Remove the box_pointers lint.

As the comment says, this lint "is mostly historical, and not
particularly useful". It's not worth keeping it around.

Author: nnethercote

compiler/rustc_lint/messages.ftl

@@ -56,8 +56,6 @@ lint_builtin_asm_labels = avoid using named labels in inline assembly
     .help = only local labels of the form `<number>:` should be used in inline asm
     .note = see the asm section of Rust By Example <https://doc.rust-lang.org/nightly/rust-by-example/unsafe/asm.html#labels> for more information
 
-lint_builtin_box_pointers = type uses owned (Box type) pointers: {$ty}
-
 lint_builtin_clashing_extern_diff_name = `{$this}` redeclares `{$orig}` with a different signature
     .previous_decl_label = `{$orig}` previously declared here
     .mismatch_label = this signature doesn't match the previous declaration

compiler/rustc_lint/src/builtin.rs

@@ -24,9 +24,9 @@ use crate::fluent_generated as fluent;
 use crate::{
     errors::BuiltinEllipsisInclusiveRangePatterns,
     lints::{
-        BuiltinAnonymousParams, BuiltinBoxPointers, BuiltinConstNoMangle,
-        BuiltinDeprecatedAttrLink, BuiltinDeprecatedAttrLinkSuggestion, BuiltinDeprecatedAttrUsed,
-        BuiltinDerefNullptr, BuiltinEllipsisInclusiveRangePatternsLint, BuiltinExplicitOutlives,
+        BuiltinAnonymousParams, BuiltinConstNoMangle, BuiltinDeprecatedAttrLink,
+        BuiltinDeprecatedAttrLinkSuggestion, BuiltinDeprecatedAttrUsed, BuiltinDerefNullptr,
+        BuiltinEllipsisInclusiveRangePatternsLint, BuiltinExplicitOutlives,
         BuiltinExplicitOutlivesSuggestion, BuiltinFeatureIssueNote, BuiltinIncompleteFeatures,
         BuiltinIncompleteFeaturesHelp, BuiltinInternalFeatures, BuiltinKeywordIdents,
         BuiltinMissingCopyImpl, BuiltinMissingDebugImpl, BuiltinMissingDoc,
@@ -56,7 +56,6 @@ use rustc_middle::bug;
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty::layout::LayoutOf;
 use rustc_middle::ty::print::with_no_trimmed_paths;
-use rustc_middle::ty::GenericArgKind;
 use rustc_middle::ty::TypeVisitableExt;
 use rustc_middle::ty::Upcast;
 use rustc_middle::ty::{self, Ty, TyCtxt, VariantDef};
@@ -134,80 +133,6 @@ impl EarlyLintPass for WhileTrue {
     }
 }
 
-declare_lint! {
-    /// The `box_pointers` lints use of the Box type.
-    ///
-    /// ### Example
-    ///
-    /// ```rust,compile_fail
-    /// #![deny(box_pointers)]
-    /// struct Foo {
-    ///     x: Box<i32>,
-    /// }
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// This lint is mostly historical, and not particularly useful. `Box<T>`
-    /// used to be built into the language, and the only way to do heap
-    /// allocation. Today's Rust can call into other allocators, etc.
-    BOX_POINTERS,
-    Allow,
-    "use of owned (Box type) heap memory"
-}
-
-declare_lint_pass!(BoxPointers => [BOX_POINTERS]);
-
-impl BoxPointers {
-    fn check_heap_type(&self, cx: &LateContext<'_>, span: Span, ty: Ty<'_>) {
-        for leaf in ty.walk() {
-            if let GenericArgKind::Type(leaf_ty) = leaf.unpack()
-                && leaf_ty.is_box()
-            {
-                cx.emit_span_lint(BOX_POINTERS, span, BuiltinBoxPointers { ty });
-            }
-        }
-    }
-}
-
-impl<'tcx> LateLintPass<'tcx> for BoxPointers {
-    fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
-        match it.kind {
-            hir::ItemKind::Fn(..)
-            | hir::ItemKind::TyAlias(..)
-            | hir::ItemKind::Enum(..)
-            | hir::ItemKind::Struct(..)
-            | hir::ItemKind::Union(..) => self.check_heap_type(
-                cx,
-                it.span,
-                cx.tcx.type_of(it.owner_id).instantiate_identity(),
-            ),
-            _ => (),
-        }
-
-        // If it's a struct, we also have to check the fields' types
-        match it.kind {
-            hir::ItemKind::Struct(ref struct_def, _) | hir::ItemKind::Union(ref struct_def, _) => {
-                for field in struct_def.fields() {
-                    self.check_heap_type(
-                        cx,
-                        field.span,
-                        cx.tcx.type_of(field.def_id).instantiate_identity(),
-                    );
-                }
-            }
-            _ => (),
-        }
-    }
-
-    fn check_expr(&mut self, cx: &LateContext<'_>, e: &hir::Expr<'_>) {
-        let ty = cx.typeck_results().node_type(e.hir_id);
-        self.check_heap_type(cx, e.span, ty);
-    }
-}
-
 declare_lint! {
     /// The `non_shorthand_field_patterns` lint detects using `Struct { x: x }`
     /// instead of `Struct { x }` in a pattern.
@@ -1640,7 +1565,6 @@ declare_lint_pass!(
     /// which are used by other parts of the compiler.
     SoftLints => [
         WHILE_TRUE,
-        BOX_POINTERS,
         NON_SHORTHAND_FIELD_PATTERNS,
         UNSAFE_CODE,
         MISSING_DOCS,

