Don't introduce a block if a block exists

compiler/rustc_typeck/src/check/upvar.rs

@@ -495,10 +495,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     let closure_body_span = self.tcx.hir().span(body_id.hir_id);
                     let (sugg, app) =
                         match self.tcx.sess.source_map().span_to_snippet(closure_body_span) {
-                            Ok(s) => (
-                                format!("{{ {}; {} }}", migration_string, s),
-                                Applicability::MachineApplicable,
-                            ),
+                            Ok(s) => {
+                                let trimmed = s.trim_start();
+
+                                // If the closure contains a block then replace the opening brace
+                                // with "{ let _ = (..); "
+                                let sugg = if let Some('{') = trimmed.chars().next() {
+                                    format!("{{ {}; {}", migration_string, &trimmed[1..])
+                                } else {
+                                    format!("{{ {}; {} }}", migration_string, s)
+                                };
+                                (sugg, Applicability::MachineApplicable)
+                            }
                             Err(_) => (migration_string.clone(), Applicability::HasPlaceholders),
                         };
 

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

@@ -12,14 +12,14 @@ fn test1_all_need_migration() {
     let t1 = (String::new(), String::new());
     let t2 = (String::new(), String::new());
 
-    let c = || { let _ = (&t, &t1, &t2); {
+    let c = || { let _ = (&t, &t1, &t2); 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP:` let _ = (&t, &t1, &t2)` causes `t`, `t1`, `t2` to be fully captured
 
         let _t = t.0;
         let _t1 = t1.0;
         let _t2 = t2.0;
-    } };
+    };
 
     c();
 }
@@ -31,13 +31,13 @@ fn test2_only_precise_paths_need_migration() {
     let t1 = (String::new(), String::new());
     let t2 = (String::new(), String::new());
 
-    let c = || { let _ = (&t, &t1); {
+    let c = || { let _ = (&t, &t1); 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP:` let _ = (&t, &t1)` causes `t`, `t1` to be fully captured
         let _t = t.0;
         let _t1 = t1.0;
         let _t2 = t2;
-    } };
+    };
 
     c();
 }
@@ -47,12 +47,12 @@ fn test2_only_precise_paths_need_migration() {
 fn test3_only_by_value_need_migration() {
     let t = (String::new(), String::new());
     let t1 = (String::new(), String::new());
-    let c = || { let _ = &t; {
+    let c = || { let _ = &t; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &t` causes `t` to be fully captured
         let _t = t.0;
         println!("{}", t1.1);
-    } };
+    };
 
     c();
 }
@@ -65,12 +65,12 @@ fn test4_only_non_copy_types_need_migration() {
     // `t1` is Copy because all of its elements are Copy
     let t1 = (0i32, 0i32);
 
-    let c = || { let _ = &t; {
+    let c = || { let _ = &t; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &t` causes `t` to be fully captured
         let _t = t.0;
         let _t1 = t1.0;
-    } };
+    };
 
     c();
 }
@@ -83,12 +83,12 @@ fn test5_only_drop_types_need_migration() {
     // `s` doesn't implement Drop or any elements within it, and doesn't need migration
     let s = S(0i32, 0i32);
 
-    let c = || { let _ = &t; {
+    let c = || { let _ = &t; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &t` causes `t` to be fully captured
         let _t = t.0;
         let _s = s.0;
-    } };
+    };
 
     c();
 }
@@ -98,11 +98,11 @@ fn test5_only_drop_types_need_migration() {
 fn test6_move_closures_non_copy_types_might_need_migration() {
     let t = (String::new(), String::new());
     let t1 = (String::new(), String::new());
-    let c = move || { let _ = (&t1, &t); {
+    let c = move || { let _ = (&t1, &t); 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = (&t1, &t)` causes `t1`, `t` to be fully captured
         println!("{} {}", t1.1, t.1);
-    } };
+    };
 
     c();
 }
@@ -113,11 +113,11 @@ fn test6_move_closures_non_copy_types_might_need_migration() {
 fn test7_drop_non_drop_aggregate_need_migration() {
     let t = (String::new(), String::new(), 0i32);
 
