Separate unsized fn params from unsized locals

library/alloc/src/lib.rs

@@ -121,7 +121,8 @@
 #![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)]

library/core/src/lib.rs

@@ -122,7 +122,8 @@
 #![feature(stmt_expr_attributes)]
 #![feature(transparent_unions)]
 #![feature(unboxed_closures)]
-#![feature(unsized_locals)]
+#![cfg_attr(not(bootstrap), feature(unsized_fn_params))]
+#![cfg_attr(bootstrap, feature(unsized_locals))]
 #![feature(untagged_unions)]
 #![feature(unwind_attributes)]
 #![feature(variant_count)]

src/doc/unstable-book/src/language-features/unsized-locals.md

@@ -11,7 +11,8 @@ This implements [RFC1909]. When turned on, you can have unsized arguments and lo
 [RFC1909]: https://github.com/rust-lang/rfcs/blob/master/text/1909-unsized-rvalues.md
 
 ```rust
-#![feature(unsized_locals)]
+#![allow(incomplete_features)]
+#![feature(unsized_locals, unsized_fn_params)]
 
 use std::any::Any;
 
@@ -85,7 +86,7 @@ fn main() {
 With this feature, you can have by-value `self` arguments without `Self: Sized` bounds.
 
 ```rust
-#![feature(unsized_locals)]
+#![feature(unsized_fn_params)]
 
