Suggest labeling block if break is in bare block

Fix #103982.

Author: estebank

compiler/rustc_passes/messages.ftl

@@ -580,6 +580,8 @@ passes_outside_loop =
         *[false] {""}
     }
 
+passes_outside_loop_suggestion = consider labeling this block to be able to break within it
+
 passes_params_not_allowed =
     referencing function parameters is not allowed in naked functions
     .help = follow the calling convention in asm block to use parameters

compiler/rustc_passes/src/errors.rs

@@ -1099,6 +1099,16 @@ pub struct OutsideLoop<'a> {
     pub span: Span,
     pub name: &'a str,
     pub is_break: bool,
+    #[subdiagnostic]
+    pub suggestion: Option<OutsideLoopSuggestion>,
+}
+#[derive(Subdiagnostic)]
+#[multipart_suggestion(passes_outside_loop_suggestion, applicability = "maybe-incorrect")]
+pub struct OutsideLoopSuggestion {
+    #[suggestion_part(code = "'block: ")]
+    pub block_span: Span,
+    #[suggestion_part(code = " 'block")]
+    pub break_span: Span,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_passes/src/loops.rs

@@ -1,7 +1,7 @@
 use Context::*;
 
 use rustc_hir as hir;
-use rustc_hir::def_id::LocalModDefId;
+use rustc_hir::def_id::{LocalDefId, LocalModDefId};
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::{Destination, Movability, Node};
 use rustc_middle::hir::map::Map;
@@ -10,19 +10,21 @@ use rustc_middle::query::Providers;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
 use rustc_span::hygiene::DesugaringKind;
-use rustc_span::Span;
+use rustc_span::{BytePos, Span};
 
 use crate::errors::{
     BreakInsideAsyncBlock, BreakInsideClosure, BreakNonLoop, ContinueLabeledBlock, OutsideLoop,
-    UnlabeledCfInWhileCondition, UnlabeledInLabeledBlock,
+    OutsideLoopSuggestion, UnlabeledCfInWhileCondition, UnlabeledInLabeledBlock,
 };
 
 #[derive(Clone, Copy, Debug, PartialEq)]
 enum Context {
     Normal,
+    Fn,
     Loop(hir::LoopSource),
     Closure(Span),
     AsyncClosure(Span),
+    UnlabeledBlock(Span),
     LabeledBlock,
     Constant,
 }
@@ -60,6 +62,25 @@ impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
         self.with_context(Constant, |v| intravisit::walk_inline_const(v, c));
     }
 
+    fn visit_fn(
+        &mut self,
+        fk: hir::intravisit::FnKind<'hir>,
+        fd: &'hir hir::FnDecl<'hir>,
+        b: hir::BodyId,
+        _: Span,
+        id: LocalDefId,
+    ) {
+        self.with_context(Fn, |v| intravisit::walk_fn(v, fk, fd, b, id));
+    }
+
+    fn visit_trait_item(&mut self, trait_item: &'hir hir::TraitItem<'hir>) {
+        self.with_context(Fn, |v| intravisit::walk_trait_item(v, trait_item));
+    }
+
+    fn visit_impl_item(&mut self, impl_item: &'hir hir::ImplItem<'hir>) {
+        self.with_context(Fn, |v| intravisit::walk_impl_item(v, impl_item));
+    }
+
     fn visit_expr(&mut self, e: &'hir hir::Expr<'hir>) {
         match e.kind {
             hir::ExprKind::Loop(ref b, _, source, _) => {
@@ -83,6 +104,14 @@ impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
             hir::ExprKind::Block(ref b, Some(_label)) => {
                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
             }
+            hir::ExprKind::Block(ref b, None) if matches!(self.cx, Fn) => {
+                self.with_context(Normal, |v| v.visit_block(&b));
+            }
+            hir::ExprKind::Block(ref b, None)
+                if matches!(self.cx, Normal | Constant | UnlabeledBlock(_)) =>
+            {
+                self.with_context(UnlabeledBlock(b.span.shrink_to_lo()), |v| v.visit_block(&b));
+            }
             hir::ExprKind::Break(break_label, ref opt_expr) => {
                 if let Some(e) = opt_expr {
                     self.visit_expr(e);
@@ -147,7 +176,12 @@ impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
                     }
                 }
 
