A small diagnostic improvement for dropping_copy_types

fixes #125189
rust-lang · May 24, 2024 · 9672368 · 9672368
1 parent 9f432d7
commit 9672368
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Showing 8 changed files with 124 additions and 2 deletions.
diff --git a/compiler/rustc_lint/messages.ftl b/compiler/rustc_lint/messages.ftl
@@ -197,6 +197,7 @@ lint_drop_trait_constraints =
 lint_dropping_copy_types = calls to `std::mem::drop` with a value that implements `Copy` does nothing
     .label = argument has type `{$arg_ty}`
     .note = use `let _ = ...` to ignore the expression or result
+    .suggestion = ignore the value
 
 lint_dropping_references = calls to `std::mem::drop` with a reference instead of an owned value does nothing
     .label = argument has type `{$arg_ty}`

diff --git a/compiler/rustc_lint/src/drop_forget_useless.rs b/compiler/rustc_lint/src/drop_forget_useless.rs
@@ -1,4 +1,4 @@
-use rustc_hir::{Arm, Expr, ExprKind, Node};
+use rustc_hir::{Arm, Expr, ExprKind, Node, StmtKind};
 use rustc_middle::ty;
 use rustc_span::sym;
 
@@ -163,10 +163,22 @@ impl<'tcx> LateLintPass<'tcx> for DropForgetUseless {
                     );
                 }
                 sym::mem_drop if is_copy && !drop_is_single_call_in_arm => {
+                    let (sugg, replace) = if let Some((_, node)) =
+                        cx.tcx.hir().parent_iter(expr.hir_id).nth(0)
+                        && let Node::Stmt(stmt) = node
+                        && let StmtKind::Semi(e) = stmt.kind
+                        && e.hir_id == expr.hir_id
+                        && let Ok(value) = cx.sess().source_map().span_to_snippet(arg.span)
+                    {
+                        (Some(expr.span), format!("let _ = {}", value))
+                    } else {
+                        (None, "".to_string())
+                    };
+
                     cx.emit_span_lint(
                         DROPPING_COPY_TYPES,
                         expr.span,
-                        DropCopyDiag { arg_ty, label: arg.span },
+                        DropCopyDiag { arg_ty, label: arg.span, sugg, replace },
                     );
                 }
                 sym::mem_forget if is_copy => {

diff --git a/compiler/rustc_lint/src/lints.rs b/compiler/rustc_lint/src/lints.rs
@@ -674,6 +674,9 @@ pub struct DropCopyDiag<'a> {
     pub arg_ty: Ty<'a>,
     #[label]
     pub label: Span,
+    #[suggestion(style = "verbose", code = "{replace}", applicability = "maybe-incorrect")]
+    pub sugg: Option<Span>,
+    pub replace: String,
 }
 
 #[derive(LintDiagnostic)]

diff --git a/tests/ui/associated-types/defaults-unsound-62211-1.next.stderr b/tests/ui/associated-types/defaults-unsound-62211-1.next.stderr
@@ -8,6 +8,10 @@ LL |     drop(origin);
    |
    = note: use `let _ = ...` to ignore the expression or result
    = note: `#[warn(dropping_copy_types)]` on by default
+help: ignore the value
+   |
+LL |     let _ = origin;
+   |     ~~~~~~~~~~~~~~
 
 warning: 1 warning emitted
 
diff --git a/tests/ui/associated-types/defaults-unsound-62211-2.next.stderr b/tests/ui/associated-types/defaults-unsound-62211-2.next.stderr
@@ -8,6 +8,10 @@ LL |     drop(origin);
    |
    = note: use `let _ = ...` to ignore the expression or result
    = note: `#[warn(dropping_copy_types)]` on by default
+help: ignore the value
+   |
+LL |     let _ = origin;
+   |     ~~~~~~~~~~~~~~
 
