Support skipping struct fields

CHANGELOG.md

@@ -16,6 +16,9 @@
 
 ## improvements
 
+* Support skipping struct fields by [@sphynx](https://github.com/sphynx)
+ ([#174](https://github.com/TeXitoi/structopt/issues/174))
+
 * Add optional feature to support `paw` by [@gameldar](https://github.com/gameldar)
   ([#187](https://github.com/TeXitoi/structopt/issues/187))
 

examples/example.rs

@@ -46,6 +46,11 @@ struct Opt {
     /// argument list is provided (e.g. `--optv a b c`).
     #[structopt(long = "optv")]
     optv: Option<Vec<String>>,
+
+    /// Skipped option: it won't be parsed and will be filled with the
+    /// default value for its type (in this case '').
+    #[structopt(skip)]
+    skipped: String,
 }
 
 fn main() {

src/lib.rs

@@ -179,6 +179,11 @@
 //! If an argument is renamed using `name = $NAME` any following call to
 //! `short` or `long` will use the new name.
 //!
+//! If you want to omit a struct field from the parsing process
+//! altogether and just use a default value for it, you can annotate
+//! the field with `#[structopt(skip)]`. Note that the field type has
+//! to implement `std::default::Default` then.
+//!
 //! **Attention**: If these arguments are used without an explicit name
 //! the resulting flag is going to be renamed using `kebab-case` if the
 //! `rename_all` attribute was not specified previously. The same is true
@@ -212,6 +217,12 @@
 //!     /// This option is positional, meaning it is the first unadorned string
 //!     /// you provide (multiple others could follow).
 //!     my_positional: String,
+//!
+//!     /// This option is skipped and will be filled with the default value
+//!     /// for its type (in this case 0).
+//!     #[structopt(skip)]
+//!     skipped: u32,
+//!
 //! }
 //!
 //! # fn main() {

structopt-derive/src/attrs.rs

@@ -23,6 +23,7 @@ pub enum Kind {
     Arg(Ty),
     Subcommand(Ty),
     FlattenStruct,
+    Skip,
 }
 
 #[derive(Copy, Clone, PartialEq, Debug)]
@@ -179,6 +180,10 @@ impl Attrs {
                     self.set_kind(Kind::FlattenStruct);
                 }
 
+                Skip => {
+                    self.set_kind(Kind::Skip);
+                }
+
                 NameLitStr(name, lit) => {
                     self.push_str_method(&name.to_string(), &lit.value());
                 }
@@ -346,6 +351,7 @@ impl Attrs {
         match res.kind {
             Kind::Subcommand(_) => panic!("subcommand is only allowed on fields"),
             Kind::FlattenStruct => panic!("flatten is only allowed on fields"),
+            Kind::Skip => panic!("skip is only allowed on fields"),
             Kind::Arg(_) => res,
         }
     }
@@ -405,6 +411,11 @@ impl Attrs {
 
                 res.kind = Kind::Subcommand(ty);
             }
+            Kind::Skip => {
+                if !res.methods.iter().all(|m| m.name == "help") {
+                    panic!("methods are not allowed for skipped fields");
+                }
+            }
             Kind::Arg(_) => {
                 let mut ty = Self::ty_from_field(&field.ty);
                 if res.has_custom_parser {
@@ -455,7 +466,7 @@ impl Attrs {
         if let Kind::Arg(_) = self.kind {
             self.kind = kind;
         } else {
-            panic!("subcommands cannot be flattened");
+            panic!("subcommand, flatten and skip cannot be used together");
         }
     }
     pub fn has_method(&self, method: &str) -> bool {

