Rollup merge of rust-lang#90901 - rukai:improve_manuallydrop_help, r=estebank

matthiaskrgr · web-flow · commit 469faa2b667d · 2021-11-17T15:58:06.000+01:00
Improve ManuallyDrop suggestion closes rust-lang#90585 * Fixes the recommended change to use ManuallyDrop as per the issue * Changes the note to a help * improves the span so it only points at the type.
diff --git a/compiler/rustc_typeck/src/check/check.rs b/compiler/rustc_typeck/src/check/check.rs
@@ -371,16 +371,26 @@ fn check_union_fields(tcx: TyCtxt<'_>, span: Span, item_def_id: LocalDefId) -> b
         let param_env = tcx.param_env(item_def_id);
         for field in fields {
             let field_ty = field.ty(tcx, substs);
-            // We are currently checking the type this field came from, so it must be local.
-            let field_span = tcx.hir().span_if_local(field.did).unwrap();
             if field_ty.needs_drop(tcx, param_env) {
+                let (field_span, ty_span) = match tcx.hir().get_if_local(field.did) {
+                    // We are currently checking the type this field came from, so it must be local.
+                    Some(Node::Field(field)) => (field.span, field.ty.span),
+                    _ => unreachable!("mir field has to correspond to hir field"),
+                };
                 struct_span_err!(
                     tcx.sess,
                     field_span,
                     E0740,
                     "unions may not contain fields that need dropping"
                 )
-                .span_note(field_span, "`std::mem::ManuallyDrop` can be used to wrap the type")
+                .multipart_suggestion_verbose(
+                    "wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped",
+                    vec![
+                        (ty_span.shrink_to_lo(), format!("std::mem::ManuallyDrop<")),
+                        (ty_span.shrink_to_hi(), ">".into()),
+                    ],
+                    Applicability::MaybeIncorrect,
+                )
                 .emit();
                 return false;
             }
diff --git a/src/test/ui/feature-gates/feature-gate-untagged_unions.stderr b/src/test/ui/feature-gates/feature-gate-untagged_unions.stderr
@@ -13,23 +13,21 @@ error[E0740]: unions may not contain fields that need dropping
 LL |     a: String,
    |     ^^^^^^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/feature-gate-untagged_unions.rs:16:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     a: String,
-   |     ^^^^^^^^^
+LL |     a: std::mem::ManuallyDrop<String>,
+   |        +++++++++++++++++++++++      +
 
 error[E0740]: unions may not contain fields that need dropping
   --> $DIR/feature-gate-untagged_unions.rs:24:5
    |
 LL |     a: T,
    |     ^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/feature-gate-untagged_unions.rs:24:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     a: T,
-   |     ^^^^
+LL |     a: std::mem::ManuallyDrop<T>,
+   |        +++++++++++++++++++++++ +
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/union/issue-41073.stderr b/src/test/ui/union/issue-41073.stderr
@@ -4,11 +4,10 @@ error[E0740]: unions may not contain fields that need dropping
 LL |     a: A,
    |     ^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/issue-41073.rs:4:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     a: A,
-   |     ^^^^
+LL |     a: std::mem::ManuallyDrop<A>,
+   |        +++++++++++++++++++++++ +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/union/union-custom-drop.stderr b/src/test/ui/union/union-custom-drop.stderr
@@ -4,11 +4,10 @@ error[E0740]: unions may not contain fields that need dropping
 LL |     bar: Bar,
    |     ^^^^^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/union-custom-drop.rs:7:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     bar: Bar,
-   |     ^^^^^^^^
+LL |     bar: std::mem::ManuallyDrop<Bar>,
+   |          +++++++++++++++++++++++   +
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/union/union-with-drop-fields.mirunsafeck.stderr b/src/test/ui/union/union-with-drop-fields.mirunsafeck.stderr
@@ -4,35 +4,32 @@ error[E0740]: unions may not contain fields that need dropping
 LL |     a: String,
    |     ^^^^^^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/union-with-drop-fields.rs:11:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     a: String,
-   |     ^^^^^^^^^
+LL |     a: std::mem::ManuallyDrop<String>,
+   |        +++++++++++++++++++++++      +
 
