Parse exceptions during reloads

[9999years]

The reload summary ("Ok, 10 modules loaded") is still responsible for whether or not "All good!" is printed, so this still needs some work. We could just check if any exceptions (or errors?) are printed and mark it as a compilation failure if so?

[linear]

DUX-3144 GHCi exceptions are not "all good"

[evanrelf]

EDIT: I realized you already know this in the comment below this.

I think the most correct parser of a GHCi exception would parse until a prompt, not a newline. But until a newline would handle this particular exception, if that's all you're going for right now.

[9999years]

Yeah, the issue is we get these in a stream of arbitrary GHC output, which may include other diagnostics we want to parse, compiling-such-and-such-a-module messages, etc.

[evanrelf]

Ah okay you already know that. Glad to see it still works in the presence of multi-line exception messages?

[evanrelf]

If you don't plan to mutate this string, you could use less memory:

Suggested change

	Exception(String),
	Exception(Box<str>),

If you think GhcMessages will be cloned a lot, you could account for that too:

Suggested change

	Exception(String),
	Exception(Arc<str>),

[lf-]

seems like kinda a yak shave imo and the ergonomics of dealing with both of those types are worse. it's pretty regular to just put String places that it doesn't strictly have to be because it's easy. if the memory usage starts mattering it can be changed.

[9999years]

Yeah I'm pretty sure zero-copy parsing is kind of an ergonomic nightmare, even if it's technically possible

[evanrelf]

the ergonomics of dealing with both of those types are worse

Not true. All of the &str API is still available thanks to the Deref impl for Box<T> and Arc<T>.

zero-copy parsing is kind of an ergonomic nightmare

This is not zero-copy, and this would not require adding lifetimes.

---

I don't feel strongly about which type you choose, but I do wanna make sure you understand the tradeoffs correctly! I am not suggesting any ergonomic sacrifice here!

This video explains things better: https://www.youtube.com/watch?v=A4cKi7PTJSs

[evanrelf]

Here's all you'd need to change:

Diff

diff --git a/src/ghci/parse/ghc_message/exception.rs b/src/ghci/parse/ghc_message/exception.rs
index b09906d..55f4222 100644
--- a/src/ghci/parse/ghc_message/exception.rs
+++ b/src/ghci/parse/ghc_message/exception.rs
@@ -1,3 +1,4 @@
+use std::sync::Arc;
 use winnow::PResult;
 use winnow::Parser;
 
@@ -15,7 +16,7 @@ pub fn exception(input: &mut &str) -> PResult<GhcMessage> {
 
     let message = until_newline.parse_next(input)?;
 
-    Ok(GhcMessage::Exception(message.to_owned()))
+    Ok(GhcMessage::Exception(Arc::from(message)))
 }
 
 #[cfg(test)]
@@ -29,12 +30,12 @@ mod tests {
     fn test_parse_exception() {
         assert_eq!(
             exception.parse("*** Exception: Uh oh!\n").unwrap(),
-            GhcMessage::Exception("Uh oh!".into())
+            GhcMessage::Exception(Arc::new("Uh oh!"))
         );
 
         assert_eq!(
             exception.parse("*** Exception: /Users/.../dist-newstyle/ghc82733_tmp_1/ghc_tmp_34657.h: withFile: does not exist (No such file or directory)\n").unwrap(),
-            GhcMessage::Exception("/Users/.../dist-newstyle/ghc82733_tmp_1/ghc_tmp_34657.h: withFile: does not exist (No such file or directory)".into())
+            GhcMessage::Exception(Arc::new("/Users/.../dist-newstyle/ghc82733_tmp_1/ghc_tmp_34657.h: withFile: does not exist (No such file or directory)"))
         );
 
         // Doesn't parse subsequent lines (even if they're relevant, unfortunately).
@@ -48,7 +49,7 @@ mod tests {
                     "
                 ))
                 .unwrap(),
-            GhcMessage::Exception("puppy doggy".into())
+            GhcMessage::Exception(Arc::new("puppy doggy"))
         );
     }
 }
diff --git a/src/ghci/parse/ghc_message/mod.rs b/src/ghci/parse/ghc_message/mod.rs
index 6036a1d..34e2692 100644
--- a/src/ghci/parse/ghc_message/mod.rs
+++ b/src/ghci/parse/ghc_message/mod.rs
@@ -1,6 +1,7 @@
 //! Parser for GHC compiler output.
 
 use std::fmt::Display;
+use std::sync::Arc;
 
 use camino::Utf8PathBuf;
 use miette::miette;
@@ -75,7 +76,7 @@ pub enum GhcMessage {
     /// ```text
     /// *** Exception: /Users/.../dist-newstyle/ghc82733_tmp_1/ghc_tmp_34657.h: withFile: does not exist (No such file or directory)
     /// ```
-    Exception(String),
+    Exception(Arc<str>),
     /// A configuration file being loaded.
     ///
     /// ```text
@@ -336,7 +337,7 @@ mod tests {
                         ].join("\n"),
                     },
                 ),
-                GhcMessage::Exception("/Users/.../dist-newstyle/ghc82733_tmp_1/ghc_tmp_34657.h: withFile: does not exist (No such file or directory)".to_owned()),
+                GhcMessage::Exception(Arc::new("/Users/.../dist-newstyle/ghc82733_tmp_1/ghc_tmp_34657.h: withFile: does not exist (No such file or directory)")),
                 GhcMessage::Summary(
                     CompilationSummary {
                         result: CompilationResult::Err,