Split serde_macros into multiple files

serde_macros/src/field.rs

@@ -0,0 +1,29 @@
+use syntax::ast;
+
+pub fn field_alias(field: &ast::StructField) -> Option<&ast::Lit> {
+    field.node.attrs.iter()
+        .find(|sa| {
+            if let ast::MetaList(ref n, _) = sa.node.value.node {
+                n == &"serde"
+            } else {
+                false
+            }
+        })
+        .and_then(|sa| {
+            if let ast::MetaList(_, ref vals) = sa.node.value.node {
+                vals.iter().fold(None, |v, mi| {
+                    if let ast::MetaNameValue(ref n, ref lit) = mi.node {
+                        if n == &"alias" {
+                            Some(lit)
+                        } else {
+                            v
+                        }
+                    } else {
+                        v
+                    }
+                })
+            } else {
+                None
+            }
+        })
+}