Rollup merge of #136598 - compiler-errors:unit-fallback, r=WaffleLapkin

Fix suggestion for `dependency_on_unit_never_type_fallback` involving closures + format args expansions

fixes #136562

r? wafflelapkin or reassign

Author: matthiaskrgr

Diff for: compiler/rustc_hir_typeck/src/fallback.rs

@@ -651,6 +651,7 @@ impl<'tcx> Visitor<'tcx> for AnnotateUnitFallbackVisitor<'_, 'tcx> {
         if let Some(ty) = self.fcx.typeck_results.borrow().node_type_opt(inf_id)
             && let Some(vid) = self.fcx.root_vid(ty)
             && self.reachable_vids.contains(&vid)
+            && inf_span.can_be_used_for_suggestions()
         {
             return ControlFlow::Break(errors::SuggestAnnotation::Unit(inf_span));
         }
@@ -662,7 +663,7 @@ impl<'tcx> Visitor<'tcx> for AnnotateUnitFallbackVisitor<'_, 'tcx> {
         &mut self,
         qpath: &'tcx rustc_hir::QPath<'tcx>,
         id: HirId,
-        _span: Span,
+        span: Span,
     ) -> Self::Result {
         let arg_segment = match qpath {
             hir::QPath::Resolved(_, path) => {
@@ -674,13 +675,21 @@ impl<'tcx> Visitor<'tcx> for AnnotateUnitFallbackVisitor<'_, 'tcx> {
             }
         };
         // Alternatively, try to turbofish `::<_, (), _>`.
-        if let Some(def_id) = self.fcx.typeck_results.borrow().qpath_res(qpath, id).opt_def_id() {
+        if let Some(def_id) = self.fcx.typeck_results.borrow().qpath_res(qpath, id).opt_def_id()
+            && span.can_be_used_for_suggestions()
+        {
             self.suggest_for_segment(arg_segment, def_id, id)?;
         }
         hir::intravisit::walk_qpath(self, qpath, id)
     }
 
     fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) -> Self::Result {
+        if let hir::ExprKind::Closure(&hir::Closure { body, .. })
+        | hir::ExprKind::ConstBlock(hir::ConstBlock { body, .. }) = expr.kind
+        {
+            self.visit_body(self.fcx.tcx.hir().body(body))?;
+        }
+
         // Try to suggest adding an explicit qself `()` to a trait method path.
         // i.e. changing `Default::default()` to `<() as Default>::default()`.
         if let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind
@@ -691,17 +700,21 @@ impl<'tcx> Visitor<'tcx> for AnnotateUnitFallbackVisitor<'_, 'tcx> {
             && let Some(vid) = self.fcx.root_vid(self_ty)
             && self.reachable_vids.contains(&vid)
             && let [.., trait_segment, _method_segment] = path.segments
+            && expr.span.can_be_used_for_suggestions()
         {
             let span = path.span.shrink_to_lo().to(trait_segment.ident.span);
             return ControlFlow::Break(errors::SuggestAnnotation::Path(span));
         }
+
         // Or else, try suggesting turbofishing the method args.
         if let hir::ExprKind::MethodCall(segment, ..) = expr.kind
             && let Some(def_id) =
                 self.fcx.typeck_results.borrow().type_dependent_def_id(expr.hir_id)
+            && expr.span.can_be_used_for_suggestions()
         {
             self.suggest_for_segment(segment, def_id, expr.hir_id)?;
         }
+
         hir::intravisit::walk_expr(self, expr)
     }
 
@@ -712,6 +725,7 @@ impl<'tcx> Visitor<'tcx> for AnnotateUnitFallbackVisitor<'_, 'tcx> {
             && let Some(ty) = self.fcx.typeck_results.borrow().node_type_opt(local.hir_id)
             && let Some(vid) = self.fcx.root_vid(ty)
             && self.reachable_vids.contains(&vid)
+            && local.span.can_be_used_for_suggestions()
         {
             return ControlFlow::Break(errors::SuggestAnnotation::Local(
                 local.pat.span.shrink_to_hi(),

Diff for: tests/ui/never_type/dont-suggest-turbofish-from-expansion.rs

@@ -0,0 +1,20 @@
+#![deny(dependency_on_unit_never_type_fallback)]
+
+fn create_ok_default<C>() -> Result<C, ()>
+where
+    C: Default,
+{
+    Ok(C::default())
+}
+
+fn main() -> Result<(), ()> {
+    //~^ ERROR this function depends on never type fallback being `()`
+    //~| WARN this was previously accepted by the compiler but is being phased out
+    let (returned_value, _) = (|| {
+        let created = create_ok_default()?;
+        Ok((created, ()))
+    })()?;
+
+    let _ = format_args!("{:?}", returned_value);
+    Ok(())
+}

Diff for: tests/ui/never_type/dont-suggest-turbofish-from-expansion.stderr

@@ -0,0 +1,26 @@
+error: this function depends on never type fallback being `()`
+  --> $DIR/dont-suggest-turbofish-from-expansion.rs:10:1
+   |
+LL | fn main() -> Result<(), ()> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in Rust 2024 and in a future release in all editions!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
+   = help: specify the types explicitly
+note: in edition 2024, the requirement `!: Default` will fail
+  --> $DIR/dont-suggest-turbofish-from-expansion.rs:14:23
+   |
+LL |         let created = create_ok_default()?;
+   |                       ^^^^^^^^^^^^^^^^^^^
+note: the lint level is defined here
+  --> $DIR/dont-suggest-turbofish-from-expansion.rs:1:9
+   |
+LL | #![deny(dependency_on_unit_never_type_fallback)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: use `()` annotations to avoid fallback changes
+   |
+LL |         let created: () = create_ok_default()?;
+   |                    ++++
+
+error: aborting due to 1 previous error
+

Diff for: tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.e2015.stderr

@@ -130,10 +130,6 @@ LL |         msg_send!();
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the type explicitly
    = note: this warning originates in the macro `msg_send` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: use `()` annotations to avoid fallback changes
-   |
-LL |             match send_message::<() /* ?0 */>() {
-   |                                  ~~
 
 warning: 10 warnings emitted
 

Diff for: tests/ui/never_type/lint-never-type-fallback-flowing-into-unsafe.e2024.stderr

@@ -130,10 +130,6 @@ LL |         msg_send!();
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2024/never-type-fallback.html>
    = help: specify the type explicitly
    = note: this error originates in the macro `msg_send` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: use `()` annotations to avoid fallback changes
-   |
-LL |             match send_message::<() /* ?0 */>() {
-   |                                  ~~
 
 warning: the type `!` does not permit zero-initialization
   --> $DIR/lint-never-type-fallback-flowing-into-unsafe.rs:12:18