Make most constructors fallible (relates #815)

README.md

@@ -47,9 +47,9 @@ Consider using `NaiveDateTime` with the implicit TAI (International Atomic Time)
 if you want.
 
 Chrono inherently does not support an inaccurate or partial date and time representation.
-Any operation that can be ambiguous will return `None` in such cases.
+Any operation that can be ambiguous will return `Err(chrono::Error)` in such cases.
 For example, "a month later" of 2014-01-30 is not well-defined
-and consequently `Utc.ymd(2014, 1, 30).with_month(2)` returns `None`.
+and consequently `Utc.ymd(2014, 1, 30)?.with_month(2)?` returns `Err(chrono::Error)`.
 
 Non ISO week handling is not yet supported.
 For now you can use the [chrono_ext](https://crates.io/crates/chrono_ext)

benches/chrono.rs

@@ -35,14 +35,14 @@ fn bench_datetime_from_str(c: &mut Criterion) {
 }
 
 fn bench_datetime_to_rfc2822(c: &mut Criterion) {
-    let pst = FixedOffset::east(8 * 60 * 60);
-    let dt = pst.ymd(2018, 1, 11).and_hms_nano(10, 5, 13, 84_660_000);
+    let pst = FixedOffset::east(8 * 60 * 60).unwrap();
+    let dt = pst.ymd(2018, 1, 11).unwrap().and_hms_nano(10, 5, 13, 84_660_000).unwrap();
     c.bench_function("bench_datetime_to_rfc2822", |b| b.iter(|| black_box(dt).to_rfc2822()));
 }
 
 fn bench_datetime_to_rfc3339(c: &mut Criterion) {
-    let pst = FixedOffset::east(8 * 60 * 60);
-    let dt = pst.ymd(2018, 1, 11).and_hms_nano(10, 5, 13, 84_660_000);
+    let pst = FixedOffset::east(8 * 60 * 60).unwrap();
+    let dt = pst.ymd(2018, 1, 11).unwrap().and_hms_nano(10, 5, 13, 84_660_000).unwrap();
     c.bench_function("bench_datetime_to_rfc3339", |b| b.iter(|| black_box(dt).to_rfc3339()));
 }
 
@@ -90,7 +90,7 @@ fn num_days_from_ce_alt<Date: Datelike>(date: &Date) -> i32 {
 fn bench_num_days_from_ce(c: &mut Criterion) {
     let mut group = c.benchmark_group("num_days_from_ce");
     for year in &[1, 500, 2000, 2019] {
-        let d = NaiveDate::from_ymd(*year, 1, 1);
+        let d = NaiveDate::from_ymd(*year, 1, 1).unwrap();
         group.bench_with_input(BenchmarkId::new("new", year), &d, |b, y| {
             b.iter(|| num_days_from_ce_alt(y))
         });

ci/core-test/src/lib.rs

@@ -3,5 +3,5 @@
 use chrono::{TimeZone, Utc};
 
 pub fn create_time() {
-    let _ = Utc.ymd(2019, 1, 1).and_hms(0, 0, 0);
+    let _ = Utc.ymd(2019, 1, 1).unwrap().and_hms(0, 0, 0).unwrap();
 }