-                self.require_break_cx("break", e.span);
+                let sp_lo = e.span.with_lo(e.span.lo() + BytePos("break".len() as u32));
+                let label_sp = match break_label.label {
+                    Some(label) => sp_lo.with_hi(label.ident.span.hi()),
+                    None => sp_lo.shrink_to_lo(),
+                };
+                self.require_break_cx("break", e.span, label_sp);
             }
             hir::ExprKind::Continue(destination) => {
                 self.require_label_in_labeled_block(e.span, &destination, "continue");
@@ -169,7 +203,7 @@ impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
                     }
                     Err(_) => {}
                 }
-                self.require_break_cx("continue", e.span)
+                self.require_break_cx("continue", e.span, e.span)
             }
             _ => intravisit::walk_expr(self, e),
         }
@@ -187,7 +221,8 @@ impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
         self.cx = old_cx;
     }
 
-    fn require_break_cx(&self, name: &str, span: Span) {
+    fn require_break_cx(&self, name: &str, span: Span, break_span: Span) {
+        let is_break = name == "break";
         match self.cx {
             LabeledBlock | Loop(_) => {}
             Closure(closure_span) => {
@@ -196,8 +231,12 @@ impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
             AsyncClosure(closure_span) => {
                 self.sess.emit_err(BreakInsideAsyncBlock { span, closure_span, name });
             }
-            Normal | Constant => {
-                self.sess.emit_err(OutsideLoop { span, name, is_break: name == "break" });
+            UnlabeledBlock(block_span) if is_break => {
+                let suggestion = Some(OutsideLoopSuggestion { block_span, break_span });
+                self.sess.emit_err(OutsideLoop { span, name, is_break, suggestion });
+            }
+            Normal | Constant | Fn | UnlabeledBlock(_) => {
+                self.sess.emit_err(OutsideLoop { span, name, is_break, suggestion: None });
             }
         }
     }

tests/ui/parser/break-in-unlabeled-block.fixed

@@ -0,0 +1,12 @@
+// run-rustfix
+fn main() {
+    'block: {
+        break 'block (); //~ ERROR `break` outside of a loop or labeled block
+    }
+    {
+        'block: {
+            break 'block (); //~ ERROR `break` outside of a loop or labeled block
+        }
+    }
+}
+

tests/ui/parser/break-in-unlabeled-block.rs

@@ -0,0 +1,11 @@
+// run-rustfix
+fn main() {
+    {
+        break (); //~ ERROR `break` outside of a loop or labeled block
+    }
+    {
+        {
+            break (); //~ ERROR `break` outside of a loop or labeled block
+        }
+    }
+}

tests/ui/parser/break-in-unlabeled-block.stderr

@@ -0,0 +1,27 @@
+error[E0268]: `break` outside of a loop or labeled block
+  --> $DIR/break-in-unlabeled-block.rs:4:9
+   |
+LL |         break ();
+   |         ^^^^^^^^ cannot `break` outside of a loop or labeled block
+   |
+help: consider labeling this block to be able to break within it
+   |
+LL ~     'block: {
+LL ~         break 'block ();
+   |
+
+error[E0268]: `break` outside of a loop or labeled block
+  --> $DIR/break-in-unlabeled-block.rs:8:13
+   |
+LL |             break ();
+   |             ^^^^^^^^ cannot `break` outside of a loop or labeled block
+   |
+help: consider labeling this block to be able to break within it
+   |
+LL ~         'block: {
+LL ~             break 'block ();
+   |
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0268`.