Auto merge of rust-lang#137298 - compiler-errors:mir-wf, r=<try>

Check signature WF when lowering MIR body

Alternative to rust-lang#137233.

rust-lang#137233 (comment)

Fixes rust-lang#137186

We do this check in `mir_drops_elaborated_and_const_checked` and not during `mir_promoted` because that may result in borrowck cycles if WF requires looking into an opaque hidden type. This causes some TAIT tests to fail unnecessarily.

r? lcnr

try-job: test-various

Author: bors

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -201,7 +201,7 @@ fn check_well_formed(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(), ErrorGua
         hir::Node::ImplItem(item) => check_impl_item(tcx, item),
         hir::Node::ForeignItem(item) => check_foreign_item(tcx, item),
         hir::Node::OpaqueTy(_) => Ok(crate::check::check::check_item_type(tcx, def_id)),
-        _ => unreachable!(),
+        _ => unreachable!("{node:?}"),
     };
 
     if let Some(generics) = node.generics() {
@@ -1108,7 +1108,13 @@ fn check_associated_item(
                 let ty = tcx.type_of(item.def_id).instantiate_identity();
                 let ty = wfcx.normalize(span, Some(WellFormedLoc::Ty(item_id)), ty);
                 wfcx.register_wf_obligation(span, loc, ty.into());
-                check_sized_if_body(wfcx, item.def_id.expect_local(), ty, Some(span));
+                check_sized_if_body(
+                    wfcx,
+                    item.def_id.expect_local(),
+                    ty,
+                    Some(span),
+                    ObligationCauseCode::SizedConstOrStatic,
+                );
                 Ok(())
             }
             ty::AssocKind::Fn => {
@@ -1354,7 +1360,7 @@ fn check_item_type(
                 traits::ObligationCause::new(
                     ty_span,
                     wfcx.body_def_id,
-                    ObligationCauseCode::WellFormed(None),
+                    ObligationCauseCode::SizedConstOrStatic,
                 ),
                 wfcx.param_env,
                 item_ty,
@@ -1698,6 +1704,7 @@ fn check_fn_or_method<'tcx>(
             hir::FnRetTy::Return(ty) => Some(ty.span),
             hir::FnRetTy::DefaultReturn(_) => None,
         },
+        ObligationCauseCode::SizedReturnType,
     );
 }
 
@@ -1706,13 +1713,14 @@ fn check_sized_if_body<'tcx>(
     def_id: LocalDefId,
     ty: Ty<'tcx>,
     maybe_span: Option<Span>,
+    code: ObligationCauseCode<'tcx>,
 ) {
     let tcx = wfcx.tcx();
     if let Some(body) = tcx.hir_maybe_body_owned_by(def_id) {
         let span = maybe_span.unwrap_or(body.value.span);
 
         wfcx.register_bound(
-            ObligationCause::new(span, def_id, traits::ObligationCauseCode::SizedReturnType),
+            ObligationCause::new(span, def_id, code),
             wfcx.param_env,
             ty,
             tcx.require_lang_item(LangItem::Sized, Some(span)),

compiler/rustc_hir_typeck/src/expr.rs

@@ -1810,7 +1810,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         crate::GatherLocalsVisitor::new(&fcx).visit_body(body);
 
         let ty = fcx.check_expr_with_expectation(body.value, expected);
-        fcx.require_type_is_sized(ty, body.value.span, ObligationCauseCode::ConstSized);
+        fcx.require_type_is_sized(ty, body.value.span, ObligationCauseCode::SizedConstOrStatic);
         fcx.write_ty(block.hir_id, ty);
         ty
     }

compiler/rustc_middle/src/traits/mod.rs

@@ -273,7 +273,7 @@ pub enum ObligationCauseCode<'tcx> {
     },
 
     /// Constant expressions must be sized.
-    ConstSized,
+    SizedConstOrStatic,
 
     /// `static` items must have `Sync` type.
     SharedStatic,

compiler/rustc_mir_transform/src/lib.rs

@@ -513,6 +513,24 @@ fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &
         body.tainted_by_errors = Some(error_reported);
     }
 
