Show $PS2 prompt for continuation lines in the read built-in (#380)

check-extra.sh

@@ -18,11 +18,15 @@ cargo tomlfmt --dryrun --path yash-syntax/Cargo.toml
 
 # Make sure we don't have any unnecessary dependencies in Cargo.toml.
 RUSTFLAGS='-D unused_crate_dependencies' cargo check --lib --all-features
+RUSTFLAGS='-D unused_crate_dependencies' cargo check --package 'yash-builtin' --no-default-features
+RUSTFLAGS='-D unused_crate_dependencies' cargo check --package 'yash-builtin' --no-default-features --features yash-semantics
+RUSTFLAGS='-D unused_crate_dependencies' cargo check --package 'yash-syntax' --no-default-features
 
 # Make sure the crates can be built with all combinations of features.
 cargo build --package 'yash-arith' --all-targets
 cargo build --package 'yash-builtin' --all-targets
 cargo build --package 'yash-builtin' --all-targets --no-default-features
+cargo build --package 'yash-builtin' --all-targets --no-default-features --features yash-semantics
 cargo build --package 'yash-cli' --all-targets
 cargo build --package 'yash-env' --all-targets
 cargo build --package 'yash-env-test-helper' --all-targets

yash-builtin/CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- The read built-in now shows a prompt when reading a continued line.
 - The break and continue built-ins now return `ExitStatus::ERROR` for syntax
   errors and `ExitStatus::FAILURE` for semantic errors. Previously, they always
   returned `ExitStatus::ERROR` for both types of errors, while the documentation

yash-builtin/Cargo.toml

@@ -14,7 +14,9 @@ keywords = ["posix", "shell"]
 categories = ["command-line-utilities"]
 
 [features]
-default = ["yash-semantics"]
+default = ["yash-prompt", "yash-semantics"]
+# yash-prompt is used in the read built-in, which requires yash-semantics.
+yash-prompt = ["dep:yash-prompt", "yash-semantics"]
 yash-semantics = ["dep:yash-semantics", "dep:enumset"]
 
 [dependencies]
@@ -23,6 +25,7 @@ enumset = { version = "1.1.2", optional = true }
 itertools = "0.13.0"
 thiserror = "1.0.47"
 yash-env = { path = "../yash-env", version = "0.2.0" }
+yash-prompt = { path = "../yash-prompt", version = "0.1.0", optional = true }
 yash-quote = { path = "../yash-quote", version = "1.1.1" }
 yash-semantics = { path = "../yash-semantics", version = "0.2.0", optional = true }
 yash-syntax = { path = "../yash-syntax", version = "0.9.0" }

yash-builtin/src/read.rs

@@ -51,6 +51,8 @@
 //! value of the `PS2` variable as a prompt if the shell is interactive and the
 //! input is from a terminal.
 //!
+//! Prompting requires the optional `yash-prompt` feature.
+//!
 //! # Options
 //!
 //! The **`-r`** option disables the interpretation of backslashes.

yash-builtin/src/read/input.rs

@@ -95,7 +95,8 @@ fn plain(value: char) -> AttrChar {
 /// continuation, this function removes the backslash-newline pair and continues
 /// reading the next line. When reading the second and subsequent lines, this
 /// function displays the value of the `PS2` variable as a prompt if the shell
-/// is interactive and the input is from a terminal.
+/// is interactive and the input is from a terminal. This requires the optional
+/// `yash-prompt` feature.
 ///
 /// If successful, this function returns a vector of [`AttrChar`]s representing
 /// the line read and a boolean value indicating whether the line was terminated
@@ -114,7 +115,7 @@ pub async fn read(env: &mut Env, is_raw: bool) -> Result<(Vec<AttrChar>, bool),
                 let c = read_char(env).await?;
                 if c == Some('\n') {
                     // Line continuation
-                    // TODO Display $PS2
+                    print_prompt(env).await;
                     continue;
                 }
                 result.push(quoting('\\'));
@@ -179,6 +180,36 @@ async fn read_char(env: &mut Env) -> Result<Option<char>, Error> {
     }
 }
 
