Auto merge of #67866 - GuillaumeGomez:rollup-32vsg5b, r=GuillaumeGomez

Rollup of 4 pull requests

Successful merges:

 - #67822 (Revert `const_err` lint checking of casts)
 - #67823 (improve some `Drop`-related error messages)
 - #67837 (Clean up err codes)
 - #67848 (Remove unused `#[link_name = "m"]` attributes)

Failed merges:

r? @ghost

Author: bors

src/librustc_error_codes/error_codes/E0136.md

@@ -1,5 +1,4 @@
-A binary can only have one entry point, and by default that entry point is the
-function `main()`. If there are multiple such functions, please rename one.
+More than one `main` function was found.
 
 Erroneous code example:
 
@@ -14,3 +13,7 @@ fn main() { // error!
     // ...
 }
 ```
+
+A binary can only have one entry point, and by default that entry point is the
+`main()` function. If there are multiple instances of this function, please
+rename one of them.

src/librustc_error_codes/error_codes/E0161.md

@@ -1,5 +1,4 @@
-A value was moved. However, its size was not known at compile time, and only
-values of a known size can be moved.
+A value was moved whose size was not known at compile time.
 
 Erroneous code example:
 

src/librustc_error_codes/error_codes/E0164.md

@@ -1,24 +1,44 @@
-This error means that an attempt was made to match a struct type enum
-variant as a non-struct type:
+Something which is neither a tuple struct nor a tuple variant was used as a
+pattern.
+
+Erroneous code example:
 
 ```compile_fail,E0164
-enum Foo { B { i: u32 } }
+enum A {
+    B,
+    C,
+}
+
+impl A {
+    fn new() {}
+}
 
-fn bar(foo: Foo) -> u32 {
+fn bar(foo: A) {
     match foo {
-        Foo::B(i) => i, // error E0164
+        A::new() => (), // error!
+        _ => {}
     }
 }
 ```
 
-Try using `{}` instead:
+This error means that an attempt was made to match something which is neither a
+tuple struct nor a tuple variant. Only these two elements are allowed as a
+pattern:
 
 ```
-enum Foo { B { i: u32 } }
+enum A {
+    B,
+    C,
+}
+
+impl A {
+    fn new() {}
+}
 
