macros: subdiagnostic derive

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -237,7 +237,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     err.span_suggestion_verbose(
                         span,
                         "consider changing this to be mutable",
-                        " mut ".into(),
+                        " mut ",
                         Applicability::MaybeIncorrect,
                     );
                 }

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -235,7 +235,7 @@ fn validate_default_attribute(
             .span_suggestion_hidden(
                 attr.span,
                 "try using `#[default]`",
-                "#[default]".into(),
+                "#[default]",
                 Applicability::MaybeIncorrect,
             )
             .emit();

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

@@ -82,3 +82,11 @@ typeck-value-of-associated-struct-already-specified =
 
 typeck-address-of-temporary-taken = cannot take address of a temporary
     .label = temporary value
+
+typeck-add-return-type-add = try adding a return type
+
+typeck-add-return-type-missing-here = a return type might be missing here
+
+typeck-expected-default-return-type = expected `()` because of default return type
+
+typeck-expected-return-type = expected `{$expected}` because of return type

compiler/rustc_errors/src/diagnostic.rs

@@ -78,6 +78,13 @@ impl<'source> Into<FluentValue<'source>> for DiagnosticArgValue<'source> {
     }
 }
 
+/// Trait implemented by error types. This should not be implemented manually. Instead, use
+/// `#[derive(SessionSubdiagnostic)]` -- see [rustc_macros::SessionSubdiagnostic].
+pub trait AddSubdiagnostic {
+    /// Add a subdiagnostic to an existing diagnostic.
+    fn add_to_diagnostic(self, diag: &mut Diagnostic);
+}
+
 #[must_use]
 #[derive(Clone, Debug, Encodable, Decodable)]
 pub struct Diagnostic {
@@ -605,7 +612,7 @@ impl Diagnostic {
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self {
         self.span_suggestion_with_style(
@@ -623,13 +630,13 @@ impl Diagnostic {
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
         style: SuggestionStyle,
     ) -> &mut Self {
         self.push_suggestion(CodeSuggestion {
             substitutions: vec![Substitution {
-                parts: vec![SubstitutionPart { snippet: suggestion, span: sp }],
+                parts: vec![SubstitutionPart { snippet: suggestion.to_string(), span: sp }],
             }],
             msg: msg.into(),
             style,
@@ -643,7 +650,7 @@ impl Diagnostic {
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self {
         self.span_suggestion_with_style(
@@ -711,7 +718,7 @@ impl Diagnostic {
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self {
         self.span_suggestion_with_style(
@@ -734,7 +741,7 @@ impl Diagnostic {
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self {
         self.span_suggestion_with_style(
@@ -755,7 +762,7 @@ impl Diagnostic {
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self {
         self.span_suggestion_with_style(
@@ -768,6 +775,13 @@ impl Diagnostic {
         self
     }
 
+    /// Add a subdiagnostic from a type that implements `SessionSubdiagnostic` - see
+    /// [rustc_macros::SessionSubdiagnostic].
+    pub fn subdiagnostic(&mut self, subdiagnostic: impl AddSubdiagnostic) -> &mut Self {
+        subdiagnostic.add_to_diagnostic(self);
+        self
+    }
+
     pub fn set_span<S: Into<MultiSpan>>(&mut self, sp: S) -> &mut Self {
         self.span = sp.into();
         if let Some(span) = self.span.primary_span() {

compiler/rustc_errors/src/diagnostic_builder.rs

@@ -477,7 +477,7 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self);
     forward!(pub fn span_suggestions(
@@ -497,28 +497,28 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self);
     forward!(pub fn span_suggestion_verbose(
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self);
     forward!(pub fn span_suggestion_hidden(
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self);
     forward!(pub fn tool_only_span_suggestion(
         &mut self,
         sp: Span,
         msg: impl Into<DiagnosticMessage>,
-        suggestion: String,
+        suggestion: impl ToString,
         applicability: Applicability,
     ) -> &mut Self);
 
