downgrade borrowck suggestion level due to possible span conflict

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -128,7 +128,7 @@ pub(crate) fn add_explanation_to_diagnostic(
                     && pat.span.can_be_used_for_suggestions()
                     && let Ok(pat) = tcx.sess.source_map().span_to_snippet(pat.span)
                 {
-                    suggest_rewrite_if_let(expr, &pat, init, conseq, alt, err);
+                    suggest_rewrite_if_let(tcx, expr, &pat, init, conseq, alt, err);
                 } else if path_span.map_or(true, |path_span| path_span == var_or_use_span) {
                     // We can use `var_or_use_span` if either `path_span` is not present, or both spans are the same
                     if borrow_span.map_or(true, |sp| !sp.overlaps(var_or_use_span)) {
@@ -292,7 +292,7 @@ pub(crate) fn add_explanation_to_diagnostic(
                             && pat.span.can_be_used_for_suggestions()
                             && let Ok(pat) = tcx.sess.source_map().span_to_snippet(pat.span)
                         {
-                            suggest_rewrite_if_let(expr, &pat, init, conseq, alt, err);
+                            suggest_rewrite_if_let(tcx, expr, &pat, init, conseq, alt, err);
                         }
                     }
                 }
@@ -428,34 +428,49 @@ fn add_lifetime_bound_suggestion_to_diagnostic(
     }
 }
 
-fn suggest_rewrite_if_let<'tcx>(
+fn suggest_rewrite_if_let(
-    expr: &hir::Expr<'tcx>,
+    tcx: TyCtxt<'_>,
+    expr: &hir::Expr<'_>,
     pat: &str,
-    init: &hir::Expr<'tcx>,
+    init: &hir::Expr<'_>,
-    conseq: &hir::Expr<'tcx>,
+    conseq: &hir::Expr<'_>,
-    alt: Option<&hir::Expr<'tcx>>,
+    alt: Option<&hir::Expr<'_>>,
     err: &mut Diag<'_>,
 ) {
+    let source_map = tcx.sess.source_map();
     err.span_note(
-        conseq.span.shrink_to_hi(),
+        source_map.end_point(conseq.span),
-        "lifetime for temporaries generated in `if let`s have been shorted in Edition 2024",
+        "lifetimes for temporaries generated in `if let`s have been shortened in Edition 2024 so that they are dropped here instead",
     );
     if expr.span.can_be_used_for_suggestions() && conseq.span.can_be_used_for_suggestions() {
+        let needs_block = if let Some(hir::Node::Expr(expr)) =
+            alt.and_then(|alt| tcx.hir().parent_iter(alt.hir_id).next()).map(|(_, node)| node)
+        {
+            matches!(expr.kind, hir::ExprKind::If(..))
+        } else {
+            false
+        };
         let mut sugg = vec![
-            (expr.span.shrink_to_lo().between(init.span), "match ".into()),
+            (
+                expr.span.shrink_to_lo().between(init.span),
+                if needs_block { "{ match ".into() } else { "match ".into() },
+            ),
             (conseq.span.shrink_to_lo(), format!(" {{ {pat} => ")),
         ];
         let expr_end = expr.span.shrink_to_hi();
+        let mut expr_end_code;
         if let Some(alt) = alt {
-            sugg.push((conseq.span.between(alt.span), format!(" _ => ")));
+            sugg.push((conseq.span.between(alt.span), " _ => ".into()));
-            sugg.push((expr_end, "}".into()));
+            expr_end_code = "}".to_string();
         } else {
-            sugg.push((expr_end, " _ => {} }".into()));
+            expr_end_code = " _ => {} }".into();
         }
+        expr_end_code.push('}');
+        sugg.push((expr_end, expr_end_code));
         err.multipart_suggestion(
             "consider rewriting the `if` into `match` which preserves the extended lifetime",
             sugg,
-            Applicability::MachineApplicable,
+            Applicability::MaybeIncorrect,
         );
     }
 }

tests/ui/drop/if-let-rescope-borrowck-suggestions.fixed

@@ -1,26 +0,0 @@
-//@ edition: 2024
-//@ compile-flags: -Z validate-mir -Zunstable-options
-//@ run-rustfix
-
-#![feature(if_let_rescope)]
-#![deny(if_let_rescope)]
-
-struct Droppy;
-impl Drop for Droppy {
-    fn drop(&mut self) {
-        println!("dropped");
-    }
-}
-impl Droppy {
-    fn get_ref(&self) -> Option<&u8> {
-        None
-    }
-}
-
-fn do_something<T>(_: &T) {}
-
-fn main() {
-    let binding = Droppy;
-    do_something(match binding.get_ref()  { Some(value) => { value } _ => { &0 }});
-    //~^ ERROR: temporary value dropped while borrowed
-}

tests/ui/drop/if-let-rescope-borrowck-suggestions.rs

@@ -1,6 +1,5 @@
 //@ edition: 2024
 //@ compile-flags: -Z validate-mir -Zunstable-options
-//@ run-rustfix
 
