errors: implement fallback diagnostic translation

This commit updates the signatures of all diagnostic functions to accept
types that can be converted into a `DiagnosticMessage`. This enables
existing diagnostic calls to continue to work as before and Fluent
identifiers to be provided. The `SessionDiagnostic` derive just
generates normal diagnostic calls, so these APIs had to be modified to
accept Fluent identifiers.

In addition, loading of the "fallback" Fluent bundle, which contains the
built-in English messages, has been implemented.

Each diagnostic now has "arguments" which correspond to variables in the
Fluent messages (necessary to render a Fluent message) but no API for
adding arguments has been added yet. Therefore, diagnostics (that do not
require interpolation) can be converted to use Fluent identifiers and
will be output as before.

compiler/rustc_errors/src/json.rs

@@ -15,10 +15,11 @@ use crate::emitter::{Emitter, HumanReadableErrorType};
 use crate::registry::Registry;
 use crate::DiagnosticId;
 use crate::ToolMetadata;
-use crate::{CodeSuggestion, MultiSpan, SpanLabel, SubDiagnostic};
+use crate::{CodeSuggestion, FluentBundle, MultiSpan, SpanLabel, SubDiagnostic};
 use rustc_lint_defs::Applicability;
 
 use rustc_data_structures::sync::Lrc;
+use rustc_error_messages::FluentArgs;
 use rustc_span::hygiene::ExpnData;
 use rustc_span::Span;
 use std::io::{self, Write};
@@ -36,6 +37,7 @@ pub struct JsonEmitter {
     dst: Box<dyn Write + Send>,
     registry: Option<Registry>,
     sm: Lrc<SourceMap>,
+    fallback_bundle: Lrc<FluentBundle>,
     pretty: bool,
     ui_testing: bool,
     json_rendered: HumanReadableErrorType,
@@ -47,6 +49,7 @@ impl JsonEmitter {
     pub fn stderr(
         registry: Option<Registry>,
         source_map: Lrc<SourceMap>,
+        fallback_bundle: Lrc<FluentBundle>,
         pretty: bool,
         json_rendered: HumanReadableErrorType,
         terminal_width: Option<usize>,
@@ -56,6 +59,7 @@ impl JsonEmitter {
             dst: Box::new(io::BufWriter::new(io::stderr())),
             registry,
             sm: source_map,
+            fallback_bundle,
             pretty,
             ui_testing: false,
             json_rendered,
@@ -67,6 +71,7 @@ impl JsonEmitter {
     pub fn basic(
         pretty: bool,
         json_rendered: HumanReadableErrorType,
+        fallback_bundle: Lrc<FluentBundle>,
         terminal_width: Option<usize>,
         macro_backtrace: bool,
     ) -> JsonEmitter {
@@ -74,6 +79,7 @@ impl JsonEmitter {
         JsonEmitter::stderr(
             None,
             Lrc::new(SourceMap::new(file_path_mapping)),
+            fallback_bundle,
             pretty,
             json_rendered,
             terminal_width,
@@ -85,6 +91,7 @@ impl JsonEmitter {
         dst: Box<dyn Write + Send>,
         registry: Option<Registry>,
         source_map: Lrc<SourceMap>,
+        fallback_bundle: Lrc<FluentBundle>,
         pretty: bool,
         json_rendered: HumanReadableErrorType,
         terminal_width: Option<usize>,
@@ -94,6 +101,7 @@ impl JsonEmitter {
             dst,
             registry,
             sm: source_map,
+            fallback_bundle,
             pretty,
             ui_testing: false,
             json_rendered,
@@ -173,6 +181,14 @@ impl Emitter for JsonEmitter {
         Some(&self.sm)
     }
 
+    fn fluent_bundle(&self) -> Option<&Lrc<FluentBundle>> {
+        None
+    }
+
+    fn fallback_fluent_bundle(&self) -> &Lrc<FluentBundle> {
+        &self.fallback_bundle
+    }
+
     fn should_show_explain(&self) -> bool {
         !matches!(self.json_rendered, HumanReadableErrorType::Short(_))
     }
@@ -345,14 +361,18 @@ struct UnusedExterns<'a, 'b, 'c> {
 
 impl Diagnostic {
     fn from_errors_diagnostic(diag: &crate::Diagnostic, je: &JsonEmitter) -> Diagnostic {
-        let sugg = diag.suggestions.iter().flatten().map(|sugg| Diagnostic {
-            message: sugg.msg.clone().to_string(),
-            code: None,
-            level: "help",
-            spans: DiagnosticSpan::from_suggestion(sugg, je),
-            children: vec![],
-            rendered: None,
-            tool_metadata: sugg.tool_metadata.clone(),
+        let args = je.to_fluent_args(diag.args());
+        let sugg = diag.suggestions.iter().flatten().map(|sugg| {
+            let translated_message = je.translate_message(&sugg.msg, &args);
+            Diagnostic {
+                message: translated_message.to_string(),
+                code: None,
+                level: "help",
+                spans: DiagnosticSpan::from_suggestion(sugg, &args, je),
+                children: vec![],
+                rendered: None,
+                tool_metadata: sugg.tool_metadata.clone(),
+            }
         });
 
