Rollup merge of #78152 - spastorino:separate-unsized-locals, r=oli-obk

Separate unsized locals

Closes #71694

Takes over again #72029 and #74971

cc @RalfJung @oli-obk @pnkfelix @eddyb as they've participated in previous reviews of this PR.

Author: Dylan-DPC

compiler/rustc_feature/src/active.rs

@@ -607,6 +607,9 @@ declare_features! (
     /// Allow anonymous constants from an inline `const` block
     (active, inline_const, "1.49.0", Some(76001), None),
 
+    /// Allows unsized fn parameters.
+    (active, unsized_fn_params, "1.49.0", Some(48055), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------
@@ -629,6 +632,7 @@ pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::specialization,
     sym::inline_const,
     sym::repr128,
+    sym::unsized_locals,
 ];
 
 /// Some features are not allowed to be used together at the same time, if

compiler/rustc_mir/src/borrow_check/type_check/mod.rs

@@ -974,6 +974,11 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         checker
     }
 
+    fn unsized_feature_enabled(&self) -> bool {
+        let features = self.tcx().features();
+        features.unsized_locals || features.unsized_fn_params
+    }
+
     /// Equate the inferred type and the annotated type for user type annotations
     fn check_user_type_annotations(&mut self) {
         debug!(
@@ -1456,7 +1461,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 }
 
                 self.check_rvalue(body, rv, location);
-                if !self.tcx().features().unsized_locals {
+                if !self.unsized_feature_enabled() {
                     let trait_ref = ty::TraitRef {
                         def_id: tcx.require_lang_item(LangItem::Sized, Some(self.last_span)),
                         substs: tcx.mk_substs_trait(place_ty, &[]),
@@ -1717,9 +1722,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     );
                 }
 
-                // When `#![feature(unsized_locals)]` is not enabled,
+                // When `unsized_fn_params` and `unsized_locals` are both not enabled,
                 // this check is done at `check_local`.
-                if self.tcx().features().unsized_locals {
+                if self.unsized_feature_enabled() {
                     let span = term.source_info.span;
                     self.ensure_place_sized(dest_ty, span);
                 }
@@ -1880,9 +1885,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             LocalKind::Var | LocalKind::Temp => {}
         }
 
-        // When `#![feature(unsized_locals)]` is enabled, only function calls
+        // When `unsized_fn_params` or `unsized_locals` is enabled, only function calls
         // and nullary ops are checked in `check_call_dest`.
-        if !self.tcx().features().unsized_locals {
+        if !self.unsized_feature_enabled() {
             let span = local_decl.source_info.span;
             let ty = local_decl.ty;
             self.ensure_place_sized(ty, span);
@@ -2024,7 +2029,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
 
             Rvalue::NullaryOp(_, ty) => {
                 // Even with unsized locals cannot box an unsized value.
-                if self.tcx().features().unsized_locals {
+                if self.unsized_feature_enabled() {
                     let span = body.source_info(location).span;
                     self.ensure_place_sized(ty, span);
                 }

compiler/rustc_mir_build/src/build/expr/as_operand.rs

@@ -165,7 +165,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
         let tcx = this.hir.tcx();
 
-        if tcx.features().unsized_locals {
+        if tcx.features().unsized_fn_params {
             let ty = expr.ty;
             let span = expr.span;
             let param_env = this.hir.param_env;

compiler/rustc_span/src/symbol.rs

@@ -1163,6 +1163,7 @@ symbols! {
         unsafe_cell,
         unsafe_no_drop_flag,
         unsize,
+        unsized_fn_params,
         unsized_locals,
         unsized_tuple_coercion,
         unstable,

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1845,9 +1845,9 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                     err.note("all function arguments must have a statically known size");
                 }
                 if tcx.sess.opts.unstable_features.is_nightly_build()
-                    && !self.tcx.features().unsized_locals
+                    && !self.tcx.features().unsized_fn_params
                 {
-                    err.help("unsized locals are gated as an unstable feature");
+                    err.help("unsized fn params are gated as an unstable feature");
                 }
             }
             ObligationCauseCode::SizedReturnType => {

compiler/rustc_typeck/src/check/check.rs

@@ -131,7 +131,7 @@ pub(super) fn check_fn<'a, 'tcx>(
         // The check for a non-trivial pattern is a hack to avoid duplicate warnings
         // for simple cases like `fn foo(x: Trait)`,
         // where we would error once on the parameter as a whole, and once on the binding `x`.
-        if param.pat.simple_ident().is_none() && !tcx.features().unsized_locals {
+        if param.pat.simple_ident().is_none() && !tcx.features().unsized_fn_params {
             fcx.require_type_is_sized(param_ty, param.pat.span, traits::SizedArgumentType(ty_span));
         }
 

