make trim apply to strings contained in tables (also at deeper nesting (#1664)

* make trim apply to strings contained in tables (also at deeper nesting
levels), not just top-level strings

* remove unnecessary clone (thanks clippy)

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

@@ -37,6 +37,7 @@ mod split_by;
 mod split_column;
 mod sum;
 mod touch;
+mod trim;
 mod uniq;
 mod where_;
 mod wrap;

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

@@ -0,0 +1,85 @@
+use nu_test_support::fs::Stub::FileWithContent;
+use nu_test_support::playground::Playground;
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn string() {
+    Playground::setup("trim_test_1", |dirs, _sandbox| {
+        let test_strings = ["\n", " \n ", "\thi\n\n", "\u{2003}a"];
+        assert!(test_strings[3].chars().count() == 2);
+
+        for test_string in &test_strings {
+            let commandline = format!(
+                r#"
+                        echo {}
+                        | trim
+                    "#,
+                test_string
+            );
+            let actual = nu!(
+                cwd: dirs.test(), pipeline(&commandline
+            ));
+            assert_eq!(actual, test_string.trim())
+        }
+    })
+}
+
+#[test]
+fn row() {
+    Playground::setup("trim_test_2", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            FileWithContent("lines.csv", "lines\n l0\n\tl1\n l2\t \n\n"),
+            FileWithContent("lines_trimmed.csv", "lines\nl0\nl1\nl2\n"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                open lines.csv
+                | trim
+            "#
+        ));
+
+        let expected = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                open lines_trimmed.csv
+            "#
+        ));
+
+        assert_eq!(actual, expected)
+    })
+}
+
+#[test]
+fn nested() {
+    Playground::setup("trim_test_3", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            FileWithContent(
+                "nested.json",
+                r#"{ "l0" : {"l1": {"l2" : {"a" : "  s0", "b" : "\t\ts1\n"} } } }"#,
+            ),
+            FileWithContent(
+                "nested_trimmed.json",
+                r#"{ "l0" : {"l1": {"l2" : {"a" : "s0", "b" : "s1"} } } }"#,
+            ),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                open nested.json
+                | trim
+            "#
+        ));
+
+        let expected = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                open nested_trimmed.json
+            "#
+        ));
+
+        assert_eq!(actual, expected)
+    })
+}