Extract Translator struct

7 files changed, 112 insertions, 138 deletions

diff --git a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
index f3aeb8d224b..2eb3c23259f 100644
--- a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
+++ b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
@@ -15,17 +15,15 @@ use rustc_span::source_map::SourceMap;
 use crate::emitter::FileWithAnnotatedLines;
 use crate::registry::Registry;
 use crate::snippet::Line;
-use crate::translation::{Translate, to_fluent_args};
+use crate::translation::{Translator, to_fluent_args};
 use crate::{
-    CodeSuggestion, DiagInner, DiagMessage, Emitter, ErrCode, FluentBundle, LazyFallbackBundle,
-    Level, MultiSpan, Style, Subdiag,
+    CodeSuggestion, DiagInner, DiagMessage, Emitter, ErrCode, Level, MultiSpan, Style, Subdiag,
 };
 
 /// Generates diagnostics using annotate-snippet
 pub struct AnnotateSnippetEmitter {
     source_map: Option<Arc<SourceMap>>,
-    fluent_bundle: Option<Arc<FluentBundle>>,
-    fallback_bundle: LazyFallbackBundle,
+    translator: Translator,
 
     /// If true, hides the longer explanation text
     short_message: bool,
@@ -35,16 +33,6 @@ pub struct AnnotateSnippetEmitter {
     macro_backtrace: bool,
 }
 
-impl Translate for AnnotateSnippetEmitter {
-    fn fluent_bundle(&self) -> Option<&FluentBundle> {
-        self.fluent_bundle.as_deref()
-    }
-
-    fn fallback_fluent_bundle(&self) -> &FluentBundle {
-        &self.fallback_bundle
-    }
-}
-
 impl Emitter for AnnotateSnippetEmitter {
     /// The entry point for the diagnostics generation
     fn emit_diagnostic(&mut self, mut diag: DiagInner, _registry: &Registry) {
@@ -78,6 +66,10 @@ impl Emitter for AnnotateSnippetEmitter {
     fn should_show_explain(&self) -> bool {
         !self.short_message
     }
+
+    fn translator(&self) -> &Translator {
+        &self.translator
+    }
 }
 
 /// Provides the source string for the given `line` of `file`
@@ -104,19 +96,11 @@ fn annotation_level_for_level(level: Level) -> annotate_snippets::Level {
 impl AnnotateSnippetEmitter {
     pub fn new(
         source_map: Option<Arc<SourceMap>>,
-        fluent_bundle: Option<Arc<FluentBundle>>,
-        fallback_bundle: LazyFallbackBundle,
+        translator: Translator,
         short_message: bool,
         macro_backtrace: bool,
     ) -> Self {
-        Self {
-            source_map,
-            fluent_bundle,
-            fallback_bundle,
-            short_message,
-            ui_testing: false,
-            macro_backtrace,
-        }
+        Self { source_map, translator, short_message, ui_testing: false, macro_backtrace }
     }
 
     /// Allows to modify `Self` to enable or disable the `ui_testing` flag.
@@ -137,7 +121,7 @@ impl AnnotateSnippetEmitter {
         _children: &[Subdiag],
         _suggestions: &[CodeSuggestion],
     ) {
-        let message = self.translate_messages(messages, args);
+        let message = self.translator.translate_messages(messages, args);
         if let Some(source_map) = &self.source_map {
             // Make sure our primary file comes first
             let primary_lo = if let Some(primary_span) = msp.primary_span().as_ref() {
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 6ab6f96079e..494f15cc639 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -35,10 +35,10 @@ use crate::snippet::{
 };
 use crate::styled_buffer::StyledBuffer;
 use crate::timings::TimingRecord;
-use crate::translation::{Translate, to_fluent_args};
+use crate::translation::{Translator, to_fluent_args};
 use crate::{
-    CodeSuggestion, DiagInner, DiagMessage, ErrCode, FluentBundle, LazyFallbackBundle, Level,
-    MultiSpan, Subdiag, SubstitutionHighlight, SuggestionStyle, TerminalUrl,
+    CodeSuggestion, DiagInner, DiagMessage, ErrCode, Level, MultiSpan, Subdiag,
+    SubstitutionHighlight, SuggestionStyle, TerminalUrl,
 };
 