structopt-derive/src/lib.rs

@@ -87,7 +87,7 @@ fn gen_augmentation(
     let args = fields.iter().filter_map(|field| {
         let attrs = Attrs::from_field(field, parent_attribute.casing());
         match attrs.kind() {
-            Kind::Subcommand(_) => None,
+            Kind::Subcommand(_) | Kind::Skip => None,
             Kind::FlattenStruct => {
                 let ty = &field.ty;
                 Some(quote! {
@@ -183,6 +183,7 @@ fn gen_constructor(fields: &Punctuated<Field, Comma>, parent_attribute: &Attrs)
                 quote!(#field_name: <#subcmd_type>::from_subcommand(matches.subcommand())#unwrapper)
             }
             Kind::FlattenStruct => quote!(#field_name: ::structopt::StructOpt::from_clap(matches)),
+            Kind::Skip => quote!(#field_name: Default::default()),
             Kind::Arg(ty) => {
                 use crate::Parser::*;
                 let (value_of, values_of, parse) = match *attrs.parser() {

structopt-derive/src/parse.rs

@@ -23,6 +23,7 @@ pub enum StructOptAttr {
     Long,
     Flatten,
     Subcommand,
+    Skip,
     Parse(ParserSpec),
     RenameAll(LitStr),
     NameLitStr(Ident, LitStr),
@@ -94,6 +95,7 @@ impl Parse for StructOptAttr {
                 "short" => Ok(Short),
                 "flatten" => Ok(Flatten),
                 "subcommand" => Ok(Subcommand),
+                "skip" => Ok(Skip),
                 _ => {
                     let msg = format!("unexpected attribute: {}", name_str);
                     Err(input.error(&msg))

tests/skip.rs

@@ -0,0 +1,94 @@
+// Copyright 2018 Guillaume Pinot (@TeXitoi) <[email protected]>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use structopt::StructOpt;
+
+#[test]
+fn skip_1() {
+    #[derive(StructOpt, Debug, PartialEq)]
+    struct Opt {
+        #[structopt(short)]
+        x: u32,
+        #[structopt(skip)]
+        s: u32,
+    }
+
+    assert!(Opt::from_iter_safe(&["test", "-x", "10", "20"]).is_err());
+    assert_eq!(
+        Opt::from_iter(&["test", "-x", "10"]),
+        Opt {
+            x: 10,
+            s: 0, // default
+        }
+    );
+}
+
+#[test]
+fn skip_2() {
+    #[derive(StructOpt, Debug, PartialEq)]
+    struct Opt {
+        #[structopt(short)]
+        x: u32,
+        #[structopt(skip)]
+        ss: String,
+        #[structopt(skip)]
+        sn: u8,
+        y: u32,
+        #[structopt(skip)]
+        sz: u16,
+        t: u32,
+    }
+
+    assert_eq!(
+        Opt::from_iter(&["test", "-x", "10", "20", "30"]),
+        Opt {
+            x: 10,
+            ss: String::from(""),
+            sn: 0,
+            y: 20,
+            sz: 0,
+            t: 30,
+        }
+    );
+}
+
+#[test]
+fn skip_enum() {
+    #[derive(Debug, PartialEq)]
+    #[allow(unused)]
+    enum Kind {
+        A,
+        B,
+    }
+
+    impl Default for Kind {
+        fn default() -> Self {
+            return Kind::B;
+        }
+    }
+
+    #[derive(StructOpt, Debug, PartialEq)]
+    #[structopt(name = "a")]
+    pub struct Opt {
+        #[structopt(long, short)]
+        number: u32,
+        #[structopt(skip)]
+        k: Kind,
+        #[structopt(skip)]
+        v: Vec<u32>,
+    }
+
+    assert_eq!(
+        Opt::from_iter(&["test", "-n", "10"]),
+        Opt {
+            number: 10,
+            k: Kind::B,
+            v: vec![],
+        }
+    );
+}

tests/ui/skip_flatten.rs

@@ -0,0 +1,42 @@
+// Copyright 2018 Guillaume Pinot (@TeXitoi) <[email protected]>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use structopt::StructOpt;
+
+#[derive(StructOpt)]
+#[structopt(name = "make-cookie")]
+struct MakeCookie {
+    #[structopt(short)]
+    s: String,
+
+    #[structopt(skip, flatten)]
+    cmd: Command,
+}
+
+#[derive(StructOpt)]
+enum Command {
+    #[structopt(name = "pound")]
+    /// Pound acorns into flour for cookie dough.
+    Pound { acorns: u32 },
+
+    Sparkle {
+        #[structopt(short)]
+        color: String,
+    },
+}
+
+impl Default for Command {
+    fn default() -> Self {
+        Pound { acorns: 0 }
+    }
+}
+
+fn main() {
+    let opt = Opt::from_args();
+    println!("{:?}", opt);
+}

