Add cal command (#1739)

* Add cal command

* Fix docmentation to show commands on two lines

* Use bullet points on flag documentation for cal

* Dereference day before calling string method

* Silence Clippy warning regarding a function with too many arguments

* Update cal flag descriptions and documentation

* Add some tests for the cal command

crates/nu-cli/tests/commands/cal.rs

@@ -0,0 +1,39 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn cal_february_2020_leap_year() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        cal -my 2020 | where month == "february" | to json
+        "#
+    ));
+
+    let cal_february_json = r#"[{"year":2020,"month":"february","sunday":null,"monday":null,"tuesday":null,"wednesday":null,"thurday":null,"friday":null,"saturday":1},{"year":2020,"month":"february","sunday":2,"monday":3,"tuesday":4,"wednesday":5,"thurday":6,"friday":7,"saturday":8},{"year":2020,"month":"february","sunday":9,"monday":10,"tuesday":11,"wednesday":12,"thurday":13,"friday":14,"saturday":15},{"year":2020,"month":"february","sunday":16,"monday":17,"tuesday":18,"wednesday":19,"thurday":20,"friday":21,"saturday":22},{"year":2020,"month":"february","sunday":23,"monday":24,"tuesday":25,"wednesday":26,"thurday":27,"friday":28,"saturday":29}]"#;
+
+    assert_eq!(actual.out, cal_february_json);
+}
+
+#[test]
+fn cal_friday_the_thirteenths_in_2015() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        cal -ym 2015 | where friday == 13 | count
+        "#
+    ));
+
+    assert!(actual.out.contains("3"));
+}
+
+#[test]
+fn cal_rows_in_2020() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        cal -y 2020 | count
+        "#
+    ));
+
+    assert!(actual.out.contains("62"));
+}

crates/nu-cli/tests/commands/mod.rs

@@ -1,5 +1,6 @@
 mod alias;
 mod append;
+mod cal;
 mod calc;
 mod cd;
 mod compact;