 /// Default column width, used in tests and when terminal dimensions cannot be determined.
@@ -175,7 +175,7 @@ const ANONYMIZED_LINE_NUM: &str = "LL";
 pub type DynEmitter = dyn Emitter + DynSend;
 
 /// Emitter trait for emitting errors and other structured information.
-pub trait Emitter: Translate {
+pub trait Emitter {
     /// Emit a structured diagnostic.
     fn emit_diagnostic(&mut self, diag: DiagInner, registry: &Registry);
 
@@ -212,6 +212,8 @@ pub trait Emitter: Translate {
 
     fn source_map(&self) -> Option<&SourceMap>;
 
+    fn translator(&self) -> &Translator;
+
     /// Formats the substitutions of the primary_span
     ///
     /// There are a lot of conditions to this method, but in short:
@@ -224,13 +226,17 @@ pub trait Emitter: Translate {
     /// * If the current `DiagInner` has multiple suggestions,
     ///   we leave `primary_span` and the suggestions untouched.
     fn primary_span_formatted(
-        &mut self,
+        &self,
         primary_span: &mut MultiSpan,
         suggestions: &mut Vec<CodeSuggestion>,
         fluent_args: &FluentArgs<'_>,
     ) {
         if let Some((sugg, rest)) = suggestions.split_first() {
-            let msg = self.translate_message(&sugg.msg, fluent_args).map_err(Report::new).unwrap();
+            let msg = self
+                .translator()
+                .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
@@ -491,16 +497,6 @@ pub trait Emitter: Translate {
     }
 }
 
-impl Translate for HumanEmitter {
-    fn fluent_bundle(&self) -> Option<&FluentBundle> {
-        self.fluent_bundle.as_deref()
-    }
-
-    fn fallback_fluent_bundle(&self) -> &FluentBundle {
-        &self.fallback_bundle
-    }
-}
-
 impl Emitter for HumanEmitter {
     fn source_map(&self) -> Option<&SourceMap> {
         self.sm.as_deref()
@@ -538,6 +534,10 @@ impl Emitter for HumanEmitter {
     fn supports_color(&self) -> bool {
         self.dst.supports_color()
     }
+
+    fn translator(&self) -> &Translator {
+        &self.translator
+    }
 }
 
 /// An emitter that does nothing when emitting a non-fatal diagnostic.
@@ -549,16 +549,6 @@ pub struct SilentEmitter {
     pub emit_fatal_diagnostic: bool,
 }
 
-impl Translate for SilentEmitter {
-    fn fluent_bundle(&self) -> Option<&FluentBundle> {
-        None
-    }
-
-    fn fallback_fluent_bundle(&self) -> &FluentBundle {
-        self.fatal_emitter.fallback_fluent_bundle()
-    }
-}
-
 impl Emitter for SilentEmitter {
     fn source_map(&self) -> Option<&SourceMap> {
         None
@@ -572,6 +562,10 @@ impl Emitter for SilentEmitter {
             self.fatal_emitter.emit_diagnostic(diag, registry);
         }
     }
+
+    fn translator(&self) -> &Translator {
+        self.fatal_emitter.translator()
+    }
 }
 
