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.

Author: nnethercote

Diff for: compiler/rustc_builtin_macros/src/format.rs

@@ -529,7 +529,7 @@ fn make_format_args(
 
     // Only check for unused named argument names if there are no other errors to avoid causing
     // too much noise in output errors, such as when a named argument is entirely unused.
-    if invalid_refs.is_empty() && ecx.dcx().err_count() == 0 {
+    if invalid_refs.is_empty() && ecx.dcx().has_errors().is_none() {
         for &(index, span, used_as) in &numeric_refences_to_named_arg {
             let (position_sp_to_replace, position_sp_for_msg) = match used_as {
                 Placeholder(pspan) => (span, pspan),

Diff for: compiler/rustc_errors/src/lib.rs

@@ -931,42 +931,38 @@ 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)]
             ErrorGuaranteed::unchecked_claim_error_was_emitted()
         })
     }
 
+    /// 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()
         })

Diff for: compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -117,7 +117,7 @@ where
     let errors = wfcx.select_all_or_error();
     if !errors.is_empty() {
         let err = infcx.err_ctxt().report_fulfillment_errors(errors);
-        if tcx.dcx().err_count() > 0 {
+        if tcx.dcx().has_errors().is_some() {
             return Err(err);
         } else {
             // HACK(oli-obk): tests/ui/specialization/min_specialization/specialize_on_type_error.rs

Diff for: compiler/rustc_incremental/src/persist/fs.rs

@@ -312,7 +312,7 @@ pub fn finalize_session_directory(sess: &Session, svh: Option<Svh>) {
 
     let incr_comp_session_dir: PathBuf = sess.incr_comp_session_dir().clone();
 
-    if let Some(_) = sess.dcx().has_errors_or_span_delayed_bugs() {
+    if sess.dcx().has_errors_or_lint_errors_or_delayed_bugs().is_some() {
         // If there have been any errors during compilation, we don't want to
         // publish this session directory. Rather, we'll just delete it.
 

Diff for: compiler/rustc_incremental/src/persist/save.rs

@@ -31,8 +31,8 @@ pub fn save_dep_graph(tcx: TyCtxt<'_>) {
         if sess.opts.incremental.is_none() {
             return;
         }
-        // This is going to be deleted in finalize_session_directory, so let's not create it
-        if let Some(_) = sess.dcx().has_errors_or_span_delayed_bugs() {
+        // This is going to be deleted in finalize_session_directory, so let's not create it.
+        if sess.dcx().has_errors_or_lint_errors_or_delayed_bugs().is_some() {
             return;
         }
 
@@ -87,7 +87,7 @@ pub fn save_work_product_index(
         return;
     }
     // This is going to be deleted in finalize_session_directory, so let's not create it
-    if let Some(_) = sess.dcx().has_errors_or_span_delayed_bugs() {
+    if sess.dcx().has_errors_or_lint_errors().is_some() {
         return;
     }
 

Diff for: compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -117,9 +117,9 @@ fn escape_literal(s: &str) -> String {
 /// field is only populated during an in-progress typeck.
 /// Get an instance by calling `InferCtxt::err_ctxt` or `FnCtxt::err_ctxt`.
 ///
-/// You must only create this if you intend to actually emit an error.
-/// This provides a lot of utility methods which should not be used
-/// during the happy path.
+/// You must only create this if you intend to actually emit an error (or
+/// perhaps a warning, though preferably not.) It provides a lot of utility
+/// methods which should not be used during the happy path.
 pub struct TypeErrCtxt<'a, 'tcx> {
     pub infcx: &'a InferCtxt<'tcx>,
     pub typeck_results: Option<std::cell::Ref<'a, ty::TypeckResults<'tcx>>>,
@@ -133,9 +133,10 @@ pub struct TypeErrCtxt<'a, 'tcx> {
 
 impl Drop for TypeErrCtxt<'_, '_> {
     fn drop(&mut self) {
-        if let Some(_) = self.dcx().has_errors_or_span_delayed_bugs() {
-            // ok, emitted an error.
+        if self.dcx().has_errors().is_some() {
+            // Ok, emitted an error.
         } else {
+            // Didn't emit an error; maybe it was created but not yet emitted.
             self.infcx
                 .tcx
                 .sess

