fix: fix commandline when called with no arguments (#8207)

# Description

This fixes the `commandline` command when it's run with no arguments, so
it outputs the command being run. New line characters are included.

This allows for:

- [A way to get current command inside pre_execution hook · Issue #6264
· nushell/nushell](https://github.com/nushell/nushell/issues/6264)
- The possibility of *Atuin* to work work *Nushell*. *Atuin* hooks need
to know the current repl input before it is run.

# User-Facing Changes

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

Cargo.lock

@@ -2746,6 +2746,7 @@ dependencies = [
  "nu-test-support",
  "nu-utils",
  "shadow-rs",
+ "unicode-segmentation",
 ]
 
 [[package]]

crates/nu-cli/src/repl.rs

@@ -14,7 +14,7 @@ use nu_parser::{lex, parse, trim_quotes_str};
 use nu_protocol::{
     ast::PathMember,
     config::NuCursorShape,
-    engine::{EngineState, ReplOperation, Stack, StateWorkingSet},
+    engine::{EngineState, Stack, StateWorkingSet},
     format_duration, BlockId, HistoryFileFormat, PipelineData, PositionalArg, ShellError, Span,
     Spanned, Type, Value, VarId,
 };
@@ -459,18 +459,30 @@ pub fn evaluate_repl(
                         .into_diagnostic()?; // todo: don't stop repl if error here?
                 }
 
-                engine_state
-                    .repl_buffer_state
-                    .lock()
-                    .expect("repl buffer state mutex")
-                    .replace(line_editor.current_buffer_contents().to_string());
-
                 // Right before we start running the code the user gave us,
                 // fire the "pre_execution" hook
                 if let Some(hook) = config.hooks.pre_execution.clone() {
+                    // Set the REPL buffer to the current command for the "pre_execution" hook
+                    let mut repl_buffer = engine_state
+                        .repl_buffer_state
+                        .lock()
+                        .expect("repl buffer state mutex");
+                    let next_repl_buffer = repl_buffer.to_string();
+                    *repl_buffer = s.to_string();
+                    drop(repl_buffer);
+
                     if let Err(err) = eval_hook(engine_state, stack, None, vec![], &hook) {
                         report_error_new(engine_state, &err);
                     }
+
+                    // Restore the REPL buffer state for the next command. It could've been edited
+                    // by `commandline`.
+                    let mut repl_buffer = engine_state
+                        .repl_buffer_state
+                        .lock()
+                        .expect("repl buffer state mutex");
+                    *repl_buffer = next_repl_buffer;
+                    drop(repl_buffer);
                 }
 
                 if shell_integration {
@@ -628,23 +640,23 @@ pub fn evaluate_repl(
                     run_ansi_sequence(RESET_APPLICATION_MODE)?;
                 }
 
-                let mut ops = engine_state
-                    .repl_operation_queue
+                let mut repl_buffer = engine_state
+                    .repl_buffer_state
                     .lock()
-                    .expect("repl op queue mutex");
-                while let Some(op) = ops.pop_front() {
-                    match op {
-                        ReplOperation::Append(s) => line_editor.run_edit_commands(&[
-                            EditCommand::MoveToEnd,
-                            EditCommand::InsertString(s),
-                        ]),
-                        ReplOperation::Insert(s) => {
-                            line_editor.run_edit_commands(&[EditCommand::InsertString(s)])
-                        }
-                        ReplOperation::Replace(s) => line_editor
-                            .run_edit_commands(&[EditCommand::Clear, EditCommand::InsertString(s)]),
-                    }
-                }
+                    .expect("repl buffer state mutex");
+                let mut repl_cursor_pos = engine_state
+                    .repl_cursor_pos
+                    .lock()
+                    .expect("repl cursor pos mutex");
+                line_editor.run_edit_commands(&[
+                    EditCommand::Clear,
+                    EditCommand::InsertString(repl_buffer.to_string()),
+                    EditCommand::MoveToPosition(*repl_cursor_pos),
+                ]);
+                *repl_buffer = "".to_string();
+                drop(repl_buffer);
+                *repl_cursor_pos = 0;
+                drop(repl_cursor_pos);
             }
             Ok(Signal::CtrlC) => {
                 // `Reedline` clears the line content. New prompt is shown