 error[E0740]: unions may not contain fields that need dropping
   --> $DIR/union-with-drop-fields.rs:19:5
    |
 LL |     a: S,
    |     ^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/union-with-drop-fields.rs:19:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     a: S,
-   |     ^^^^
+LL |     a: std::mem::ManuallyDrop<S>,
+   |        +++++++++++++++++++++++ +
 
 error[E0740]: unions may not contain fields that need dropping
   --> $DIR/union-with-drop-fields.rs:24:5
    |
 LL |     a: T,
    |     ^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/union-with-drop-fields.rs:24:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     a: T,
-   |     ^^^^
+LL |     a: std::mem::ManuallyDrop<T>,
+   |        +++++++++++++++++++++++ +
 
 error: aborting due to 3 previous errors
 
diff --git a/src/test/ui/union/union-with-drop-fields.thirunsafeck.stderr b/src/test/ui/union/union-with-drop-fields.thirunsafeck.stderr
@@ -4,35 +4,32 @@ error[E0740]: unions may not contain fields that need dropping
 LL |     a: String,
    |     ^^^^^^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/union-with-drop-fields.rs:11:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     a: String,
-   |     ^^^^^^^^^
+LL |     a: std::mem::ManuallyDrop<String>,
+   |        +++++++++++++++++++++++      +
 
 error[E0740]: unions may not contain fields that need dropping
   --> $DIR/union-with-drop-fields.rs:19:5
    |
 LL |     a: S,
    |     ^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/union-with-drop-fields.rs:19:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     a: S,
-   |     ^^^^
+LL |     a: std::mem::ManuallyDrop<S>,
+   |        +++++++++++++++++++++++ +
 
 error[E0740]: unions may not contain fields that need dropping
   --> $DIR/union-with-drop-fields.rs:24:5
    |
 LL |     a: T,
    |     ^^^^
    |
-note: `std::mem::ManuallyDrop` can be used to wrap the type
-  --> $DIR/union-with-drop-fields.rs:24:5
+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
    |
-LL |     a: T,
-   |     ^^^^
+LL |     a: std::mem::ManuallyDrop<T>,
+   |        +++++++++++++++++++++++ +
 
