Add unsized_fn_params feature

Author: spastorino

src/liballoc/lib.rs

@@ -118,6 +118,7 @@
 #![feature(unboxed_closures)]
 #![feature(unicode_internals)]
 #![feature(unsize)]
+#![cfg_attr(not(bootstrap), feature(unsized_fn_params))]
 #![feature(unsized_locals)]
 #![feature(allocator_internals)]
 #![feature(slice_partition_dedup)]

src/libcore/lib.rs

@@ -117,6 +117,7 @@
 #![feature(track_caller)]
 #![feature(transparent_unions)]
 #![feature(unboxed_closures)]
+#![cfg_attr(not(bootstrap), feature(unsized_fn_params))]
 #![feature(unsized_locals)]
 #![feature(untagged_unions)]
 #![feature(unwind_attributes)]

src/librustc_feature/active.rs

@@ -571,6 +571,9 @@ declare_features! (
     /// Allows the use of `#[ffi_const]` on foreign functions.
     (active, ffi_const, "1.45.0", Some(58328), None),
 
+    /// Allows unsized fn parameters.
+    (active, unsized_fn_params, "1.45.0", Some(48055), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

src/librustc_mir/borrow_check/type_check/mod.rs

@@ -1729,7 +1729,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
 
                 // When `#![feature(unsized_locals)]` is not enabled,
                 // this check is done at `check_local`.
-                if self.tcx().features().unsized_locals {
+                if self.tcx().features().unsized_fn_params {
                     let span = term.source_info.span;
                     self.ensure_place_sized(dest_ty, span);
                 }

src/librustc_mir_build/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;

src/librustc_span/symbol.rs

@@ -807,6 +807,7 @@ symbols! {
         unreachable_code,
         unrestricted_attribute_tokens,
         unsafe_no_drop_flag,
+        unsized_fn_params,
         unsized_locals,
         unsized_tuple_coercion,
         unstable,

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -1749,8 +1749,8 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             }
             ObligationCauseCode::SizedArgumentType => {
                 err.note("all function arguments must have a statically known size");
-                if !self.tcx.features().unsized_locals {
-                    err.help("unsized locals are gated as an unstable feature");
+                if !self.tcx.features().unsized_fn_params {
+                    err.help("unsized fn params are gated as an unstable feature");
                 }
             }
             ObligationCauseCode::SizedReturnType => {

src/librustc_typeck/check/expr.rs

@@ -486,7 +486,7 @@ 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

src/librustc_typeck/check/mod.rs

@@ -1053,7 +1053,8 @@ fn typeck_tables_of_with_fallback<'tcx>(
             };
 
             // Gather locals in statics (because of block expressions).
-            GatherLocalsVisitor { fcx: &fcx, parent_id: id }.visit_body(body);
+            GatherLocalsVisitor { fcx: &fcx, parent_id: id, within_fn_param: false }
+                .visit_body(body);
 
             fcx.check_expr_coercable_to_type(&body.value, revealed_ty);
 
@@ -1156,6 +1157,10 @@ fn check_abi(tcx: TyCtxt<'_>, span: Span, abi: Abi) {
 struct GatherLocalsVisitor<'a, 'tcx> {
     fcx: &'a FnCtxt<'a, 'tcx>,
     parent_id: hir::HirId,
+    // params are special cases of pats, but we want to handle them as
+    // *distinct* cases. so track when we are hitting a pat *within* an fn
+    // param.
+    within_fn_param: bool,
 }
 
 impl<'a, 'tcx> GatherLocalsVisitor<'a, 'tcx> {
@@ -1226,13 +1231,25 @@ impl<'a, 'tcx> Visitor<'tcx> for GatherLocalsVisitor<'a, 'tcx> {
         intravisit::walk_local(self, local);
     }
 
+    fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
+        self.within_fn_param = true;
+        intravisit::walk_param(self, param);
+        self.within_fn_param = false;
+    }
+
     // 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.within_fn_param {
+                if !self.fcx.tcx.features().unsized_fn_params {
+                    self.fcx.require_type_is_sized(var_ty, p.span, traits::SizedArgumentType);
+                }
+            } else {
+                if !self.fcx.tcx.features().unsized_locals {
+                    self.fcx.require_type_is_sized(var_ty, p.span, traits::VariableType(p.hir_id));
+                }
             }
 
             debug!(
@@ -1332,7 +1349,8 @@ fn check_fn<'a, 'tcx>(
 
     let outer_def_id = tcx.closure_base_def_id(hir.local_def_id(fn_id).to_def_id());
     let outer_hir_id = hir.as_local_hir_id(outer_def_id.expect_local());
-    GatherLocalsVisitor { fcx: &fcx, parent_id: outer_hir_id }.visit_body(body);
+    GatherLocalsVisitor { fcx: &fcx, parent_id: outer_hir_id, within_fn_param: false }
+        .visit_body(body);
 
     // C-variadic fns also have a `VaList` input that's not listed in `fn_sig`
     // (as it's created inside the body itself, not passed in from outside).
@@ -1360,7 +1378,7 @@ 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);
         }
 

src/test/run-pass-valgrind/unsized-locals/long-live-the-unsized-temporary.rs

@@ -1,4 +1,5 @@
-#![feature(unsized_locals)]
+#![allow(incomplete_features)]
+#![feature(unsized_locals, unsized_fn_params)]
 
 use std::fmt;
 
@@ -45,11 +46,7 @@ fn main() {
 
     {
         let x: fmt::Display = *gen_foo();
-        let x = if true {
-            x
-        } else {
-            *gen_foo()
-        };
+        let x = if true { x } else { *gen_foo() };
         foo(x);
     }
 }