New feature: #[structopt(external_subcommand)]

.gitignore

@@ -1,6 +1,7 @@
 target
 Cargo.lock
 *~
+expanded.rs
 
 .idea/
 .vscode/

src/lib.rs

@@ -47,6 +47,7 @@
 //! - [Skipping fields](#skipping-fields)
 //! - [Subcommands](#subcommands)
 //!     - [Optional subcommands](#optional-subcommands)
+//!     - [External subcommands](#external-subcommands)
 //! - [Flattening](#flattening)
 //! - [Custom string parsers](#custom-string-parsers)
 //!
@@ -867,6 +868,60 @@
 //! }
 //! ```
 //!
+//! ### External subcommands
+//!
+//! Sometimes you want to support not only the set of well-known subcommands
+//! but you also want to allow other, user-driven subcommands. `clap` supports
+//! this via [`AppSettings::AllowExternalSubcommands`].
+//!
+//! `structopt` provides it's own dedicated syntax for that:
+//!
+//! ```
+//! # use structopt::StructOpt;
+//! #[derive(Debug, PartialEq, StructOpt)]
+//! struct Opt {
+//!     #[structopt(subcommand)]
+//!     sub: Subcommands,
+//! }
+//!
+//! #[derive(Debug, PartialEq, StructOpt)]
+//! enum Subcommands {
+//!     // normal subcommand
+//!     Add,
+//!
+//!     // `external_subcommand` tells structopt to put
+//!     // all the extra arguments into this Vec
+//!     #[structopt(external_subcommand)]
+//!     Other(Vec<String>),
+//! }
+//!
+//! // normal subcommand
+//! assert_eq!(
+//!     Opt::from_iter(&["test", "add"]),
+//!     Opt {
+//!         sub: Subcommands::Add
+//!     }
+//! );
+//!
+//! assert_eq!(
+//!     Opt::from_iter(&["test", "git", "status"]),
+//!     Opt {
+//!         sub: Subcommands::Other(vec!["git".into(), "status".into()])
+//!     }
+//! );
+//!
+//! // Please note that if you'd wanted to allow "no subcommands at all" case
+//! // you should have used `sub: Option<Subcommands>` above
+//! assert!(Opt::from_iter_safe(&["test"]).is_err());
+//! ```
+//!
+//! In other words, you just add an extra tuple variant marked with
+//! `#[structopt(subcommand)]`, and its type must be either
+//! `Vec<String>` or `Vec<OsString>`. `structopt` will detect `String` in this context
+//! and use appropriate `clap` API.
+//!
+//! [`AppSettings::AllowExternalSubcommands`]: https://docs.rs/clap/2.32.0/clap/enum.AppSettings.html#variant.AllowExternalSubcommands
+//!
 //! ## Flattening
 //!
 //! It can sometimes be useful to group related arguments in a substruct,

structopt-derive/src/attrs.rs

@@ -23,6 +23,7 @@ use syn::{
 pub enum Kind {
     Arg(Sp<Ty>),
     Subcommand(Sp<Ty>),
+    ExternalSubcommand,
     FlattenStruct,
     Skip(Option<Expr>),
 }
@@ -282,6 +283,10 @@ impl Attrs {
                     self.set_kind(kind);
                 }
 
+                ExternalSubcommand(ident) => {
+                    self.kind = Sp::new(Kind::ExternalSubcommand, ident.span());
+                }
+
                 Flatten(ident) => {
                     let kind = Sp::new(Kind::FlattenStruct, ident.span());
                     self.set_kind(kind);
@@ -407,7 +412,7 @@ impl Attrs {
             Kind::Subcommand(_) => abort!(res.kind.span(), "subcommand is only allowed on fields"),
             Kind::FlattenStruct => abort!(res.kind.span(), "flatten is only allowed on fields"),
             Kind::Skip(_) => abort!(res.kind.span(), "skip is only allowed on fields"),
-            Kind::Arg(_) => res,
+            Kind::Arg(_) | Kind::ExternalSubcommand => res,
         }
     }
 
@@ -444,6 +449,9 @@ impl Attrs {
                     );
                 }
             }
+
+            Kind::ExternalSubcommand => {}
+
             Kind::Subcommand(_) => {
                 if res.has_custom_parser {
                     abort!(

structopt-derive/src/lib.rs

@@ -23,7 +23,7 @@ mod ty;
 use crate::{
     attrs::{Attrs, CasingStyle, Kind, Name, ParserKind},
     spanned::Sp,
-    ty::{sub_type, Ty},
+    ty::{is_simple_ty, sub_type, subty_if_name, Ty},
 };
 