compiler/rustc_lint/src/lib.rs

@@ -187,7 +187,6 @@ late_lint_methods!(
             ImproperCTypesDefinitions: ImproperCTypesDefinitions,
             InvalidFromUtf8: InvalidFromUtf8,
             VariantSizeDifferences: VariantSizeDifferences,
-            BoxPointers: BoxPointers,
             PathStatements: PathStatements,
             LetUnderscore: LetUnderscore,
             InvalidReferenceCasting: InvalidReferenceCasting,
@@ -551,6 +550,10 @@ fn register_builtins(store: &mut LintStore) {
         "converted into hard error, see RFC #3535 \
          <https://rust-lang.github.io/rfcs/3535-constants-in-patterns.html> for more information",
     );
+    store.register_removed(
+        "box_pointers",
+        "it does not detect other kinds of allocations, and existed only for historical reasons",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {

compiler/rustc_lint/src/lints.rs

@@ -66,12 +66,6 @@ pub struct BuiltinWhileTrue {
     pub replace: String,
 }
 
-#[derive(LintDiagnostic)]
-#[diag(lint_builtin_box_pointers)]
-pub struct BuiltinBoxPointers<'a> {
-    pub ty: Ty<'a>,
-}
-
 #[derive(LintDiagnostic)]
 #[diag(lint_builtin_non_shorthand_field_patterns)]
 pub struct BuiltinNonShorthandFieldPatterns {

src/tools/rust-analyzer/crates/ide-db/src/generated/lints.rs

@@ -49,7 +49,6 @@ pub const DEFAULT_LINTS: &[Lint] = &[
         label: "bindings_with_variant_name",
         description: r##"detects pattern bindings with the same name as one of the matched variants"##,
     },
-    Lint { label: "box_pointers", description: r##"use of owned (Box type) heap memory"## },
     Lint {
         label: "break_with_label_and_loop",
         description: r##"`break` expression with label and unlabeled loop as value expression"##,

tests/ui/lint/lint-owned-heap-memory.rs

@@ -9,7 +9,7 @@
 #![warn(bare_trait_objects, reasons = "leaders to no sure land, guides their bearings lost")]
 //~^ ERROR malformed lint attribute
 //~| NOTE bad attribute argument
-#![warn(box_pointers, blerp = "or in league with robbers have reversed the signposts")]
+#![warn(unsafe_code, blerp = "or in league with robbers have reversed the signposts")]
 //~^ ERROR malformed lint attribute
 //~| NOTE bad attribute argument
 #![warn(elided_lifetimes_in_paths, reason("disrespectful to ancestors", "irresponsible to heirs"))]

tests/ui/lint/lint-owned-heap-memory.stderr

@@ -17,10 +17,10 @@ LL | #![warn(bare_trait_objects, reasons = "leaders to no sure land, guides thei
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
 
 error[E0452]: malformed lint attribute input
-  --> $DIR/reasons-erroneous.rs:12:23
+  --> $DIR/reasons-erroneous.rs:12:22
    |
-LL | #![warn(box_pointers, blerp = "or in league with robbers have reversed the signposts")]
-   |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
+LL | #![warn(unsafe_code, blerp = "or in league with robbers have reversed the signposts")]
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ bad attribute argument
 
 error[E0452]: malformed lint attribute input
   --> $DIR/reasons-erroneous.rs:15:36