 trait Foo {
     fn foo(self) {}
@@ -102,7 +103,7 @@ fn main() {
 And `Foo` will also be object-safe.
 
 ```rust
-#![feature(unsized_locals)]
+#![feature(unsized_fn_params)]
 
 trait Foo {
     fn foo(self) {}

src/librustc_feature/active.rs

@@ -579,6 +579,9 @@ declare_features! (
     /// Alloc calling `transmute` in const fn
     (active, const_fn_transmute, "1.46.0", Some(53605), None),
 
+    /// Allows unsized fn parameters.
+    (active, unsized_fn_params, "1.47.0", Some(48055), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------
@@ -597,4 +600,5 @@ pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::const_trait_bound_opt_out,
     sym::lazy_normalization_consts,
     sym::specialization,
+    sym::unsized_locals,
 ];

src/librustc_mir/borrow_check/type_check/mod.rs

@@ -1472,7 +1472,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 }
 
                 self.check_rvalue(body, rv, location);
-                if !self.tcx().features().unsized_locals {
+                if !(self.tcx().features().unsized_locals
+                    || self.tcx().features().unsized_fn_params)
+                {
                     let trait_ref = ty::TraitRef {
                         def_id: tcx.require_lang_item(SizedTraitLangItem, Some(self.last_span)),
                         substs: tcx.mk_substs_trait(place_ty, &[]),
@@ -1732,9 +1734,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     );
                 }
 
-                // When `#![feature(unsized_locals)]` is not enabled,
+                // When `unsized_fn_params` or `unsized_locals` is not enabled,
                 // this check is done at `check_local`.
-                if self.tcx().features().unsized_locals {
+                if self.tcx().features().unsized_locals || self.tcx().features().unsized_fn_params {
                     let span = term.source_info.span;
                     self.ensure_place_sized(dest_ty, span);
                 }
@@ -1895,9 +1897,9 @@ 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.tcx().features().unsized_locals || self.tcx().features().unsized_fn_params) {
             let span = local_decl.source_info.span;
             let ty = local_decl.ty;
             self.ensure_place_sized(ty, span);
@@ -2043,7 +2045,7 @@ 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.tcx().features().unsized_locals || self.tcx().features().unsized_fn_params {
                     let span = body.source_info(location).span;
                     self.ensure_place_sized(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

@@ -1144,6 +1144,7 @@ symbols! {
         unsafe_cell,
         unsafe_no_drop_flag,
         unsize,
+        unsized_fn_params,
         unsized_locals,
         unsized_tuple_coercion,
         unstable,

src/librustc_trait_selection/traits/error_reporting/suggestions.rs

@@ -1833,9 +1833,9 @@ 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 => {

src/librustc_typeck/check/expr.rs

@@ -464,7 +464,7 @@ 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

@@ -1051,7 +1051,8 @@ fn typeck_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, None);
 
@@ -1154,6 +1155,10 @@ 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> {
@@ -1228,13 +1233,25 @@ 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(None));
+                }
+            } else {
+                if !self.fcx.tcx.features().unsized_locals {
+                    self.fcx.require_type_is_sized(var_ty, p.span, traits::VariableType(p.hir_id));
+                }
             }
 
             debug!(
@@ -1334,7 +1351,8 @@ fn check_fn<'a, 'tcx>(
 
     let outer_def_id = tcx.closure_base_def_id(hir.local_def_id(fn_id).to_def_id()).expect_local();
     let outer_hir_id = hir.as_local_hir_id(outer_def_id);
-    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(ty_span));
         }
 

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);
     }
 }

src/test/ui/async-await/issue-72590-type-error-sized.stderr

@@ -18,11 +18,8 @@ LL |     async fn frob(self) {}
    |
    = help: within `Foo`, the trait `std::marker::Sized` is not implemented for `str`
    = note: required because it appears within the type `Foo`
-   = help: unsized locals are gated as an unstable feature
-help: function arguments must have a statically known size, borrowed types always have a known size
-   |
-LL |     async fn frob(&self) {}
-   |                   ^
+   = note: all function arguments must have a statically known size
+   = help: unsized fn params are gated as an unstable feature
 
 error: aborting due to 3 previous errors
 

src/test/ui/error-codes/E0161.rs

@@ -9,13 +9,13 @@
 //[zflagsul]compile-flags: -Z borrowck=migrate
 //[editionul]edition:2018
 
+#![allow(incomplete_features)]
 #![cfg_attr(nll, feature(nll))]
 #![cfg_attr(nllul, feature(nll))]
 #![cfg_attr(migrateul, feature(unsized_locals))]
 #![cfg_attr(zflagsul, feature(unsized_locals))]
 #![cfg_attr(nllul, feature(unsized_locals))]
 #![cfg_attr(editionul, feature(unsized_locals))]
-
 #![feature(box_syntax)]
 
 fn foo(x: Box<[i32]>) {

src/test/ui/error-codes/E0277.stderr

@@ -6,11 +6,8 @@ LL | fn f(p: Path) { }
    |
    = help: within `std::path::Path`, the trait `std::marker::Sized` is not implemented for `[u8]`
    = note: required because it appears within the type `std::path::Path`
-   = help: unsized locals are gated as an unstable feature
-help: function arguments must have a statically known size, borrowed types always have a known size
-   |
-LL | fn f(p: &Path) { }
-   |         ^
+   = note: all function arguments must have a statically known size
+   = help: unsized fn params are gated as an unstable feature
 
 error[E0277]: the trait bound `i32: Foo` is not satisfied
   --> $DIR/E0277.rs:17:15

src/test/ui/feature-gates/feature-gate-unsized_fn_params.rs

@@ -0,0 +1,26 @@
+#[repr(align(256))]
+#[allow(dead_code)]
+struct A {
+    v: u8,
+}
+
+trait Foo {
+    fn foo(&self);
+}
+
+impl Foo for A {
+    fn foo(&self) {
+        assert_eq!(self as *const A as usize % 256, 0);
+    }
+}
+
+fn foo(x: dyn Foo) {
+    //~^ ERROR [E0277]
+    x.foo()
+}
+
+fn main() {
+    let x: Box<dyn Foo> = Box::new(A { v: 22 });
+    foo(*x);
+    //~^ ERROR [E0277]
+}

src/test/ui/feature-gates/feature-gate-unsized_fn_params.stderr

@@ -0,0 +1,23 @@
+error[E0277]: the size for values of type `(dyn Foo + 'static)` cannot be known at compilation time
+  --> $DIR/feature-gate-unsized_fn_params.rs:17:8
+   |
+LL | fn foo(x: dyn Foo) {
+   |        ^ doesn't have a size known at compile-time
+   |
+   = help: the trait `std::marker::Sized` is not implemented for `(dyn Foo + 'static)`
+   = note: all function arguments must have a statically known size
+   = help: unsized fn params are gated as an unstable feature
+
+error[E0277]: the size for values of type `(dyn Foo + 'static)` cannot be known at compilation time
+  --> $DIR/feature-gate-unsized_fn_params.rs:24:5
+   |
+LL |     foo(*x);
+   |     ^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `std::marker::Sized` is not implemented for `(dyn Foo + 'static)`
+   = note: all function arguments must have a statically known size
+   = help: unsized fn params are gated as an unstable feature
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/feature-gates/feature-gate-unsized_locals.stderr

@@ -5,11 +5,8 @@ LL | fn f(f: dyn FnOnce()) {}
    |      ^ doesn't have a size known at compile-time
    |
    = help: the trait `std::marker::Sized` is not implemented for `(dyn std::ops::FnOnce() + 'static)`
-   = help: unsized locals are gated as an unstable feature
-help: function arguments must have a statically known size, borrowed types always have a known size
-   |
-LL | fn f(f: &dyn FnOnce()) {}
-   |         ^
+   = note: all function arguments must have a statically known size
+   = help: unsized fn params are gated as an unstable feature
 
 error: aborting due to previous error
 

src/test/ui/fn/dyn-fn-alignment.rs

@@ -1,6 +1,5 @@
 // run-pass
 
-#![feature(unsized_locals)]
 #![allow(dead_code)]
 #[repr(align(256))]
 struct A {

src/test/ui/issues/issue-17651.stderr

@@ -15,7 +15,7 @@ LL |     (|| Box::new(*(&[0][..])))();
    |
    = help: the trait `std::marker::Sized` is not implemented for `[{integer}]`
    = note: all function arguments must have a statically known size
-   = help: unsized locals are gated as an unstable feature
+   = help: unsized fn params are gated as an unstable feature
 
 error: aborting due to 2 previous errors
 

src/test/ui/issues/issue-27078.stderr

@@ -4,15 +4,12 @@ error[E0277]: the size for values of type `Self` cannot be known at compilation
 LL |     fn foo(self) -> &'static i32 {
    |            ^^^^ doesn't have a size known at compile-time
    |
-   = help: unsized locals are gated as an unstable feature
+   = note: all function arguments must have a statically known size
+   = help: unsized fn params are gated as an unstable feature
 help: consider further restricting `Self`
    |
 LL |     fn foo(self) -> &'static i32 where Self: std::marker::Sized {
    |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-help: function arguments must have a statically known size, borrowed types always have a known size
-   |
-LL |     fn foo(&self) -> &'static i32 {
-   |            ^
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-30355.stderr

@@ -6,7 +6,7 @@ LL |     &X(*Y)
    |
    = help: the trait `std::marker::Sized` is not implemented for `[u8]`
    = note: all function arguments must have a statically known size
-   = help: unsized locals are gated as an unstable feature
+   = help: unsized fn params are gated as an unstable feature
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-38954.stderr

@@ -5,7 +5,7 @@ LL | fn _test(ref _p: str) {}
    |          ^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `std::marker::Sized` is not implemented for `str`
-   = help: unsized locals are gated as an unstable feature
+   = help: unsized fn params are gated as an unstable feature
 help: function arguments must have a statically known size, borrowed types always have a known size
    |
 LL | fn _test(ref _p: &str) {}