Migrate rustc_session::expr_parentheses_needed to Subdiagnostic struct

Author: Xiretza

compiler/rustc_error_messages/locales/en-US/session.ftl

@@ -66,3 +66,5 @@ session_crate_name_invalid = crate names cannot start with a `-`, but `{$s}` has
 session_crate_name_empty = crate name must not be empty
 
 session_invalid_character_in_create_name = invalid character `{$character}` in crate name: `{$crate_name}`
+
+session_expr_parentheses_needed = parentheses are required to parse this as an expression

compiler/rustc_session/src/errors.rs

@@ -219,3 +219,18 @@ impl IntoDiagnostic<'_> for InvalidCharacterInCrateName<'_> {
         diag
     }
 }
+
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(session::expr_parentheses_needed, applicability = "machine-applicable")]
+pub struct ExprParenthesesNeeded {
+    #[suggestion_part(code = "(")]
+    pub left: Span,
+    #[suggestion_part(code = ")")]
+    pub right: Span,
+}
+
+impl ExprParenthesesNeeded {
+    pub fn surrounding(s: Span) -> Self {
+        ExprParenthesesNeeded { left: s.shrink_to_lo(), right: s.shrink_to_hi() }
+    }
+}

compiler/rustc_session/src/parse.rs

@@ -2,7 +2,9 @@
 //! It also serves as an input to the parser itself.
 
 use crate::config::CheckCfg;
-use crate::errors::{FeatureDiagnosticForIssue, FeatureDiagnosticHelp, FeatureGateError};
+use crate::errors::{
+    ExprParenthesesNeeded, FeatureDiagnosticForIssue, FeatureDiagnosticHelp, FeatureGateError,
+};
 use crate::lint::{
     builtin::UNSTABLE_SYNTAX_PRE_EXPANSION, BufferedEarlyLint, BuiltinLintDiagnostics, Lint, LintId,
 };
@@ -11,7 +13,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_data_structures::sync::{Lock, Lrc};
 use rustc_errors::{emitter::SilentEmitter, ColorConfig, Handler};
 use rustc_errors::{
-    fallback_fluent_bundle, Applicability, Diagnostic, DiagnosticBuilder, DiagnosticId,
+    fallback_fluent_bundle, AddToDiagnostic, Diagnostic, DiagnosticBuilder, DiagnosticId,
     DiagnosticMessage, EmissionGuarantee, ErrorGuaranteed, IntoDiagnostic, MultiSpan, StashKey,
 };
 use rustc_feature::{find_feature_issue, GateIssue, UnstableFeatures};
@@ -325,11 +327,7 @@ impl ParseSess {
     /// Extend an error with a suggestion to wrap an expression with parentheses to allow the
     /// parser to continue parsing the following operation as part of the same expression.
     pub fn expr_parentheses_needed(&self, err: &mut Diagnostic, span: Span) {
-        err.multipart_suggestion(
-            "parentheses are required to parse this as an expression",
-            vec![(span.shrink_to_lo(), "(".to_string()), (span.shrink_to_hi(), ")".to_string())],
-            Applicability::MachineApplicable,
-        );
+        ExprParenthesesNeeded::surrounding(span).add_to_diagnostic(err);
     }
 
     pub fn save_proc_macro_span(&self, span: Span) -> usize {