 warning: 1 warning emitted
 
diff --git a/tests/ui/lint/dropping_copy_types-issue-125189.rs b/tests/ui/lint/dropping_copy_types-issue-125189.rs
@@ -0,0 +1,17 @@
+//@ check-fail
+
+#![deny(dropping_copy_types)]
+
+fn main() {
+   let y = 1;
+   let z = 2;
+    match y {
+        1 => drop(3), //~ ERROR calls to `std::mem::drop`
+        2 => drop(y), //~ ERROR calls to `std::mem::drop`
+        3 => if drop(z) == () {}, //~ ERROR calls to `std::mem::drop`
+        _ => (),
+    }
+
+    drop(3.2); //~ ERROR calls to `std::mem::drop`
+    drop(y); //~ ERROR calls to `std::mem::drop`
+}
diff --git a/tests/ui/lint/dropping_copy_types-issue-125189.stderr b/tests/ui/lint/dropping_copy_types-issue-125189.stderr
@@ -0,0 +1,65 @@
+error: calls to `std::mem::drop` with a value that implements `Copy` does nothing
+  --> $DIR/dropping_copy_types-issue-125189.rs:9:14
+   |
+LL |         1 => drop(3),
+   |              ^^^^^-^
+   |                   |
+   |                   argument has type `i32`
+   |
+   = note: use `let _ = ...` to ignore the expression or result
+note: the lint level is defined here
+  --> $DIR/dropping_copy_types-issue-125189.rs:3:9
+   |
+LL | #![deny(dropping_copy_types)]
+   |         ^^^^^^^^^^^^^^^^^^^
+
+error: calls to `std::mem::drop` with a value that implements `Copy` does nothing
+  --> $DIR/dropping_copy_types-issue-125189.rs:10:14
+   |
+LL |         2 => drop(y),
+   |              ^^^^^-^
+   |                   |
+   |                   argument has type `i32`
+   |
+   = note: use `let _ = ...` to ignore the expression or result
+
+error: calls to `std::mem::drop` with a value that implements `Copy` does nothing
+  --> $DIR/dropping_copy_types-issue-125189.rs:11:17
+   |
+LL |         3 => if drop(z) == () {},
+   |                 ^^^^^-^
+   |                      |
+   |                      argument has type `i32`
+   |
+   = note: use `let _ = ...` to ignore the expression or result
+
+error: calls to `std::mem::drop` with a value that implements `Copy` does nothing
+  --> $DIR/dropping_copy_types-issue-125189.rs:15:5
+   |
+LL |     drop(3.2);
+   |     ^^^^^---^
+   |          |
+   |          argument has type `f64`
+   |
+   = note: use `let _ = ...` to ignore the expression or result
+help: ignore the value
+   |
+LL |     let _ = 3.2;
+   |     ~~~~~~~~~~~
+
+error: calls to `std::mem::drop` with a value that implements `Copy` does nothing
+  --> $DIR/dropping_copy_types-issue-125189.rs:16:5
+   |
+LL |     drop(y);
+   |     ^^^^^-^
+   |          |
+   |          argument has type `i32`
+   |
+   = note: use `let _ = ...` to ignore the expression or result
+help: ignore the value
+   |
+LL |     let _ = y;
+   |     ~~~~~~~~~
+
+error: aborting due to 5 previous errors
+
diff --git a/tests/ui/lint/dropping_copy_types.stderr b/tests/ui/lint/dropping_copy_types.stderr
@@ -12,6 +12,10 @@ note: the lint level is defined here
    |
 LL | #![warn(dropping_copy_types)]
    |         ^^^^^^^^^^^^^^^^^^^
+help: ignore the value
+   |
+LL |     let _ = s1;
+   |     ~~~~~~~~~~
 
 warning: calls to `std::mem::drop` with a value that implements `Copy` does nothing
   --> $DIR/dropping_copy_types.rs:35:5
@@ -22,6 +26,10 @@ LL |     drop(s2);
    |          argument has type `SomeStruct`
    |
    = note: use `let _ = ...` to ignore the expression or result
+help: ignore the value
+   |
+LL |     let _ = s2;
+   |     ~~~~~~~~~~
 
 warning: calls to `std::mem::drop` with a reference instead of an owned value does nothing
   --> $DIR/dropping_copy_types.rs:36:5
@@ -43,6 +51,10 @@ LL |     drop(s4);
    |          argument has type `SomeStruct`
    |
    = note: use `let _ = ...` to ignore the expression or result
+help: ignore the value
+   |
+LL |     let _ = s4;
+   |     ~~~~~~~~~~
 
 warning: calls to `std::mem::drop` with a reference instead of an owned value does nothing
   --> $DIR/dropping_copy_types.rs:38:5
@@ -83,6 +95,10 @@ LL |             drop(println_and(13));
    |                  argument has type `i32`
    |
    = note: use `let _ = ...` to ignore the expression or result
+help: ignore the value
+   |
+LL |             let _ = println_and(13);
+   |             ~~~~~~~~~~~~~~~~~~~~~~~
 
 warning: calls to `std::mem::drop` with a value that implements `Copy` does nothing
   --> $DIR/dropping_copy_types.rs:74:14