 /// Maximum number of suggestions to be shown
@@ -615,9 +609,8 @@ pub struct HumanEmitter {
     #[setters(skip)]
     dst: IntoDynSyncSend<Destination>,
     sm: Option<Arc<SourceMap>>,
-    fluent_bundle: Option<Arc<FluentBundle>>,
     #[setters(skip)]
-    fallback_bundle: LazyFallbackBundle,
+    translator: Translator,
     short_message: bool,
     ui_testing: bool,
     ignored_directories_in_source_blocks: Vec<String>,
@@ -637,12 +630,11 @@ pub(crate) struct FileWithAnnotatedLines {
 }
 
 impl HumanEmitter {
-    pub fn new(dst: Destination, fallback_bundle: LazyFallbackBundle) -> HumanEmitter {
+    pub fn new(dst: Destination, translator: Translator) -> HumanEmitter {
         HumanEmitter {
             dst: IntoDynSyncSend(dst),
             sm: None,
-            fluent_bundle: None,
-            fallback_bundle,
+            translator,
             short_message: false,
             ui_testing: false,
             ignored_directories_in_source_blocks: Vec::new(),
@@ -1433,7 +1425,7 @@ impl HumanEmitter {
         //                very *weird* formats
         //                see?
         for (text, style) in msgs.iter() {
-            let text = self.translate_message(text, args).map_err(Report::new).unwrap();
+            let text = self.translator.translate_message(text, args).map_err(Report::new).unwrap();
             let text = &normalize_whitespace(&text);
             let lines = text.split('\n').collect::<Vec<_>>();
             if lines.len() > 1 {
@@ -1528,7 +1520,8 @@ impl HumanEmitter {
             }
             let mut line = 0;
             for (text, style) in msgs.iter() {
-                let text = self.translate_message(text, args).map_err(Report::new).unwrap();
+                let text =
+                    self.translator.translate_message(text, args).map_err(Report::new).unwrap();
                 // Account for newlines to align output to its label.
                 for text in normalize_whitespace(&text).lines() {
                     buffer.append(
@@ -1560,7 +1553,7 @@ impl HumanEmitter {
                     .into_iter()
                     .filter_map(|label| match label.label {
                         Some(msg) if label.is_primary => {
-                            let text = self.translate_message(&msg, args).ok()?;
+                            let text = self.translator.translate_message(&msg, args).ok()?;
                             if !text.trim().is_empty() { Some(text.to_string()) } else { None }
                         }
                         _ => None,
@@ -3104,7 +3097,11 @@ impl FileWithAnnotatedLines {
 
                 let label = label.as_ref().map(|m| {
                     normalize_whitespace(
-                        &emitter.translate_message(m, args).map_err(Report::new).unwrap(),
+                        &emitter
+                            .translator()
+                            .translate_message(m, args)
+                            .map_err(Report::new)
+                            .unwrap(),
                     )
                 });
 
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index d67e2ba2d60..6d600f896a0 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -32,11 +32,8 @@ use crate::emitter::{
 };
 use crate::registry::Registry;
 use crate::timings::{TimingRecord, TimingSection};
-use crate::translation::{Translate, to_fluent_args};
-use crate::{
-    CodeSuggestion, FluentBundle, LazyFallbackBundle, MultiSpan, SpanLabel, Subdiag, Suggestions,
-    TerminalUrl,
-};
+use crate::translation::{Translator, to_fluent_args};
+use crate::{CodeSuggestion, MultiSpan, SpanLabel, Subdiag, Suggestions, TerminalUrl};
 
 #[cfg(test)]
 mod tests;
@@ -47,9 +44,8 @@ pub struct JsonEmitter {
     dst: IntoDynSyncSend<Box<dyn Write + Send>>,
     #[setters(skip)]
     sm: Option<Arc<SourceMap>>,
-    fluent_bundle: Option<Arc<FluentBundle>>,
     #[setters(skip)]
-    fallback_bundle: LazyFallbackBundle,
+    translator: Translator,
     #[setters(skip)]
     pretty: bool,
     ui_testing: bool,
@@ -67,7 +63,7 @@ impl JsonEmitter {
     pub fn new(
         dst: Box<dyn Write + Send>,
         sm: Option<Arc<SourceMap>>,
-        fallback_bundle: LazyFallbackBundle,
+        translator: Translator,
         pretty: bool,
         json_rendered: HumanReadableErrorType,
         color_config: ColorConfig,
@@ -75,8 +71,7 @@ impl JsonEmitter {
         JsonEmitter {
             dst: IntoDynSyncSend(dst),
             sm,
-            fluent_bundle: None,
-            fallback_bundle,
+            translator,
             pretty,
             ui_testing: false,
             ignored_directories_in_source_blocks: Vec::new(),
@@ -110,16 +105,6 @@ enum EmitTyped<'a> {
     UnusedExtern(UnusedExterns<'a>),
 }
 
