Only run $env.PROMPT_COMMAND once per prompt (copy of #10986) (#11366)

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# Description
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This PR is basically a copy of #10986 by @CAD97, which made
`$env.PROMPT_COMMAND` only run once per prompt, but @fdncred found an
issue where hitting Enter would make the transient prompt appear and be
immediately overwritten by the regular prompt, so it was
[reverted](https://github.com/nushell/nushell/pull/11340).
https://github.com/nushell/nushell/pull/10788 was also made to do the
same thing as #10986 but that ended up having the same issue. For some
reason, this branch doesn't have that problem, although I haven't
figured out why yet.

@CAD97, if you have any inputs or want to make your own PR, let me know.

# User-Facing Changes
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helps us keep track of breaking changes. -->

When hitting enter, the prompt shouldn't blink in place anymore.

# Tests + Formatting
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crates/nu-cli/src/prompt_update.rs

@@ -7,8 +7,6 @@ use nu_protocol::{
     Config, PipelineData, Value,
 };
 use reedline::Prompt;
-use std::borrow::Cow;
-use std::sync::{Arc, RwLock};
 
 // Name of environment variable where the prompt could be stored
 pub(crate) const PROMPT_COMMAND: &str = "PROMPT_COMMAND";
@@ -102,7 +100,7 @@ pub(crate) fn update_prompt(
     config: &Config,
     engine_state: &EngineState,
     stack: &Stack,
-    nu_prompt: Arc<RwLock<NushellPrompt>>,
+    nu_prompt: &mut NushellPrompt,
 ) {
     let mut stack = stack.clone();
 
@@ -138,145 +136,63 @@ pub(crate) fn update_prompt(
         get_prompt_string(PROMPT_INDICATOR_VI_NORMAL, config, engine_state, &mut stack);
 
     // apply the other indicators
-    nu_prompt
-        .write()
-        .expect("Could not lock on nu_prompt to update")
-        .update_all_prompt_strings(
-            left_prompt_string,
-            right_prompt_string,
-            prompt_indicator_string,
-            prompt_multiline_string,
-            (prompt_vi_insert_string, prompt_vi_normal_string),
-            config.render_right_prompt_on_last_line,
-        );
-
+    nu_prompt.update_all_prompt_strings(
+        left_prompt_string,
+        right_prompt_string,
+        prompt_indicator_string,
+        prompt_multiline_string,
+        (prompt_vi_insert_string, prompt_vi_normal_string),
+        config.render_right_prompt_on_last_line,
+    );
     trace!("update_prompt {}:{}:{}", file!(), line!(), column!());
 }
 