crates/nu-cmd-lang/Cargo.toml

@@ -24,6 +24,7 @@ fancy-regex = "0.11.0"
 itertools = "0.10.0"
 log = "0.4.14"
 shadow-rs = { version = "0.21.0", default-features = false }
+unicode-segmentation = "1.10.0"
 
 [build-dependencies]
 shadow-rs = { version = "0.21.0", default-features = false }

crates/nu-cmd-lang/src/core_commands/commandline.rs

@@ -1,10 +1,10 @@
 use nu_engine::CallExt;
 use nu_protocol::ast::Call;
-use nu_protocol::engine::ReplOperation;
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::Category;
 use nu_protocol::IntoPipelineData;
 use nu_protocol::{PipelineData, ShellError, Signature, SyntaxShape, Type, Value};
+use unicode_segmentation::UnicodeSegmentation;
 
 #[derive(Clone)]
 pub struct Commandline;
@@ -17,6 +17,11 @@ impl Command for Commandline {
     fn signature(&self) -> Signature {
         Signature::build("commandline")
             .input_output_types(vec![(Type::Nothing, Type::Nothing)])
+            .switch(
+                "cursor",
+                "Set or get the current cursor position",
+                Some('c'),
+            )
             .switch(
                 "append",
                 "appends the string to the end of the buffer",
@@ -56,30 +61,77 @@ impl Command for Commandline {
         _input: PipelineData,
     ) -> Result<PipelineData, ShellError> {
         if let Some(cmd) = call.opt::<Value>(engine_state, stack, 0)? {
-            let mut ops = engine_state
-                .repl_operation_queue
-                .lock()
-                .expect("repl op queue mutex");
-            ops.push_back(if call.has_flag("append") {
-                ReplOperation::Append(cmd.as_string()?)
-            } else if call.has_flag("insert") {
-                ReplOperation::Insert(cmd.as_string()?)
-            } else {
-                ReplOperation::Replace(cmd.as_string()?)
-            });
-            Ok(Value::Nothing { span: call.head }.into_pipeline_data())
-        } else if let Some(ref cmd) = *engine_state
+            let mut buffer = engine_state
                 .repl_buffer_state
                 .lock()
-            .expect("repl buffer state mutex")
-        {
+                .expect("repl buffer state mutex");
+            let mut cursor_pos = engine_state
+                .repl_cursor_pos
+                .lock()
+                .expect("repl cursor pos mutex");
+
+            if call.has_flag("cursor") {
+                let cmd_str = cmd.as_string()?;
+                match cmd_str.parse::<i64>() {
+                    Ok(n) => {
+                        *cursor_pos = if n <= 0 {
+                            0usize
+                        } else {
+                            buffer
+                                .grapheme_indices(true)
+                                .map(|(i, _c)| i)
+                                .nth(n as usize)
+                                .unwrap_or(buffer.len())
+                        }
+                    }
+                    Err(_) => {
+                        return Err(ShellError::CantConvert {
+                            to_type: "int".to_string(),
+                            from_type: "string".to_string(),
+                            span: cmd.span()?,
+                            help: Some(format!(
+                                r#"string "{cmd_str}" does not represent a valid integer"#
+                            )),
+                        })
+                    }
+                }
+            } else if call.has_flag("append") {
+                buffer.push_str(&cmd.as_string()?);
+            } else if call.has_flag("insert") {
+                let cmd_str = cmd.as_string()?;
+                buffer.insert_str(*cursor_pos, &cmd_str);
+                *cursor_pos += cmd_str.len();
+            } else {
+                *buffer = cmd.as_string()?;
+                *cursor_pos = buffer.len();
+            }
+            Ok(Value::Nothing { span: call.head }.into_pipeline_data())
+        } else {
+            let buffer = engine_state
+                .repl_buffer_state
+                .lock()
+                .expect("repl buffer state mutex");
+            if call.has_flag("cursor") {
+                let cursor_pos = engine_state
+                    .repl_cursor_pos
+                    .lock()
+                    .expect("repl cursor pos mutex");
+                let char_pos = buffer
+                    .grapheme_indices(true)
+                    .position(|(i, _c)| i == *cursor_pos)
+                    .unwrap_or(buffer.len());
                 Ok(Value::String {
-                val: cmd.clone(),
+                    val: char_pos.to_string(),
                     span: call.head,
                 }
                 .into_pipeline_data())
             } else {
-            Ok(Value::Nothing { span: call.head }.into_pipeline_data())
+                Ok(Value::String {
+                    val: buffer.to_string(),
+                    span: call.head,
+                }
+                .into_pipeline_data())
+            }
         }
     }
 }

