Implement a Method to Seal DiagInner's Suggestions

compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs

@@ -48,7 +48,7 @@ impl Emitter for AnnotateSnippetEmitter {
     fn emit_diagnostic(&mut self, mut diag: DiagInner) {
         let fluent_args = to_fluent_args(diag.args.iter());
 
-        let mut suggestions = diag.suggestions.unwrap_or(vec![]);
+        let mut suggestions = diag.suggestions.unwrap_tag();
         self.primary_span_formatted(&mut diag.span, &mut suggestions, &fluent_args);
 
         self.fix_multispans_in_extern_macros_and_render_macro_backtrace(

compiler/rustc_errors/src/diagnostic.rs

@@ -19,13 +19,9 @@ use crate::snippet::Style;
 use crate::{
     CodeSuggestion, DiagCtxtHandle, DiagMessage, ErrCode, ErrorGuaranteed, ExplicitBug, Level,
     MultiSpan, StashKey, SubdiagMessage, Substitution, SubstitutionPart, SuggestionStyle,
+    Suggestions,
 };
 
-/// Error type for `DiagInner`'s `suggestions` field, indicating that
-/// `.disable_suggestions()` was called on the `DiagInner`.
-#[derive(Clone, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
-pub struct SuggestionsDisabled;
-
 /// Simplified version of `FluentArg` that can implement `Encodable` and `Decodable`. Collection of
 /// `DiagArg` are converted to `FluentArgs` (consuming the collection) at the start of diagnostic
 /// emission.
@@ -296,7 +292,7 @@ pub struct DiagInner {
     pub code: Option<ErrCode>,
     pub span: MultiSpan,
     pub children: Vec<Subdiag>,
-    pub suggestions: Result<Vec<CodeSuggestion>, SuggestionsDisabled>,
+    pub suggestions: Suggestions,
     pub args: DiagArgMap,
 
     /// This is not used for highlighting or rendering any error message. Rather, it can be used
@@ -325,7 +321,7 @@ impl DiagInner {
             code: None,
             span: MultiSpan::new(),
             children: vec![],
-            suggestions: Ok(vec![]),
+            suggestions: Suggestions::Enabled(vec![]),
             args: Default::default(),
             sort_span: DUMMY_SP,
             is_lint: None,
@@ -409,7 +405,7 @@ impl DiagInner {
         &Option<ErrCode>,
         &MultiSpan,
         &[Subdiag],
-        &Result<Vec<CodeSuggestion>, SuggestionsDisabled>,
+        &Suggestions,
         Vec<(&DiagArgName, &DiagArgValue)>,
         &Option<IsLint>,
     ) {
@@ -823,16 +819,32 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
         self
     }
 
-    /// Disallow attaching suggestions this diagnostic.
+    /// Disallow attaching suggestions to this diagnostic.
     /// Any suggestions attached e.g. with the `span_suggestion_*` methods
     /// (before and after the call to `disable_suggestions`) will be ignored.
     #[rustc_lint_diagnostics]
     pub fn disable_suggestions(&mut self) -> &mut Self {
-        self.suggestions = Err(SuggestionsDisabled);
+        self.suggestions = Suggestions::Disabled;
         self
     }
 
-    /// Helper for pushing to `self.suggestions`, if available (not disable).
+    /// Prevent new suggestions from being added to this diagnostic.
+    ///
+    /// Suggestions added before the call to `.seal_suggestions()` will be preserved
+    /// and new suggestions will be ignored.
+    #[rustc_lint_diagnostics]
+    pub fn seal_suggestions(&mut self) -> &mut Self {
+        if let Suggestions::Enabled(suggestions) = &mut self.suggestions {
+            let suggestions_slice = std::mem::take(suggestions).into_boxed_slice();
+            self.suggestions = Suggestions::Sealed(suggestions_slice);
+        }
+        self
+    }
+
+    /// Helper for pushing to `self.suggestions`.
+    ///
+    /// A new suggestion is added if suggestions are enabled for this diagnostic.
+    /// Otherwise, they are ignored.
     #[rustc_lint_diagnostics]
     fn push_suggestion(&mut self, suggestion: CodeSuggestion) {
         for subst in &suggestion.substitutions {
@@ -846,7 +858,7 @@ impl<'a, G: EmissionGuarantee> Diag<'a, G> {
             }
         }
 