-struct TransientPrompt {
-    prompt_lock: Arc<RwLock<NushellPrompt>>,
-    engine_state: Arc<EngineState>,
-    stack: Stack,
-}
-
-impl TransientPrompt {
-    fn new_prompt(&self, shell_integration: bool) -> NushellPrompt {
-        if let Ok(prompt) = self.prompt_lock.read() {
-            prompt.clone()
-        } else {
-            NushellPrompt::new(shell_integration)
-        }
-    }
-}
-
-impl Prompt for TransientPrompt {
-    fn render_prompt_left(&self) -> Cow<str> {
-        let config = self.engine_state.get_config();
-        let mut nu_prompt = self.new_prompt(config.shell_integration);
-        let mut stack = self.stack.clone();
-        if let Some(s) = get_prompt_string(
-            TRANSIENT_PROMPT_COMMAND,
-            config,
-            &self.engine_state,
-            &mut stack,
-        ) {
-            nu_prompt.update_prompt_left(Some(s))
-        }
-        let left_prompt = nu_prompt.render_prompt_left();
-        if config.shell_integration {
-            format!("{PRE_PROMPT_MARKER}{left_prompt}{POST_PROMPT_MARKER}").into()
-        } else {
-            left_prompt.to_string().into()
-        }
-    }
-
-    fn render_prompt_right(&self) -> Cow<str> {
-        let config = self.engine_state.get_config();
-        let mut nu_prompt = self.new_prompt(config.shell_integration);
-        let mut stack = self.stack.clone();
-        if let Some(s) = get_prompt_string(
-            TRANSIENT_PROMPT_COMMAND_RIGHT,
-            config,
-            &self.engine_state,
-            &mut stack,
-        ) {
-            nu_prompt.update_prompt_right(Some(s), config.render_right_prompt_on_last_line)
-        }
-        nu_prompt.render_prompt_right().to_string().into()
-    }
-
-    fn render_prompt_indicator(&self, prompt_mode: reedline::PromptEditMode) -> Cow<str> {
-        let config = self.engine_state.get_config();
-        let mut nu_prompt = self.new_prompt(config.shell_integration);
-        let mut stack = self.stack.clone();
-        if let Some(s) = get_prompt_string(
-            TRANSIENT_PROMPT_INDICATOR,
-            config,
-            &self.engine_state,
-            &mut stack,
-        ) {
-            nu_prompt.update_prompt_indicator(Some(s))
-        }
-        if let Some(s) = get_prompt_string(
-            TRANSIENT_PROMPT_INDICATOR_VI_INSERT,
-            config,
-            &self.engine_state,
-            &mut stack,
-        ) {
-            nu_prompt.update_prompt_vi_insert(Some(s))
-        }
-        if let Some(s) = get_prompt_string(
-            TRANSIENT_PROMPT_INDICATOR_VI_NORMAL,
-            config,
-            &self.engine_state,
-            &mut stack,
-        ) {
-            nu_prompt.update_prompt_vi_normal(Some(s))
-        }
-        nu_prompt
-            .render_prompt_indicator(prompt_mode)
-            .to_string()
-            .into()
-    }
-
-    fn render_prompt_multiline_indicator(&self) -> Cow<str> {
-        let config = self.engine_state.get_config();
-        let mut nu_prompt = self.new_prompt(config.shell_integration);
-        let mut stack = self.stack.clone();
-        if let Some(s) = get_prompt_string(
-            TRANSIENT_PROMPT_MULTILINE_INDICATOR,
-            config,
-            &self.engine_state,
-            &mut stack,
-        ) {
-            nu_prompt.update_prompt_multiline(Some(s))
-        }
-        nu_prompt
-            .render_prompt_multiline_indicator()
-            .to_string()
-            .into()
-    }
-
-    fn render_prompt_history_search_indicator(
-        &self,
-        history_search: reedline::PromptHistorySearch,
-    ) -> Cow<str> {
-        NushellPrompt::new(self.engine_state.get_config().shell_integration)
-            .render_prompt_history_search_indicator(history_search)
-            .to_string()
-            .into()
-    }
-}
-
-/// Construct the transient prompt
-pub(crate) fn transient_prompt(
-    prompt_lock: Arc<RwLock<NushellPrompt>>,
-    engine_state: Arc<EngineState>,
-    stack: &Stack,
+/// Construct the transient prompt based on the normal nu_prompt
+pub(crate) fn make_transient_prompt(
+    config: &Config,
+    engine_state: &EngineState,
+    stack: &mut Stack,
+    nu_prompt: &NushellPrompt,
 ) -> Box<dyn Prompt> {
-    Box::new(TransientPrompt {
-        prompt_lock,
+    let mut nu_prompt = nu_prompt.clone();
+
+    if let Some(s) = get_prompt_string(TRANSIENT_PROMPT_COMMAND, config, engine_state, stack) {
+        nu_prompt.update_prompt_left(Some(s))
+    }
+
+    if let Some(s) = get_prompt_string(TRANSIENT_PROMPT_COMMAND_RIGHT, config, engine_state, stack)
+    {
+        nu_prompt.update_prompt_right(Some(s), config.render_right_prompt_on_last_line)
+    }
+
+    if let Some(s) = get_prompt_string(TRANSIENT_PROMPT_INDICATOR, config, engine_state, stack) {
+        nu_prompt.update_prompt_indicator(Some(s))
+    }
+    if let Some(s) = get_prompt_string(
+        TRANSIENT_PROMPT_INDICATOR_VI_INSERT,
+        config,
         engine_state,
-        stack: stack.clone(),
-    })
+        stack,
+    ) {
+        nu_prompt.update_prompt_vi_insert(Some(s))
+    }
+    if let Some(s) = get_prompt_string(
+        TRANSIENT_PROMPT_INDICATOR_VI_NORMAL,
+        config,
+        engine_state,
+        stack,
+    ) {
+        nu_prompt.update_prompt_vi_normal(Some(s))
+    }
+
+    if let Some(s) = get_prompt_string(
+        TRANSIENT_PROMPT_MULTILINE_INDICATOR,
+        config,
+        engine_state,
+        stack,
+    ) {
+        nu_prompt.update_prompt_multiline(Some(s))
+    }
+
+    Box::new(nu_prompt)
 }

crates/nu-cli/src/repl.rs

@@ -29,7 +29,7 @@ use std::{
     env::temp_dir,
     io::{self, IsTerminal, Write},
     path::Path,
-    sync::{atomic::Ordering, Arc, RwLock},
+    sync::atomic::Ordering,
     time::Instant,
 };
 use sysinfo::SystemExt;
@@ -69,7 +69,7 @@ pub fn evaluate_repl(
 
     let mut entry_num = 0;
 
-    let nu_prompt = Arc::new(RwLock::new(NushellPrompt::new(config.shell_integration)));
+    let mut nu_prompt = NushellPrompt::new(config.shell_integration);
 
     let start_time = std::time::Instant::now();
     // Translate environment variables from Strings to Values
@@ -268,12 +268,7 @@ pub fn evaluate_repl(
             .with_quick_completions(config.quick_completions)
             .with_partial_completions(config.partial_completions)
             .with_ansi_colors(config.use_ansi_coloring)
-            .with_cursor_config(cursor_config)
-            .with_transient_prompt(prompt_update::transient_prompt(
-                Arc::clone(&nu_prompt),
-                engine_reference.clone(),
-                stack,
-            ));
+            .with_cursor_config(cursor_config);
         perf(
             "reedline builder",
             start_time,
@@ -426,7 +421,9 @@ pub fn evaluate_repl(
 
         start_time = std::time::Instant::now();
         let config = &engine_state.get_config().clone();
-        prompt_update::update_prompt(config, engine_state, stack, Arc::clone(&nu_prompt));
+        prompt_update::update_prompt(config, engine_state, stack, &mut nu_prompt);
+        let transient_prompt =
+            prompt_update::make_transient_prompt(config, engine_state, stack, &nu_prompt);
         perf(
             "update_prompt",
             start_time,
@@ -439,14 +436,8 @@ pub fn evaluate_repl(
         entry_num += 1;
 
         start_time = std::time::Instant::now();
-        let input = {
-            line_editor.read_line(
-                &nu_prompt
-                    .read()
-                    .expect("Could not lock on prompt to pass to read_line")
-                    .to_owned(),
-            )
-        };
+        line_editor = line_editor.with_transient_prompt(transient_prompt);
+        let input = line_editor.read_line(&nu_prompt);
         let shell_integration = config.shell_integration;
 
         match input {