@@ -530,6 +530,11 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
         name: impl Into<Cow<'static, str>>,
         arg: DiagnosticArgValue<'static>,
     ) -> &mut Self);
+
+    forward!(pub fn subdiagnostic(
+        &mut self,
+        subdiagnostic: impl crate::AddSubdiagnostic
+    ) -> &mut Self);
 }
 
 impl<G: EmissionGuarantee> Debug for DiagnosticBuilder<'_, G> {

compiler/rustc_errors/src/lib.rs

@@ -370,8 +370,8 @@ impl fmt::Display for ExplicitBug {
 impl error::Error for ExplicitBug {}
 
 pub use diagnostic::{
-    Diagnostic, DiagnosticArg, DiagnosticArgValue, DiagnosticId, DiagnosticStyledString,
-    IntoDiagnosticArg, SubDiagnostic,
+    AddSubdiagnostic, Diagnostic, DiagnosticArg, DiagnosticArgValue, DiagnosticId,
+    DiagnosticStyledString, IntoDiagnosticArg, SubDiagnostic,
 };
 pub use diagnostic_builder::{DiagnosticBuilder, EmissionGuarantee};
 use std::backtrace::Backtrace;

compiler/rustc_expand/src/config.rs

@@ -511,7 +511,7 @@ pub fn parse_cfg<'a>(meta_item: &'a MetaItem, sess: &Session) -> Option<&'a Meta
             err.span_suggestion(
                 span,
                 "expected syntax is",
-                suggestion.into(),
+                suggestion,
                 Applicability::HasPlaceholders,
             );
         }

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -2198,7 +2198,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             err.span_suggestion(
                 span.with_hi(before_close).shrink_to_hi(),
                 msg,
-                ",".into(),
+                ",",
                 Applicability::MachineApplicable,
             );
         } else {

compiler/rustc_lint/src/array_into_iter.rs

@@ -129,7 +129,7 @@ impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
                 diag.span_suggestion(
                     call.ident.span,
                     "use `.iter()` instead of `.into_iter()` to avoid ambiguity",
-                    "iter".into(),
+                    "iter",
                     Applicability::MachineApplicable,
                 );
                 if self.for_expr_span == expr.span {

compiler/rustc_lint/src/context.rs

@@ -738,7 +738,7 @@ pub trait LintContext: Sized {
                     db.span_suggestion_verbose(
                         span.shrink_to_hi(),
                         "insert whitespace here to avoid this being parsed as a prefix in Rust 2021",
-                        " ".into(),
+                        " ",
                         Applicability::MachineApplicable,
                     );
                 }

compiler/rustc_lint/src/non_fmt_panic.rs

@@ -176,7 +176,7 @@ fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tc
                 l.span_suggestion_verbose(
                     arg_span.shrink_to_lo(),
                     "add a \"{}\" format string to Display the message",
-                    "\"{}\", ".into(),
+                    "\"{}\", ",
                     fmt_applicability,
                 );
             } else if suggest_debug {
@@ -186,7 +186,7 @@ fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tc
                         "add a \"{{:?}}\" format string to use the Debug implementation of `{}`",
                         ty,
                     ),
-                    "\"{:?}\", ".into(),
+                    "\"{:?}\", ",
                     fmt_applicability,
                 );
             }
@@ -266,13 +266,13 @@ fn check_panic_str<'tcx>(
                 l.span_suggestion(
                     arg.span.shrink_to_hi(),
                     &format!("add the missing argument{}", pluralize!(n_arguments)),
-                    ", ...".into(),
+                    ", ...",
                     Applicability::HasPlaceholders,
                 );
                 l.span_suggestion(
                     arg.span.shrink_to_lo(),
                     "or add a \"{}\" format string to use the message literally",
-                    "\"{}\", ".into(),
+                    "\"{}\", ",
                     Applicability::MachineApplicable,
                 );
             }
@@ -297,7 +297,7 @@ fn check_panic_str<'tcx>(
                 l.span_suggestion(
                     arg.span.shrink_to_lo(),
                     "add a \"{}\" format string to use the message literally",
-                    "\"{}\", ".into(),
+                    "\"{}\", ",
                     Applicability::MachineApplicable,
                 );
             }