-    let c = || { let _ = &t; {
+    let c = || { let _ = &t; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &t` causes `t` to be fully captured
         let _t = t.0;
-    } };
+    };
 
     c();
 }

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

@@ -18,7 +18,7 @@ LL | #![deny(disjoint_capture_drop_reorder)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: `let _ = (&t, &t1, &t2)` causes `t`, `t1`, `t2` to be fully captured
    |
-LL |     let c = || { let _ = (&t, &t1, &t2); {
+LL |     let c = || { let _ = (&t, &t1, &t2); 
 LL |
 LL |
 LL | 
@@ -41,7 +41,7 @@ LL | |     };
    |
 help: `let _ = (&t, &t1)` causes `t`, `t1` to be fully captured
    |
-LL |     let c = || { let _ = (&t, &t1); {
+LL |     let c = || { let _ = (&t, &t1); 
 LL |
 LL |
 LL |         let _t = t.0;
@@ -63,12 +63,12 @@ LL | |     };
    |
 help: `let _ = &t` causes `t` to be fully captured
    |
-LL |     let c = || { let _ = &t; {
+LL |     let c = || { let _ = &t; 
 LL |
 LL |
 LL |         let _t = t.0;
 LL |         println!("{}", t1.1);
-LL |     } };
+LL |     };
    |
 
 error: drop order affected for closure because of `capture_disjoint_fields`
@@ -85,12 +85,12 @@ LL | |     };
    |
 help: `let _ = &t` causes `t` to be fully captured
    |
-LL |     let c = || { let _ = &t; {
+LL |     let c = || { let _ = &t; 
 LL |
 LL |
 LL |         let _t = t.0;
 LL |         let _t1 = t1.0;
-LL |     } };
+LL |     };
    |
 
 error: drop order affected for closure because of `capture_disjoint_fields`
@@ -107,12 +107,12 @@ LL | |     };
    |
 help: `let _ = &t` causes `t` to be fully captured
    |
-LL |     let c = || { let _ = &t; {
+LL |     let c = || { let _ = &t; 
 LL |
 LL |
 LL |         let _t = t.0;
 LL |         let _s = s.0;
-LL |     } };
+LL |     };
    |
 
 error: drop order affected for closure because of `capture_disjoint_fields`
@@ -128,11 +128,11 @@ LL | |     };
    |
 help: `let _ = (&t1, &t)` causes `t1`, `t` to be fully captured
    |
-LL |     let c = move || { let _ = (&t1, &t); {
+LL |     let c = move || { let _ = (&t1, &t); 
 LL |
 LL |
 LL |         println!("{} {}", t1.1, t.1);
-LL |     } };
+LL |     };
    |
 
 error: drop order affected for closure because of `capture_disjoint_fields`
@@ -148,11 +148,11 @@ LL | |     };
    |
 help: `let _ = &t` causes `t` to be fully captured
    |
-LL |     let c = || { let _ = &t; {
+LL |     let c = || { let _ = &t; 
 LL |
 LL |
 LL |         let _t = t.0;
-LL |     } };
+LL |     };
    |
 
 error: aborting due to 7 previous errors

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

@@ -0,0 +1,40 @@
+// run-rustfix
+#![deny(disjoint_capture_drop_reorder)]
+//~^ NOTE: the lint level is defined here
+
+// Test the two possible cases for automated migartion using rustfix
+// - Closure contains a block i.e.  `|| { .. };`
+// - Closure contains just an expr `|| ..;`
+
+#[derive(Debug)]
+struct Foo(i32);
+impl Drop for Foo {
+    fn drop(&mut self) {
+        println!("{:?} dropped", self.0);
+    }
+}
+
+fn closure_contains_block() {
+    let t = (Foo(0), Foo(0));
+    let c = || { let _ = &t; 
+        //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
+        //~| HELP: `let _ = &t` causes `t` to be fully captured
+        let _t = t.0;
+    };
+
+    c();
+}
+
+fn closure_doesnt_contain_block() {
+    let t = (Foo(0), Foo(0));
+    let c = || { let _ = &t; t.0 };
+    //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
+    //~| HELP: `let _ = &t` causes `t` to be fully captured
+
+    c();
+}
+
+fn main() {
+    closure_contains_block();
+    closure_doesnt_contain_block();
+}

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

@@ -0,0 +1,40 @@
+// run-rustfix
+#![deny(disjoint_capture_drop_reorder)]
+//~^ NOTE: the lint level is defined here
+
+// Test the two possible cases for automated migartion using rustfix
+// - Closure contains a block i.e.  `|| { .. };`
+// - Closure contains just an expr `|| ..;`
+
+#[derive(Debug)]
+struct Foo(i32);
+impl Drop for Foo {
+    fn drop(&mut self) {
+        println!("{:?} dropped", self.0);
+    }
+}
+
+fn closure_contains_block() {
+    let t = (Foo(0), Foo(0));
+    let c = || {
+        //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
+        //~| HELP: `let _ = &t` causes `t` to be fully captured
+        let _t = t.0;
+    };
+
+    c();
+}
+
+fn closure_doesnt_contain_block() {
+    let t = (Foo(0), Foo(0));
+    let c = || t.0;
+    //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
+    //~| HELP: `let _ = &t` causes `t` to be fully captured
+
+    c();
+}
+
+fn main() {
+    closure_contains_block();
+    closure_doesnt_contain_block();
+}