-impl Translate for JsonEmitter {
-    fn fluent_bundle(&self) -> Option<&FluentBundle> {
-        self.fluent_bundle.as_deref()
-    }
-
-    fn fallback_fluent_bundle(&self) -> &FluentBundle {
-        &self.fallback_bundle
-    }
-}
-
 impl Emitter for JsonEmitter {
     fn emit_diagnostic(&mut self, diag: crate::DiagInner, registry: &Registry) {
         let data = Diagnostic::from_errors_diagnostic(diag, self, registry);
@@ -194,6 +179,10 @@ impl Emitter for JsonEmitter {
     fn should_show_explain(&self) -> bool {
         !self.json_rendered.short()
     }
+
+    fn translator(&self) -> &Translator {
+        &self.translator
+    }
 }
 
 // The following data types are provided just for serialisation.
@@ -324,7 +313,7 @@ impl Diagnostic {
         let args = to_fluent_args(diag.args.iter());
         let sugg_to_diag = |sugg: &CodeSuggestion| {
             let translated_message =
-                je.translate_message(&sugg.msg, &args).map_err(Report::new).unwrap();
+                je.translator.translate_message(&sugg.msg, &args).map_err(Report::new).unwrap();
             Diagnostic {
                 message: translated_message.to_string(),
                 code: None,
@@ -368,7 +357,7 @@ impl Diagnostic {
             }
         }
 
-        let translated_message = je.translate_messages(&diag.messages, &args);
+        let translated_message = je.translator.translate_messages(&diag.messages, &args);
 
         let code = if let Some(code) = diag.code {
             Some(DiagnosticCode {
@@ -396,10 +385,9 @@ impl Diagnostic {
             ColorConfig::Always | ColorConfig::Auto => dst = Box::new(termcolor::Ansi::new(dst)),
             ColorConfig::Never => {}
         }
-        HumanEmitter::new(dst, Arc::clone(&je.fallback_bundle))
+        HumanEmitter::new(dst, je.translator.clone())
             .short_message(short)
             .sm(je.sm.clone())
-            .fluent_bundle(je.fluent_bundle.clone())
             .diagnostic_width(je.diagnostic_width)
             .macro_backtrace(je.macro_backtrace)
             .track_diagnostics(je.track_diagnostics)
@@ -430,7 +418,7 @@ impl Diagnostic {
         args: &FluentArgs<'_>,
         je: &JsonEmitter,
     ) -> Diagnostic {
-        let translated_message = je.translate_messages(&subdiag.messages, args);
+        let translated_message = je.translator.translate_messages(&subdiag.messages, args);
         Diagnostic {
             message: translated_message.to_string(),
             code: None,
@@ -454,7 +442,7 @@ impl DiagnosticSpan {
             span.is_primary,
             span.label
                 .as_ref()
-                .map(|m| je.translate_message(m, args).unwrap())
+                .map(|m| je.translator.translate_message(m, args).unwrap())
                 .map(|m| m.to_string()),
             suggestion,
             je,
diff --git a/compiler/rustc_errors/src/json/tests.rs b/compiler/rustc_errors/src/json/tests.rs
index 40973e8e5d8..8cf81f467d8 100644
--- a/compiler/rustc_errors/src/json/tests.rs
+++ b/compiler/rustc_errors/src/json/tests.rs
@@ -41,14 +41,14 @@ fn test_positions(code: &str, span: (u32, u32), expected_output: SpanTestData) {
     rustc_span::create_default_session_globals_then(|| {
         let sm = Arc::new(SourceMap::new(FilePathMapping::empty()));
         sm.new_source_file(Path::new("test.rs").to_owned().into(), code.to_owned());
-        let fallback_bundle =
-            crate::fallback_fluent_bundle(vec![crate::DEFAULT_LOCALE_RESOURCE], false);
+        let translator =
+            Translator::with_fallback_bundle(vec![crate::DEFAULT_LOCALE_RESOURCE], false);
 