-fn bar(foo: Foo) -> u32 {
+fn bar(foo: A) {
     match foo {
-        Foo::B{i} => i,
+        A::B => (), // ok!
+        _ => {}
     }
 }
 ```

src/librustc_mir/transform/const_prop.rs

@@ -12,10 +12,10 @@ use rustc::mir::visit::{
     MutVisitor, MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor,
 };
 use rustc::mir::{
-    read_only, AggregateKind, BasicBlock, BinOp, Body, BodyAndCache, CastKind, ClearCrossCrate,
-    Constant, Local, LocalDecl, LocalKind, Location, Operand, Place, PlaceBase,
-    ReadOnlyBodyAndCache, Rvalue, SourceInfo, SourceScope, SourceScopeData, Statement,
-    StatementKind, Terminator, TerminatorKind, UnOp, RETURN_PLACE,
+    read_only, AggregateKind, BasicBlock, BinOp, Body, BodyAndCache, ClearCrossCrate, Constant,
+    Local, LocalDecl, LocalKind, Location, Operand, Place, PlaceBase, ReadOnlyBodyAndCache, Rvalue,
+    SourceInfo, SourceScope, SourceScopeData, Statement, StatementKind, Terminator, TerminatorKind,
+    UnOp, RETURN_PLACE,
 };
 use rustc::ty::layout::{
     HasDataLayout, HasTyCtxt, LayoutError, LayoutOf, Size, TargetDataLayout, TyLayout,
@@ -29,9 +29,9 @@ use syntax::ast::Mutability;
 
 use crate::const_eval::error_to_const_error;
 use crate::interpret::{
-    self, intern_const_alloc_recursive, truncate, AllocId, Allocation, Frame, ImmTy, Immediate,
-    InterpCx, LocalState, LocalValue, Memory, MemoryKind, OpTy, Operand as InterpOperand, PlaceTy,
-    Pointer, ScalarMaybeUndef, StackPopCleanup,
+    self, intern_const_alloc_recursive, AllocId, Allocation, Frame, ImmTy, Immediate, InterpCx,
+    LocalState, LocalValue, Memory, MemoryKind, OpTy, Operand as InterpOperand, PlaceTy, Pointer,
+    ScalarMaybeUndef, StackPopCleanup,
 };
 use crate::rustc::ty::subst::Subst;
 use crate::transform::{MirPass, MirSource};
@@ -539,57 +539,6 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
         Some(())
     }
 
-    fn check_cast(
-        &mut self,
-        op: &Operand<'tcx>,
-        ty: Ty<'tcx>,
-        source_info: SourceInfo,
-        place_layout: TyLayout<'tcx>,
-    ) -> Option<()> {
-        if !ty.is_integral() || !op.ty(&self.local_decls, self.tcx).is_integral() {
-            return Some(());
-        }
-
-        let value = self.use_ecx(source_info, |this| {
-            this.ecx.read_immediate(this.ecx.eval_operand(op, None)?)
-        })?;
-
-        // Do not try to read bits for ZSTs. This can occur when casting an enum with one variant
-        // to an integer. Such enums are represented as ZSTs but still have a discriminant value
-        // which can be casted.
-        if value.layout.is_zst() {
-            return Some(());
-        }
-
-        let value_size = value.layout.size;
-        let value_bits = value.to_scalar().and_then(|r| r.to_bits(value_size));
-        if let Ok(value_bits) = value_bits {
-            let truncated = truncate(value_bits, place_layout.size);
-            if truncated != value_bits {
-                let scope = source_info.scope;
-                let lint_root = match &self.source_scopes[scope].local_data {
-                    ClearCrossCrate::Set(data) => data.lint_root,
-                    ClearCrossCrate::Clear => return None,
-                };
-                self.tcx.lint_hir(
-                    ::rustc::lint::builtin::CONST_ERR,
-                    lint_root,
-                    source_info.span,
-                    &format!(
-                        "truncating cast: the value {} requires {} bits but the target type is \
-                                          only {} bits",
-                        value_bits,
-                        value_size.bits(),
-                        place_layout.size.bits()
-                    ),
-                );
-                return None;
-            }
-        }
-
-        Some(())
-    }
-
     fn const_prop(
         &mut self,
         rvalue: &Rvalue<'tcx>,
@@ -651,11 +600,6 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                 }
             }
 
-            Rvalue::Cast(CastKind::Misc, op, ty) => {
-                trace!("checking Cast(Misc, {:?}, {:?})", op, ty);
-                self.check_cast(op, ty, source_info, place_layout)?;
-            }
-
             _ => {}
         }
 

src/librustc_typeck/check/dropck.rs

@@ -47,7 +47,6 @@ pub fn check_drop_impl(tcx: TyCtxt<'_>, drop_impl_did: DefId) -> Result<(), Erro
 
             ensure_drop_predicates_are_implied_by_item_defn(
                 tcx,
-                drop_impl_did,
                 dtor_predicates,
                 adt_def.did,
                 self_to_impl_substs,
@@ -95,16 +94,23 @@ fn ensure_drop_params_and_item_params_correspond<'tcx>(
             }
             Err(_) => {
                 let item_span = tcx.def_span(self_type_did);
+                let self_descr = tcx
+                    .def_kind(self_type_did)
+                    .map(|kind| kind.descr(self_type_did))
+                    .unwrap_or("type");
                 struct_span_err!(
                     tcx.sess,
                     drop_impl_span,
                     E0366,
-                    "Implementations of Drop cannot be specialized"
+                    "`Drop` impls cannot be specialized"
                 )
                 .span_note(
                     item_span,
-                    "Use same sequence of generic type and region \
-                     parameters that is on the struct/enum definition",
+                    &format!(
+                        "use the same sequence of generic type, lifetime and const parameters \
+                        as the {} definition",
+                        self_descr,
+                    ),
                 )
                 .emit();
                 return Err(ErrorReported);
@@ -143,7 +149,6 @@ fn ensure_drop_params_and_item_params_correspond<'tcx>(
