feat(snix/eval): proper error handling for invalid regexes

We don't want to crash the evaluator when an invalid regex is passed,
but instead display a user-facing error message. This CL does that.

Change-Id: I81fd8e342fc877344f8d2a3704ef53caf5190aa3
Reviewed-on: https://cl.snix.dev/c/snix/+/30588
Reviewed-by: Vova Kryachko <v.kryachko@gmail.com>
Tested-by: besadii
Reviewed-by: Bence Nemes <nemes.bence1@gmail.com>

snix/eval/src/builtins/mod.rs

@@ -991,8 +991,9 @@ mod pure_builtins {
             return Ok(re);
         }
         let re = re.to_str()?;
-        let re: Regex =
-            cached_regex(&format!("^{}$", re.to_str()?)).expect("TODO(tazjin): propagate error");
+        let re = re.to_str()?;
+        let re: Regex = cached_regex(&format!("^{}$", re))
+            .map_err(|_| ErrorKind::InvalidRegex(re.to_string()))?;
 
         match re.captures(s.to_str()?) {
             Some(caps) => Ok(Value::List(
@@ -1213,7 +1214,8 @@ mod pure_builtins {
         let s = str.to_contextful_str()?;
         let text = s.to_str()?;
         let re = regex.to_str()?;
-        let re = cached_regex(re.to_str()?).unwrap();
+        let re = re.to_str()?;
+        let re = cached_regex(re).map_err(|_| ErrorKind::InvalidRegex(re.to_string()))?;
         let mut capture_locations = re.capture_locations();
         let num_captures = capture_locations.len();
         let mut ret = Vec::new();

snix/eval/src/errors.rs

@@ -294,6 +294,10 @@ to a missing value in the attribute set(s) included via `with`."#
     /// or "sha512"
     #[error("unknown hash type '{0}'")]
     UnknownHashType(String),
+
+    /// An invalid regular expression was passed.
+    #[error("invalid regular expression '{0}'")]
+    InvalidRegex(String),
 }
 
 impl error::Error for Error {
@@ -688,6 +692,7 @@ impl Error {
             | ErrorKind::WithContext { .. }
             | ErrorKind::UnknownHashType(_)
             | ErrorKind::InvalidHash(_)
+            | ErrorKind::InvalidRegex(_)
             | ErrorKind::CatchableError(_) => return None,
         };
 
@@ -735,6 +740,7 @@ impl Error {
             ErrorKind::UnknownHashType(_) => "E039",
             ErrorKind::UnexpectedArgumentBuiltin { .. } => "E040",
             ErrorKind::InvalidHash(_) => "E041",
+            ErrorKind::InvalidRegex(_) => "E042",
 
             // Special error code for errors from other Snix
             // components. We may want to introduce a code namespacing

snix/eval/src/tests/snix_tests/eval-fail-match-invalid-regex.nix

@@ -0,0 +1 @@
+builtins.match "a(b))c" "abc"