[edn] Round-trip instants. (#686) (#687) r=rnewman

First, the parser had a small grouping bug where-by it wouldn't parse
Z as timezone correctly.  Second, we weren't printing instants in the format
that we parse.

edn/src/edn.rustpeg

@@ -101,7 +101,7 @@ inst_string -> DateTime<Utc> =
               "T"
               [0-2][0-9] ":" [0-5][0-9] ":" [0-6][0-9]
               ("." [0-9]+)?
-              "Z" / (("+" / "-") [0-2][0-9] ":" [0-5][0-9])
+              ("Z" / (("+" / "-") [0-2][0-9] ":" [0-5][0-9]))
             )
     "\"" {?
         DateTime::parse_from_rfc3339(d)

edn/src/pretty_print.rs

@@ -8,6 +8,10 @@
 // CONDITIONS OF ANY KIND, either express or implied. See the License for the
 // specific language governing permissions and limitations under the License.
 
+use chrono::{
+    SecondsFormat,
+};
+
 use itertools::Itertools;
 use pretty;
 
@@ -70,6 +74,7 @@ impl Value {
             Value::Keyword(ref v) => pp.text(":").append(v.0.as_ref()),
             Value::Text(ref v) => pp.text("\"").append(v.as_ref()).append("\""),
             Value::Uuid(ref u) => pp.text("#uuid \"").append(u.hyphenated().to_string()).append("\""),
+            Value::Instant(ref v) => pp.text("#inst \"").append(v.to_rfc3339_opts(SecondsFormat::AutoSi, true)).append("\""),
             _ => pp.text(self.to_string())
         }
     }

edn/src/types.rs

@@ -17,6 +17,7 @@ use std::f64;
 
 use chrono::{
     DateTime,
+    SecondsFormat,
     TimeZone,           // For Utc::timestamp. The compiler incorrectly complains that this is unused.
     Utc,
 };
@@ -461,7 +462,7 @@ macro_rules! def_common_value_display {
             $t::Nil => write!($f, "nil"),
             $t::Boolean(v) => write!($f, "{}", v),
             $t::Integer(v) => write!($f, "{}", v),
-            $t::Instant(v) => write!($f, "{}", v),
+            $t::Instant(v) => write!($f, "#inst \"{}\"", v.to_rfc3339_opts(SecondsFormat::AutoSi, true)),
             $t::BigInteger(ref v) => write!($f, "{}N", v),
             // TODO: make sure float syntax is correct.
             $t::Float(ref v) => {

edn/tests/tests.rs

@@ -264,10 +264,31 @@ fn test_uuid() {
 
     let expected = uuid::Uuid::parse_str("550e8400-e29b-41d4-a716-446655440000")
                        .expect("valid UUID");
-    let actual = parse::uuid("#uuid \"550e8400-e29b-41d4-a716-446655440000\"")
+    let s = "#uuid \"550e8400-e29b-41d4-a716-446655440000\"";
+    let actual = parse::uuid(s)
                        .expect("parse success")
                        .into();
-    assert_eq!(self::Value::Uuid(expected), actual);
+    let value = self::Value::Uuid(expected);
+    assert_eq!(value, actual);
+    assert_eq!(format!("{}", value), s);
+    assert_eq!(value.to_pretty(100).unwrap(), s);
+}
+
+#[test]
+fn test_inst() {
+    assert!(parse::value("#inst\"2016-01-01T11:00:00.000Z\"").is_err());   // No whitespace.
+    assert!(parse::value("#inst \"2016-01-01T11:00:00.000\"").is_err());   // No timezone.
+    assert!(parse::value("#inst \"2016-01-01T11:00:00.000z\"").is_err());  // Lowercase timezone.
+
+    let expected = Utc.timestamp(1493410985, 187000000);
+    let s = "#inst \"2017-04-28T20:23:05.187Z\"";
+    let actual = parse::value(s)
+                       .expect("parse success")
+                       .into();
+    let value = self::Value::Instant(expected);
+    assert_eq!(value, actual);
+    assert_eq!(format!("{}", value), s);
+    assert_eq!(value.to_pretty(100).unwrap(), s);
 }
 
 #[test]