 /// implied by assuming the predicates attached to self_type_did.
 fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
     tcx: TyCtxt<'tcx>,
-    drop_impl_did: DefId,
     dtor_predicates: ty::GenericPredicates<'tcx>,
     self_type_did: DefId,
     self_to_impl_substs: SubstsRef<'tcx>,
@@ -187,8 +192,6 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
 
     let self_type_hir_id = tcx.hir().as_local_hir_id(self_type_did).unwrap();
 
-    let drop_impl_span = tcx.def_span(drop_impl_did);
-
     // We can assume the predicates attached to struct/enum definition
     // hold.
     let generic_assumptions = tcx.predicates_of(self_type_did);
@@ -205,7 +208,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
     // just to look for all the predicates directly.
 
     assert_eq!(dtor_predicates.parent, None);
-    for (predicate, _) in dtor_predicates.predicates {
+    for (predicate, predicate_sp) in dtor_predicates.predicates {
         // (We do not need to worry about deep analysis of type
         // expressions etc because the Drop impls are already forced
         // to take on a structure that is roughly an alpha-renaming of
@@ -241,18 +244,17 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
 
         if !assumptions_in_impl_context.iter().any(predicate_matches_closure) {
             let item_span = tcx.hir().span(self_type_hir_id);
+            let self_descr =
+                tcx.def_kind(self_type_did).map(|kind| kind.descr(self_type_did)).unwrap_or("type");
             struct_span_err!(
                 tcx.sess,
-                drop_impl_span,
+                *predicate_sp,
                 E0367,
-                "The requirement `{}` is added only by the Drop impl.",
-                predicate
-            )
-            .span_note(
-                item_span,
-                "The same requirement must be part of \
-                 the struct/enum definition",
+                "`Drop` impl requires `{}` but the {} it is implemented for does not",
+                predicate,
+                self_descr,
             )
+            .span_note(item_span, "the implementor must specify the same requirement")
             .emit();
             result = Err(ErrorReported);
         }

src/librustc_typeck/coherence/builtin.rs

@@ -13,7 +13,6 @@ use rustc::ty::util::CopyImplementationError;
 use rustc::ty::TypeFoldable;
 use rustc::ty::{self, Ty, TyCtxt};
 
-use hir::Node;
 use rustc::hir::def_id::DefId;
 use rustc::hir::{self, ItemKind};
 
@@ -51,35 +50,25 @@ impl<'tcx> Checker<'tcx> {
 }
 
 fn visit_implementation_of_drop(tcx: TyCtxt<'_>, impl_did: DefId) {
-    if let ty::Adt(..) = tcx.type_of(impl_did).kind {
-        /* do nothing */
-    } else {
-        // Destructors only work on nominal types.
-        if let Some(impl_hir_id) = tcx.hir().as_local_hir_id(impl_did) {
-            if let Some(Node::Item(item)) = tcx.hir().find(impl_hir_id) {
-                let span = match item.kind {
-                    ItemKind::Impl(.., ref ty, _) => ty.span,
-                    _ => item.span,
-                };
-                struct_span_err!(
-                    tcx.sess,
-                    span,
-                    E0120,
-                    "the Drop trait may only be implemented on \
-                                  structures"
-                )
-                .span_label(span, "implementing Drop requires a struct")
-                .emit();
-            } else {
-                bug!("didn't find impl in ast map");
-            }
-        } else {
-            bug!(
-                "found external impl of Drop trait on \
-                  something other than a struct"
-            );
-        }
+    // Destructors only work on nominal types.
+    if let ty::Adt(..) | ty::Error = tcx.type_of(impl_did).kind {
+        return;
     }
+
+    let impl_hir_id = tcx.hir().as_local_hir_id(impl_did).expect("foreign Drop impl on non-ADT");
+    let sp = match tcx.hir().expect_item(impl_hir_id).kind {
+        ItemKind::Impl(.., ty, _) => ty.span,
+        _ => bug!("expected Drop impl item"),
+    };
+
+    struct_span_err!(
+        tcx.sess,
+        sp,
+        E0120,
+        "the `Drop` trait may only be implemented for structs, enums, and unions",
+    )
+    .span_label(sp, "must be a struct, enum, or union")
+    .emit();
 }
 
 fn visit_implementation_of_copy(tcx: TyCtxt<'_>, impl_did: DefId) {

src/libstd/sys/unix/cmath.rs

@@ -2,7 +2,6 @@
 
 use libc::{c_double, c_float};
 
-#[link_name = "m"]
 extern "C" {
     pub fn acos(n: c_double) -> c_double;
     pub fn acosf(n: c_float) -> c_float;

src/libstd/sys/vxworks/cmath.rs

@@ -2,7 +2,6 @@
 
 use libc::{c_double, c_float};
 
-#[link_name = "m"]
 extern "C" {
     pub fn acos(n: c_double) -> c_double;
     pub fn acosf(n: c_float) -> c_float;

src/libstd/sys/windows/cmath.rs

@@ -2,7 +2,6 @@
 
 use libc::{c_double, c_float};
 
-#[link_name = "m"]
 extern "C" {
     pub fn acos(n: c_double) -> c_double;
     pub fn asin(n: c_double) -> c_double;

src/test/ui/consts/const-prop-overflowing-casts.rs

@@ -1,9 +1,15 @@
-// build-fail
-// ignore-tidy-linelength
+// check-pass
+
+enum Foo {
+    Bar = -42,
+    Baz = 42,
+}
 
 fn main() {
     let _ = 0u8 as u32;
-    let _ = (1u32 << 31) as u16; //~ ERROR truncating cast: the value 2147483648 requires 32 bits but the target type is only 16 bits
-    let _ = (1u16 << 15) as u8; //~ ERROR truncating cast: the value 32768 requires 16 bits but the target type is only 8 bits
-    let _ = (!0u16) as u8; //~ ERROR truncating cast: the value 65535 requires 16 bits but the target type is only 8 bits
+    let _ = (1u32 << 31) as u16;
+    let _ = (1u16 << 15) as u8;
+    let _ = (!0u16) as u8;
+    let _ = (-1i16) as i8;
+    let _ = (Foo::Bar) as i8;
 }