From 6ff5c445f37083c785111c904426c94b7a01f4b4 Mon Sep 17 00:00:00 2001
From: John-John Tedro <udoprog@tedro.se>
Date: Mon, 7 May 2018 03:47:09 +0200
Subject: Use custom struct/field naming to deserialize spans

---
 src/spanned.rs | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 120 insertions(+), 16 deletions(-)

(limited to 'src/spanned.rs')

diff --git a/src/spanned.rs b/src/spanned.rs
index 04ec9b8..1673d66 100644
--- a/src/spanned.rs
+++ b/src/spanned.rs
@@ -6,43 +6,147 @@
 //! use toml::spanned::Spanned;
 //!
 //! #[derive(Deserialize)]
-//! struct Udoprog {
+//! struct Value {
 //!     s: Spanned<String>,
 //! }
 //!
 //! fn main() {
-//!     let t = "s = \"udoprog\"\n";
+//!     let t = "s = \"value\"\n";
 //!
-//!     let u: Udoprog = toml::from_str(t).unwrap();
+//!     let u: Value = toml::from_str(t).unwrap();
 //!
 //!     assert_eq!(u.s.start, 4);
-//!     assert_eq!(u.s.end, 13);
+//!     assert_eq!(u.s.end, 11);
 //! }
 //! ```
 
-use serde::{Serialize, Serializer};
+use serde::{de, ser};
+use std::fmt;
 
-// FIXME: use a more unique name like "toml::Spanned".
 #[doc(hidden)]
-pub const NAME: &str = "Spanned";
+pub const NAME: &'static str = "$__toml_private_Spanned";
 #[doc(hidden)]
-pub const FIELDS: &[&str] = &["value", "start", "end"];
+pub const START: &'static str = "$__toml_private_start";
+#[doc(hidden)]
+pub const END: &'static str = "$__toml_private_end";
+#[doc(hidden)]
+pub const VALUE: &'static str = "$__toml_private_value";
+
+macro_rules! key_deserialize {
+    ($ident:ident, $field:expr, $name:expr) => {
+        struct $ident;
+
+        impl<'de> de::Deserialize<'de> for $ident {
+            fn deserialize<D>(deserializer: D) -> Result<$ident, D::Error>
+                where D: de::Deserializer<'de>
+            {
+                struct FieldVisitor;
+
+                impl<'de> de::Visitor<'de> for FieldVisitor {
+                    type Value = ();
+
+                    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                        formatter.write_str("a valid spanned field")
+                    }
+
+                    fn visit_str<E>(self, s: &str) -> Result<(), E>
+                        where E: de::Error
+                    {
+                        if s == $field {
+                            Ok(())
+                        } else {
+                            Err(de::Error::custom(
+                                concat!("expected spanned field `", $name, "`")))
+                        }
+                    }
+                }
+
+                deserializer.deserialize_identifier(FieldVisitor)?;
+                Ok($ident)
+            }
+        }
+    }
+}
 
-///
-#[derive(Deserialize, Debug)]
+
+/// A spanned value, indicating the range at which it is defined in the source.
+#[derive(Debug)]
 pub struct Spanned<T> {
-    ///
-    pub value: T,
-    ///
+    /// The start range.
     pub start: usize,
-    ///
+    /// The end range (exclusive).
     pub end: usize,
+    /// The spanned value.
+    pub value: T,
+}
+
+impl<'de, T> de::Deserialize<'de> for Spanned<T>
+    where T: de::Deserialize<'de>
+{
+    fn deserialize<D>(deserializer: D) -> Result<Spanned<T>, D::Error>
+        where D: de::Deserializer<'de>
+    {
+        struct SpannedVisitor<T>(::std::marker::PhantomData<T>);
+
+        impl<'de, T> de::Visitor<'de> for SpannedVisitor<T>
+            where T: de::Deserialize<'de>
+        {
+            type Value = Spanned<T>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a TOML spanned")
+            }
+
+            fn visit_map<V>(self, mut visitor: V) -> Result<Spanned<T>, V::Error>
+                where V: de::MapAccess<'de>
+            {
+                let start = visitor.next_key::<StartKey>()?;
+
+                if start.is_none() {
+                    return Err(de::Error::custom("spanned start key not found"))
+                }
+
+                let start: usize = visitor.next_value()?;
+
+                let end = visitor.next_key::<EndKey>()?;
+
+                if end.is_none() {
+                    return Err(de::Error::custom("spanned end key not found"))
+                }
+
+                let end: usize = visitor.next_value()?;
+
+                let value = visitor.next_key::<ValueKey>()?;
+
+                if value.is_none() {
+                    return Err(de::Error::custom("spanned value key not found"))
+                }
+
+                let value: T = visitor.next_value()?;
+
+                Ok(Spanned {
+                    start: start,
+                    end: end,
+                    value: value
+                })
+            }
+        }
+
+        key_deserialize!(StartKey, START, "start");
+        key_deserialize!(EndKey, END, "end");
+        key_deserialize!(ValueKey, VALUE, "value");
+
+        let visitor = SpannedVisitor(::std::marker::PhantomData);
+
+        static FIELDS: [&'static str; 3] = [START, END, VALUE];
+        deserializer.deserialize_struct(NAME, &FIELDS, visitor)
+    }
 }
 
-impl<T: Serialize> Serialize for Spanned<T> {
+impl<T: ser::Serialize> ser::Serialize for Spanned<T> {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
-        S: Serializer,
+        S: ser::Serializer,
     {
         self.value.serialize(serializer)
     }
-- 
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