Introduce TryFromOperatorError

TryFrom implementations should return a specific error type, not just
().

Author: magicant

yash-syntax/CHANGELOG.md

@@ -14,14 +14,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `impl FromStr for parser::lex::Keyword`
 - `parser::lex::Operator::as_str`
 - `parser::lex::ParseOperatorError`
+- `parser::lex::TryFromOperatorError`
 
 ### Changed
 
 - `parser::lex::Keyword::is_clause_delimiter` now `const` and `#[must_use]`
 - `parser::lex::Operator::is_clause_delimiter` now `const` and `#[must_use]`
 - `<parser::lex::Operator as FromStr>::Err` from `()` to `ParseOperatorError`
 - `<syntax::AndOr as FromStr>::Err` from `()` to `ParseOperatorError`
+- `<syntax::AndOr as TryFrom<parser::lex::Operator>>::Error` from `()` to `TryFromOperatorError`
 - `<syntax::RedirOp as FromStr>::Err` from `()` to `ParseOperatorError`
+- `<syntax::RedirOp as TryFrom<parser::lex::Operator>>::Error` from `()` to `TryFromOperatorError`
 
 ### Removed
 

yash-syntax/src/parser/lex.rs

@@ -43,6 +43,7 @@ pub use self::keyword::Keyword;
 pub use self::keyword::ParseKeywordError;
 pub use self::op::is_operator_char;
 pub use self::op::Operator;
+pub use self::op::TryFromOperatorError;
 pub use self::raw_param::is_portable_name_char;
 pub use self::raw_param::is_special_parameter_char;
 pub use self::token::is_token_delimiter_char;

yash-syntax/src/parser/lex/op.rs

@@ -26,6 +26,7 @@ use crate::syntax::Word;
 use std::fmt;
 use std::future::Future;
 use std::pin::Pin;
+use thiserror::Error;
 
 /// Operator token identifier.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
@@ -376,6 +377,16 @@ impl Lexer<'_> {
     }
 }
 
+/// Error value indicating an operand conversion failure
+#[derive(Clone, Debug, Eq, Error, PartialEq)]
+pub struct TryFromOperatorError {}
+
+impl fmt::Display for TryFromOperatorError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("inconvertible operator")
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

yash-syntax/src/syntax.rs

@@ -74,6 +74,7 @@
 //! with here-document contents included, you can use ... TODO TBD.
 
 use crate::parser::lex::Operator;
+use crate::parser::lex::TryFromOperatorError;
 use crate::source::Location;
 use itertools::Itertools;
 use std::cell::OnceCell;
@@ -785,8 +786,8 @@ pub enum RedirOp {
 }
 
 impl TryFrom<Operator> for RedirOp {
-    type Error = ();
-    fn try_from(op: Operator) -> Result<RedirOp, ()> {
+    type Error = TryFromOperatorError;
+    fn try_from(op: Operator) -> Result<RedirOp, TryFromOperatorError> {
         use Operator::*;
         use RedirOp::*;
         match op {
@@ -799,7 +800,7 @@ impl TryFrom<Operator> for RedirOp {
             GreaterAnd => Ok(FdOut),
             GreaterGreaterBar => Ok(Pipe),
             LessLessLess => Ok(String),
-            _ => Err(()),
+            _ => Err(TryFromOperatorError {}),
         }
     }
 }
@@ -1177,12 +1178,12 @@ pub enum AndOr {
 }
 
 impl TryFrom<Operator> for AndOr {
-    type Error = ();
-    fn try_from(op: Operator) -> Result<AndOr, ()> {
+    type Error = TryFromOperatorError;
+    fn try_from(op: Operator) -> Result<AndOr, TryFromOperatorError> {
         match op {
             Operator::AndAnd => Ok(AndOr::AndThen),
             Operator::BarBar => Ok(AndOr::OrElse),
-            _ => Err(()),
+            _ => Err(TryFromOperatorError {}),
         }
     }
 }