 error: aborting due to 3 previous errors
 

Original file line number	Diff line number	Diff line change
`@@ -13,23 +13,21 @@ error[E0740]: unions may not contain fields that need dropping`
`13`	`13`	`LL \| a: String,`
`14`	`14`	`\| ^^^^^^^^^`
`15`	`15`	`\|`
`16`		-note: `std::mem::ManuallyDrop` can be used to wrap the type
`17`		`- --> $DIR/feature-gate-untagged_unions.rs:16:5`
	`16`	+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
`18`	`17`	`\|`
`19`		`-LL \| a: String,`
`20`		`- \| ^^^^^^^^^`
	`18`	`+LL \| a: std::mem::ManuallyDrop<String>,`
	`19`	`+ \| +++++++++++++++++++++++ +`
`21`	`20`
`22`	`21`	`error[E0740]: unions may not contain fields that need dropping`
`23`	`22`	`--> $DIR/feature-gate-untagged_unions.rs:24:5`
`24`	`23`	`\|`
`25`	`24`	`LL \| a: T,`
`26`	`25`	`\| ^^^^`
`27`	`26`	`\|`
`28`		-note: `std::mem::ManuallyDrop` can be used to wrap the type
`29`		`- --> $DIR/feature-gate-untagged_unions.rs:24:5`
	`27`	+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
`30`	`28`	`\|`
`31`		`-LL \| a: T,`
`32`		`- \| ^^^^`
	`29`	`+LL \| a: std::mem::ManuallyDrop<T>,`
	`30`	`+ \| +++++++++++++++++++++++ +`
`33`	`31`
`34`	`32`	`error: aborting due to 3 previous errors`
`35`	`33`
Original file line number	Diff line number	Diff line change
`@@ -4,11 +4,10 @@ error[E0740]: unions may not contain fields that need dropping`
`4`	`4`	`LL \| a: A,`
`5`	`5`	`\| ^^^^`
`6`	`6`	`\|`
`7`		-note: `std::mem::ManuallyDrop` can be used to wrap the type
`8`		`- --> $DIR/issue-41073.rs:4:5`
	`7`	+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
`9`	`8`	`\|`
`10`		`-LL \| a: A,`
`11`		`- \| ^^^^`
	`9`	`+LL \| a: std::mem::ManuallyDrop<A>,`
	`10`	`+ \| +++++++++++++++++++++++ +`
`12`	`11`
`13`	`12`	`error: aborting due to previous error`
`14`	`13`
Original file line number	Diff line number	Diff line change
`@@ -4,11 +4,10 @@ error[E0740]: unions may not contain fields that need dropping`
`4`	`4`	`LL \| bar: Bar,`
`5`	`5`	`\| ^^^^^^^^`
`6`	`6`	`\|`
`7`		-note: `std::mem::ManuallyDrop` can be used to wrap the type
`8`		`- --> $DIR/union-custom-drop.rs:7:5`
	`7`	+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
`9`	`8`	`\|`
`10`		`-LL \| bar: Bar,`
`11`		`- \| ^^^^^^^^`
	`9`	`+LL \| bar: std::mem::ManuallyDrop<Bar>,`
	`10`	`+ \| +++++++++++++++++++++++ +`
`12`	`11`
`13`	`12`	`error: aborting due to previous error`
`14`	`13`
Original file line number	Diff line number	Diff line change
`@@ -4,35 +4,32 @@ error[E0740]: unions may not contain fields that need dropping`
`4`	`4`	`LL \| a: String,`
`5`	`5`	`\| ^^^^^^^^^`
`6`	`6`	`\|`
`7`		-note: `std::mem::ManuallyDrop` can be used to wrap the type
`8`		`- --> $DIR/union-with-drop-fields.rs:11:5`
	`7`	+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
`9`	`8`	`\|`
`10`		`-LL \| a: String,`
`11`		`- \| ^^^^^^^^^`
	`9`	`+LL \| a: std::mem::ManuallyDrop<String>,`
	`10`	`+ \| +++++++++++++++++++++++ +`
`12`	`11`
`13`	`12`	`error[E0740]: unions may not contain fields that need dropping`
`14`	`13`	`--> $DIR/union-with-drop-fields.rs:19:5`
`15`	`14`	`\|`
`16`	`15`	`LL \| a: S,`
`17`	`16`	`\| ^^^^`
`18`	`17`	`\|`
`19`		-note: `std::mem::ManuallyDrop` can be used to wrap the type
`20`		`- --> $DIR/union-with-drop-fields.rs:19:5`
	`18`	+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
`21`	`19`	`\|`
`22`		`-LL \| a: S,`
`23`		`- \| ^^^^`
	`20`	`+LL \| a: std::mem::ManuallyDrop<S>,`
	`21`	`+ \| +++++++++++++++++++++++ +`
`24`	`22`
`25`	`23`	`error[E0740]: unions may not contain fields that need dropping`
`26`	`24`	`--> $DIR/union-with-drop-fields.rs:24:5`
`27`	`25`	`\|`
`28`	`26`	`LL \| a: T,`
`29`	`27`	`\| ^^^^`
`30`	`28`	`\|`
`31`		-note: `std::mem::ManuallyDrop` can be used to wrap the type
`32`		`- --> $DIR/union-with-drop-fields.rs:24:5`
	`29`	+help: wrap the type with `std::mem::ManuallyDrop` and ensure it is manually dropped
`33`	`30`	`\|`
`34`		`-LL \| a: T,`
`35`		`- \| ^^^^`
	`31`	`+LL \| a: std::mem::ManuallyDrop<T>,`
	`32`	`+ \| +++++++++++++++++++++++ +`
`36`	`33`
`37`	`34`	`error: aborting due to 3 previous errors`
`38`	`35`