+/// Prints the prompt string for the continuation line.
+///
+/// This function prints the value of the `PS2` variable as a prompt for the
+/// continuation line. If the shell is not interactive or the standard input
+/// is not a terminal, this function does nothing.
+async fn print_prompt(env: &mut Env) {
+    #[cfg(feature = "yash-prompt")]
+    {
+        use yash_env::System as _;
+        if !env.is_interactive() {
+            return;
+        }
+        if env.system.isatty(Fd::STDIN) != Ok(true) {
+            return;
+        }
+
+        // Obtain the prompt string
+        let mut context = yash_env::input::Context::default();
+        context.set_is_first_line(false);
+        let prompt = yash_prompt::fetch_posix(&env.variables, &context);
+        let prompt = yash_prompt::expand_posix(env, &prompt, false).await;
+        env.system.print_error(&prompt).await;
+    }
+
+    #[cfg(not(feature = "yash-prompt"))]
+    {
+        _ = env;
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -320,4 +351,6 @@ mod tests {
             assert_eq!(result, Err(Errno::EILSEQ.into()));
         });
     }
+
+    // TODO Test PS2 prompt
 }

yash-cli/CHANGELOG.md

@@ -34,6 +34,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - The break and continue built-ins no longer allow exiting a trap.
+- The read built-in now shows a prompt when reading a continued line.
 
 ## [0.1.0-beta.1] - 2024-06-09
 

yash-env/CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- `Env::is_interactive`
 - `impl yash_system::alias::Glossary for Env`
 - `input::Echo`
     - This is a decorator of `Input` that implements the behavior of the verbose shell option.

yash-env/src/lib.rs

@@ -40,7 +40,7 @@ use self::job::Pid;
 use self::job::ProcessState;
 use self::option::On;
 use self::option::OptionSet;
-use self::option::{AllExport, ErrExit, Monitor};
+use self::option::{AllExport, ErrExit, Interactive, Monitor};
 use self::semantics::Divert;
 use self::semantics::ExitStatus;
 use self::stack::Frame;
@@ -303,6 +303,17 @@ impl Env {
         final_fd
     }
 
+    /// Tests whether the current environment is an interactive shell.
+    ///
+    /// This function returns true if and only if:
+    ///
+    /// - the [`Interactive`] option is `On` in `self.options`, and
+    /// - the current context is not in a subshell (no `Frame::Subshell` in `self.stack`).
+    #[must_use]
+    pub fn is_interactive(&self) -> bool {
+        self.options.get(Interactive) == On && !self.stack.contains(&Frame::Subshell)
+    }
+
     /// Tests whether the shell is performing job control.
     ///
     /// This function returns true if and only if:

yash-prompt/src/lib.rs

@@ -27,6 +27,8 @@
 //! used to create an interactive shell prompt. The prompter internally uses
 //! the following functions to expand prompt strings:
 //!
+//! - [`fetch_posix`]: Fetches the value of a variable defined by POSIX for
+//!   a prompt string.
 //! - [`expand_posix`]: Expands a prompt string in a POSIX-compliant manner.
 //! - `expand_ex`: Expands a prompt string with yash-specific expansions.
 //!   (This function is not yet implemented.)
@@ -70,4 +72,5 @@ pub use expand_posix::expand_posix;
 // TODO Yash-specific prompt expansion
 
 mod prompter;
+pub use prompter::fetch_posix;
 pub use prompter::Prompter;

yash-prompt/src/prompter.rs

@@ -19,7 +19,7 @@
 use async_trait::async_trait;
 use std::cell::RefCell;
 use yash_env::input::{Context, Input, Result};
-use yash_env::variable::{Expansion, PS1, PS2};
+use yash_env::variable::{Expansion, VariableSet, PS1, PS2};
 use yash_env::Env;
 use yash_syntax::source::Location;
 