 use proc_macro2::{Span, TokenStream};
@@ -116,9 +116,14 @@ fn gen_augmentation(
         );
         let kind = attrs.kind();
         match &*kind {
+            Kind::ExternalSubcommand => abort!(
+                kind.span(),
+                "`external_subcommand` is only allowed on enum variants"
+            ),
             Kind::Subcommand(_) | Kind::Skip(_) => None,
             Kind::FlattenStruct => {
                 let ty = &field.ty;
+                // let settings = gen_subcommand_settings(&a);
                 Some(quote_spanned! { kind.span()=>
                     let #app_var = <#ty as ::structopt::StructOptInternal>::augment_clap(#app_var);
                     let #app_var = if <#ty as ::structopt::StructOptInternal>::is_subcommand() {
@@ -244,6 +249,11 @@ fn gen_constructor(fields: &Punctuated<Field, Comma>, parent_attribute: &Attrs)
         let field_name = field.ident.as_ref().unwrap();
         let kind = attrs.kind();
         match &*kind {
+            Kind::ExternalSubcommand => abort!(
+                kind.span(),
+                "`external_subcommand` is allowed only on enum variants"
+            ),
+
             Kind::Subcommand(ty) => {
                 let subcmd_type = match (**ty, sub_type(&field.ty)) {
                     (Ty::Option, Some(sub_type)) => sub_type,
@@ -457,6 +467,13 @@ fn gen_augment_clap_enum(
             parent_attribute.casing(),
             parent_attribute.env_casing(),
         );
+
+        if let Kind::ExternalSubcommand = *attrs.kind() {
+            return quote_spanned! { attrs.kind().span()=>
+                .setting(::structopt::clap::AppSettings::AllowExternalSubcommands)
+            };
+        }
+
         let app_var = Ident::new("subcommand", Span::call_site());
         let arg_block = match variant.fields {
             Named(ref fields) => gen_augmentation(&fields.named, &app_var, &attrs),
@@ -520,40 +537,123 @@ fn gen_from_subcommand(
 ) -> TokenStream {
     use syn::Fields::*;
 
-    let match_arms = variants.iter().map(|variant| {
-        let attrs = Attrs::from_struct(
-            variant.span(),
-            &variant.attrs,
-            Name::Derived(variant.ident.clone()),
-            Some(parent_attribute),
-            parent_attribute.casing(),
-            parent_attribute.env_casing(),
-        );
-        let sub_name = attrs.cased_name();
-        let variant_name = &variant.ident;
-        let constructor_block = match variant.fields {
-            Named(ref fields) => gen_constructor(&fields.named, &attrs),
-            Unit => quote!(),
-            Unnamed(ref fields) if fields.unnamed.len() == 1 => {
-                let ty = &fields.unnamed[0];
-                quote!( ( <#ty as ::structopt::StructOpt>::from_clap(matches) ) )
+    let mut ext_subcmd = None;
+
+    let match_arms: Vec<_> = variants
+        .iter()
+        .filter_map(|variant| {
+            let attrs = Attrs::from_struct(
+                variant.span(),
+                &variant.attrs,
+                Name::Derived(variant.ident.clone()),
+                Some(parent_attribute),
+                parent_attribute.casing(),
+                parent_attribute.env_casing(),
+            );
+
+            let sub_name = attrs.cased_name();
+            let variant_name = &variant.ident;
+
+            if let Kind::ExternalSubcommand = *attrs.kind() {
+                if ext_subcmd.is_some() {
+                    abort!(
+                        attrs.kind().span(),
+                        "Only one variant can be marked with `external_subcommand`, \
+                         this is the second"
+                    );
+                }
+
+                let ty = match variant.fields {
+                    Unnamed(ref fields) if fields.unnamed.len() == 1 => &fields.unnamed[0].ty,
+
+                    _ => abort!(
+                        variant.span(),
+                        "The enum variant marked with `external_attribute` must be \
+                         a single-typed tuple, and the type must be either `Vec<String>` \
+                         or `Vec<OsString>`."
+                    ),
+                };
+
+                let (span, str_ty, values_of) = match subty_if_name(ty, "Vec") {
+                    Some(subty) => {
+                        if is_simple_ty(subty, "String") {
+                            (
+                                subty.span(),
+                                quote!(::std::string::String),
+                                quote!(values_of),
+                            )
+                        } else {
+                            (
+                                subty.span(),
+                                quote!(::std::ffi::OsString),
+                                quote!(values_of_os),
+                            )
+                        }
+                    }
+
+                    None => abort!(
+                        ty.span(),
+                        "The type must be either `Vec<String>` or `Vec<OsString>` \
+                         to be used with `external_subcommand`."
+                    ),
+                };
+
+                ext_subcmd = Some((span, variant_name, str_ty, values_of));
+                None
+            } else {
+                let constructor_block = match variant.fields {
+                    Named(ref fields) => gen_constructor(&fields.named, &attrs),
+                    Unit => quote!(),
+                    Unnamed(ref fields) if fields.unnamed.len() == 1 => {
+                        let ty = &fields.unnamed[0];
+                        quote!( ( <#ty as ::structopt::StructOpt>::from_clap(matches) ) )
+                    }
+                    Unnamed(..) => {
+                        abort_call_site!("{}: tuple enums are not supported", variant.ident)
+                    }
+                };
+
+                Some(quote! {
+                    (#sub_name, Some(matches)) =>
+                        Some(#name :: #variant_name #constructor_block)
+                })
+            }
+        })
+        .collect();
+
+    let wildcard = match ext_subcmd {
+        Some((span, var_name, str_ty, values_of)) => quote_spanned! { span=>
+            ("", ::std::option::Option::None) => None,
+
+            (external, Some(matches)) => {
+                ::std::option::Option::Some(#name::#var_name(
+                    ::std::iter::once(#str_ty::from(external))
+                    .chain(
+                        matches.#values_of("").unwrap().map(#str_ty::from)
+                    )
+                    .collect::<::std::vec::Vec<_>>()
+                ))
             }
-            Unnamed(..) => abort_call_site!("{}: tuple enums are not supported", variant.ident),
-        };
 
