Auto merge of rust-lang#106934 - DrMeepster:offset_of, r=WaffleLapkin

Add offset_of! macro (RFC 3308)

Implements rust-lang/rfcs#3308 (tracking issue rust-lang#106655) by adding the built in macro `core::mem::offset_of`. Two of the future possibilities are also implemented:

* Nested field accesses (without array indexing)
* DST support (for `Sized` fields)

I wrote this a few months ago, before the RFC merged. Now that it's merged, I decided to rebase and finish it.

cc `@thomcc` (RFC author)

clippy_lints/src/loops/never_loop.rs

@@ -226,7 +226,8 @@ fn never_loop_expr(expr: &Expr<'_>, ignore_ids: &mut Vec<HirId>, main_loop_id: H
  | InlineAsmOperand::SymStatic { .. } => NeverLoopResult::Otherwise,
  })
  .fold(NeverLoopResult::Otherwise, combine_seq),
- ExprKind::Yield(_, _)
+ ExprKind::OffsetOf(_, _)
+ | ExprKind::Yield(_, _)
  | ExprKind::Closure { .. }
  | ExprKind::Path(_)
  | ExprKind::ConstBlock(_)

clippy_lints/src/matches/significant_drop_in_scrutinee.rs

@@ -342,6 +342,7 @@ impl<'a, 'tcx> Visitor<'tcx> for SigDropHelper<'a, 'tcx> {
  ExprKind::DropTemps(_) |
  ExprKind::Err(_) |
  ExprKind::InlineAsm(_) |
+ ExprKind::OffsetOf(_, _) |
  ExprKind::Let(_) |
  ExprKind::Lit(_) |
  ExprKind::Loop(_, _, _, _) |

clippy_lints/src/utils/author.rs

@@ -558,6 +558,10 @@ impl<'a, 'tcx> PrintVisitor<'a, 'tcx> {
  kind!("InlineAsm(_)");
  out!("// unimplemented: `ExprKind::InlineAsm` is not further destructured at the moment");
  },
+ ExprKind::OffsetOf(container, ref fields) => {
+ bind!(self, container, fields);
+ kind!("OffsetOf({container}, {fields})");
+ }
  ExprKind::Struct(qpath, fields, base) => {
  bind!(self, qpath, fields);
  opt_bind!(self, base);

clippy_utils/src/eager_or_lazy.rs

@@ -218,7 +218,8 @@ fn expr_eagerness<'tcx>(cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) -> EagernessS
  | ExprKind::AddrOf(..)
  | ExprKind::Struct(..)
  | ExprKind::Repeat(..)
- | ExprKind::Block(Block { stmts: [], .. }, _) => (),
+ | ExprKind::Block(Block { stmts: [], .. }, _)
+ | ExprKind::OffsetOf(..) => (),
 
  // Assignment might be to a local defined earlier, so don't eagerly evaluate.
  // Blocks with multiple statements might be expensive, so don't eagerly evaluate.

clippy_utils/src/hir_utils.rs

@@ -301,6 +301,9 @@ impl HirEqInterExpr<'_, '_, '_> {
  (&ExprKind::Unary(l_op, le), &ExprKind::Unary(r_op, re)) => l_op == r_op && self.eq_expr(le, re),
  (&ExprKind::Array(l), &ExprKind::Array(r)) => self.eq_exprs(l, r),
  (&ExprKind::DropTemps(le), &ExprKind::DropTemps(re)) => self.eq_expr(le, re),
+ (&ExprKind::OffsetOf(l_container, ref l_fields), &ExprKind::OffsetOf(r_container, ref r_fields)) => {
+ self.eq_ty(l_container, r_container) && over(l_fields, r_fields, |l, r| l.name == r.name)
+ },
  _ => false,
  };
  (is_eq && (!self.should_ignore(left) || !self.should_ignore(right)))
@@ -701,6 +704,12 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
  }
  }
  },
+ ExprKind::OffsetOf(container, fields) => {
+ self.hash_ty(container);
+ for field in fields {
+ self.hash_name(field.name);
+ }
+ },
  ExprKind::Let(Let { pat, init, ty, .. }) => {
  self.hash_expr(init);
  if let Some(ty) = ty {

clippy_utils/src/qualify_min_const_fn.rs

@@ -194,7 +194,7 @@ fn check_rvalue<'tcx>(
  ))
  }
  },
- Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf, _) | Rvalue::ShallowInitBox(_, _) => Ok(()),
+ Rvalue::NullaryOp(NullOp::SizeOf | NullOp::AlignOf | NullOp::OffsetOf(_), _) | Rvalue::ShallowInitBox(_, _) => Ok(()),
  Rvalue::UnaryOp(_, operand) => {
  let ty = operand.ty(body, tcx);
  if ty.is_integral() || ty.is_bool() {

clippy_utils/src/sugg.rs

@@ -139,6 +139,7 @@ impl<'a> Sugg<'a> {
  | hir::ExprKind::Field(..)
  | hir::ExprKind::Index(..)
  | hir::ExprKind::InlineAsm(..)
+ | hir::ExprKind::OffsetOf(..)
  | hir::ExprKind::ConstBlock(..)
  | hir::ExprKind::Lit(..)
  | hir::ExprKind::Loop(..)
@@ -197,6 +198,7 @@ impl<'a> Sugg<'a> {
  | ast::ExprKind::ForLoop(..)
  | ast::ExprKind::Index(..)
  | ast::ExprKind::InlineAsm(..)
+ | ast::ExprKind::OffsetOf(..)
  | ast::ExprKind::ConstBlock(..)
  | ast::ExprKind::Lit(..)
  | ast::ExprKind::IncludedBytes(..)

clippy_utils/src/visitors.rs

@@ -662,6 +662,7 @@ pub fn for_each_unconsumed_temporary<'tcx, B>(
  | ExprKind::Path(_)
  | ExprKind::Continue(_)
  | ExprKind::InlineAsm(_)
+ | ExprKind::OffsetOf(..)
  | ExprKind::Err(_) => (),
  }
  ControlFlow::Continue(())