refactor Unsupported error to take rpc & arg

Author: sander2

client/src/client.rs

@@ -290,7 +290,7 @@ pub trait RpcApi: Sized {
         if self.version()? < 210000 {
             // note: we allow Some(false) since it's the default behavior
             if let Some(true) = descriptors {
-                return Err(Error::Unsupported);
+                return Err(Error::UnsupportedArgument("createwallet", "descriptors"));
             }
             // no descriptors argument yet
             let mut args = [

client/src/error.rs

@@ -31,8 +31,8 @@ pub enum Error {
     UnexpectedStructure,
     /// The daemon returned an error string.
     ReturnedError(String),
-    /// Feature not supported by the connected bitcoin version.
-    Unsupported,
+    /// The {0} RPC does not support the {1} argument on the connected bitcoin version.
+    UnsupportedArgument(&'static str, &'static str),
 }
 
 impl From<jsonrpc::error::Error> for Error {
@@ -90,8 +90,8 @@ impl fmt::Display for Error {
             Error::InvalidCookieFile => write!(f, "invalid cookie file"),
             Error::UnexpectedStructure => write!(f, "the JSON result had an unexpected structure"),
             Error::ReturnedError(ref s) => write!(f, "the daemon returned an error string: {}", s),
-            Error::Unsupported => {
-                write!(f, "the daemon version does not support the accessed feature")
+            Error::UnsupportedArgument(rpc, arg) => {
+                write!(f, "the daemon version does not support the {} argument for {}", arg, rpc)
             }
         }
     }