PROMPT_STRING env variable (#3918)

* prompt string env variable

* cargo clippy

crates/nu-cli/src/cli.rs

@@ -31,9 +31,12 @@ use std::error::Error;
 use std::iter::Iterator;
 use std::path::PathBuf;
 
+// Name of environment variable where the prompt could be stored
+#[cfg(feature = "rustyline-support")]
+const PROMPT_STRING: &str = "PROMPT_STRING";
+
 pub fn search_paths() -> Vec<std::path::PathBuf> {
     use std::env;
-
     let mut search_paths = Vec::new();
 
     // Automatically add path `nu` is in as a search path
@@ -83,6 +86,66 @@ pub fn run_script_file(
     Ok(())
 }
 
+#[cfg(feature = "rustyline-support")]
+fn default_prompt_string(cwd: &str) -> String {
+    format!(
+        "{}{}{}{}{}{}> ",
+        Color::Green.bold().prefix().to_string(),
+        cwd,
+        nu_ansi_term::ansi::RESET,
+        Color::Cyan.bold().prefix().to_string(),
+        current_branch(),
+        nu_ansi_term::ansi::RESET
+    )
+}
+
+#[cfg(feature = "rustyline-support")]
+fn evaluate_prompt_string(prompt_line: &str, context: &EvaluationContext, cwd: &str) -> String {
+    context.scope.enter_scope();
+    let (prompt_block, err) = nu_parser::parse(prompt_line, 0, &context.scope);
+
+    if err.is_some() {
+        context.scope.exit_scope();
+        default_prompt_string(cwd)
+    } else {
+        let run_result = run_block(
+            &prompt_block,
+            context,
+            InputStream::empty(),
+            ExternalRedirection::Stdout,
+        );
+        context.scope.exit_scope();
+
+        match run_result {
+            Ok(result) => match result.collect_string(Tag::unknown()) {
+                Ok(string_result) => {
+                    let errors = context.get_errors();
+                    maybe_print_errors(context, Text::from(prompt_line));
+                    context.clear_errors();
+
+                    if !errors.is_empty() {
+                        "> ".into()
+                    } else {
+                        string_result.item
+                    }
+                }
+                Err(e) => {
+                    context.host().lock().print_err(e, &Text::from(prompt_line));
+                    context.clear_errors();
+
+                    "> ".into()
+                }
+            },
+            Err(e) => {
+                context.host().lock().print_err(e, &Text::from(prompt_line));
+                context.clear_errors();
+
+                "> ".into()
+            }
+        }
+    }
+}
+
 #[cfg(feature = "rustyline-support")]
 pub fn cli(
     context: EvaluationContext,
@@ -235,72 +298,17 @@ pub fn cli(
 
         let cwd = context.shell_manager().path();
 
-        let colored_prompt = {
+        // Check if the PROMPT_STRING env variable is set. This env variable
-            if let Some(prompt) = &prompt {
+        // contains nu code that is used to overwrite the prompt
-                let prompt_line = prompt.as_string()?;
+        let colored_prompt = match context.scope.get_env(PROMPT_STRING) {
-
+            Some(env_prompt) => evaluate_prompt_string(&env_prompt, &context, &cwd),
-                context.scope.enter_scope();
+            None => {
-                let (prompt_block, err) = nu_parser::parse(&prompt_line, 0, &context.scope);
+                if let Some(prompt) = &prompt {
-
+                    let prompt_line = prompt.as_string()?;
-                if err.is_some() {
+                    evaluate_prompt_string(&prompt_line, &context, &cwd)
-                    context.scope.exit_scope();
-
-                    format!(
-                        "{}{}{}{}{}{}> ",
-                        Color::Green.bold().prefix().to_string(),
-                        cwd,
-                        nu_ansi_term::ansi::RESET,
-                        Color::Cyan.bold().prefix().to_string(),
-                        current_branch(),
-                        nu_ansi_term::ansi::RESET
-                    )
                 } else {
-                    let run_result = run_block(
+                    default_prompt_string(&cwd)
-                        &prompt_block,
-                        &context,
-                        InputStream::empty(),
-                        ExternalRedirection::Stdout,
-                    );
-                    context.scope.exit_scope();
-
-                    match run_result {
-                        Ok(result) => match result.collect_string(Tag::unknown()) {
-                            Ok(string_result) => {
-                                let errors = context.get_errors();
-                                maybe_print_errors(&context, Text::from(prompt_line));
-                                context.clear_errors();
-
-                                if !errors.is_empty() {
-                                    "> ".to_string()
-                                } else {
-                                    string_result.item
-                                }
-                            }
-                            Err(e) => {
-                                context.host().lock().print_err(e, &Text::from(prompt_line));
-                                context.clear_errors();
-
-                                "> ".to_string()
-                            }
-                        },
-                        Err(e) => {
-                            context.host().lock().print_err(e, &Text::from(prompt_line));
-                            context.clear_errors();
-
-                            "> ".to_string()
-                        }
-                    }
                 }
-            } else {
-                format!(
-                    "{}{}{}{}{}{}> ",
-                    Color::Green.bold().prefix().to_string(),
-                    cwd,
-                    nu_ansi_term::ansi::RESET,
-                    Color::Cyan.bold().prefix().to_string(),
-                    current_branch(),
-                    nu_ansi_term::ansi::RESET
-                )
             }
         };
 
@@ -432,6 +440,7 @@ pub fn cli(
     Ok(())
 }
 
+#[cfg(feature = "rustyline-support")]
 pub fn load_local_cfg_if_present(context: &EvaluationContext) {
     trace!("Loading local cfg if present");
     match config::loadable_cfg_exists_in_dir(PathBuf::from(context.shell_manager().path())) {