Reject serializing maps to JSON with non-string keys

Closes #122. This is a breaking change since it modifies the
return type of serde_json::to_vec{,pretty}, so it'll require a major
version bump of serde_json.

serde_tests/benches/bench_log.rs

@@ -1123,18 +1123,18 @@ fn bench_encoder(b: &mut Bencher) {
 #[test]
 fn test_serializer() {
     let log = Log::new();
-    let json = serde_json::to_vec(&log);
+    let json = serde_json::to_vec(&log).unwrap();
     assert_eq!(json, JSON_STR.as_bytes());
 }
 
 #[bench]
 fn bench_serializer(b: &mut Bencher) {
     let log = Log::new();
-    let json = serde_json::to_vec(&log);
+    let json = serde_json::to_vec(&log).unwrap();
     b.bytes = json.len() as u64;
 
     b.iter(|| {
-        let _ = serde_json::to_vec(&log);
+        serde_json::to_vec(&log).unwrap();
     });
 }
 
@@ -1152,7 +1152,7 @@ fn test_serializer_vec() {
 #[bench]
 fn bench_serializer_vec(b: &mut Bencher) {
     let log = Log::new();
-    let json = serde_json::to_vec(&log);
+    let json = serde_json::to_vec(&log).unwrap();
     b.bytes = json.len() as u64;
 
     let mut wr = Vec::with_capacity(1024);
@@ -1169,7 +1169,7 @@ fn bench_serializer_vec(b: &mut Bencher) {
 #[bench]
 fn bench_serializer_slice(b: &mut Bencher) {
     let log = Log::new();
-    let json = serde_json::to_vec(&log);
+    let json = serde_json::to_vec(&log).unwrap();
     b.bytes = json.len() as u64;
 
     let mut buf = [0; 1024];
@@ -1202,7 +1202,7 @@ fn test_serializer_my_mem_writer0() {
 #[bench]
 fn bench_serializer_my_mem_writer0(b: &mut Bencher) {
     let log = Log::new();
-    let json = serde_json::to_vec(&log);
+    let json = serde_json::to_vec(&log).unwrap();
     b.bytes = json.len() as u64;
 
     let mut wr = MyMemWriter0::with_capacity(1024);
@@ -1234,7 +1234,7 @@ fn test_serializer_my_mem_writer1() {
 #[bench]
 fn bench_serializer_my_mem_writer1(b: &mut Bencher) {
     let log = Log::new();
-    let json = serde_json::to_vec(&log);
+    let json = serde_json::to_vec(&log).unwrap();
     b.bytes = json.len() as u64;
 
     let mut wr = MyMemWriter1::with_capacity(1024);

serde_tests/tests/test_json.rs

@@ -1348,3 +1348,16 @@ fn test_deserialize_from_stream() {
 
     assert_eq!(request, response);
 }
+
+#[test]
+fn test_serialize_rejects_non_key_maps() {
+    let map = treemap!(
+        1 => 2,
+        3 => 4
+    );
+
+    match serde_json::to_vec(&map).unwrap_err() {
+        serde_json::Error::SyntaxError(serde_json::ErrorCode::KeyMustBeAString, 0, 0) => {}
+        _ => panic!("integers used as keys"),
+    }
+}