+    // Also taint the body if it's within a top-level item that is not well formed.
+    //
+    // We do this check here and not during `mir_promoted` because that may result
+    // in borrowck cycles if WF requires looking into an opaque hidden type.
+    let root = tcx.typeck_root_def_id(def.to_def_id());
+    match tcx.def_kind(root) {
+        DefKind::Fn
+        | DefKind::AssocFn
+        | DefKind::Static { .. }
+        | DefKind::Const
+        | DefKind::AssocConst => {
+            if let Err(guar) = tcx.check_well_formed(root.expect_local()) {
+                body.tainted_by_errors = Some(guar);
+            }
+        }
+        _ => {}
+    }
+
     run_analysis_to_runtime_passes(tcx, &mut body);
 
     tcx.alloc_steal_mir(body)

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

@@ -3125,8 +3125,8 @@ impl<'a, 'tcx> TypeErrCtxt<'a, 'tcx> {
                     Applicability::MachineApplicable,
                 );
             }
-            ObligationCauseCode::ConstSized => {
-                err.note("constant expressions must have a statically known size");
+            ObligationCauseCode::SizedConstOrStatic => {
+                err.note("statics and constants must have a statically known size");
             }
             ObligationCauseCode::InlineAsmSized => {
                 err.note("all inline asm arguments must have a statically known size");

tests/crashes/129095.rs

@@ -1,10 +1,13 @@
 //@ known-bug: rust-lang/rust#129095
 //@ compile-flags: -Zmir-enable-passes=+GVN -Zmir-enable-passes=+Inline -Zvalidate-mir
 
+#![feature(adt_const_params, unsized_const_params)]
+#![allow(incomplete_features)]
+
 pub fn function_with_bytes<const BYTES: &'static [u8; 4]>() -> &'static [u8] {
     BYTES
 }
 
 pub fn main() {
-    assert_eq!(function_with_bytes::<b"AAAAb">(), &[0x41, 0x41, 0x41, 0x41]);
+    assert_eq!(function_with_bytes::<b"AAAAA">(), &[0x41, 0x41, 0x41, 0x41]);
 }

tests/crashes/132960.rs

@@ -1,6 +1,6 @@
 //@ known-bug: #132960
 
-#![feature(adt_const_params, const_ptr_read, generic_const_exprs)]
+#![feature(adt_const_params, const_ptr_read, generic_const_exprs, unsized_const_params)]
 
 const fn concat_strs<const A: &'static str, const B: &'static str>() -> &'static str
 where

tests/crashes/134654.rs

@@ -2,6 +2,9 @@
 //@ compile-flags: -Zmir-enable-passes=+GVN -Zmir-enable-passes=+Inline -Zvalidate-mir
 //@ only-x86_64
 
+#![feature(adt_const_params, unsized_const_params)]
+#![allow(incomplete_features)]
+
 fn function_with_bytes<const BYTES:
     &'static [u8; 0xa9008fb6c9d81e42_0e25730562a601c8_u128]>() -> &'static [u8] {
     BYTES

tests/crashes/135128.rs

@@ -1,6 +1,8 @@
 //@ known-bug: #135128
 //@ compile-flags: -Copt-level=1 --edition=2021
 
+#![feature(trivial_bounds)]
+
 async fn return_str() -> str
 where
     str: Sized,

tests/crashes/135570.rs

@@ -2,6 +2,9 @@
 //@compile-flags: -Zvalidate-mir -Zmir-enable-passes=+Inline -Copt-level=0 -Zmir-enable-passes=+GVN
 //@ only-x86_64
 
+#![feature(adt_const_params, unsized_const_params)]
+#![allow(incomplete_features)]
+
 fn function_with_bytes<const BYTES: &'static [u8; 0xc7b889180b67b07d_bc1a3c88783d35b5_u128]>(
 ) -> &'static [u8] {
     BYTES

tests/ui/consts/const-slice-array-deref.stderr

@@ -5,6 +5,7 @@ LL | const ONE: [u16] = [1];
    |            ^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[u16]`
+   = note: statics and constants must have a statically known size
 
