From 1fca7dbb322d40368a91e1a5d0a17f4f851fea18 Mon Sep 17 00:00:00 2001
From: "Craig M. Brandenburg" <c.m.brandenburg@gmail.com>
Date: Sat, 23 Jan 2016 05:57:25 -0700
Subject: [PATCH] Fix: Report correct error code for missing field

This resolves #22, resolves #29, and resolves #30.

* The reported error code is now `MissingField`, not `ExpectedSomeValue`.
* A missing `()` field now causes a `MissingField` error.
* A missing `Vec<_>` field now causes a `MissingField` error.

Tests have been updated to check these cases.
---
 json/src/de.rs                | 25 +++++++++++++++++++++++--
 json_tests/tests/test_json.rs | 25 +++++++++++++++----------
 2 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/json/src/de.rs b/json/src/de.rs
index 7b9bc8e..02b22c2 100644
--- a/json/src/de.rs
+++ b/json/src/de.rs
@@ -745,10 +745,31 @@ impl<'a, Iter> de::MapVisitor for MapVisitor<'a, Iter>
         }
     }
 
-    fn missing_field<V>(&mut self, _field: &'static str) -> Result<V>
+    fn missing_field<V>(&mut self, field: &'static str) -> Result<V>
         where V: de::Deserialize,
     {
-        let mut de = de::value::ValueDeserializer::into_deserializer(());
+        use std;
+
+        struct MissingFieldDeserializer(&'static str);
+
+        impl de::Deserializer for MissingFieldDeserializer {
+            type Error = de::value::Error;
+
+            fn visit<V>(&mut self, _visitor: V) -> std::result::Result<V::Value, Self::Error>
+                where V: de::Visitor,
+            {
+                let &mut MissingFieldDeserializer(field) = self;
+                Err(de::value::Error::MissingFieldError(field))
+            }
+
+            fn visit_option<V>(&mut self, mut visitor: V) -> std::result::Result<V::Value, Self::Error>
+                where V: de::Visitor,
+            {
+                visitor.visit_none()
+            }
+        }
+
+        let mut de = MissingFieldDeserializer(field);
         Ok(try!(de::Deserialize::deserialize(&mut de)))
     }
 }
diff --git a/json_tests/tests/test_json.rs b/json_tests/tests/test_json.rs
index d5ad4c9..dd4e857 100644
--- a/json_tests/tests/test_json.rs
+++ b/json_tests/tests/test_json.rs
@@ -911,6 +911,8 @@ fn test_parse_struct() {
         ("5", Error::SyntaxError(ErrorCode::ExpectedSomeValue, 1, 1)),
         ("\"hello\"", Error::SyntaxError(ErrorCode::ExpectedSomeValue, 1, 7)),
         ("{\"inner\": true}", Error::SyntaxError(ErrorCode::ExpectedSomeValue, 1, 14)),
+        ("{}", Error::SyntaxError(ErrorCode::MissingField("inner"), 1, 2)),
+        (r#"{"inner": [{"b": 42, "c": []}]}"#, Error::SyntaxError(ErrorCode::MissingField("a"), 1, 29)),
     ]);
 
     test_parse_ok(vec![
@@ -936,15 +938,6 @@ fn test_parse_struct() {
         ),
     ]);
 
-    let v: Outer = from_str("{}").unwrap();
-
-    assert_eq!(
-        v,
-        Outer {
-            inner: vec![],
-        }
-    );
-
     let v: Outer = from_str(
         "[
             [
@@ -1057,7 +1050,7 @@ fn test_multiline_errors() {
 }
 
 #[test]
-fn test_missing_field() {
+fn test_missing_option_field() {
     #[derive(Debug, PartialEq, Deserialize)]
     struct Foo {
         x: Option<u32>,
@@ -1078,6 +1071,18 @@ fn test_missing_field() {
     assert_eq!(value, Foo { x: Some(5) });
 }
 
+#[test]
+fn test_missing_nonoption_field() {
+    #[derive(Debug, PartialEq, Deserialize)]
+    struct Foo {
+        x: u32,
+    }
+
+    test_parse_err::<Foo>(vec![
+        ("{}", Error::SyntaxError(ErrorCode::MissingField("x"), 1, 2)),
+    ]);
+}
+
 #[test]
 fn test_missing_renamed_field() {
     #[derive(Debug, PartialEq, Deserialize)]