Move most of the root package into a subcrate. (#1445)

This improves incremental build time when working on what was previously
the root package. For example, previously all plugins would be rebuilt
with a change to `src/commands/classified/external.rs`, but now only
`nu-cli` will have to be rebuilt (and anything that depends on it).

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

@@ -0,0 +1,133 @@
+use nu_test_support::fs::Stub::EmptyFile;
+use nu_test_support::playground::Playground;
+use nu_test_support::{nu, nu_error, pipeline};
+
+#[test]
+fn lists_regular_files() {
+    Playground::setup("ls_test_1", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("yehuda.txt"),
+            EmptyFile("jonathan.txt"),
+            EmptyFile("andres.txt"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                ls
+                | count
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual, "3");
+    })
+}
+
+#[test]
+fn lists_regular_files_using_asterisk_wildcard() {
+    Playground::setup("ls_test_2", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("los.txt"),
+            EmptyFile("tres.txt"),
+            EmptyFile("amigos.txt"),
+            EmptyFile("arepas.clu"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                ls *.txt
+                | count
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual, "3");
+    })
+}
+
+#[test]
+fn lists_regular_files_using_question_mark_wildcard() {
+    Playground::setup("ls_test_3", |dirs, sandbox| {
+        sandbox.with_files(vec![
+            EmptyFile("yehuda.10.txt"),
+            EmptyFile("jonathan.10.txt"),
+            EmptyFile("andres.10.txt"),
+            EmptyFile("chicken_not_to_be_picked_up.100.txt"),
+        ]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                ls *.??.txt
+                | count
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual, "3");
+    })
+}
+
+#[test]
+fn lists_all_files_in_directories_from_stream() {
+    Playground::setup("ls_test_4", |dirs, sandbox| {
+        sandbox
+            .with_files(vec![EmptyFile("root1.txt"), EmptyFile("root2.txt")])
+            .within("dir_a")
+            .with_files(vec![
+                EmptyFile("yehuda.10.txt"),
+                EmptyFile("jonathan.10.txt"),
+            ])
+            .within("dir_b")
+            .with_files(vec![
+                EmptyFile("andres.10.txt"),
+                EmptyFile("chicken_not_to_be_picked_up.100.txt"),
+            ]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                echo dir_a dir_b
+                | ls $it
+                | count
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual, "4");
+    })
+}
+
+#[test]
+fn does_not_fail_if_glob_matches_empty_directory() {
+    Playground::setup("ls_test_5", |dirs, sandbox| {
+        sandbox.within("dir_a");
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                ls dir_a
+                | count
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual, "0");
+    })
+}
+
+#[test]
+fn fails_when_glob_doesnt_match() {
+    Playground::setup("ls_test_5", |dirs, sandbox| {
+        sandbox.with_files(vec![EmptyFile("root1.txt"), EmptyFile("root2.txt")]);
+
+        let actual = nu_error!(
+            cwd: dirs.test(),
+            "ls root3*"
+        );
+
+        assert!(actual.contains("invalid file or pattern"));
+    })
+}