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_session/src/errors.rs

@@ -4,8 +4,7 @@ use crate::parse::ParseSess;
 use rustc_ast::token;
 use rustc_ast::util::literal::LitError;
 use rustc_errors::{
-    error_code, DiagCtxt, DiagnosticBuilder, DiagnosticMessage, ErrorGuaranteed, IntoDiagnostic,
-    Level, MultiSpan,
+    error_code, DiagCtxt, DiagnosticBuilder, DiagnosticMessage, IntoDiagnostic, Level, MultiSpan,
 };
 use rustc_macros::Diagnostic;
 use rustc_span::{BytePos, Span, Symbol};
@@ -18,11 +17,7 @@ pub struct FeatureGateError {
 
 impl<'a> IntoDiagnostic<'a> for FeatureGateError {
     #[track_caller]
-    fn into_diagnostic(
-        self,
-        dcx: &'a DiagCtxt,
-        level: Level,
-    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    fn into_diagnostic(self, dcx: &'a DiagCtxt, level: Level) -> DiagnosticBuilder<'a> {
         let mut diag = DiagnosticBuilder::new(dcx, level, self.explain);
         diag.set_span(self.span);
         diag.code(error_code!(E0658));

compiler/rustc_session/src/parse.rs

@@ -83,7 +83,7 @@ pub fn feature_err(
     feature: Symbol,
     span: impl Into<MultiSpan>,
     explain: impl Into<DiagnosticMessage>,
-) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+) -> DiagnosticBuilder<'_> {
     feature_err_issue(sess, feature, span, GateIssue::Language, explain)
 }
 
@@ -98,7 +98,7 @@ pub fn feature_err_issue(
     span: impl Into<MultiSpan>,
     issue: GateIssue,
     explain: impl Into<DiagnosticMessage>,
-) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+) -> DiagnosticBuilder<'_> {
     let span = span.into();
 
     // Cancel an earlier warning for this same error, if it exists.
@@ -318,10 +318,7 @@ impl ParseSess {
     }
 
     #[track_caller]
-    pub fn create_err<'a>(
-        &'a self,
-        err: impl IntoDiagnostic<'a>,
-    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    pub fn create_err<'a>(&'a self, err: impl IntoDiagnostic<'a>) -> DiagnosticBuilder<'a> {
         err.into_diagnostic(&self.dcx, Level::Error { lint: false })
     }
 
@@ -371,10 +368,7 @@ impl ParseSess {
 
     #[rustc_lint_diagnostics]
     #[track_caller]
-    pub fn struct_err(
-        &self,
-        msg: impl Into<DiagnosticMessage>,
-    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+    pub fn struct_err(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_> {
         self.dcx.struct_err(msg)
     }
 

compiler/rustc_session/src/session.rs

@@ -354,7 +354,7 @@ impl Session {
         &self,
         sp: S,
         msg: impl Into<DiagnosticMessage>,
-    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'_> {
         self.dcx().struct_span_err(sp, msg)
     }
     #[rustc_lint_diagnostics]
@@ -364,16 +364,13 @@ impl Session {
         sp: S,
         msg: impl Into<DiagnosticMessage>,
         code: DiagnosticId,
-    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'_> {
         self.dcx().struct_span_err_with_code(sp, msg, code)
     }
     // FIXME: This method should be removed (every error should have an associated error code).
     #[rustc_lint_diagnostics]
     #[track_caller]
-    pub fn struct_err(
-        &self,
-        msg: impl Into<DiagnosticMessage>,
-    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+    pub fn struct_err(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_> {
         self.parse_sess.struct_err(msg)
     }
     #[track_caller]
@@ -382,7 +379,7 @@ impl Session {
         &self,
         msg: impl Into<DiagnosticMessage>,
         code: DiagnosticId,
-    ) -> DiagnosticBuilder<'_, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'_> {
         self.dcx().struct_err_with_code(msg, code)
     }
     #[rustc_lint_diagnostics]
@@ -463,10 +460,7 @@ impl Session {
         self.dcx().err(msg)
     }
     #[track_caller]
-    pub fn create_err<'a>(
-        &'a self,
-        err: impl IntoDiagnostic<'a>,
-    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    pub fn create_err<'a>(&'a self, err: impl IntoDiagnostic<'a>) -> DiagnosticBuilder<'a> {
         self.parse_sess.create_err(err)
     }
     #[track_caller]
@@ -474,7 +468,7 @@ impl Session {
         &'a self,
         err: impl IntoDiagnostic<'a>,
         feature: Symbol,
-    ) -> DiagnosticBuilder<'a, ErrorGuaranteed> {
+    ) -> DiagnosticBuilder<'a> {
         let mut err = self.parse_sess.create_err(err);
         if err.code.is_none() {
             err.code = std::option::Option::Some(error_code!(E0658));