Rollup merge of #117556 - obeis:static-mut-ref-lint, r=davidtwco

Disallow reference to `static mut` and adding `static_mut_ref` lint

Closes #114447

r? `@scottmcm`

compiler/rustc_hir_analysis/src/check/errs.rs

@@ -0,0 +1,97 @@
+use rustc_hir as hir;
+use rustc_hir_pretty::qpath_to_string;
+use rustc_lint_defs::builtin::STATIC_MUT_REF;
+use rustc_middle::ty::TyCtxt;
+use rustc_span::Span;
+use rustc_type_ir::Mutability;
+
+use crate::errors;
+
+/// Check for shared or mutable references of `static mut` inside expression
+pub fn maybe_expr_static_mut(tcx: TyCtxt<'_>, expr: hir::Expr<'_>) {
+    let span = expr.span;
+    let hir_id = expr.hir_id;
+    if let hir::ExprKind::AddrOf(borrow_kind, m, expr) = expr.kind
+        && matches!(borrow_kind, hir::BorrowKind::Ref)
+        && let Some(var) = is_path_static_mut(*expr)
+    {
+        handle_static_mut_ref(
+            tcx,
+            span,
+            var,
+            span.edition().at_least_rust_2024(),
+            matches!(m, Mutability::Mut),
+            hir_id,
+        );
+    }
+}
+
+/// Check for shared or mutable references of `static mut` inside statement
+pub fn maybe_stmt_static_mut(tcx: TyCtxt<'_>, stmt: hir::Stmt<'_>) {
+    if let hir::StmtKind::Local(loc) = stmt.kind
+        && let hir::PatKind::Binding(ba, _, _, _) = loc.pat.kind
+        && matches!(ba.0, rustc_ast::ByRef::Yes)
+        && let Some(init) = loc.init
+        && let Some(var) = is_path_static_mut(*init)
+    {
+        handle_static_mut_ref(
+            tcx,
+            init.span,
+            var,
+            loc.span.edition().at_least_rust_2024(),
+            matches!(ba.1, Mutability::Mut),
+            stmt.hir_id,
+        );
+    }
+}
+
+fn is_path_static_mut(expr: hir::Expr<'_>) -> Option<String> {
+    if let hir::ExprKind::Path(qpath) = expr.kind
+        && let hir::QPath::Resolved(_, path) = qpath
+        && let hir::def::Res::Def(def_kind, _) = path.res
+        && let hir::def::DefKind::Static(mt) = def_kind
+        && matches!(mt, Mutability::Mut)
+    {
+        return Some(qpath_to_string(&qpath));
+    }
+    None
+}
+
+fn handle_static_mut_ref(
+    tcx: TyCtxt<'_>,
+    span: Span,
+    var: String,
+    e2024: bool,
+    mutable: bool,
+    hir_id: hir::HirId,
+) {
+    if e2024 {
+        let sugg = if mutable {
+            errors::StaticMutRefSugg::Mut { span, var }
+        } else {
+            errors::StaticMutRefSugg::Shared { span, var }
+        };
+        tcx.sess.parse_sess.dcx.emit_err(errors::StaticMutRef { span, sugg });
+        return;
+    }
+
+    let (label, sugg, shared) = if mutable {
+        (
+            errors::RefOfMutStaticLabel::Mut { span },
+            errors::RefOfMutStaticSugg::Mut { span, var },
+            "mutable ",
+        )
+    } else {
+        (
+            errors::RefOfMutStaticLabel::Shared { span },
+            errors::RefOfMutStaticSugg::Shared { span, var },
+            "shared ",
+        )
+    };
+    tcx.emit_spanned_lint(
+        STATIC_MUT_REF,
+        hir_id,
+        span,
+        errors::RefOfMutStatic { shared, why_note: (), label, sugg },
+    );
+}

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -66,6 +66,7 @@ mod check;
 mod compare_impl_item;
 pub mod dropck;
 mod entry;
+mod errs;
 pub mod intrinsic;
 pub mod intrinsicck;
 mod region;

compiler/rustc_hir_analysis/src/check/region.rs

@@ -18,6 +18,8 @@ use rustc_middle::ty::TyCtxt;
 use rustc_span::source_map;
 use rustc_span::Span;
 
+use super::errs::{maybe_expr_static_mut, maybe_stmt_static_mut};
+
 use std::mem;
 
 #[derive(Debug, Copy, Clone)]
@@ -224,6 +226,8 @@ fn resolve_stmt<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, stmt: &'tcx h
     let stmt_id = stmt.hir_id.local_id;
     debug!("resolve_stmt(stmt.id={:?})", stmt_id);
 
+    maybe_stmt_static_mut(visitor.tcx, *stmt);
+
     // Every statement will clean up the temporaries created during
     // execution of that statement. Therefore each statement has an
     // associated destruction scope that represents the scope of the
@@ -242,6 +246,8 @@ fn resolve_stmt<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, stmt: &'tcx h
 fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
     debug!("resolve_expr - pre-increment {} expr = {:?}", visitor.expr_and_pat_count, expr);
 
+    maybe_expr_static_mut(visitor.tcx, *expr);
+
     let prev_cx = visitor.cx;
     visitor.enter_node_scope_with_dtor(expr.hir_id.local_id);