types/datetime: replace deprecated chrono::Date* with NaiveDate

The chrono crate deprecated the Date and DateTime APIs in favor
of NaiveDate* and also added interfaces like from_ymd_opt()
which return Options. Many APIs inside Utc::* have also been
deprecated.

Eventually the deprecated APIs will be removed so this migrates
to the new APIs (NaiveDate is already implemented, so we just
do the minimal required migration).

Deprecation  started since 0.4.23:
https://docs.rs/chrono/0.4.31/chrono/struct.Date.html

While at it, also bump the chrono dep 0.4.20 -> 0.4.31 and fix
all test cases.

Closes: #530

Author: 10ne1

plotters/Cargo.toml

@@ -14,7 +14,7 @@ exclude = ["doc-template", "plotters-doc-data"]
 
 [dependencies]
 num-traits = "0.2.14"
-chrono = { version = "0.4.19", optional = true }
+chrono = { version = "0.4.31", optional = true }
 
 [dependencies.plotters-backend]
 path = "../plotters-backend"

plotters/examples/slc-temp.rs

@@ -1,9 +1,16 @@
 use plotters::prelude::*;
 
-use chrono::{TimeZone, Utc};
+use chrono::NaiveDate;
 
 use std::error::Error;
 
+// it's safe to use unwrap because we use known good values in test cases
+macro_rules! create_date {
+    ($year:expr, $month:expr, $day:expr) => {
+        NaiveDate::from_ymd_opt($year, $month, $day).unwrap()
+    };
+}
+
 const OUT_FILE_NAME: &'static str = "plotters-doc-data/slc-temp.png";
 fn main() -> Result<(), Box<dyn Error>> {
     let root = BitMapBackend::new(OUT_FILE_NAME, (1024, 768)).into_drawing_area();
@@ -20,11 +27,11 @@ fn main() -> Result<(), Box<dyn Error>> {
         .set_label_area_size(LabelAreaPosition::Right, 60)
         .set_label_area_size(LabelAreaPosition::Bottom, 40)
         .build_cartesian_2d(
-            (Utc.ymd(2010, 1, 1)..Utc.ymd(2018, 12, 1)).monthly(),
+            (create_date!(2010, 1, 1)..create_date!(2018, 12, 1)).monthly(),
             14.0..104.0,
         )?
         .set_secondary_coord(
-            (Utc.ymd(2010, 1, 1)..Utc.ymd(2018, 12, 1)).monthly(),
+            (create_date!(2010, 1, 1)..create_date!(2018, 12, 1)).monthly(),
             -10.0..40.0,
         );
 
@@ -42,13 +49,13 @@ fn main() -> Result<(), Box<dyn Error>> {
         .draw()?;
 
     chart.draw_series(LineSeries::new(
-        DATA.iter().map(|(y, m, t)| (Utc.ymd(*y, *m, 1), *t)),
+        DATA.iter().map(|(y, m, t)| (create_date!(*y, *m, 1), *t)),
         &BLUE,
     ))?;
 
     chart.draw_series(
         DATA.iter()
-            .map(|(y, m, t)| Circle::new((Utc.ymd(*y, *m, 1), *t), 3, BLUE.filled())),
+            .map(|(y, m, t)| Circle::new((create_date!(*y, *m, 1), *t), 3, BLUE.filled())),
     )?;
 
     // To avoid the IO failure being ignored silently, we manually call the present function

plotters/examples/stock.rs

@@ -1,11 +1,9 @@
-use chrono::offset::{Local, TimeZone};
-use chrono::{Date, Duration};
+use chrono::{DateTime, Duration, NaiveDate};
 use plotters::prelude::*;
-fn parse_time(t: &str) -> Date<Local> {
-    Local
-        .datetime_from_str(&format!("{} 0:0", t), "%Y-%m-%d %H:%M")
+fn parse_time(t: &str) -> NaiveDate {
+    DateTime::parse_from_str(&format!("{} 0:0", t), "%Y-%m-%d %H:%M")
         .unwrap()
-        .date()
+        .date_naive()
 }
 const OUT_FILE_NAME: &'static str = "plotters-doc-data/stock.png";
 fn main() -> Result<(), Box<dyn std::error::Error>> {