nu_cli refactor in preparation for a crate called nu_command (#2907)

* move basic_shell_manager to nu-engine

* move basic_evaluation_context to nu-engine

* fix failing test in feature which commands/classified/external.rs

crates/nu-engine/src/basic_evaluation_context.rs

@@ -0,0 +1,20 @@
+use crate::basic_shell_manager;
+use crate::env::basic_host::BasicHost;
+use crate::EvaluationContext;
+use crate::Scope;
+use parking_lot::Mutex;
+use std::error::Error;
+use std::sync::atomic::AtomicBool;
+use std::sync::Arc;
+
+pub fn basic_evaluation_context() -> Result<EvaluationContext, Box<dyn Error>> {
+    Ok(EvaluationContext {
+        scope: Scope::new(),
+        host: Arc::new(parking_lot::Mutex::new(Box::new(BasicHost))),
+        current_errors: Arc::new(Mutex::new(vec![])),
+        ctrl_c: Arc::new(AtomicBool::new(false)),
+        user_recently_used_autoenv_untrust: Arc::new(AtomicBool::new(false)),
+        shell_manager: basic_shell_manager::basic_shell_manager()?,
+        windows_drives_previous_cwd: Arc::new(Mutex::new(std::collections::HashMap::new())),
+    })
+}

crates/nu-engine/src/basic_shell_manager.rs

@@ -0,0 +1,14 @@
+use crate::filesystem::filesystem_shell::FilesystemShell;
+use crate::shell::shell_manager::ShellManager;
+
+use parking_lot::Mutex;
+use std::error::Error;
+use std::sync::atomic::AtomicUsize;
+use std::sync::Arc;
+
+pub fn basic_shell_manager() -> Result<ShellManager, Box<dyn Error>> {
+    Ok(ShellManager {
+        current_shell: Arc::new(AtomicUsize::new(0)),
+        shells: Arc::new(Mutex::new(vec![Box::new(FilesystemShell::basic()?)])),
+    })
+}

crates/nu-engine/src/env/basic_host.rs

@@ -0,0 +1,77 @@
+use crate::Host;
+use nu_protocol::{errln, outln};
+use std::ffi::OsString;
+
+#[derive(Debug)]
+pub struct BasicHost;
+
+impl Host for BasicHost {
+    fn stdout(&mut self, out: &str) {
+        match out {
+            "\n" => outln!(""),
+            other => outln!("{}", other),
+        }
+    }
+
+    fn stderr(&mut self, out: &str) {
+        match out {
+            "\n" => errln!(""),
+            other => errln!("{}", other),
+        }
+    }
+
+    #[allow(unused_variables)]
+    fn vars(&mut self) -> Vec<(String, String)> {
+        #[cfg(not(target_arch = "wasm32"))]
+        {
+            std::env::vars().collect::<Vec<_>>()
+        }
+
+        #[cfg(target_arch = "wasm32")]
+        {
+            vec![]
+        }
+    }
+
+    #[allow(unused_variables)]
+    fn env_get(&mut self, key: OsString) -> Option<OsString> {
+        #[cfg(not(target_arch = "wasm32"))]
+        {
+            std::env::var_os(key)
+        }
+        #[cfg(target_arch = "wasm32")]
+        {
+            None
+        }
+    }
+
+    #[allow(unused_variables)]
+    fn env_set(&mut self, key: OsString, value: OsString) {
+        #[cfg(not(target_arch = "wasm32"))]
+        {
+            std::env::set_var(key, value);
+        }
+    }
+
+    #[allow(unused_variables)]
+    fn env_rm(&mut self, key: OsString) {
+        #[cfg(not(target_arch = "wasm32"))]
+        {
+            std::env::remove_var(key);
+        }
+    }
+
+    fn out_termcolor(&self) -> termcolor::StandardStream {
+        termcolor::StandardStream::stdout(termcolor::ColorChoice::Auto)
+    }
+
+    fn err_termcolor(&self) -> termcolor::StandardStream {
+        termcolor::StandardStream::stderr(termcolor::ColorChoice::Auto)
+    }
+
+    fn width(&self) -> usize {
+        let (mut term_width, _) = term_size::dimensions().unwrap_or((80, 20));
+        term_width -= 1;
+        term_width
+    }
+}

crates/nu-engine/src/env/mod.rs

@@ -1,2 +1,3 @@
+pub(crate) mod basic_host;
 pub(crate) mod environment;
 pub(crate) mod host;

crates/nu-engine/src/lib.rs

@@ -1,3 +1,5 @@
+pub mod basic_evaluation_context;
+pub mod basic_shell_manager;
 mod call_info;
 mod command_args;
 pub mod deserializer;
@@ -13,6 +15,8 @@ pub mod plugin;
 pub mod shell;
 mod whole_stream_command;
 
+pub use crate::basic_evaluation_context::basic_evaluation_context;
+pub use crate::basic_shell_manager::basic_shell_manager;
 pub use crate::call_info::UnevaluatedCallInfo;
 pub use crate::command_args::{
     CommandArgs, EvaluatedCommandArgs, EvaluatedWholeStreamCommandArgs, RawCommandArgs,