Improve fluent error messages

compiler/rustc_errors/src/emitter.rs

@@ -28,6 +28,7 @@ use rustc_error_messages::{FluentArgs, SpanLabel};
 use rustc_span::hygiene::{ExpnKind, MacroKind};
 use std::borrow::Cow;
 use std::cmp::{max, min, Reverse};
+use std::error::Report;
 use std::io::prelude::*;
 use std::io::{self, IsTerminal};
 use std::iter;
@@ -250,7 +251,7 @@ pub trait Emitter: Translate {
         let mut primary_span = diag.span.clone();
         let suggestions = diag.suggestions.as_deref().unwrap_or(&[]);
         if let Some((sugg, rest)) = suggestions.split_first() {
-            let msg = self.translate_message(&sugg.msg, fluent_args);
+            let msg = self.translate_message(&sugg.msg, fluent_args).map_err(Report::new).unwrap();
             if rest.is_empty() &&
                // ^ if there is only one suggestion
                // don't display multi-suggestions as labels
@@ -1325,7 +1326,7 @@ impl EmitterWriter {
         //                very *weird* formats
         //                see?
         for (text, style) in msg.iter() {
-            let text = self.translate_message(text, args);
+            let text = self.translate_message(text, args).map_err(Report::new).unwrap();
             let lines = text.split('\n').collect::<Vec<_>>();
             if lines.len() > 1 {
                 for (i, line) in lines.iter().enumerate() {
@@ -1387,7 +1388,7 @@ impl EmitterWriter {
                 label_width += 2;
             }
             for (text, _) in msg.iter() {
-                let text = self.translate_message(text, args);
+                let text = self.translate_message(text, args).map_err(Report::new).unwrap();
                 // Account for newlines to align output to its label.
                 for (line, text) in normalize_whitespace(&text).lines().enumerate() {
                     buffer.append(
@@ -2301,7 +2302,9 @@ impl FileWithAnnotatedLines {
                     hi.col_display += 1;
                 }
 
-                let label = label.as_ref().map(|m| emitter.translate_message(m, args).to_string());
+                let label = label.as_ref().map(|m| {
+                    emitter.translate_message(m, args).map_err(Report::new).unwrap().to_string()
+                });
 
                 if lo.line != hi.line {
                     let ml = MultilineAnnotation {

compiler/rustc_errors/src/error.rs

@@ -0,0 +1,137 @@
+use rustc_error_messages::{
+    fluent_bundle::resolver::errors::{ReferenceKind, ResolverError},
+    FluentArgs, FluentError,
+};
+use std::borrow::Cow;
+use std::error::Error;
+use std::fmt;
+
+#[derive(Debug)]
+pub enum TranslateError<'args> {
+    One {
+        id: &'args Cow<'args, str>,
+        args: &'args FluentArgs<'args>,
+        kind: TranslateErrorKind<'args>,
+    },
+    Two {
+        primary: Box<TranslateError<'args>>,
+        fallback: Box<TranslateError<'args>>,
+    },
+}
+
+impl<'args> TranslateError<'args> {
+    pub fn message(id: &'args Cow<'args, str>, args: &'args FluentArgs<'args>) -> Self {
+        Self::One { id, args, kind: TranslateErrorKind::MessageMissing }
+    }
+    pub fn primary(id: &'args Cow<'args, str>, args: &'args FluentArgs<'args>) -> Self {
+        Self::One { id, args, kind: TranslateErrorKind::PrimaryBundleMissing }
+    }
+    pub fn attribute(
+        id: &'args Cow<'args, str>,
+        args: &'args FluentArgs<'args>,
+        attr: &'args str,
+    ) -> Self {
+        Self::One { id, args, kind: TranslateErrorKind::AttributeMissing { attr } }
+    }
+    pub fn value(id: &'args Cow<'args, str>, args: &'args FluentArgs<'args>) -> Self {
+        Self::One { id, args, kind: TranslateErrorKind::ValueMissing }
+    }
+
+    pub fn fluent(
+        id: &'args Cow<'args, str>,
+        args: &'args FluentArgs<'args>,
+        errs: Vec<FluentError>,
+    ) -> Self {
+        Self::One { id, args, kind: TranslateErrorKind::Fluent { errs } }
+    }
+
+    pub fn and(self, fallback: TranslateError<'args>) -> TranslateError<'args> {
+        Self::Two { primary: Box::new(self), fallback: Box::new(fallback) }
+    }
+}
+
+#[derive(Debug)]
+pub enum TranslateErrorKind<'args> {
+    MessageMissing,
+    PrimaryBundleMissing,
+    AttributeMissing { attr: &'args str },
+    ValueMissing,
+    Fluent { errs: Vec<FluentError> },
+}
+
+impl fmt::Display for TranslateError<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use TranslateErrorKind::*;
+
+        match self {
+            Self::One { id, args, kind } => {
+                writeln!(f, "failed while formatting fluent string `{id}`: ")?;
+                match kind {
+                    MessageMissing => writeln!(f, "message was missing")?,
+                    PrimaryBundleMissing => writeln!(f, "the primary bundle was missing")?,
+                    AttributeMissing { attr } => {
+                        writeln!(f, "the attribute `{attr}` was missing")?;
+                        writeln!(f, "help: add `.{attr} = <message>`")?;
+                    }
+                    ValueMissing => writeln!(f, "the value was missing")?,
+                    Fluent { errs } => {
+                        for err in errs {
+                            match err {
+                                FluentError::ResolverError(ResolverError::Reference(
+                                    ReferenceKind::Message { id, .. }
+                                    | ReferenceKind::Variable { id, .. },
+                                )) => {
+                                    if args.iter().any(|(arg_id, _)| arg_id == id) {
+                                        writeln!(
+                                            f,
+                                            "argument `{id}` exists but was not referenced correctly"
+                                        )?;
+                                        writeln!(f, "help: try using `{{${id}}}` instead")?;
+                                    } else {
+                                        writeln!(
+                                            f,
+                                            "the fluent string has an argument `{id}` that was not found."
+                                        )?;
+                                        let vars: Vec<&str> =
+                                            args.iter().map(|(a, _v)| a).collect();
+                                        match &*vars {
+                                            [] => writeln!(f, "help: no arguments are available")?,
+                                            [one] => writeln!(
+                                                f,
+                                                "help: the argument `{one}` is available"
+                                            )?,
+                                            [first, middle @ .., last] => {
+                                                write!(f, "help: the arguments `{first}`")?;
+                                                for a in middle {
+                                                    write!(f, ", `{a}`")?;
+                                                }
+                                                writeln!(f, " and `{last}` are available")?;
+                                            }
+                                        }
+                                    }
+                                }
+                                _ => writeln!(f, "{err}")?,
+                            }
+                        }
+                    }
+                }
+            }
+            // If someone cares about primary bundles, they'll probably notice it's missing
+            // regardless or will be using `debug_assertions`
+            // so we skip the arm below this one to avoid confusing the regular user.
+            Self::Two { primary: box Self::One { kind: PrimaryBundleMissing, .. }, fallback } => {
+                fmt::Display::fmt(fallback, f)?;
+            }
+            Self::Two { primary, fallback } => {
+                writeln!(
+                    f,
+                    "first, fluent formatting using the primary bundle failed:\n {primary}\n \
+                    while attempting to recover by using the fallback bundle instead, another error occurred:\n{fallback}"
+                )?;
+            }
+        }
+        Ok(())
+    }
+}
+
+impl Error for TranslateError<'_> {}

