errors: lazily load fallback fluent bundle

Loading the fallback bundle in compilation sessions that won't go on to
emit any errors unnecessarily degrades compile time performance, so
lazily create the Fluent bundle when it is first required.

Signed-off-by: David Wood <david.wood@huawei.com>

Author: davidtwco

clippy_lints/src/doc.rs

@@ -621,8 +621,10 @@ fn check_code(cx: &LateContext<'_>, text: &str, edition: Edition, span: Span) {
                 let filename = FileName::anon_source_code(&code);
 
                 let sm = Lrc::new(SourceMap::new(FilePathMapping::empty()));
-                let fallback_bundle =
-                    rustc_errors::fallback_fluent_bundle(false).expect("failed to load fallback fluent bundle");
+                let fallback_bundle = rustc_errors::fallback_fluent_bundle(
+                    rustc_errors::DEFAULT_LOCALE_RESOURCES,
+                    false
+                );
                 let emitter = EmitterWriter::new(
                     Box::new(io::sink()),
                     None,

src/driver.rs

@@ -165,7 +165,8 @@ fn report_clippy_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str) {
     // Separate the output with an empty line
     eprintln!();
 
-    let fallback_bundle = rustc_errors::fallback_fluent_bundle(false).expect("failed to load fallback fluent bundle");
+    let fallback_bundle =
+        rustc_errors::fallback_fluent_bundle(rustc_errors::DEFAULT_LOCALE_RESOURCES, false);
     let emitter = Box::new(rustc_errors::emitter::EmitterWriter::stderr(
         rustc_errors::ColorConfig::Auto,
         None,