         // generate regular command line output and store it in the json
@@ -375,6 +395,7 @@ impl Diagnostic {
             .new_emitter(
                 Box::new(buf),
                 Some(je.sm.clone()),
+                je.fallback_bundle.clone(),
                 false,
                 je.terminal_width,
                 je.macro_backtrace,
@@ -384,15 +405,16 @@ impl Diagnostic {
         let output = Arc::try_unwrap(output.0).unwrap().into_inner().unwrap();
         let output = String::from_utf8(output).unwrap();
 
+        let translated_message = je.translate_messages(&diag.message, &args);
         Diagnostic {
-            message: diag.message().to_string(),
+            message: translated_message.to_string(),
             code: DiagnosticCode::map_opt_string(diag.code.clone(), je),
             level: diag.level.to_str(),
-            spans: DiagnosticSpan::from_multispan(&diag.span, je),
+            spans: DiagnosticSpan::from_multispan(&diag.span, &args, je),
             children: diag
                 .children
                 .iter()
-                .map(|c| Diagnostic::from_sub_diagnostic(c, je))
+                .map(|c| Diagnostic::from_sub_diagnostic(c, &args, je))
                 .chain(sugg)
                 .collect(),
             rendered: Some(output),
@@ -400,16 +422,21 @@ impl Diagnostic {
         }
     }
 
-    fn from_sub_diagnostic(diag: &SubDiagnostic, je: &JsonEmitter) -> Diagnostic {
+    fn from_sub_diagnostic(
+        diag: &SubDiagnostic,
+        args: &FluentArgs<'_>,
+        je: &JsonEmitter,
+    ) -> Diagnostic {
+        let translated_message = je.translate_messages(&diag.message, args);
         Diagnostic {
-            message: diag.message().to_string(),
+            message: translated_message.to_string(),
             code: None,
             level: diag.level.to_str(),
             spans: diag
                 .render_span
                 .as_ref()
-                .map(|sp| DiagnosticSpan::from_multispan(sp, je))
-                .unwrap_or_else(|| DiagnosticSpan::from_multispan(&diag.span, je)),
+                .map(|sp| DiagnosticSpan::from_multispan(sp, args, je))
+                .unwrap_or_else(|| DiagnosticSpan::from_multispan(&diag.span, args, je)),
             children: vec![],
             rendered: None,
             tool_metadata: ToolMetadata::default(),
@@ -421,12 +448,13 @@ impl DiagnosticSpan {
     fn from_span_label(
         span: SpanLabel,
         suggestion: Option<(&String, Applicability)>,
+        args: &FluentArgs<'_>,
         je: &JsonEmitter,
     ) -> DiagnosticSpan {
         Self::from_span_etc(
             span.span,
             span.is_primary,
-            span.label.map(|m| m.to_string()),
+            span.label.as_ref().map(|m| je.translate_message(m, args)).map(|m| m.to_string()),
             suggestion,
             je,
         )
@@ -492,14 +520,22 @@ impl DiagnosticSpan {
         }
     }
 
-    fn from_multispan(msp: &MultiSpan, je: &JsonEmitter) -> Vec<DiagnosticSpan> {
+    fn from_multispan(
+        msp: &MultiSpan,
+        args: &FluentArgs<'_>,
+        je: &JsonEmitter,
+    ) -> Vec<DiagnosticSpan> {
         msp.span_labels()
             .into_iter()
-            .map(|span_str| Self::from_span_label(span_str, None, je))
+            .map(|span_str| Self::from_span_label(span_str, None, args, je))
             .collect()
     }
 
-    fn from_suggestion(suggestion: &CodeSuggestion, je: &JsonEmitter) -> Vec<DiagnosticSpan> {
+    fn from_suggestion(
+        suggestion: &CodeSuggestion,
+        args: &FluentArgs<'_>,
+        je: &JsonEmitter,
+    ) -> Vec<DiagnosticSpan> {
         suggestion
             .substitutions
             .iter()
@@ -510,6 +546,7 @@ impl DiagnosticSpan {
                     DiagnosticSpan::from_span_label(
                         span_label,
                         Some((&suggestion_inner.snippet, suggestion.applicability)),
+                        args,
                         je,
                     )
                 })