 #![feature(if_let_rescope)]
 #![deny(if_let_rescope)]
@@ -22,4 +21,13 @@ fn do_something<T>(_: &T) {}
 fn main() {
     do_something(if let Some(value) = Droppy.get_ref() { value } else { &0 });
     //~^ ERROR: temporary value dropped while borrowed
+    do_something(if let Some(value) = Droppy.get_ref() {
+        //~^ ERROR: temporary value dropped while borrowed
+        value
+    } else if let Some(value) = Droppy.get_ref() {
+        //~^ ERROR: temporary value dropped while borrowed
+        value
+    } else {
+        &0
+    });
 }

tests/ui/drop/if-let-rescope-borrowck-suggestions.stderr

@@ -1,13 +1,13 @@
 error[E0716]: temporary value dropped while borrowed
-  --> $DIR/if-let-rescope-borrowck-suggestions.rs:23:39
+  --> $DIR/if-let-rescope-borrowck-suggestions.rs:22:39
    |
 LL |     do_something(if let Some(value) = Droppy.get_ref() { value } else { &0 });
    |                                       ^^^^^^                   - temporary value is freed at the end of this statement
    |                                       |
    |                                       creates a temporary value which is freed while still in use
    |
-note: lifetime for temporaries generated in `if let`s have been shorted in Edition 2024
+note: lifetimes for temporaries generated in `if let`s have been shortened in Edition 2024 so that they are dropped here instead
-  --> $DIR/if-let-rescope-borrowck-suggestions.rs:23:65
+  --> $DIR/if-let-rescope-borrowck-suggestions.rs:22:64
    |
 LL |     do_something(if let Some(value) = Droppy.get_ref() { value } else { &0 });
    |                                                                ^
@@ -18,9 +18,72 @@ LL ~     do_something(if let Some(value) = binding.get_ref() { value } else { &0
    |
 help: consider rewriting the `if` into `match` which preserves the extended lifetime
    |
-LL |     do_something(match Droppy.get_ref()  { Some(value) => { value } _ => { &0 }});
+LL |     do_something({ match Droppy.get_ref()  { Some(value) => { value } _ => { &0 }}});
-   |                  ~~~~~                   ++++++++++++++++           ~~~~       +
+   |                  ~~~~~~~                   ++++++++++++++++           ~~~~       ++
 
-error: aborting due to 1 previous error
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/if-let-rescope-borrowck-suggestions.rs:24:39
+   |
+LL |     do_something(if let Some(value) = Droppy.get_ref() {
+   |                                       ^^^^^^ creates a temporary value which is freed while still in use
+...
+LL |     } else if let Some(value) = Droppy.get_ref() {
+   |     - temporary value is freed at the end of this statement
+   |
+note: lifetimes for temporaries generated in `if let`s have been shortened in Edition 2024 so that they are dropped here instead
+  --> $DIR/if-let-rescope-borrowck-suggestions.rs:27:5
+   |
+LL |     } else if let Some(value) = Droppy.get_ref() {
+   |     ^
+help: consider using a `let` binding to create a longer lived value
+   |
+LL ~     let binding = Droppy;
+LL ~     do_something(if let Some(value) = binding.get_ref() {
+   |
+help: consider rewriting the `if` into `match` which preserves the extended lifetime
+   |
+LL ~     do_something({ match Droppy.get_ref()  { Some(value) => {
+LL |
+LL |         value
+LL ~     } _ => if let Some(value) = Droppy.get_ref() {
+LL |
+...
+LL |         &0
+LL ~     }}});
+   |
+
+error[E0716]: temporary value dropped while borrowed
+  --> $DIR/if-let-rescope-borrowck-suggestions.rs:27:33
+   |
+LL |     } else if let Some(value) = Droppy.get_ref() {
+   |                                 ^^^^^^ creates a temporary value which is freed while still in use
+...
+LL |     } else {
+   |     - temporary value is freed at the end of this statement
+   |
+note: lifetimes for temporaries generated in `if let`s have been shortened in Edition 2024 so that they are dropped here instead
+  --> $DIR/if-let-rescope-borrowck-suggestions.rs:30:5
+   |
+LL |     } else {
+   |     ^
+help: consider using a `let` binding to create a longer lived value
+   |
+LL ~     let binding = Droppy;
+LL ~     do_something(if let Some(value) = Droppy.get_ref() {
+LL |
+LL |         value
+LL ~     } else if let Some(value) = binding.get_ref() {
+   |
+help: consider rewriting the `if` into `match` which preserves the extended lifetime
+   |
+LL ~     } else { match Droppy.get_ref()  { Some(value) => {
+LL |
+LL |         value
+LL ~     } _ => {
+LL |         &0
+LL ~     }}});
+   |
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0716`.