fix(derive): Re-allow expressions for id's

Fixes #5407

Author: epage

clap_derive/src/derives/args.rs

@@ -717,9 +717,21 @@ fn gen_parsers(
         },
 
         Ty::Other => {
-            quote_spanned! { ty.span()=>
-                #arg_matches.#get_one(#id)
-                    .ok_or_else(|| clap::Error::raw(clap::error::ErrorKind::MissingRequiredArgument, concat!("The following required argument was not provided: ", #id)))?
+            // Prefer `concat` where possible for reduced code size but fallback to `format!` to
+            // allow non-literal `id`s
+            match id {
+                Name::Assigned(_) => {
+                    quote_spanned! { ty.span()=>
+                        #arg_matches.#get_one(#id)
+                            .ok_or_else(|| clap::Error::raw(clap::error::ErrorKind::MissingRequiredArgument, format!("The following required argument was not provided: {}", #id)))?
+                    }
+                }
+                Name::Derived(_) => {
+                    quote_spanned! { ty.span()=>
+                        #arg_matches.#get_one(#id)
+                            .ok_or_else(|| clap::Error::raw(clap::error::ErrorKind::MissingRequiredArgument, concat!("The following required argument was not provided: ", #id)))?
+                    }
+                }
             }
         }
     };

tests/derive/non_literal_attributes.rs

@@ -156,3 +156,20 @@ fn test_parse_hex_function_path() {
         err
     );
 }
+
+#[test]
+#[cfg(feature = "error-context")]
+fn test_const_name() {
+    #[derive(Parser, PartialEq, Debug)]
+    struct Opt {
+        #[arg(id = NAME, short, long)]
+        number: u64,
+    }
+
+    const NAME: &str = "fun";
+
+    assert_eq!(
+        Opt { number: 5 },
+        Opt::try_parse_from(["test", "-f", "5"]).unwrap()
+    );
+}