tests/ui/skip_flatten.stderr

@@ -0,0 +1,7 @@
+error: proc-macro derive panicked
+  --> $DIR/skip_flatten.rs:11:10
+   |
+11 | #[derive(StructOpt)]
+   |          ^^^^^^^^^
+   |
+   = help: message: subcommand, flatten and skip cannot be used together

tests/ui/skip_subcommand.rs

@@ -0,0 +1,42 @@
+// Copyright 2018 Guillaume Pinot (@TeXitoi) <[email protected]>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use structopt::StructOpt;
+
+#[derive(StructOpt)]
+#[structopt(name = "make-cookie")]
+struct MakeCookie {
+    #[structopt(short)]
+    s: String,
+
+    #[structopt(subcommand, skip)]
+    cmd: Command,
+}
+
+#[derive(StructOpt)]
+enum Command {
+    #[structopt(name = "pound")]
+    /// Pound acorns into flour for cookie dough.
+    Pound { acorns: u32 },
+
+    Sparkle {
+        #[structopt(short)]
+        color: String,
+    },
+}
+
+impl Default for Command {
+    fn default() -> Self {
+        Pound { acorns: 0 }
+    }
+}
+
+fn main() {
+    let opt = Opt::from_args();
+    println!("{:?}", opt);
+}

tests/ui/skip_subcommand.stderr

@@ -0,0 +1,7 @@
+error: proc-macro derive panicked
+  --> $DIR/skip_subcommand.rs:11:10
+   |
+11 | #[derive(StructOpt)]
+   |          ^^^^^^^^^
+   |
+   = help: message: subcommand, flatten and skip cannot be used together

tests/ui/skip_with_other_options.rs

@@ -0,0 +1,15 @@
+use structopt::StructOpt;
+
+#[derive(StructOpt, Debug)]
+#[structopt(name = "test")]
+pub struct Opts {
+    #[structopt(long)]
+    a: u32,
+    #[structopt(skip, long)]
+    b: u32,
+}
+
+fn main() {
+    let opts = Opts::from_args();
+    println!("{:?}", opts);
+}

tests/ui/skip_with_other_options.stderr

@@ -0,0 +1,7 @@
+error: proc-macro derive panicked
+ --> $DIR/skip_with_other_options.rs:3:10
+  |
+3 | #[derive(StructOpt, Debug)]
+  |          ^^^^^^^^^
+  |
+  = help: message: methods are not allowed for skipped fields

tests/ui/skip_without_default.rs

@@ -0,0 +1,29 @@
+// Copyright 2018 Guillaume Pinot (@TeXitoi) <[email protected]>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use structopt::StructOpt;
+
+#[derive(Debug)]
+enum Kind {
+    A,
+    B,
+}
+
+#[derive(StructOpt, Debug)]
+#[structopt(name = "test")]
+pub struct Opts {
+    #[structopt(short)]
+    number: u32,
+    #[structopt(skip)]
+    k: Kind,
+}
+
+fn main() {
+    let opts = Opts::from_args();
+    println!("{:?}", opts);
+}

tests/ui/skip_without_default.stderr

@@ -0,0 +1,9 @@
+error[E0277]: the trait bound `Kind: std::default::Default` is not satisfied
+  --> $DIR/skip_without_default.rs:17:10
+   |
+17 | #[derive(StructOpt, Debug)]
+   |          ^^^^^^^^^ the trait `std::default::Default` is not implemented for `Kind`
+   |
+   = note: required by `std::default::Default::default`
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/subcommand_and_flatten.stderr

@@ -4,4 +4,4 @@ error: proc-macro derive panicked
 11 | #[derive(StructOpt)]
    |          ^^^^^^^^^
    |
-   = help: message: subcommands cannot be flattened
+   = help: message: subcommand, flatten and skip cannot be used together