crates/nu-protocol/src/engine/engine_state.rs

@@ -13,7 +13,7 @@ use std::num::NonZeroUsize;
 use std::path::Path;
 use std::path::PathBuf;
 use std::{
-    collections::{HashMap, HashSet, VecDeque},
+    collections::{HashMap, HashSet},
     sync::{
         atomic::{AtomicBool, AtomicU32},
         Arc, Mutex,
@@ -22,15 +22,6 @@ use std::{
 
 static PWD_ENV: &str = "PWD";
 
-// TODO: move to different file? where?
-/// An operation to be performed with the current buffer of the interactive shell.
-#[derive(Debug, Clone)]
-pub enum ReplOperation {
-    Append(String),
-    Insert(String),
-    Replace(String),
-}
-
 /// Organizes usage messages for various primitives
 #[derive(Debug, Clone)]
 pub struct Usage {
@@ -134,8 +125,9 @@ pub struct EngineState {
     pub previous_env_vars: HashMap<String, Value>,
     pub config: Config,
     pub pipeline_externals_state: Arc<(AtomicU32, AtomicU32)>,
-    pub repl_buffer_state: Arc<Mutex<Option<String>>>,
-    pub repl_operation_queue: Arc<Mutex<VecDeque<ReplOperation>>>,
+    pub repl_buffer_state: Arc<Mutex<String>>,
+    // A byte position, as `EditCommand::MoveToPosition` is also a byte position
+    pub repl_cursor_pos: Arc<Mutex<usize>>,
     #[cfg(feature = "plugin")]
     pub plugin_signatures: Option<PathBuf>,
     #[cfg(not(windows))]
@@ -186,8 +178,8 @@ impl EngineState {
             previous_env_vars: HashMap::new(),
             config: Config::default(),
             pipeline_externals_state: Arc::new((AtomicU32::new(0), AtomicU32::new(0))),
-            repl_buffer_state: Arc::new(Mutex::new(None)),
-            repl_operation_queue: Arc::new(Mutex::new(VecDeque::new())),
+            repl_buffer_state: Arc::new(Mutex::new("".to_string())),
+            repl_cursor_pos: Arc::new(Mutex::new(0)),
             #[cfg(feature = "plugin")]
             plugin_signatures: None,
             #[cfg(not(windows))]

src/test_bins.rs

@@ -209,6 +209,12 @@ pub fn nu_repl() {
 
         // Check for pre_execution hook
         let config = engine_state.get_config();
+
+        *engine_state
+            .repl_buffer_state
+            .lock()
+            .expect("repl buffer state mutex") = line.to_string();
+
         if let Some(hook) = config.hooks.pre_execution.clone() {
             if let Err(err) = eval_hook(&mut engine_state, &mut stack, None, vec![], &hook) {
                 outcome_err(&engine_state, &err);

src/tests.rs

@@ -1,5 +1,6 @@
 mod test_bits;
 mod test_cell_path;
+mod test_commandline;
 mod test_conditionals;
 mod test_config_path;
 mod test_converters;