         let output = Arc::new(Mutex::new(Vec::new()));
         let je = JsonEmitter::new(
             Box::new(Shared { data: output.clone() }),
             Some(sm),
-            fallback_bundle,
+            translator,
             true, // pretty
             HumanReadableErrorType::Short,
             ColorConfig::Never,
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 0bd259366de..70f294b696a 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -761,14 +761,8 @@ impl DiagCtxt {
             fn source_map(&self) -> Option<&SourceMap> {
                 unimplemented!("false emitter must only used during `make_silent`")
             }
-        }
-
-        impl translation::Translate for FalseEmitter {
-            fn fluent_bundle(&self) -> Option<&FluentBundle> {
-                unimplemented!("false emitter must only used during `make_silent`")
-            }
 
-            fn fallback_fluent_bundle(&self) -> &FluentBundle {
+            fn translator(&self) -> &translation::Translator {
                 unimplemented!("false emitter must only used during `make_silent`")
             }
         }
@@ -1771,7 +1765,12 @@ impl DiagCtxtInner {
         args: impl Iterator<Item = DiagArg<'a>>,
     ) -> String {
         let args = crate::translation::to_fluent_args(args);
-        self.emitter.translate_message(&message, &args).map_err(Report::new).unwrap().to_string()
+        self.emitter
+            .translator()
+            .translate_message(&message, &args)
+            .map_err(Report::new)
+            .unwrap()
+            .to_string()
     }
 
     fn eagerly_translate_for_subdiag(
diff --git a/compiler/rustc_errors/src/tests.rs b/compiler/rustc_errors/src/tests.rs
index 376fd24d57b..34ebac0fde1 100644
--- a/compiler/rustc_errors/src/tests.rs
+++ b/compiler/rustc_errors/src/tests.rs
@@ -1,3 +1,5 @@
+use std::sync::{Arc, LazyLock};
+
 use rustc_data_structures::sync::IntoDynSyncSend;
 use rustc_error_messages::fluent_bundle::resolver::errors::{ReferenceKind, ResolverError};
 use rustc_error_messages::{DiagMessage, langid};
@@ -5,23 +7,9 @@ use rustc_error_messages::{DiagMessage, langid};
 use crate::FluentBundle;
 use crate::error::{TranslateError, TranslateErrorKind};
 use crate::fluent_bundle::*;
-use crate::translation::Translate;
-
-struct Dummy {
-    bundle: FluentBundle,
-}
-
-impl Translate for Dummy {
-    fn fluent_bundle(&self) -> Option<&FluentBundle> {
-        None
-    }
+use crate::translation::Translator;
 
-    fn fallback_fluent_bundle(&self) -> &FluentBundle {
-        &self.bundle
-    }
-}
-
-fn make_dummy(ftl: &'static str) -> Dummy {
+fn make_translator(ftl: &'static str) -> Translator {
     let resource = FluentResource::try_new(ftl.into()).expect("Failed to parse an FTL string.");
 
     let langid_en = langid!("en-US");
@@ -33,12 +21,15 @@ fn make_dummy(ftl: &'static str) -> Dummy {
 
     bundle.add_resource(resource).expect("Failed to add FTL resources to the bundle.");
 
-    Dummy { bundle }
+    Translator {
+        fluent_bundle: None,
+        fallback_fluent_bundle: Arc::new(LazyLock::new(Box::new(|| bundle))),
+    }
 }
 
