bpaf_derive: support enter as post decor

Author: pacak

bpaf_derive/src/attrs.rs

@@ -254,6 +254,7 @@ impl ToTokens for PostDecor {
             PostDecor::Hide { .. } => quote!(hide()),
             PostDecor::CustomUsage { usage, .. } => quote!(custom_usage(#usage)),
             PostDecor::HideUsage { .. } => quote!(hide_usage()),
+            PostDecor::Enter { name, .. } => quote!(enter(#name)),
         }
         .to_tokens(tokens);
     }
@@ -339,6 +340,10 @@ pub(crate) enum PostDecor {
     HideUsage {
         span: Span,
     },
+    Enter {
+        name: Box<Expr>,
+        span: Span,
+    },
 }
 impl PostDecor {
     fn span(&self) -> Span {
@@ -355,6 +360,7 @@ impl PostDecor {
             | Self::Guard { span, .. }
             | Self::Hide { span }
             | Self::CustomUsage { span, .. }
+            | Self::Enter { span, .. }
             | Self::HideUsage { span } => *span,
         }
     }
@@ -544,6 +550,9 @@ impl PostDecor {
         } else if kw == "custom_usage" {
             let usage = parse_arg(input)?;
             Self::CustomUsage { usage, span }
+        } else if kw == "enter" {
+            let name = parse_expr(input)?;
+            Self::Enter { span, name }
         } else {
             return Ok(None);
         }))

bpaf_derive/src/top_tests.rs

@@ -46,6 +46,27 @@ fn top_struct_construct() {
     assert_eq!(top.to_token_stream().to_string(), expected.to_string());
 }
 
+#[test]
+fn top_struct_enter() {
+    let top: Top = parse_quote! {
+        #[bpaf(enter("opt"))]
+        struct Opt { #[bpaf(enter("bar"))] verbose: bool }
+    };
+
+    let expected = quote! {
+        fn opt() -> impl ::bpaf::Parser<Opt> {
+            #[allow (unused_imports)]
+            use ::bpaf::Parser;
+            {
+                let verbose = ::bpaf::long("verbose").switch().enter("bar");
+                ::bpaf::construct!(Opt { verbose, })
+            }.enter("opt")
+        }
+    };
+
+    assert_eq!(top.to_token_stream().to_string(), expected.to_string());
+}
+
 #[test]
 fn top_enum_construct() {
     let top: Top = parse_quote! {