Merge pull request #3188 from epage/default

feat(derive): Don't require Display for default ArgEnum

clap_derive/src/attrs.rs

@@ -399,7 +399,9 @@ impl Attrs {
     fn push_attrs(&mut self, attrs: &[Attribute]) {
         use ClapAttr::*;
 
-        for attr in parse_clap_attributes(attrs) {
+        let parsed = parse_clap_attributes(attrs);
+        for attr in &parsed {
+            let attr = attr.clone();
             match attr {
                 Short(ident) => {
                     self.push_method(ident, self.name.clone().translate_char(*self.casing));
@@ -463,7 +465,15 @@ impl Attrs {
                         quote!(<#ty as ::std::default::Default>::default())
                     };
 
-                    let val = quote_spanned!(ident.span()=> {
+                    let val = if parsed.iter().any(|a| matches!(a, ArgEnum(_))) {
+                        quote_spanned!(ident.span()=> {
+                            {
+                                let val: #ty = #val;
+                                val.to_possible_value().unwrap().get_name()
+                            }
+                        })
+                    } else {
+                        quote_spanned!(ident.span()=> {
                             clap::lazy_static::lazy_static! {
                                 static ref DEFAULT_VALUE: &'static str = {
                                     let val: #ty = #val;
@@ -472,7 +482,8 @@ impl Attrs {
                                 };
                             }
                             *DEFAULT_VALUE
-                    });
+                        })
+                    };
 
                     let raw_ident = Ident::new("default_value", ident.span());
                     self.methods.push(Method::new(raw_ident, val));

clap_derive/src/derives/arg_enum.rs

@@ -51,7 +51,7 @@ pub fn gen_for_enum(name: &Ident, attrs: &[Attribute], e: &DataEnum) -> TokenStr
     let to_possible_value = gen_to_possible_value(&lits);
 
     quote! {
-        #[allow(dead_code, unreachable_code, unused_variables)]
+        #[allow(dead_code, unreachable_code, unused_variables, unused_braces)]
         #[allow(
             clippy::style,
             clippy::complexity,

clap_derive/src/derives/args.rs

@@ -73,7 +73,7 @@ pub fn gen_for_struct(
     quote! {
         #from_arg_matches
 
-        #[allow(dead_code, unreachable_code, unused_variables)]
+        #[allow(dead_code, unreachable_code, unused_variables, unused_braces)]
         #[allow(
             clippy::style,
             clippy::complexity,

clap_derive/src/parse.rs

@@ -21,6 +21,7 @@ pub fn parse_clap_attributes(all_attrs: &[Attribute]) -> Vec<ClapAttr> {
 }
 
 #[allow(clippy::large_enum_variant)]
+#[derive(Clone)]
 pub enum ClapAttr {
     // single-identifier attributes
     Short(Ident),

examples/derive_ref/README.md

@@ -174,7 +174,7 @@ In addition to the raw attributes, the following magic attributes are supported:
   - Without `<expr>`: fills the field with `Default::default()`
 - `default_value = <str>`: `clap::Arg::default_value` and `clap::Arg::required(false)`
 - `default_value_t [= <expr>]`: `clap::Arg::default_value` and `clap::Arg::required(false)`
-  - Requires `std::fmt::Display`
+  - Requires `std::fmt::Display` or `#[clap(arg_enum)]`
   - Without `<expr>`, relies on `Default::default()`
 
 ### Arg Types

src/build/arg/possible_value.rs

@@ -134,13 +134,13 @@ impl<'help> PossibleValue<'help> {
 impl<'help> PossibleValue<'help> {
     /// Get the name of the argument value
     #[inline]
-    pub fn get_name(&self) -> &str {
+    pub fn get_name(&self) -> &'help str {
         self.name
     }
 
     /// Get the help specified for this argument, if any
     #[inline]
-    pub fn get_help(&self) -> Option<&str> {
+    pub fn get_help(&self) -> Option<&'help str> {
         self.help
     }
 
@@ -151,7 +151,7 @@ impl<'help> PossibleValue<'help> {
     }
 
     /// Get the name if argument value is not hidden, `None` otherwise
-    pub fn get_visible_name(&self) -> Option<&str> {
+    pub fn get_visible_name(&self) -> Option<&'help str> {
         if self.hide {
             None
         } else {
@@ -162,7 +162,7 @@ impl<'help> PossibleValue<'help> {
     /// Returns all valid values of the argument value.
     ///
     /// Namely the name and all aliases.
-    pub fn get_name_and_aliases(&self) -> impl Iterator<Item = &str> {
+    pub fn get_name_and_aliases(&self) -> impl Iterator<Item = &'help str> + '_ {
         iter::once(&self.name).chain(&self.aliases).copied()
     }
 

tests/derive/arg_enum.rs

@@ -52,12 +52,6 @@ fn default_value() {
         }
     }
 
-    impl std::fmt::Display for ArgChoice {
-        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
-            std::fmt::Display::fmt(self.to_possible_value().unwrap().get_name(), f)
-        }
-    }
-
     #[derive(Parser, PartialEq, Debug)]
     struct Opt {
         #[clap(arg_enum, default_value_t)]