 #[test]
 fn wellformed_fluent() {
-    let dummy = make_dummy("mir_build_borrow_of_moved_value = borrow of moved value
+    let translator = make_translator("mir_build_borrow_of_moved_value = borrow of moved value
     .label = value moved into `{$name}` here
     .occurs_because_label = move occurs because `{$name}` has type `{$ty}` which does not implement the `Copy` trait
     .value_borrowed_label = value borrowed here after move
@@ -54,7 +45,7 @@ fn wellformed_fluent() {
         );
 
         assert_eq!(
-            dummy.translate_message(&message, &args).unwrap(),
+            translator.translate_message(&message, &args).unwrap(),
             "borrow this binding in the pattern to avoid moving the value"
         );
     }
@@ -66,7 +57,7 @@ fn wellformed_fluent() {
         );
 
         assert_eq!(
-            dummy.translate_message(&message, &args).unwrap(),
+            translator.translate_message(&message, &args).unwrap(),
             "value borrowed here after move"
         );
     }
@@ -78,7 +69,7 @@ fn wellformed_fluent() {
         );
 
         assert_eq!(
-            dummy.translate_message(&message, &args).unwrap(),
+            translator.translate_message(&message, &args).unwrap(),
             "move occurs because `\u{2068}Foo\u{2069}` has type `\u{2068}std::string::String\u{2069}` which does not implement the `Copy` trait"
         );
 
@@ -89,7 +80,7 @@ fn wellformed_fluent() {
             );
 
             assert_eq!(
-                dummy.translate_message(&message, &args).unwrap(),
+                translator.translate_message(&message, &args).unwrap(),
                 "value moved into `\u{2068}Foo\u{2069}` here"
             );
         }
@@ -98,7 +89,7 @@ fn wellformed_fluent() {
 
 #[test]
 fn misformed_fluent() {
-    let dummy = make_dummy("mir_build_borrow_of_moved_value = borrow of moved value
+    let translator = make_translator("mir_build_borrow_of_moved_value = borrow of moved value
     .label = value moved into `{name}` here
     .occurs_because_label = move occurs because `{$oops}` has type `{$ty}` which does not implement the `Copy` trait
     .suggestion = borrow this binding in the pattern to avoid moving the value");
@@ -112,7 +103,7 @@ fn misformed_fluent() {
             Some("value_borrowed_label".into()),
         );
 
-        let err = dummy.translate_message(&message, &args).unwrap_err();
+        let err = translator.translate_message(&message, &args).unwrap_err();
         assert!(
             matches!(
                 &err,
@@ -141,7 +132,7 @@ fn misformed_fluent() {
             Some("label".into()),
         );
 
-        let err = dummy.translate_message(&message, &args).unwrap_err();
+        let err = translator.translate_message(&message, &args).unwrap_err();
         if let TranslateError::Two {
             primary: box TranslateError::One { kind: TranslateErrorKind::PrimaryBundleMissing, .. },
             fallback: box TranslateError::One { kind: TranslateErrorKind::Fluent { errs }, .. },
@@ -168,7 +159,7 @@ fn misformed_fluent() {
             Some("occurs_because_label".into()),
         );
 
-        let err = dummy.translate_message(&message, &args).unwrap_err();
+        let err = translator.translate_message(&message, &args).unwrap_err();
         if let TranslateError::Two {
             primary: box TranslateError::One { kind: TranslateErrorKind::PrimaryBundleMissing, .. },
             fallback: box TranslateError::One { kind: TranslateErrorKind::Fluent { errs }, .. },
diff --git a/compiler/rustc_errors/src/translation.rs b/compiler/rustc_errors/src/translation.rs
index 156f5e5d26e..c0bcec093c7 100644
--- a/compiler/rustc_errors/src/translation.rs
+++ b/compiler/rustc_errors/src/translation.rs
@@ -1,8 +1,9 @@
 use std::borrow::Cow;
 use std::env;
 use std::error::Report;
+use std::sync::Arc;
 
