Tweak error counting.

We have several methods indicating the presence of errors, lint errors,
and delayed bugs. I find it frustrating that it's very unclear which one
you should use in any particular spot. This commit attempts to instill a
basic principle of "use the least general one possible", because that
reflects reality in practice -- `has_errors` is the least general one
and has by far the most uses (esp. via `abort_if_errors`).

Specifics:
- Add some comments giving some usage guidelines.
- Prefer `has_errors` to comparing `err_count` to zero.
- Remove `has_errors_or_span_delayed_bugs` because it's a weird one: in
  the cases where we need to count delayed bugs, we should really be
  counting lint errors as well.
- Rename `is_compilation_going_to_fail` as
  `has_errors_or_lint_errors_or_span_delayed_bugs`, for consistency with
  `has_errors` and `has_errors_or_lint_errors`.
- Change a few other `has_errors_or_lint_errors` calls to `has_errors`,
  as per the "least general" principle.

This didn't turn out to be as neat as I hoped when I started, but I
think it's still an improvement.

1 files changed, 11 insertions, 15 deletions

diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index e47daf4afa1..9d80c456517 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -927,11 +927,13 @@ impl DiagCtxt {
         self.struct_bug(msg).emit()
     }
 
+    /// This excludes lint errors and delayed bugs.
     #[inline]
     pub fn err_count(&self) -> usize {
         self.inner.borrow().err_count
     }
 
+    /// This excludes lint errors and delayed bugs.
     pub fn has_errors(&self) -> Option<ErrorGuaranteed> {
         self.inner.borrow().has_errors().then(|| {
             #[allow(deprecated)]
@@ -939,30 +941,24 @@ impl DiagCtxt {
         })
     }
 
+    /// This excludes delayed bugs. Unless absolutely necessary, prefer
+    /// `has_errors` to this method.
     pub fn has_errors_or_lint_errors(&self) -> Option<ErrorGuaranteed> {
         let inner = self.inner.borrow();
-        let has_errors_or_lint_errors = inner.has_errors() || inner.lint_err_count > 0;
-        has_errors_or_lint_errors.then(|| {
+        let result = inner.has_errors() || inner.lint_err_count > 0;
+        result.then(|| {
             #[allow(deprecated)]
             ErrorGuaranteed::unchecked_claim_error_was_emitted()
         })
     }
 
-    pub fn has_errors_or_span_delayed_bugs(&self) -> Option<ErrorGuaranteed> {
+    /// Unless absolutely necessary, prefer `has_errors` or
+    /// `has_errors_or_lint_errors` to this method.
+    pub fn has_errors_or_lint_errors_or_delayed_bugs(&self) -> Option<ErrorGuaranteed> {
         let inner = self.inner.borrow();
-        let has_errors_or_span_delayed_bugs =
-            inner.has_errors() || !inner.span_delayed_bugs.is_empty();
-        has_errors_or_span_delayed_bugs.then(|| {
-            #[allow(deprecated)]
-            ErrorGuaranteed::unchecked_claim_error_was_emitted()
-        })
-    }
-
-    pub fn is_compilation_going_to_fail(&self) -> Option<ErrorGuaranteed> {
-        let inner = self.inner.borrow();
-        let will_fail =
+        let result =
             inner.has_errors() || inner.lint_err_count > 0 || !inner.span_delayed_bugs.is_empty();
-        will_fail.then(|| {
+        result.then(|| {
             #[allow(deprecated)]
             ErrorGuaranteed::unchecked_claim_error_was_emitted()
         })