Diff for: compiler/rustc_middle/src/ty/visit.rs

@@ -55,10 +55,13 @@ pub trait TypeVisitableExt<'tcx>: TypeVisitable<TyCtxt<'tcx>> {
     }
     fn error_reported(&self) -> Result<(), ErrorGuaranteed> {
         if self.references_error() {
-            if let Some(reported) = ty::tls::with(|tcx| tcx.dcx().is_compilation_going_to_fail()) {
+            // We must include lint errors and span delayed bugs here.
+            if let Some(reported) =
+                ty::tls::with(|tcx| tcx.dcx().has_errors_or_lint_errors_or_delayed_bugs())
+            {
                 Err(reported)
             } else {
-                bug!("expect tcx.sess.is_compilation_going_to_fail return `Some`");
+                bug!("expected some kind of error in `error_reported`");
             }
         } else {
             Ok(())

Diff for: compiler/rustc_query_system/src/dep_graph/graph.rs

@@ -818,7 +818,7 @@ impl<D: Deps> DepGraphData<D> {
             None => {}
         }
 
-        if let None = qcx.dep_context().sess().dcx().has_errors_or_span_delayed_bugs() {
+        if let None = qcx.dep_context().sess().dcx().has_errors_or_lint_errors_or_delayed_bugs() {
             panic!("try_mark_previous_green() - Forcing the DepNode should have set its color")
         }
 

Diff for: compiler/rustc_session/src/session.rs

@@ -323,6 +323,7 @@ impl Session {
     }
 
     pub fn compile_status(&self) -> Result<(), ErrorGuaranteed> {
+        // We must include lint errors here.
         if let Some(reported) = self.dcx().has_errors_or_lint_errors() {
             let _ = self.dcx().emit_stashed_diagnostics();
             Err(reported)

Diff for: src/librustdoc/core.rs

@@ -449,6 +449,7 @@ pub(crate) fn run_global_ctxt(
 
     tcx.sess.time("check_lint_expectations", || tcx.check_expectations(Some(sym::rustdoc)));
 
+    // We must include lint errors here.
     if tcx.dcx().has_errors_or_lint_errors().is_some() {
         rustc_errors::FatalError.raise();
     }

Diff for: src/librustdoc/doctest.rs

@@ -150,6 +150,7 @@ pub(crate) fn run(options: RustdocOptions) -> Result<(), ErrorGuaranteed> {
 
                     collector
                 });
+                // We must include lint errors here.
                 if compiler.sess.dcx().has_errors_or_lint_errors().is_some() {
                     FatalError.raise();
                 }

Diff for: src/librustdoc/lib.rs

@@ -796,7 +796,7 @@ fn main_args(
 
         compiler.enter(|queries| {
             let mut gcx = abort_on_err(queries.global_ctxt(), sess);
-            if sess.dcx().has_errors_or_lint_errors().is_some() {
+            if sess.dcx().has_errors().is_some() {
                 sess.dcx().fatal("Compilation failed, aborting rustdoc");
             }
 

Diff for: src/librustdoc/passes/collect_trait_impls.rs

@@ -22,7 +22,7 @@ pub(crate) fn collect_trait_impls(mut krate: Crate, cx: &mut DocContext<'_>) ->
     let tcx = cx.tcx;
     // We need to check if there are errors before running this pass because it would crash when
     // we try to get auto and blanket implementations.
-    if tcx.dcx().has_errors_or_lint_errors().is_some() {
+    if tcx.dcx().has_errors().is_some() {
         return krate;
     }
 

Diff for: src/librustdoc/scrape_examples.rs

@@ -311,7 +311,7 @@ pub(crate) fn run(
 
         // The visitor might have found a type error, which we need to
         // promote to a fatal error
-        if tcx.dcx().has_errors_or_lint_errors().is_some() {
+        if tcx.dcx().has_errors().is_some() {
             return Err(String::from("Compilation failed, aborting rustdoc"));
         }