-        quote! {
-            (#sub_name, Some(matches)) =>
-                Some(#name :: #variant_name #constructor_block)
-        }
-    });
+            (external, None) => {
+                ::std::option::Option::Some(#name::#var_name({
+                    let mut v = ::std::vec::Vec::with_capacity(1);
+                    v.push(#str_ty::from(external));
+                    v
+                }))
+            }
+        },
+
+        None => quote!(_ => None),
+    };
 
     quote! {
         fn from_subcommand<'a, 'b>(
             sub: (&'b str, Option<&'b ::structopt::clap::ArgMatches<'a>>)
         ) -> Option<Self> {
             match sub {
-                #( #match_arms ),*,
-                _ => None
+                #( #match_arms, )*
+                #wildcard
             }
         }
     }
@@ -616,13 +716,14 @@ fn impl_structopt_for_enum(
     attrs: &[Attribute],
 ) -> TokenStream {
     let basic_clap_app_gen = gen_clap_enum(attrs);
+    let clap_tokens = basic_clap_app_gen.tokens;
+    let attrs = basic_clap_app_gen.attrs;
 
-    let augment_clap = gen_augment_clap_enum(variants, &basic_clap_app_gen.attrs);
+    let augment_clap = gen_augment_clap_enum(variants, &attrs);
     let from_clap = gen_from_clap_enum(name);
-    let from_subcommand = gen_from_subcommand(name, variants, &basic_clap_app_gen.attrs);
+    let from_subcommand = gen_from_subcommand(name, variants, &attrs);
     let paw_impl = gen_paw_impl(name);
 
-    let clap_tokens = basic_clap_app_gen.tokens;
     quote! {
         #[allow(unknown_lints)]
         #[allow(unused_variables, dead_code, unreachable_code)]
@@ -660,6 +761,8 @@ fn impl_structopt(input: &DeriveInput) -> TokenStream {
                 unimplemented!()
             }
         }
+
+        impl ::structopt::StructOptInternal for #struct_name {}
     });
 
     match input.data {

structopt-derive/src/parse.rs

@@ -33,6 +33,7 @@ pub enum StructOptAttr {
     Env(Ident),
     Flatten(Ident),
     Subcommand(Ident),
+    ExternalSubcommand(Ident),
     NoVersion(Ident),
     VerbatimDocComment(Ident),
 
@@ -185,6 +186,7 @@ impl Parse for StructOptAttr {
                 "env" => Ok(Env(name)),
                 "flatten" => Ok(Flatten(name)),
                 "subcommand" => Ok(Subcommand(name)),
+                "external_subcommand" => Ok(ExternalSubcommand(name)),
                 "no_version" => Ok(NoVersion(name)),
                 "verbatim_doc_comment" => Ok(VerbatimDocComment(name)),
 

structopt-derive/src/ty.rs

@@ -80,11 +80,11 @@ where
         })
 }
 
-fn subty_if_name<'a>(ty: &'a syn::Type, name: &str) -> Option<&'a syn::Type> {
+pub fn subty_if_name<'a>(ty: &'a syn::Type, name: &str) -> Option<&'a syn::Type> {
     subty_if(ty, |seg| seg.ident == name)
 }
 
-fn is_simple_ty(ty: &syn::Type, name: &str) -> bool {
+pub fn is_simple_ty(ty: &syn::Type, name: &str) -> bool {
     only_last_segment(ty)
         .map(|segment| {
             if let PathArguments::None = segment.arguments {