 error[E0308]: mismatched types
   --> $DIR/const-slice-array-deref.rs:1:20

tests/ui/consts/const-unsized.stderr

@@ -5,6 +5,7 @@ LL | const CONST_0: dyn Debug + Sync = *(&0 as &(dyn Debug + Sync));
    |                ^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `(dyn Debug + Sync + 'static)`
+   = note: statics and constants must have a statically known size
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
   --> $DIR/const-unsized.rs:7:18
@@ -13,6 +14,7 @@ LL | const CONST_FOO: str = *"foo";
    |                  ^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
+   = note: statics and constants must have a statically known size
 
 error[E0277]: the size for values of type `(dyn Debug + Sync + 'static)` cannot be known at compilation time
   --> $DIR/const-unsized.rs:11:18
@@ -21,6 +23,7 @@ LL | static STATIC_1: dyn Debug + Sync = *(&1 as &(dyn Debug + Sync));
    |                  ^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `(dyn Debug + Sync + 'static)`
+   = note: statics and constants must have a statically known size
 
 error[E0277]: the size for values of type `str` cannot be known at compilation time
   --> $DIR/const-unsized.rs:15:20
@@ -29,6 +32,7 @@ LL | static STATIC_BAR: str = *"bar";
    |                    ^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `str`
+   = note: statics and constants must have a statically known size
 
 error[E0507]: cannot move out of a shared reference
   --> $DIR/const-unsized.rs:3:35

tests/ui/consts/const_refs_to_static-ice-121413.stderr

@@ -30,6 +30,7 @@ LL |     static FOO: Sync = AtomicUsize::new(0);
    |                 ^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `(dyn Sync + 'static)`
+   = note: statics and constants must have a statically known size
 
 error: aborting due to 2 previous errors; 1 warning emitted
 

tests/ui/consts/dont-ctfe-unsized-initializer.rs

@@ -0,0 +1,7 @@
+static S: str = todo!();
+//~^ ERROR the size for values of type `str` cannot be known at compilation time
+
+const C: str = todo!();
+//~^ ERROR the size for values of type `str` cannot be known at compilation time
+
+fn main() {}

tests/ui/consts/dont-ctfe-unsized-initializer.stderr

@@ -0,0 +1,21 @@
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/dont-ctfe-unsized-initializer.rs:1:11
+   |
+LL | static S: str = todo!();
+   |           ^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `str`
+   = note: statics and constants must have a statically known size
+
+error[E0277]: the size for values of type `str` cannot be known at compilation time
+  --> $DIR/dont-ctfe-unsized-initializer.rs:4:10
+   |
+LL | const C: str = todo!();
+   |          ^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `str`
+   = note: statics and constants must have a statically known size
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/extern/issue-36122-accessing-externed-dst.stderr

@@ -5,6 +5,7 @@ LL |         static symbol: [usize];
    |                        ^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[usize]`
+   = note: statics and constants must have a statically known size
 
 error[E0133]: use of extern static is unsafe and requires unsafe function or block
   --> $DIR/issue-36122-accessing-externed-dst.rs:5:20

tests/ui/issues/issue-54410.stderr

@@ -5,6 +5,7 @@ LL |     pub static mut symbol: [i8];
    |                            ^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `[i8]`
+   = note: statics and constants must have a statically known size
 
 error: aborting due to 1 previous error
 

tests/ui/static/issue-24446.stderr

@@ -14,6 +14,7 @@ LL |     static foo: dyn Fn() -> u32 = || -> u32 {
    |                 ^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `(dyn Fn() -> u32 + 'static)`
+   = note: statics and constants must have a statically known size
 
 error[E0308]: mismatched types
   --> $DIR/issue-24446.rs:2:35

tests/ui/statics/unsized_type2.stderr

@@ -10,6 +10,7 @@ note: required because it appears within the type `Foo`
    |
 LL | pub struct Foo {
    |            ^^^
+   = note: statics and constants must have a statically known size
 
 error[E0308]: mismatched types
   --> $DIR/unsized_type2.rs:14:45

tests/ui/trait-bounds/ice-unsized-tuple-const-issue-121443.stderr

@@ -11,6 +11,7 @@ LL | const TEST: Fn = some_fn;
    |             ^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `(dyn FnOnce() -> u8 + 'static)`
+   = note: statics and constants must have a statically known size
 
 error[E0277]: the size for values of type `(dyn FnOnce() -> u8 + 'static)` cannot be known at compilation time
   --> $DIR/ice-unsized-tuple-const-issue-121443.rs:11:14