Give DiagnosticBuilder a default type.

`IntoDiagnostic` defaults to `ErrorGuaranteed`, because errors are the
most common diagnostic level. It makes sense to do likewise for the
closely-related (and much more widely used) `DiagnosticBuilder` type,
letting us write `DiagnosticBuilder<'a, ErrorGuaranteed>` as just
`DiagnosticBuilder<'a>`. This cuts over 200 lines of code due to many
multi-line things becoming single line things.

compiler/rustc_trait_selection/src/traits/error_reporting/infer_ctxt_ext.rs

@@ -1,7 +1,7 @@
 use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
 use crate::infer::InferCtxt;
 use crate::traits::{Obligation, ObligationCause, ObligationCtxt};
-use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, ErrorGuaranteed};
+use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder};
 use rustc_hir as hir;
 use rustc_hir::Node;
 use rustc_middle::ty::{self, Ty};
@@ -29,7 +29,7 @@ pub trait InferCtxtExt<'tcx> {
         found_args: Vec<ArgKind>,
         is_closure: bool,
         closure_pipe_span: Option<Span>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
+    ) -> DiagnosticBuilder<'tcx>;
 
     /// Checks if the type implements one of `Fn`, `FnMut`, or `FnOnce`
     /// in that order, and returns the generic type corresponding to the
@@ -118,7 +118,7 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
         found_args: Vec<ArgKind>,
         is_closure: bool,
         closure_arg_span: Option<Span>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'tcx> {
         let kind = if is_closure { "closure" } else { "function" };
 
         let args_str = |arguments: &[ArgKind], other: &[ArgKind]| {

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -14,7 +14,7 @@ use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::{
     error_code, pluralize, struct_span_err, Applicability, Diagnostic, DiagnosticBuilder,
-    ErrorGuaranteed, MultiSpan, Style, SuggestionStyle,
+    MultiSpan, Style, SuggestionStyle,
 };
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
@@ -207,7 +207,7 @@ pub trait TypeErrCtxtExt<'tcx> {
 
     fn point_at_returns_when_relevant(
         &self,
-        err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
+        err: &mut DiagnosticBuilder<'tcx>,
         obligation: &PredicateObligation<'tcx>,
     );
 
@@ -220,7 +220,7 @@ pub trait TypeErrCtxtExt<'tcx> {
         cause: &ObligationCauseCode<'tcx>,
         found_node: Option<Node<'_>>,
         param_env: ty::ParamEnv<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
+    ) -> DiagnosticBuilder<'tcx>;
 
     fn note_conflicting_fn_args(
         &self,
@@ -234,7 +234,7 @@ pub trait TypeErrCtxtExt<'tcx> {
     fn note_conflicting_closure_bounds(
         &self,
         cause: &ObligationCauseCode<'tcx>,
-        err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
+        err: &mut DiagnosticBuilder<'tcx>,
     );
 
     fn suggest_fully_qualified_path(
@@ -1920,7 +1920,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
 
     fn point_at_returns_when_relevant(
         &self,
-        err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
+        err: &mut DiagnosticBuilder<'tcx>,
         obligation: &PredicateObligation<'tcx>,
     ) {
         match obligation.cause.code().peel_derives() {
@@ -1961,7 +1961,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         cause: &ObligationCauseCode<'tcx>,
         found_node: Option<Node<'_>>,
         param_env: ty::ParamEnv<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'tcx> {
         pub(crate) fn build_fn_sig_ty<'tcx>(
             infcx: &InferCtxt<'tcx>,
             trait_ref: ty::PolyTraitRef<'tcx>,
@@ -2187,7 +2187,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
     fn note_conflicting_closure_bounds(
         &self,
         cause: &ObligationCauseCode<'tcx>,
-        err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
+        err: &mut DiagnosticBuilder<'tcx>,
     ) {
         // First, look for an `ExprBindingObligation`, which means we can get
         // the unsubstituted predicate list of the called function. And check

compiler/rustc_trait_selection/src/traits/error_reporting/type_err_ctxt_ext.rs

@@ -59,7 +59,7 @@ pub trait TypeErrCtxtExt<'tcx> {
         predicate: &T,
         span: Span,
         suggest_increasing_limit: bool,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>
+    ) -> DiagnosticBuilder<'tcx>
     where
         T: fmt::Display + TypeFoldable<TyCtxt<'tcx>> + Print<'tcx, FmtPrinter<'tcx, 'tcx>>;
 
