Suggest a borrow when using dbg

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -4,7 +4,7 @@
 #![allow(rustc::untranslatable_diagnostic)]
 
 use either::Either;
-use hir::ClosureKind;
+use hir::{ClosureKind, Path};
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::{codes::*, struct_span_code_err, Applicability, Diag, MultiSpan};
@@ -16,6 +16,7 @@ use rustc_hir::{CoroutineKind, CoroutineSource, LangItem};
 use rustc_middle::bug;
 use rustc_middle::hir::nested_filter::OnlyBodies;
 use rustc_middle::mir::tcx::PlaceTy;
+use rustc_middle::mir::VarDebugInfoContents;
 use rustc_middle::mir::{
     self, AggregateKind, BindingForm, BorrowKind, CallSource, ClearCrossCrate, ConstraintCategory,
     FakeBorrowKind, FakeReadCause, LocalDecl, LocalInfo, LocalKind, Location, MutBorrowKind,
@@ -546,7 +547,14 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
                     self.suggest_cloning(err, ty, expr, None, Some(move_spans));
                 }
             }
-            if let Some(pat) = finder.pat {
+
+            self.suggest_ref_for_dbg_args(expr, place, move_span, err);
+
+            // it's useless to suggest inserting `ref` when the span don't comes from local code
+            if let Some(pat) = finder.pat
+                && !move_span.is_dummy()
+                && !self.infcx.tcx.sess.source_map().is_imported(move_span)
+            {
                 *in_pattern = true;
                 let mut sugg = vec![(pat.span.shrink_to_lo(), "ref ".to_string())];
                 if let Some(pat) = finder.parent_pat {
@@ -561,6 +569,59 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         }
     }
 
+    // for dbg!(x) which may take ownership, suggest dbg!(&x) instead
+    // but here we actually do not check whether the macro name is `dbg!`
+    // so that we may extend the scope a bit larger to cover more cases
+    fn suggest_ref_for_dbg_args(
+        &self,
+        body: &hir::Expr<'_>,
+        place: &Place<'tcx>,
+        move_span: Span,
+        err: &mut Diag<'infcx>,
+    ) {
+        let var_info = self.body.var_debug_info.iter().find(|info| match info.value {
+            VarDebugInfoContents::Place(ref p) => p == place,
+            _ => false,
+        });
+        let arg_name = if let Some(var_info) = var_info {
+            var_info.name
+        } else {
+            return;
+        };
+        struct MatchArgFinder {
+            expr_span: Span,
+            match_arg_span: Option<Span>,
+            arg_name: Symbol,
+        }
+        impl Visitor<'_> for MatchArgFinder {
+            fn visit_expr(&mut self, e: &hir::Expr<'_>) {
+                // dbg! is expanded into a match pattern, we need to find the right argument span
+                if let hir::ExprKind::Match(expr, ..) = &e.kind
+                    && let hir::ExprKind::Path(hir::QPath::Resolved(
+                        _,
+                        path @ Path { segments: [seg], .. },
+                    )) = &expr.kind
+                    && seg.ident.name == self.arg_name
+                    && self.expr_span.source_callsite().contains(expr.span)
+                {
+                    self.match_arg_span = Some(path.span);
+                }
+                hir::intravisit::walk_expr(self, e);
+            }
+        }
+
+        let mut finder = MatchArgFinder { expr_span: move_span, match_arg_span: None, arg_name };
+        finder.visit_expr(body);
+        if let Some(macro_arg_span) = finder.match_arg_span {
+            err.span_suggestion_verbose(
+                macro_arg_span.shrink_to_lo(),
+                "consider borrowing instead of transferring ownership",
+                "&",
+                Applicability::MachineApplicable,
+            );
+        }
+    }
+
     fn report_use_of_uninitialized(
         &self,
         mpi: MovePathIndex,