src/tests/test_commandline.rs

@@ -0,0 +1,109 @@
+use crate::tests::{fail_test, run_test, TestResult};
+
+#[test]
+fn commandline_test_get_empty() -> TestResult {
+    run_test("commandline", "")
+}
+
+#[test]
+fn commandline_test_append() -> TestResult {
+    run_test(
+        "commandline --replace '0👩‍❤️‍👩2'\n\
+        commandline --cursor '2'\n\
+        commandline --append 'ab'\n\
+        commandline\n\
+        commandline --cursor",
+        "0👩‍❤️‍👩2ab\n\
+        2",
+    )
+}
+
+#[test]
+fn commandline_test_insert() -> TestResult {
+    run_test(
+        "commandline --replace '0👩‍❤️‍👩2'\n\
+        commandline --cursor '2'\n\
+        commandline --insert 'ab'\n\
+        commandline\n\
+        commandline --cursor",
+        "0👩‍❤️‍👩ab2\n\
+        4",
+    )
+}
+
+#[test]
+fn commandline_test_replace() -> TestResult {
+    run_test(
+        "commandline --replace '0👩‍❤️‍👩2'\n\
+        commandline --replace 'ab'\n\
+        commandline\n\
+        commandline --cursor",
+        "ab\n\
+        2",
+    )
+}
+
+#[test]
+fn commandline_test_cursor() -> TestResult {
+    run_test(
+        "commandline --replace '0👩‍❤️‍👩2'\n\
+        commandline --cursor '1' \n\
+        commandline --insert 'x'\n\
+        commandline",
+        "0x👩‍❤️‍👩2",
+    )?;
+    run_test(
+        "commandline --replace '0👩‍❤️‍👩2'\n\
+        commandline --cursor '2' \n\
+        commandline --insert 'x'\n\
+        commandline",
+        "0👩‍❤️‍👩x2",
+    )
+}
+
+#[test]
+fn commandline_test_cursor_show_pos() -> TestResult {
+    run_test(
+        "commandline --replace '0👩‍❤️‍👩2'\n\
+        commandline --cursor '1' \n\
+        commandline --cursor",
+        "1",
+    )?;
+    run_test(
+        "commandline --replace '0👩‍❤️‍👩2'\n\
+        commandline --cursor '2' \n\
+        commandline --cursor",
+        "2",
+    )
+}
+
+#[test]
+fn commandline_test_cursor_too_small() -> TestResult {
+    run_test(
+        "commandline --replace '123456'\n\
+        commandline --cursor '-1' \n\
+        commandline --insert '0'\n\
+        commandline",
+        "0123456",
+    )
+}
+
+#[test]
+fn commandline_test_cursor_too_large() -> TestResult {
+    run_test(
+        "commandline --replace '123456'\n\
+        commandline --cursor '10' \n\
+        commandline --insert '0'\n\
+        commandline",
+        "1234560",
+    )
+}
+
+#[test]
+fn commandline_test_cursor_invalid() -> TestResult {
+    fail_test(
+        "commandline --replace '123456'\n\
+        commandline --cursor 'abc'",
+        r#"string "abc" does not represent a valid integer"#,
+    )
+}

tests/hooks/mod.rs

@@ -325,6 +325,19 @@ fn pre_execution_block_preserve_env_var() {
     assert_eq!(actual_repl.out, "spam");
 }
 
+#[test]
+fn pre_execution_commandline() {
+    let inp = &[
+        &pre_execution_hook_code(r#"{ let-env repl_commandline = (commandline) }"#),
+        "echo foo!; $env.repl_commandline",
+    ];
+
+    let actual_repl = nu!(cwd: "tests/hooks", nu_repl_code(inp));
+
+    assert_eq!(actual_repl.err, "");
+    assert_eq!(actual_repl.out, "foo!echo foo!; $env.repl_commandline");
+}
+
 #[test]
 fn env_change_shadow_command() {
     let inp = &[