-        if let Ok(suggestions) = &mut self.suggestions {
+        if let Suggestions::Enabled(suggestions) = &mut self.suggestions {
             suggestions.push(suggestion);
         }
     }

compiler/rustc_errors/src/emitter.rs

@@ -498,7 +498,7 @@ impl Emitter for HumanEmitter {
     fn emit_diagnostic(&mut self, mut diag: DiagInner) {
         let fluent_args = to_fluent_args(diag.args.iter());
 
-        let mut suggestions = diag.suggestions.unwrap_or(vec![]);
+        let mut suggestions = diag.suggestions.unwrap_tag();
         self.primary_span_formatted(&mut diag.span, &mut suggestions, &fluent_args);
 
         self.fix_multispans_in_extern_macros_and_render_macro_backtrace(

compiler/rustc_errors/src/json.rs

@@ -33,7 +33,8 @@ use crate::emitter::{
 use crate::registry::Registry;
 use crate::translation::{to_fluent_args, Translate};
 use crate::{
-    CodeSuggestion, FluentBundle, LazyFallbackBundle, MultiSpan, SpanLabel, Subdiag, TerminalUrl,
+    CodeSuggestion, FluentBundle, LazyFallbackBundle, MultiSpan, SpanLabel, Subdiag, Suggestions,
+    TerminalUrl,
 };
 
 #[cfg(test)]
@@ -292,7 +293,7 @@ impl Diagnostic {
     /// Converts from `rustc_errors::DiagInner` to `Diagnostic`.
     fn from_errors_diagnostic(diag: crate::DiagInner, je: &JsonEmitter) -> Diagnostic {
         let args = to_fluent_args(diag.args.iter());
-        let sugg = diag.suggestions.iter().flatten().map(|sugg| {
+        let sugg_to_diag = |sugg: &CodeSuggestion| {
             let translated_message =
                 je.translate_message(&sugg.msg, &args).map_err(Report::new).unwrap();
             Diagnostic {
@@ -303,7 +304,12 @@ impl Diagnostic {
                 children: vec![],
                 rendered: None,
             }
-        });
+        };
+        let sugg = match &diag.suggestions {
+            Suggestions::Enabled(suggestions) => suggestions.iter().map(sugg_to_diag),
+            Suggestions::Sealed(suggestions) => suggestions.iter().map(sugg_to_diag),
+            Suggestions::Disabled => [].iter().map(sugg_to_diag),
+        };
 
         // generate regular command line output and store it in the json
 

compiler/rustc_errors/src/lib.rs

@@ -126,6 +126,41 @@ impl SuggestionStyle {
     }
 }
 
+/// Represents the help messages seen on a diagnostic.
+#[derive(Clone, Debug, PartialEq, Hash, Encodable, Decodable)]
+pub enum Suggestions {
+    /// Indicates that new suggestions can be added or removed from this diagnostic.
+    ///
+    /// `DiagInner`'s new_* methods initialize the `suggestions` field with
+    /// this variant. Also, this is the default variant for `Suggestions`.
+    Enabled(Vec<CodeSuggestion>),
+    /// Indicates that suggestions cannot be added or removed from this diagnostic.
+    ///
+    /// Gets toggled when `.seal_suggestions()` is called on the `DiagInner`.
+    Sealed(Box<[CodeSuggestion]>),
+    /// Indicates that no suggestion is available for this diagnostic.
+    ///
+    /// Gets toggled when `.disable_suggestions()` is called on the `DiagInner`.
+    Disabled,
+}
+
+impl Suggestions {
+    /// Returns the underlying list of suggestions.
+    pub fn unwrap_tag(self) -> Vec<CodeSuggestion> {
+        match self {
+            Suggestions::Enabled(suggestions) => suggestions,
+            Suggestions::Sealed(suggestions) => suggestions.into_vec(),
+            Suggestions::Disabled => Vec::new(),
+        }
+    }
+}
+
+impl Default for Suggestions {
+    fn default() -> Self {
+        Self::Enabled(vec![])
+    }
+}
+
 #[derive(Clone, Debug, PartialEq, Hash, Encodable, Decodable)]
 pub struct CodeSuggestion {
     /// Each substitute can have multiple variants due to multiple