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

@@ -0,0 +1,38 @@
+error: drop order affected for closure because of `capture_disjoint_fields`
+  --> $DIR/migrations_rustfix.rs:19:13
+   |
+LL |       let c = || {
+   |  _____________^
+LL | |
+LL | |
+LL | |         let _t = t.0;
+LL | |     };
+   | |_____^
+   |
+note: the lint level is defined here
+  --> $DIR/migrations_rustfix.rs:2:9
+   |
+LL | #![deny(disjoint_capture_drop_reorder)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: `let _ = &t` causes `t` to be fully captured
+   |
+LL |     let c = || { let _ = &t; 
+LL |
+LL |
+LL |         let _t = t.0;
+LL |     };
+   |
+
+error: drop order affected for closure because of `capture_disjoint_fields`
+  --> $DIR/migrations_rustfix.rs:30:13
+   |
+LL |     let c = || t.0;
+   |             ^^^^^^
+   |
+help: `let _ = &t` causes `t` to be fully captured
+   |
+LL |     let c = || { let _ = &t; t.0 };
+   |                ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+

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

@@ -16,12 +16,12 @@ struct ConstainsDropField(Foo, Foo);
 fn test_precise_analysis_drop_paths_not_captured_by_move() {
     let t = ConstainsDropField(Foo(10), Foo(20));
 
-    let c = || { let _ = &t; {
+    let c = || { let _ = &t; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &t` causes `t` to be fully captured
         let _t = t.0;
         let _t = &t.1;
-    } };
+    };
 
     c();
 }
@@ -39,13 +39,13 @@ struct U(T, T);
 fn test_precise_analysis_long_path_missing() {
     let u = U(T(S, S), T(S, S));
 
-    let c = || { let _ = &u; {
+    let c = || { let _ = &u; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &u` causes `u` to be fully captured
         let _x = u.0.0;
         let _x = u.0.1;
         let _x = u.1.0;
-    } };
+    };
 
     c();
 }

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

@@ -17,12 +17,12 @@ LL | #![deny(disjoint_capture_drop_reorder)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: `let _ = &t` causes `t` to be fully captured
    |
-LL |     let c = || { let _ = &t; {
+LL |     let c = || { let _ = &t; 
 LL |
 LL |
 LL |         let _t = t.0;
 LL |         let _t = &t.1;
-LL |     } };
+LL |     };
    |
 
 error: drop order affected for closure because of `capture_disjoint_fields`
@@ -40,7 +40,7 @@ LL | |     };
    |
 help: `let _ = &u` causes `u` to be fully captured
    |
-LL |     let c = || { let _ = &u; {
+LL |     let c = || { let _ = &u; 
 LL |
 LL |
 LL |         let _x = u.0.0;

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

@@ -22,13 +22,13 @@ fn test1_all_need_migration() {
     let t1 = (Foo(0), Foo(0));
     let t2 = (Foo(0), Foo(0));
 
-    let c = || { let _ = (&t, &t1, &t2); {
+    let c = || { let _ = (&t, &t1, &t2); 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP:` let _ = (&t, &t1, &t2)` causes `t`, `t1`, `t2` to be fully captured
         let _t = t.0;
         let _t1 = t1.0;
         let _t2 = t2.0;
-    } };
+    };
 
     c();
 }
@@ -40,13 +40,13 @@ fn test2_only_precise_paths_need_migration() {
     let t1 = (Foo(0), Foo(0));
     let t2 = (Foo(0), Foo(0));
 
-    let c = || { let _ = (&t, &t1); {
+    let c = || { let _ = (&t, &t1); 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP:` let _ = (&t, &t1)` causes `t`, `t1` to be fully captured
         let _t = t.0;
         let _t1 = t1.0;
         let _t2 = t2;
-    } };
+    };
 
     c();
 }
@@ -56,12 +56,12 @@ fn test2_only_precise_paths_need_migration() {
 fn test3_only_by_value_need_migration() {
     let t = (Foo(0), Foo(0));
     let t1 = (Foo(0), Foo(0));
-    let c = || { let _ = &t; {
+    let c = || { let _ = &t; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &t` causes `t` to be fully captured
         let _t = t.0;
         println!("{:?}", t1.1);
-    } };
+    };
 
     c();
 }
@@ -73,11 +73,11 @@ fn test3_only_by_value_need_migration() {
 fn test4_type_contains_drop_need_migration() {
     let t = ConstainsDropField(Foo(0), Foo(0));
 