-pub use rustc_error_messages::FluentArgs;
+pub use rustc_error_messages::{FluentArgs, LazyFallbackBundle};
 use tracing::{debug, trace};
 
 use crate::error::{TranslateError, TranslateErrorKind};
@@ -28,19 +29,33 @@ pub fn to_fluent_args<'iter>(iter: impl Iterator<Item = DiagArg<'iter>>) -> Flue
     args
 }
 
-pub trait Translate {
-    /// Return `FluentBundle` with localized diagnostics for the locale requested by the user. If no
-    /// language was requested by the user then this will be `None` and `fallback_fluent_bundle`
-    /// should be used.
-    fn fluent_bundle(&self) -> Option<&FluentBundle>;
-
+#[derive(Clone)]
+pub struct Translator {
+    /// Localized diagnostics for the locale requested by the user. If no language was requested by
+    /// the user then this will be `None` and `fallback_fluent_bundle` should be used.
+    pub fluent_bundle: Option<Arc<FluentBundle>>,
     /// Return `FluentBundle` with localized diagnostics for the default locale of the compiler.
     /// Used when the user has not requested a specific language or when a localized diagnostic is
     /// unavailable for the requested locale.
-    fn fallback_fluent_bundle(&self) -> &FluentBundle;
+    pub fallback_fluent_bundle: LazyFallbackBundle,
+}
+
+impl Translator {
+    pub fn with_fallback_bundle(
+        resources: Vec<&'static str>,
+        with_directionality_markers: bool,
+    ) -> Translator {
+        Translator {
+            fluent_bundle: None,
+            fallback_fluent_bundle: crate::fallback_fluent_bundle(
+                resources,
+                with_directionality_markers,
+            ),
+        }
+    }
 
     /// Convert `DiagMessage`s to a string, performing translation if necessary.
-    fn translate_messages(
+    pub fn translate_messages(
         &self,
         messages: &[(DiagMessage, Style)],
         args: &FluentArgs<'_>,
@@ -54,7 +69,7 @@ pub trait Translate {
     }
 
     /// Convert a `DiagMessage` to a string, performing translation if necessary.
-    fn translate_message<'a>(
+    pub fn translate_message<'a>(
         &'a self,
         message: &'a DiagMessage,
         args: &'a FluentArgs<'_>,
@@ -91,7 +106,7 @@ pub trait Translate {
             };
 
         try {
-            match self.fluent_bundle().map(|b| translate_with_bundle(b)) {
+            match self.fluent_bundle.as_ref().map(|b| translate_with_bundle(b)) {
                 // The primary bundle was present and translation succeeded
                 Some(Ok(t)) => t,
 
@@ -102,7 +117,7 @@ pub trait Translate {
                     primary @ TranslateError::One {
                         kind: TranslateErrorKind::MessageMissing, ..
                     },
-                )) => translate_with_bundle(self.fallback_fluent_bundle())
+                )) => translate_with_bundle(&self.fallback_fluent_bundle)
                     .map_err(|fallback| primary.and(fallback))?,
 
                 // Always yeet out for errors on debug (unless
@@ -118,11 +133,11 @@ pub trait Translate {
 
                 // ..otherwise, for end users, an error about this wouldn't be useful or actionable, so
                 // just hide it and try with the fallback bundle.
-                Some(Err(primary)) => translate_with_bundle(self.fallback_fluent_bundle())
+                Some(Err(primary)) => translate_with_bundle(&self.fallback_fluent_bundle)
                     .map_err(|fallback| primary.and(fallback))?,
 
                 // The primary bundle is missing, proceed to the fallback bundle
-                None => translate_with_bundle(self.fallback_fluent_bundle())
+                None => translate_with_bundle(&self.fallback_fluent_bundle)
                     .map_err(|fallback| TranslateError::primary(identifier, args).and(fallback))?,
             }
         }