Remove is_lint field from Level::Error.

Because it's redundant w.r.t. `Diagnostic::is_lint`, which is present
for every diagnostic level.

`struct_lint_level_impl` was the only place that set the `Error` field
to `true`, and it's also the only place that calls
`Diagnostic::is_lint()` to set the `is_lint` field.

compiler/rustc_errors/src/lib.rs

@@ -673,7 +673,7 @@ impl DiagCtxt {
         let key = (span.with_parent(None), key);
 
         if diag.is_error() {
-            if matches!(diag.level, Error { lint: true }) {
+            if diag.level == Error && diag.is_lint {
                 inner.lint_err_count += 1;
             } else {
                 inner.err_count += 1;
@@ -697,7 +697,7 @@ impl DiagCtxt {
         let key = (span.with_parent(None), key);
         let diag = inner.stashed_diagnostics.remove(&key)?;
         if diag.is_error() {
-            if matches!(diag.level, Error { lint: true }) {
+            if diag.level == Error && diag.is_lint {
                 inner.lint_err_count -= 1;
             } else {
                 inner.err_count -= 1;
@@ -812,7 +812,7 @@ impl DiagCtxt {
     #[rustc_lint_diagnostics]
     #[track_caller]
     pub fn struct_err(&self, msg: impl Into<DiagnosticMessage>) -> DiagnosticBuilder<'_> {
-        DiagnosticBuilder::new(self, Error { lint: false }, msg)
+        DiagnosticBuilder::new(self, Error, msg)
     }
 
     /// Construct a builder at the `Error` level with the `msg` and the `code`.
@@ -1212,7 +1212,7 @@ impl DiagCtxt {
 
     #[track_caller]
     pub fn create_err<'a>(&'a self, err: impl IntoDiagnostic<'a>) -> DiagnosticBuilder<'a> {
-        err.into_diagnostic(self, Error { lint: false })
+        err.into_diagnostic(self, Error)
     }
 
     #[track_caller]
@@ -1367,7 +1367,7 @@ impl DiagCtxtInner {
         for diag in diags {
             // Decrement the count tracking the stash; emitting will increment it.
             if diag.is_error() {
-                if matches!(diag.level, Error { lint: true }) {
+                if diag.level == Error && diag.is_lint {
                     self.lint_err_count -= 1;
                 } else {
                     self.err_count -= 1;
@@ -1398,7 +1398,7 @@ impl DiagCtxtInner {
         &mut self,
         diagnostic: &mut Diagnostic,
     ) -> Option<ErrorGuaranteed> {
-        if matches!(diagnostic.level, Error { .. } | Fatal) && self.treat_err_as_bug() {
+        if matches!(diagnostic.level, Error | Fatal) && self.treat_err_as_bug() {
             diagnostic.level = Bug;
         }
 
@@ -1499,7 +1499,7 @@ impl DiagCtxtInner {
                 }
             }
             if diagnostic.is_error() {
-                if matches!(diagnostic.level, Error { lint: true }) {
+                if diagnostic.level == Error && diagnostic.is_lint {
                     self.bump_lint_err_count();
                 } else {
                     self.bump_err_count();
@@ -1695,11 +1695,7 @@ pub enum Level {
     /// most common case.
     ///
     /// Its `EmissionGuarantee` is `ErrorGuaranteed`.
-    Error {
-        /// If this error comes from a lint, don't abort compilation even when abort_if_errors() is
-        /// called.
-        lint: bool,
-    },
+    Error,
 
     /// A warning about the code being compiled. Does not prevent compilation from finishing.
     ///
@@ -1758,7 +1754,7 @@ impl Level {
     fn color(self) -> ColorSpec {
         let mut spec = ColorSpec::new();
         match self {
-            Bug | DelayedBug | Fatal | Error { .. } => {
+            Bug | DelayedBug | Fatal | Error => {
                 spec.set_fg(Some(Color::Red)).set_intense(true);
             }
             Warning(_) => {
@@ -1779,7 +1775,7 @@ impl Level {
     pub fn to_str(self) -> &'static str {
         match self {
             Bug | DelayedBug => "error: internal compiler error",
-            Fatal | Error { .. } => "error",
+            Fatal | Error => "error",
             Warning(_) => "warning",
             Note | OnceNote => "note",
             Help | OnceHelp => "help",