-    let c = || { let _ = &t; {
+    let c = || { let _ = &t; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &t` causes `t` to be fully captured
         let _t = t.0;
-    } };
+    };
 
     c();
 }
@@ -88,11 +88,11 @@ fn test4_type_contains_drop_need_migration() {
 fn test5_drop_non_drop_aggregate_need_migration() {
     let t = (Foo(0), Foo(0), 0i32);
 
-    let c = || { let _ = &t; {
+    let c = || { let _ = &t; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &t` causes `t` to be fully captured
         let _t = t.0;
-    } };
+    };
 
     c();
 }
@@ -101,11 +101,11 @@ fn test5_drop_non_drop_aggregate_need_migration() {
 fn test6_significant_insignificant_drop_aggregate_need_migration() {
     let t = (Foo(0), String::new());
 
-    let c = || { let _ = &t; {
+    let c = || { let _ = &t; 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = &t` causes `t` to be fully captured
         let _t = t.1;
-    } };
+    };
 
     c();
 }
@@ -116,11 +116,11 @@ fn test7_move_closures_non_copy_types_might_need_migration() {
     let t = (Foo(0), Foo(0));
     let t1 = (Foo(0), Foo(0), Foo(0));
 
-    let c = move || { let _ = (&t1, &t); {
+    let c = move || { let _ = (&t1, &t); 
     //~^ ERROR: drop order affected for closure because of `capture_disjoint_fields`
     //~| HELP: `let _ = (&t1, &t)` causes `t1`, `t` to be fully captured
         println!("{:?} {:?}", t1.1, t.1);
-    } };
+    };
 
     c();
 }

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

@@ -18,7 +18,7 @@ LL | #![deny(disjoint_capture_drop_reorder)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 help: `let _ = (&t, &t1, &t2)` causes `t`, `t1`, `t2` to be fully captured
    |
-LL |     let c = || { let _ = (&t, &t1, &t2); {
+LL |     let c = || { let _ = (&t, &t1, &t2); 
 LL |
 LL |
 LL |         let _t = t.0;
@@ -41,7 +41,7 @@ LL | |     };
    |
 help: `let _ = (&t, &t1)` causes `t`, `t1` to be fully captured
    |
-LL |     let c = || { let _ = (&t, &t1); {
+LL |     let c = || { let _ = (&t, &t1); 
 LL |
 LL |
 LL |         let _t = t.0;
@@ -63,12 +63,12 @@ LL | |     };
    |
 help: `let _ = &t` causes `t` to be fully captured
    |
-LL |     let c = || { let _ = &t; {
+LL |     let c = || { let _ = &t; 
 LL |
 LL |
 LL |         let _t = t.0;
 LL |         println!("{:?}", t1.1);
-LL |     } };
+LL |     };
    |
 
 error: drop order affected for closure because of `capture_disjoint_fields`
@@ -84,11 +84,11 @@ LL | |     };
    |
 help: `let _ = &t` causes `t` to be fully captured
    |
-LL |     let c = || { let _ = &t; {
+LL |     let c = || { let _ = &t; 
 LL |
 LL |
 LL |         let _t = t.0;
-LL |     } };
+LL |     };
    |
 
 error: drop order affected for closure because of `capture_disjoint_fields`
@@ -104,11 +104,11 @@ LL | |     };
    |
 help: `let _ = &t` causes `t` to be fully captured
    |
-LL |     let c = || { let _ = &t; {
+LL |     let c = || { let _ = &t; 
 LL |
 LL |
 LL |         let _t = t.0;
-LL |     } };
+LL |     };
    |
 
 error: drop order affected for closure because of `capture_disjoint_fields`
@@ -124,11 +124,11 @@ LL | |     };
    |
 help: `let _ = &t` causes `t` to be fully captured
    |
-LL |     let c = || { let _ = &t; {
+LL |     let c = || { let _ = &t; 
 LL |
 LL |
 LL |         let _t = t.1;
-LL |     } };
+LL |     };
    |
 
 error: drop order affected for closure because of `capture_disjoint_fields`
@@ -144,11 +144,11 @@ LL | |     };
    |
 help: `let _ = (&t1, &t)` causes `t1`, `t` to be fully captured
    |
-LL |     let c = move || { let _ = (&t1, &t); {
+LL |     let c = move || { let _ = (&t1, &t); 
 LL |
 LL |
 LL |         println!("{:?} {:?}", t1.1, t.1);
-LL |     } };
+LL |     };
    |
 
 error: aborting due to 7 previous errors