Suggest adding semicolon in user code rather than macro impl details

Author: Urgau

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -349,7 +349,10 @@ impl<'tcx> BorrowExplanation<'tcx> {
                                     old.to(info.span.shrink_to_hi()).contains(new)
                                 }) {
                                     err.span_suggestion_verbose(
-                                        info.span.shrink_to_hi(),
+                                        info.span
+                                            .find_ancestor_in_same_ctxt(local_decl.source_info.span)
+                                            .unwrap_or(info.span)
+                                            .shrink_to_hi(),
                                         "consider adding semicolon after the expression so its \
                                         temporaries are dropped sooner, before the local variables \
                                         declared by the block are dropped",

tests/ui/borrowck/span-semicolon-issue-139049.fixed

@@ -0,0 +1,43 @@
+// Make sure the generated suggestion suggest editing the user
+// code instead of the std macro implementation
+
+//@ run-rustfix
+
+#![allow(dead_code)]
+
+use std::fmt::{self, Display};
+
+struct Mutex;
+
+impl Mutex {
+    fn lock(&self) -> MutexGuard<'_> {
+        MutexGuard(self)
+    }
+}
+
+struct MutexGuard<'a>(&'a Mutex);
+
+impl<'a> Drop for MutexGuard<'a> {
+    fn drop(&mut self) {}
+}
+
+struct Out;
+
+impl Out {
+    fn write_fmt(&self, _args: fmt::Arguments) {}
+}
+
+impl<'a> Display for MutexGuard<'a> {
+    fn fmt(&self, _formatter: &mut fmt::Formatter) -> fmt::Result {
+        Ok(())
+    }
+}
+
+fn main() {
+    let _write = {
+        let mutex = Mutex;
+        write!(Out, "{}", mutex.lock());
+        //~^ ERROR `mutex` does not live long enough
+        //~| SUGGESTION ;
+    };
+}

tests/ui/borrowck/span-semicolon-issue-139049.rs

@@ -0,0 +1,43 @@
+// Make sure the generated suggestion suggest editing the user
+// code instead of the std macro implementation
+
+//@ run-rustfix
+
+#![allow(dead_code)]
+
+use std::fmt::{self, Display};
+
+struct Mutex;
+
+impl Mutex {
+    fn lock(&self) -> MutexGuard<'_> {
+        MutexGuard(self)
+    }
+}
+
+struct MutexGuard<'a>(&'a Mutex);
+
+impl<'a> Drop for MutexGuard<'a> {
+    fn drop(&mut self) {}
+}
+
+struct Out;
+
+impl Out {
+    fn write_fmt(&self, _args: fmt::Arguments) {}
+}
+
+impl<'a> Display for MutexGuard<'a> {
+    fn fmt(&self, _formatter: &mut fmt::Formatter) -> fmt::Result {
+        Ok(())
+    }
+}
+
+fn main() {
+    let _write = {
+        let mutex = Mutex;
+        write!(Out, "{}", mutex.lock())
+        //~^ ERROR `mutex` does not live long enough
+        //~| SUGGESTION ;
+    };
+}

tests/ui/borrowck/span-semicolon-issue-139049.stderr

@@ -0,0 +1,24 @@
+error[E0597]: `mutex` does not live long enough
+  --> $DIR/span-semicolon-issue-139049.rs:39:27
+   |
+LL |         let mutex = Mutex;
+   |             ----- binding `mutex` declared here
+LL |         write!(Out, "{}", mutex.lock())
+   |                           ^^^^^-------
+   |                           |
+   |                           borrowed value does not live long enough
+   |                           a temporary with access to the borrow is created here ...
+...
+LL |     };
+   |     -- ... and the borrow might be used here, when that temporary is dropped and runs the `Drop` code for type `MutexGuard`
+   |     |
+   |     `mutex` dropped here while still borrowed
+   |
+help: consider adding semicolon after the expression so its temporaries are dropped sooner, before the local variables declared by the block are dropped
+   |
+LL |         write!(Out, "{}", mutex.lock());
+   |                                        +
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0597`.