Add the cbor!() macro

The cbor!() macro is inspired by serde_json::json!(), but the
implementation is simpler and the macro should be more useful. In
particular, the cbor!() macro returns Result<Value, Error>, so it can be
used in places that need careful error handling.

Cargo.toml

@@ -22,6 +22,7 @@ serde = { version = "1.0.14", default-features = false }
 
 [dev-dependencies]
 serde_derive = { version = "1.0.14", default-features = false }
+serde_bytes = { version = "0.11", default-features = false }
 
 [features]
 default = ["std"]

src/lib.rs

@@ -325,6 +325,9 @@ extern crate std;
 #[cfg(feature = "alloc")]
 extern crate alloc;
 
+#[cfg(feature = "std")]
+mod macros;
+
 pub mod de;
 pub mod error;
 mod read;

src/macros.rs

@@ -0,0 +1,122 @@
+/// Build a `Value` conveniently.
+///
+/// The syntax should be intuitive if you are familiar with JSON. You can also
+/// inline simple Rust expressions, including custom values that implement
+/// `serde::Serialize`. Note that this macro returns `Result<Value, Error>`,
+/// so you should handle the error appropriately.
+///
+/// ```
+/// use serde_cbor::cbor;
+///
+/// let bytes = serde_bytes::Bytes::new(b"\x00\x01\x02");
+/// let value = cbor!({
+///     "code" => 415,
+///     "message" => null,
+///     "continue" => false,
+///     "extra" => { "numbers" => [8.2341e+4, 0.251425] },
+///     "data" => bytes,
+/// }).unwrap();
+/// ```
+
+#[macro_export]
+macro_rules! cbor {
+    (@map {$($key:expr => $val:expr),*} $(,)?) => {{
+        #[allow(unused_mut)]
+        let mut map = ::std::collections::BTreeMap::new();
+
+        $(
+            map.insert(
+                $crate::value::to_value(cbor!( $key )?)?,
+                $crate::value::to_value(cbor!( $val )?)?,
+            );
+        )*
+
+        $crate::Value::Map(map)
+    }};
+
+    (@map {$($key:expr => $val:expr),*} { $($nkey:tt)* } => $($next:tt)*) => {
+        cbor!(
+            @map
+            { $($key => $val),* }
+            cbor!({ $($nkey)* })? =>
+            $($next)*
+        )
+    };
+
+    (@map {$($key:expr => $val:expr),*} [ $($nkey:tt)* ] => $($next:tt)*) => {
+        cbor!(
+            @map
+            { $($key => $val),* }
+            cbor!([ $($nkey)* ])? =>
+            $($next)*
+        )
+    };
+
+    (@map {$($key:expr => $val:expr),*} $nkey:expr => { $($nval:tt)* }, $($next:tt)*) => {
+        cbor!(
+            @map
+            { $($key => $val,)* $nkey => cbor!({ $($nval)* })? }
+            $($next)*
+        )
+    };
+
+    (@map {$($key:expr => $val:expr),*} $nkey:expr => [ $($nval:tt)* ], $($next:tt)*) => {
+        cbor!(
+            @map
+            { $($key => $val,)* $nkey => cbor!([ $($nval)* ])? }
+            $($next)*
+        )
+    };
+
+    (@map {$($key:expr => $val:expr),*} $nkey:expr => $nval:expr, $($next:tt)*) => {
+        cbor!(
+            @map
+            { $($key => $val,)* $nkey => cbor!($nval)? }
+            $($next)*
+        )
+    };
+
+    (@array [$($val:expr),*] $(,)?) => {
+        $crate::Value::Array(
+            vec![$( cbor!($val)? ),*]
+        )
+    };
+
+    (@array [$($val:expr),*] { $($item:tt)* }, $($next:tt)*) => {
+        cbor!(
+            @array
+            [ $($val,)* cbor!({ $($item)* })? ]
+            $($next)*
+        )
+    };
+
+    (@array [$($val:expr),*] [ $($item:tt)* ], $($next:tt)*) => {
+        cbor!(
+            @array
+            [ $($val,)* cbor!([ $($item)* ])? ]
+            $($next)*
+        )
+    };
+
+    (@array [$($val:expr),*] $item:expr, $($next:tt)*) => {
+        cbor!(
+            @array
+            [ $($val,)* $item ]
+            $($next)*
+        )
+    };
+
+    ({ $($next:tt)* }) => {(||{
+        ::core::result::Result::<_, $crate::Error>::from(Ok(cbor!(@map {} $($next)* ,)))
+    })()};
+
+    ([ $($next:tt)* ]) => {(||{
+        ::core::result::Result::<_, $crate::Error>::from(Ok(cbor!(@array [] $($next)* ,)))
+    })()};
+
+    ($val:expr) => {{
+        #[allow(unused_imports)]
+        use $crate::Value::Null as null;
+        $crate::value::to_value(&$val)
+    }};
+}