Auto merge of rust-lang#87956 - m-ou-se:closure-migration-macro-body, r=Aaron1011

Fix closure migration suggestion when the body is a macro.

Fixes rust-lang#87955

Before:
```
warning: changes to closure capture in Rust 2021 will affect drop order
 --> src/main.rs:5:13
  |
5 |     let _ = || panic!(a.0);
  |             ^^^^^^^^^^---^
  |                       |
  |                       in Rust 2018, closure captures all of `a`, but in Rust 2021, it only captures `a.0`
6 | }
  | - in Rust 2018, `a` would be dropped here, but in Rust 2021, only `a.0` would be dropped here alongside the closure
  |

help: add a dummy let to cause `a` to be fully captured
  |
20~     ($msg:expr $(,)?) => ({ let _ = &a;
21+         $crate::rt::begin_panic($msg)
22~     }),
  |
```

After:
```
warning: changes to closure capture in Rust 2021 will affect drop order
 --> src/main.rs:5:13
  |
5 |     let _ = || panic!(a.0);
  |             ^^^^^^^^^^---^
  |                       |
  |                       in Rust 2018, closure captures all of `a`, but in Rust 2021, it only captures `a.0`
6 | }
  | - in Rust 2018, `a` would be dropped here, but in Rust 2021, only `a.0` would be dropped here alongside the closure
  |
help: add a dummy let to cause `a` to be fully captured
  |
5 |     let _ = || { let _ = &a; panic!(a.0) };
  |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

Author: bors

compiler/rustc_typeck/src/check/upvar.rs

@@ -47,7 +47,7 @@ use rustc_middle::ty::{
 };
 use rustc_session::lint;
 use rustc_span::sym;
-use rustc_span::{MultiSpan, Span, Symbol};
+use rustc_span::{MultiSpan, Span, Symbol, DUMMY_SP};
 use rustc_trait_selection::infer::InferCtxtExt;
 
 use rustc_data_structures::stable_map::FxHashMap;
@@ -644,8 +644,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         }
                     }
                     diagnostics_builder.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>");
-                    let closure_body_span = self.tcx.hir().span(body_id.hir_id);
-                    let (sugg, app) =
+
+                    let mut closure_body_span = self.tcx.hir().span(body_id.hir_id);
+
+                    // If the body was entirely expanded from a macro
+                    // invocation, i.e. the body is not contained inside the
+                    // closure span, then we walk up the expansion until we
+                    // find the span before the expansion.
+                    while !closure_body_span.is_dummy() && !closure_span.contains(closure_body_span) {
+                        closure_body_span = closure_body_span.parent().unwrap_or(DUMMY_SP);
+                    }
+
+                    let (span, sugg, app) =
                         match self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
                             Ok(s) => {
                                 let trimmed = s.trim_start();
@@ -666,9 +676,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 } else {
                                     format!("{{ {}; {} }}", migration_string, s)
                                 };
-                                (sugg, Applicability::MachineApplicable)
+                                (closure_body_span, sugg, Applicability::MachineApplicable)
                             }
-                            Err(_) => (migration_string.clone(), Applicability::HasPlaceholders),
+                            Err(_) => (closure_span, migration_string.clone(), Applicability::HasPlaceholders),
                         };
 
                     let diagnostic_msg = format!(
@@ -677,7 +687,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     );
 
                     diagnostics_builder.span_suggestion(
-                        closure_body_span,
+                        span,
                         &diagnostic_msg,
                         sugg,
                         app,

src/test/ui/closures/2229_closure_analysis/migrations/macro.fixed

@@ -0,0 +1,16 @@
+// run-rustfix
+
+// See https://github.com/rust-lang/rust/issues/87955
+
+#![deny(rust_2021_incompatible_closure_captures)]
+//~^ NOTE: the lint level is defined here
+
+fn main() {
+    let a = ("hey".to_string(), "123".to_string());
+    let _ = || { let _ = &a; dbg!(a.0) };
+    //~^ ERROR: drop order
+    //~| NOTE: only captures `a.0`
+    //~| NOTE: for more information, see
+    //~| HELP: add a dummy let to cause `a` to be fully captured
+}
+//~^ NOTE: dropped here

src/test/ui/closures/2229_closure_analysis/migrations/macro.rs

@@ -0,0 +1,16 @@
+// run-rustfix
+
+// See https://github.com/rust-lang/rust/issues/87955
+
+#![deny(rust_2021_incompatible_closure_captures)]
+//~^ NOTE: the lint level is defined here
+
+fn main() {
+    let a = ("hey".to_string(), "123".to_string());
+    let _ = || dbg!(a.0);
+    //~^ ERROR: drop order
+    //~| NOTE: only captures `a.0`
+    //~| NOTE: for more information, see
+    //~| HELP: add a dummy let to cause `a` to be fully captured
+}
+//~^ NOTE: dropped here

src/test/ui/closures/2229_closure_analysis/migrations/macro.stderr

@@ -0,0 +1,24 @@
+error: changes to closure capture in Rust 2021 will affect drop order
+  --> $DIR/macro.rs:10:13
+   |
+LL |     let _ = || dbg!(a.0);
+   |             ^^^^^^^^---^
+   |                     |
+   |                     in Rust 2018, closure captures all of `a`, but in Rust 2021, it only captures `a.0`
+...
+LL | }
+   | - in Rust 2018, `a` would be dropped here, but in Rust 2021, only `a.0` would be dropped here alongside the closure
+   |
+note: the lint level is defined here
+  --> $DIR/macro.rs:5:9
+   |
+LL | #![deny(rust_2021_incompatible_closure_captures)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/disjoint-capture-in-closures.html>
+help: add a dummy let to cause `a` to be fully captured
+   |
+LL |     let _ = || { let _ = &a; dbg!(a.0) };
+   |                ~~~~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to previous error
+