@@ -60,24 +60,40 @@ where
 }
 
 async fn print_prompt(env: &mut Env, context: &Context) {
-    let location = Location::dummy(""); // TODO context.location;
-
-    // TODO Yash-specific prompt variables
-    let var = if context.is_first_line() { PS1 } else { PS2 };
-    // https://github.com/rust-lang/rust-clippy/issues/13031
-    #[allow(clippy::manual_unwrap_or_default)]
-    let prompt = match env.variables.get(var).map(|v| v.expand(&location)) {
-        Some(Expansion::Scalar(s)) => s.into_owned(),
-        _ => Default::default(),
-    };
+    // Obtain the prompt string
+    let prompt = fetch_posix(&env.variables, context);
 
     // Perform parameter expansion in the prompt string
-    let expanded_prompt = super::expand_posix(env, &prompt, true).await;
+    let expanded_prompt = super::expand_posix(env, &prompt, context.is_first_line()).await;
 
     // Print the prompt to the standard error
     env.system.print_error(&expanded_prompt).await;
 }
 
+/// Fetches the command prompt string from the variable set.
+///
+/// The return value is the raw value taken from the `PS1` or `PS2` variable
+/// in the set. [`Context::is_first_line`] determines which variable is used.
+/// An empty string is returned if the variable is not found.
+///
+/// The returned prompt string should be expanded before being shown to the
+/// user.
+///
+/// This function does not consider yash-specific prompt variables.
+pub fn fetch_posix(variables: &VariableSet, context: &Context) -> String {
+    // TODO context.location;
+    let location = Location::dummy("");
+
+    let var = if context.is_first_line() { PS1 } else { PS2 };
+    // https://github.com/rust-lang/rust-clippy/issues/13031
+    match variables.get(var).map(|v| v.expand(&location)) {
+        Some(Expansion::Scalar(s)) => s.into_owned(),
+        _ => Default::default(),
+    }
+}
+
+// TODO pub fn fetch_ex: yash-specific prompt variables
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -145,7 +161,7 @@ mod tests {
         let system = Box::new(VirtualSystem::new());
         let state = Rc::clone(&system.state);
         let mut env = Env::with_system(system);
-        define_variable(&mut env, PS1, "my_custom_prompt>");
+        define_variable(&mut env, PS1, "my_custom_prompt !! >");
         let ref_env = RefCell::new(&mut env);
         let mut prompter = Prompter::new(Memory::new(""), &ref_env);
 
@@ -154,22 +170,24 @@ mod tests {
             .now_or_never()
             .unwrap()
             .ok();
-        assert_stderr(&state, |stderr| assert_eq!(stderr, "my_custom_prompt>"));
+        assert_stderr(&state, |stderr| assert_eq!(stderr, "my_custom_prompt ! >"));
+        // Note that "!!" is expanded to "!" in the prompt string.
     }
 
     #[test]
     fn ps2_variable_defines_continuation_prompt() {
         let system = Box::new(VirtualSystem::new());
         let state = Rc::clone(&system.state);
         let mut env = Env::with_system(system);
-        define_variable(&mut env, PS2, "continuation_prompt>");
+        define_variable(&mut env, PS2, "continuation ! >");
         let ref_env = RefCell::new(&mut env);
         let mut prompter = Prompter::new(Memory::new(""), &ref_env);
         let mut context = Context::default();
         context.set_is_first_line(false);
 
         prompter.next_line(&context).now_or_never().unwrap().ok();
-        assert_stderr(&state, |stderr| assert_eq!(stderr, "continuation_prompt>"));
+        assert_stderr(&state, |stderr| assert_eq!(stderr, "continuation ! >"));
+        // Note that "!" is not expanded in the prompt string.
     }
 
     #[test]