Define Handle and implement for expansion error

yash-semantics/src/expansion.rs

@@ -73,9 +73,10 @@ pub use yash_env::expansion::*;
 pub use quote_removal::*;
 
 /// Types of errors that may occur in the word expansion.
-#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+#[derive(Clone, Debug, Eq, PartialEq)]
 pub enum ErrorCause {
     // TODO Define error cause types
+    Dummy(String),
 }
 
 /// Explanation of an expansion failure.

yash-semantics/src/handle_impl.rs

@@ -0,0 +1,45 @@
+// This file is part of yash, an extended POSIX shell.
+// Copyright (C) 2021 WATANABE Yuki
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+//! Implementations of [`Handle`].
+
+use crate::ExitStatus;
+use crate::Handle;
+use async_trait::async_trait;
+use yash_env::Env;
+
+#[async_trait(?Send)]
+impl Handle<crate::expansion::Error> for Env {
+    /// Prints an error message and sets the exit status to non-zero.
+    ///
+    /// This function handles an expansion error by printing an error message
+    /// that describes the error to the standard error and setting the exit
+    /// status to [`ExitStatus::ERROR`]. Note that other POSIX-compliant
+    /// implementations may use different non-zero exit statuses.
+    async fn handle(&mut self, error: crate::expansion::Error) -> super::Result {
+        use crate::expansion::ErrorCause::*;
+        // TODO Localize the message
+        // TODO Pretty-print the error location
+        match error.cause {
+            Dummy(message) => {
+                self.print_error(&format_args!("dummy error: {}", message))
+                    .await
+            }
+        };
+        self.exit_status = ExitStatus::ERROR;
+        Ok(())
+    }
+}

yash-semantics/src/lib.rs

@@ -27,6 +27,7 @@ pub mod command_search;
 mod compound;
 pub mod expansion;
 mod function_definition;
+mod handle_impl;
 mod pipeline;
 mod simple_command;
 
@@ -45,6 +46,17 @@ pub trait Command {
     async fn execute(&self, env: &mut Env) -> Result;
 }
 
+/// Error handler.
+///
+/// Most errors in the shell are handled by printing an error message to the
+/// standard error and returning a non-zero exit status. This trait provides a
+/// standard interface for implementing that behavior.
+#[async_trait(?Send)]
+pub trait Handle<E> {
+    /// Handles the argument error.
+    async fn handle(&mut self, error: E) -> Result;
+}
+
 // TODO Probably we should implement a read-execute loop in here
 
 #[cfg(test)]