Rollup merge of #130116 - veera-sivarajan:freeze-suggestions, r=chenyukang

Implement a Method to Seal `DiagInner`'s Suggestions

This PR adds a method on `DiagInner` called `.seal_suggestions()` to prevent new suggestions from being added while preserving existing suggestions.

This is useful because currently there is no way to prevent new suggestions from being added to a diagnostic. `.disable_suggestions()` is the closest but it gets rid of all suggestions before and after the call.

Therefore, `.seal_suggestions()` can be used when, for example, misspelled keyword is detected and reported. In such cases, we may want to prevent other suggestions from being added to the diagnostic, as they would likely be meaningless once the misspelled keyword is identified. For context: https://github.com/rust-lang/rust/pull/129899#discussion_r1741307132

To store an additional state, the type of the `suggestions` field in `DiagInner` was changed into a three variant enum. While this change affects files across different crates, care was taken to preserve the existing code's semantics. This is validated by the fact that all UI tests pass without any modifications.

r? chenyukang

5 files changed, 70 insertions, 17 deletions

diff --git a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs b/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
index d71ae9d210d..556e6d46f89 100644
--- a/compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs
+++ b/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(
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 7a4d8dba179..6b756cff225 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/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);
         }
     }
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 2b135df91a4..3ab371b8057 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/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(
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index 32e59f9ab03..6a2ecf13f7b 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/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
 
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 13da1721a4a..094e3010471 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/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