kind = attrs.kind();
         match &*kind {
             Kind::Subcommand(_) | Kind::Skip(_) => None,
@@ -219,7 +230,11 @@ fn gen_augmentation(
 
 fn gen_constructor(fields: &Punctuated<Field, Comma>, parent_attribute: &Attrs) -> TokenStream {
     let fields = fields.iter().map(|field| {
-        let attrs = Attrs::from_field(field, parent_attribute.casing());
+        let attrs = Attrs::from_field(
+            field,
+            parent_attribute.casing(),
+            parent_attribute.env_casing(),
+        );
         let field_name = field.ident.as_ref().unwrap();
         let kind = attrs.kind();
         match &*kind {
@@ -361,6 +376,7 @@ fn gen_clap(attrs: &[Attribute]) -> GenOutput {
         attrs,
         Name::Assigned(LitStr::new(&name, Span::call_site())),
         Sp::call_site(DEFAULT_CASING),
+        Sp::call_site(DEFAULT_ENV_CASING),
     );
     let tokens = {
         let name = attrs.cased_name();
@@ -429,6 +445,7 @@ fn gen_augment_clap_enum(
             &variant.attrs,
             Name::Derived(variant.ident.clone()),
             parent_attribute.casing(),
+            parent_attribute.env_casing(),
         );
         let app_var = Ident::new("subcommand", Span::call_site());
         let arg_block = match variant.fields {
@@ -497,6 +514,7 @@ fn gen_from_subcommand(
             &variant.attrs,
             Name::Derived(variant.ident.clone()),
             parent_attribute.casing(),
+            parent_attribute.env_casing(),
         );
         let sub_name = attrs.cased_name();
         let variant_name = &variant.ident;

structopt-derive/src/parse.rs

@@ -30,6 +30,7 @@ pub enum StructOptAttr {
     // single-identifier attributes
     Short(Ident),
     Long(Ident),
+    Env(Ident),
     Flatten(Ident),
     Subcommand(Ident),
     NoVersion(Ident),
@@ -40,6 +41,7 @@ pub enum StructOptAttr {
 
     // ident = "string literal"
     Version(Ident, LitStr),
+    RenameAllEnv(Ident, LitStr),
     RenameAll(Ident, LitStr),
     NameLitStr(Ident, LitStr),
 
@@ -84,6 +86,7 @@ impl Parse for StructOptAttr {
 
                 match &*name_str.to_string() {
                     "rename_all" => Ok(RenameAll(name, lit)),
+                    "rename_all_env" => Ok(RenameAllEnv(name, lit)),
 
                     "version" => {
                         check_empty_lit("version");
@@ -176,6 +179,7 @@ impl Parse for StructOptAttr {
             match name_str.as_ref() {
                 "long" => Ok(Long(name)),
                 "short" => Ok(Short(name)),
+                "env" => Ok(Env(name)),
                 "flatten" => Ok(Flatten(name)),
                 "subcommand" => Ok(Subcommand(name)),
                 "no_version" => Ok(NoVersion(name)),

tests/rename_all_env.rs

@@ -0,0 +1,46 @@
+mod utils;
+
+use structopt::StructOpt;
+use utils::*;
+
+#[test]
+fn it_works() {
+    #[derive(Debug, PartialEq, StructOpt)]
+    #[structopt(rename_all_env = "kebab")]
+    struct BehaviorModel {
+        #[structopt(env)]
+        be_nice: String,
+    }
+
+    let help = get_help::<BehaviorModel>();
+    assert!(help.contains("[env: be-nice=]"));
+}
+
+#[test]
+fn default_is_screaming() {
+    #[derive(Debug, PartialEq, StructOpt)]
+    struct BehaviorModel {
+        #[structopt(env)]
+        be_nice: String,
+    }
+
+    let help = get_help::<BehaviorModel>();
+    assert!(help.contains("[env: BE_NICE=]"));
+}
+
+#[test]
+fn overridable() {
+    #[derive(Debug, PartialEq, StructOpt)]
+    #[structopt(rename_all_env = "kebab")]
+    struct BehaviorModel {
+        #[structopt(env)]
+        be_nice: String,
+
+        #[structopt(rename_all_env = "pascal", env)]
+        be_agressive: String,
+    }
+
+    let help = get_help::<BehaviorModel>();
+    assert!(help.contains("[env: be-nice=]"));
+    assert!(help.contains("[env: BeAgressive=]"));
+}