[core] Fix resolution of exception names in raise short form

Previous implementation fails as `resolver.get_identifier_def` in ARTIQ
would return the exception __init__ function rather than the class.

We fix this by limiting the exception class resolution to only include
raise statements, and to force the exception name to always be treated
as a class.

Fixes #501.

nac3core/src/codegen/expr.rs

@@ -2876,29 +2876,7 @@ pub fn gen_expr<'ctx, G: CodeGenerator>(
             Some((_, Some(static_value), _)) => ValueEnum::Static(static_value.clone()),
             None => {
                 let resolver = ctx.resolver.clone();
-                if let Some(res) = resolver.get_symbol_value(*id, ctx) {
+                resolver.get_symbol_value(*id, ctx).unwrap()
-                    res
-                } else {
-                    // Allow "raise Exception" short form
-                    let def_id = resolver.get_identifier_def(*id).map_err(|e| {
-                        format!("{} (at {})", e.iter().next().unwrap(), expr.location)
-                    })?;
-                    let def = ctx.top_level.definitions.read();
-                    if let TopLevelDef::Class { constructor, .. } = *def[def_id.0].read() {
-                        let TypeEnum::TFunc(signature) =
-                            ctx.unifier.get_ty(constructor.unwrap()).as_ref().clone()
-                        else {
-                            return Err(format!(
-                                "Failed to resolve symbol {} (at {})",
-                                id, expr.location
-                            ));
-                        };
-                        return Ok(generator
-                            .gen_call(ctx, None, (&signature, def_id), Vec::default())?
-                            .map(Into::into));
-                    }
-                    return Err(format!("Failed to resolve symbol {} (at {})", id, expr.location));
-                }
             }
         },
         ExprKind::List { elts, .. } => {

nac3core/src/codegen/stmt.rs

@@ -1762,7 +1762,30 @@ pub fn gen_stmt<G: CodeGenerator>(
         StmtKind::Try { .. } => gen_try(generator, ctx, stmt)?,
         StmtKind::Raise { exc, .. } => {
             if let Some(exc) = exc {
-                let exc = if let Some(v) = generator.gen_expr(ctx, exc)? {
+                let exn = if let ExprKind::Name { id, .. } = &exc.node {
+                    // Handle "raise Exception" short form
+                    let def_id = ctx.resolver.get_identifier_def(*id).map_err(|e| {
+                        format!("{} (at {})", e.iter().next().unwrap(), exc.location)
+                    })?;
+                    let def = ctx.top_level.definitions.read();
+                    let TopLevelDef::Class { constructor, .. } = *def[def_id.0].read() else {
+                        return Err(format!("Failed to resolve symbol {id} (at {})", exc.location));
+                    };
+
+                    let TypeEnum::TFunc(signature) =
+                        ctx.unifier.get_ty(constructor.unwrap()).as_ref().clone()
+                    else {
+                        return Err(format!("Failed to resolve symbol {id} (at {})", exc.location));
+                    };
+
+                    generator
+                        .gen_call(ctx, None, (&signature, def_id), Vec::default())?
+                        .map(Into::into)
+                } else {
+                    generator.gen_expr(ctx, exc)?
+                };
+
+                let exc = if let Some(v) = exn {
                     v.to_basic_value_enum(ctx, generator, exc.custom.unwrap())?
                 } else {
                     return Ok(());