@@ -118,7 +118,7 @@ pub trait TypeErrCtxtExt<'tcx> {
         &self,
         ty: Ty<'tcx>,
         obligation: &PredicateObligation<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
+    ) -> DiagnosticBuilder<'tcx>;
 }
 
 impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
@@ -263,7 +263,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         predicate: &T,
         span: Span,
         suggest_increasing_limit: bool,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>
+    ) -> DiagnosticBuilder<'tcx>
     where
         T: fmt::Display + TypeFoldable<TyCtxt<'tcx>> + Print<'tcx, FmtPrinter<'tcx, 'tcx>>,
     {
@@ -1226,7 +1226,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         &self,
         ty: Ty<'tcx>,
         obligation: &PredicateObligation<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'tcx> {
         let span = obligation.cause.span;
 
         let mut diag = match ty.kind() {
@@ -1491,7 +1491,7 @@ pub(super) trait InferCtxtPrivExt<'tcx> {
         closure_def_id: DefId,
         found_kind: ty::ClosureKind,
         kind: ty::ClosureKind,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
+    ) -> DiagnosticBuilder<'tcx>;
 
     fn report_type_parameter_mismatch_cyclic_type_error(
         &self,
@@ -1499,13 +1499,13 @@ pub(super) trait InferCtxtPrivExt<'tcx> {
         found_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
         expected_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
         terr: TypeError<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
+    ) -> DiagnosticBuilder<'tcx>;
 
     fn report_opaque_type_auto_trait_leakage(
         &self,
         obligation: &PredicateObligation<'tcx>,
         def_id: DefId,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed>;
+    ) -> DiagnosticBuilder<'tcx>;
 
     fn report_type_parameter_mismatch_error(
         &self,
@@ -1513,13 +1513,13 @@ pub(super) trait InferCtxtPrivExt<'tcx> {
         span: Span,
         found_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
         expected_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
-    ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>>;
+    ) -> Option<DiagnosticBuilder<'tcx>>;
 
     fn report_not_const_evaluatable_error(
         &self,
         obligation: &PredicateObligation<'tcx>,
         span: Span,
-    ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>>;
+    ) -> Option<DiagnosticBuilder<'tcx>>;
 }
 
 impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
@@ -3305,7 +3305,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         closure_def_id: DefId,
         found_kind: ty::ClosureKind,
         kind: ty::ClosureKind,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'tcx> {
         let closure_span = self.tcx.def_span(closure_def_id);
 
         let mut err = ClosureKindMismatch {
@@ -3347,7 +3347,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         found_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
         expected_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
         terr: TypeError<'tcx>,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'tcx> {
         let self_ty = found_trait_ref.self_ty().skip_binder();
         let (cause, terr) = if let ty::Closure(def_id, _) = self_ty.kind() {
             (
@@ -3367,7 +3367,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         &self,
         obligation: &PredicateObligation<'tcx>,
         def_id: DefId,
-    ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'tcx> {
         let name = match self.tcx.opaque_type_origin(def_id.expect_local()) {
             hir::OpaqueTyOrigin::FnReturn(_) | hir::OpaqueTyOrigin::AsyncFn(_) => {
                 "opaque type".to_string()
@@ -3409,7 +3409,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         span: Span,
         found_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
         expected_trait_ref: ty::Binder<'tcx, ty::TraitRef<'tcx>>,
-    ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
+    ) -> Option<DiagnosticBuilder<'tcx>> {
         let found_trait_ref = self.resolve_vars_if_possible(found_trait_ref);
         let expected_trait_ref = self.resolve_vars_if_possible(expected_trait_ref);
 
@@ -3515,7 +3515,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         &self,
         obligation: &PredicateObligation<'tcx>,
         span: Span,
-    ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
+    ) -> Option<DiagnosticBuilder<'tcx>> {
         if !self.tcx.features().generic_const_exprs {
             let mut err = self
                 .tcx