compiler/rustc_errors/src/json.rs

@@ -24,6 +24,7 @@ use rustc_data_structures::sync::Lrc;
 use rustc_error_messages::FluentArgs;
 use rustc_span::hygiene::ExpnData;
 use rustc_span::Span;
+use std::error::Report;
 use std::io::{self, Write};
 use std::path::Path;
 use std::sync::{Arc, Mutex};
@@ -321,7 +322,8 @@ impl Diagnostic {
     fn from_errors_diagnostic(diag: &crate::Diagnostic, je: &JsonEmitter) -> Diagnostic {
         let args = to_fluent_args(diag.args());
         let sugg = diag.suggestions.iter().flatten().map(|sugg| {
-            let translated_message = je.translate_message(&sugg.msg, &args);
+            let translated_message =
+                je.translate_message(&sugg.msg, &args).map_err(Report::new).unwrap();
             Diagnostic {
                 message: translated_message.to_string(),
                 code: None,
@@ -411,7 +413,10 @@ impl DiagnosticSpan {
         Self::from_span_etc(
             span.span,
             span.is_primary,
-            span.label.as_ref().map(|m| je.translate_message(m, args)).map(|m| m.to_string()),
+            span.label
+                .as_ref()
+                .map(|m| je.translate_message(m, args).unwrap())
+                .map(|m| m.to_string()),
             suggestion,
             je,
         )

compiler/rustc_errors/src/lib.rs

@@ -11,6 +11,10 @@
 #![feature(never_type)]
 #![feature(result_option_inspect)]
 #![feature(rustc_attrs)]
+#![feature(yeet_expr)]
+#![feature(try_blocks)]
+#![feature(box_patterns)]
+#![feature(error_reporter)]
 #![allow(incomplete_features)]
 
 #[macro_use]
@@ -42,6 +46,7 @@ use rustc_span::{Loc, Span};
 
 use std::any::Any;
 use std::borrow::Cow;
+use std::error::Report;
 use std::fmt;
 use std::hash::Hash;
 use std::num::NonZeroUsize;
@@ -55,11 +60,14 @@ mod diagnostic;
 mod diagnostic_builder;
 mod diagnostic_impls;
 pub mod emitter;
+pub mod error;
 pub mod json;
 mod lock;
 pub mod registry;
 mod snippet;
 mod styled_buffer;
+#[cfg(test)]
+mod tests;
 pub mod translation;
 
 pub use diagnostic_builder::IntoDiagnostic;
@@ -622,7 +630,14 @@ impl Handler {
     ) -> SubdiagnosticMessage {
         let inner = self.inner.borrow();
         let args = crate::translation::to_fluent_args(args);
-        SubdiagnosticMessage::Eager(inner.emitter.translate_message(&message, &args).to_string())
+        SubdiagnosticMessage::Eager(
+            inner
+                .emitter
+                .translate_message(&message, &args)
+                .map_err(Report::new)
+                .unwrap()
+                .to_string(),
+        )
     }
 
     // This is here to not allow mutation of flags;