compiler/rustc_typeck/src/check/expr.rs

@@ -476,7 +476,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         if let ty::FnDef(..) = ty.kind() {
             let fn_sig = ty.fn_sig(tcx);
-            if !tcx.features().unsized_locals {
+            if !tcx.features().unsized_fn_params {
                 // We want to remove some Sized bounds from std functions,
                 // but don't want to expose the removal to stable Rust.
                 // i.e., we don't want to allow

compiler/rustc_typeck/src/check/gather_locals.rs

@@ -6,15 +6,20 @@ use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKi
 use rustc_middle::ty::Ty;
 use rustc_span::Span;
 use rustc_trait_selection::traits;
+use std::mem;
 
 pub(super) struct GatherLocalsVisitor<'a, 'tcx> {
     fcx: &'a FnCtxt<'a, 'tcx>,
     parent_id: hir::HirId,
+    // parameters are special cases of patterns, but we want to handle them as
+    // *distinct* cases. so track when we are hitting a pattern *within* an fn
+    // parameter.
+    outermost_fn_param_pat: bool,
 }
 
 impl<'a, 'tcx> GatherLocalsVisitor<'a, 'tcx> {
     pub(super) fn new(fcx: &'a FnCtxt<'a, 'tcx>, parent_id: hir::HirId) -> Self {
-        Self { fcx, parent_id }
+        Self { fcx, parent_id, outermost_fn_param_pat: false }
     }
 
     fn assign(&mut self, span: Span, nid: hir::HirId, ty_opt: Option<LocalTy<'tcx>>) -> Ty<'tcx> {
@@ -88,13 +93,29 @@ impl<'a, 'tcx> Visitor<'tcx> for GatherLocalsVisitor<'a, 'tcx> {
         intravisit::walk_local(self, local);
     }
 
+    fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
+        let old_outermost_fn_param_pat = mem::replace(&mut self.outermost_fn_param_pat, true);
+        intravisit::walk_param(self, param);
+        self.outermost_fn_param_pat = old_outermost_fn_param_pat;
+    }
+
     // Add pattern bindings.
     fn visit_pat(&mut self, p: &'tcx hir::Pat<'tcx>) {
         if let PatKind::Binding(_, _, ident, _) = p.kind {
             let var_ty = self.assign(p.span, p.hir_id, None);
 
-            if !self.fcx.tcx.features().unsized_locals {
-                self.fcx.require_type_is_sized(var_ty, p.span, traits::VariableType(p.hir_id));
+            if self.outermost_fn_param_pat {
+                if !self.fcx.tcx.features().unsized_fn_params {
+                    self.fcx.require_type_is_sized(
+                        var_ty,
+                        p.span,
+                        traits::SizedArgumentType(Some(p.span)),
+                    );
+                }
+            } else {
+                if !self.fcx.tcx.features().unsized_locals {
+                    self.fcx.require_type_is_sized(var_ty, p.span, traits::VariableType(p.hir_id));
+                }
             }
 
             debug!(
@@ -104,7 +125,9 @@ impl<'a, 'tcx> Visitor<'tcx> for GatherLocalsVisitor<'a, 'tcx> {
                 var_ty
             );
         }
+        let old_outermost_fn_param_pat = mem::replace(&mut self.outermost_fn_param_pat, false);
         intravisit::walk_pat(self, p);
+        self.outermost_fn_param_pat = old_outermost_fn_param_pat;
     }
 
     // Don't descend into the bodies of nested closures.

library/alloc/src/lib.rs

@@ -130,7 +130,8 @@
 #![feature(unicode_internals)]
 #![feature(unsafe_block_in_unsafe_fn)]
 #![feature(unsize)]
-#![feature(unsized_locals)]
+#![cfg_attr(not(bootstrap), feature(unsized_fn_params))]
+#![cfg_attr(bootstrap, feature(unsized_locals))]
 #![feature(allocator_internals)]
 #![feature(slice_partition_dedup)]
 #![feature(maybe_uninit_extra, maybe_uninit_slice, maybe_uninit_uninit_array)]

library/core/src/lib.rs

@@ -132,7 +132,8 @@
 #![feature(transparent_unions)]
 #![feature(try_blocks)]
 #![feature(unboxed_closures)]
-#![feature(unsized_locals)]
+#![cfg_attr(not(bootstrap), feature(unsized_fn_params))]
+#![cfg_attr(bootstrap, feature(unsized_locals))]
 #![cfg_attr(bootstrap, feature(untagged_unions))]
 #![feature(unwind_attributes)]
 #![feature(variant_count)]