Auto merge of rust-lang#64616 - Centril:rollup-du6728f, r=Centril

Rollup of 6 pull requests

Successful merges:

 - rust-lang#63448 (fix Miri discriminant handling)
 - rust-lang#64592 (Point at original span when emitting unreachable lint)
 - rust-lang#64601 (Fix backticks in documentation)
 - rust-lang#64606 (Remove unnecessary `mut` in doc example)
 - rust-lang#64611 (rustbuild: Don't package libstd twice)
 - rust-lang#64613 (rustbuild: Copy crate doc files fewer times)

Failed merges:

r? @ghost

Author: bors

src/bootstrap/dist.rs

@@ -762,7 +762,7 @@ impl Step for Analysis {
             return distdir(builder).join(format!("{}-{}.tar.gz", name, target));
         }
 
-        builder.ensure(Std { compiler, target });
+        builder.ensure(compile::Std { compiler, target });
 
         let image = tmpdir(builder).join(format!("{}-{}-image", name, target));
 

src/bootstrap/doc.rs

@@ -476,11 +476,11 @@ impl Step for Std {
                  .arg("--index-page").arg(&builder.src.join("src/doc/index.md"));
 
             builder.run(&mut cargo);
-            builder.cp_r(&my_out, &out);
         };
         for krate in &["alloc", "core", "std", "proc_macro", "test"] {
             run_cargo_rustdoc_for(krate);
         }
+        builder.cp_r(&my_out, &out);
     }
 }
 

src/librustc/middle/region.rs

@@ -1136,7 +1136,7 @@ fn resolve_local<'tcx>(
     // Rule A. `let (ref x, ref y) = (foo().x, 44)`. The rvalue `(22, 44)`
     // would have an extended lifetime, but not `foo()`.
     //
-    // Rule B. `let x = &foo().x`. The rvalue ``foo()` would have extended
+    // Rule B. `let x = &foo().x`. The rvalue `foo()` would have extended
     // lifetime.
     //
     // In some cases, multiple rules may apply (though not to the same

src/librustc/ty/layout.rs

@@ -127,6 +127,7 @@ impl IntegerExt for Integer {
 
 pub trait PrimitiveExt {
     fn to_ty<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx>;
+    fn to_int_ty<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx>;
 }
 
 impl PrimitiveExt for Primitive {
@@ -138,6 +139,16 @@ impl PrimitiveExt for Primitive {
             Pointer => tcx.mk_mut_ptr(tcx.mk_unit()),
         }
     }
+
+    /// Return an *integer* type matching this primitive.
+    /// Useful in particular when dealing with enum discriminants.
+    fn to_int_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
+        match *self {
+            Int(i, signed) => i.to_ty(tcx, signed),
+            Pointer => tcx.types.usize,
+            Float(..) => bug!("floats do not have an int type"),
+        }
+    }
 }
 
 /// The first half of a fat pointer.

src/librustc/ty/query/on_disk_cache.rs

@@ -643,7 +643,7 @@ impl<'a, 'tcx> SpecializedDecoder<DefIndex> for CacheDecoder<'a, 'tcx> {
 
 // Both the `CrateNum` and the `DefIndex` of a `DefId` can change in between two
 // compilation sessions. We use the `DefPathHash`, which is stable across
-// sessions, to map the old DefId`` to the new one.
+// sessions, to map the old `DefId` to the new one.
 impl<'a, 'tcx> SpecializedDecoder<DefId> for CacheDecoder<'a, 'tcx> {
     #[inline]
     fn specialized_decode(&mut self) -> Result<DefId, Self::Error> {

src/librustc_mir/interpret/operand.rs

@@ -1,11 +1,11 @@
 //! Functions concerning immediate values and operands, and reading from operands.
 //! All high-level functions to read from memory work on operands as sources.
 
-use std::convert::TryInto;
+use std::convert::{TryInto, TryFrom};
 
 use rustc::{mir, ty};
 use rustc::ty::layout::{
-    self, Size, LayoutOf, TyLayout, HasDataLayout, IntegerExt, VariantIdx,
+    self, Size, LayoutOf, TyLayout, HasDataLayout, IntegerExt, PrimitiveExt, VariantIdx,
 };
 
 use rustc::mir::interpret::{
@@ -609,15 +609,20 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
     ) -> InterpResult<'tcx, (u128, VariantIdx)> {
         trace!("read_discriminant_value {:#?}", rval.layout);
 
-        let (discr_kind, discr_index) = match rval.layout.variants {
+        let (discr_layout, discr_kind, discr_index) = match rval.layout.variants {
             layout::Variants::Single { index } => {
                 let discr_val = rval.layout.ty.discriminant_for_variant(*self.tcx, index).map_or(
                     index.as_u32() as u128,
                     |discr| discr.val);
                 return Ok((discr_val, index));
             }
-            layout::Variants::Multiple { ref discr_kind, discr_index, .. } =>
-                (discr_kind, discr_index),
+            layout::Variants::Multiple {
+                discr: ref discr_layout,
+                ref discr_kind,
+                discr_index,
+                ..
+            } =>
+                (discr_layout, discr_kind, discr_index),
         };
 
         // read raw discriminant value
@@ -634,7 +639,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     .map_err(|_| err_unsup!(InvalidDiscriminant(raw_discr.erase_tag())))?;
                 let real_discr = if discr_val.layout.ty.is_signed() {
                     // going from layout tag type to typeck discriminant type
-                    // requires first sign extending with the layout discriminant
+                    // requires first sign extending with the discriminant layout
                     let sexted = sign_extend(bits_discr, discr_val.layout.size) as i128;
                     // and then zeroing with the typeck discriminant type
                     let discr_ty = rval.layout.ty
@@ -666,8 +671,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 ref niche_variants,
                 niche_start,
             } => {
-                let variants_start = niche_variants.start().as_u32() as u128;
-                let variants_end = niche_variants.end().as_u32() as u128;
+                let variants_start = niche_variants.start().as_u32();
+                let variants_end = niche_variants.end().as_u32();
                 let raw_discr = raw_discr.not_undef().map_err(|_| {
                     err_unsup!(InvalidDiscriminant(ScalarMaybeUndef::Undef))
                 })?;
@@ -682,18 +687,34 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         (dataful_variant.as_u32() as u128, dataful_variant)
                     },
                     Ok(raw_discr) => {
-                        let adjusted_discr = raw_discr.wrapping_sub(niche_start)
-                            .wrapping_add(variants_start);
-                        if variants_start <= adjusted_discr && adjusted_discr <= variants_end {
-                            let index = adjusted_discr as usize;
-                            assert_eq!(index as u128, adjusted_discr);
-                            assert!(index < rval.layout.ty
+                        // We need to use machine arithmetic to get the relative variant idx:
+                        // variant_index_relative = discr_val - niche_start_val
+                        let discr_layout = self.layout_of(discr_layout.value.to_int_ty(*self.tcx))?;
+                        let discr_val = ImmTy::from_uint(raw_discr, discr_layout);
+                        let niche_start_val = ImmTy::from_uint(niche_start, discr_layout);
+                        let variant_index_relative_val = self.binary_op(
+                            mir::BinOp::Sub,
+                            discr_val,
+                            niche_start_val,
+                        )?;
+                        let variant_index_relative = variant_index_relative_val
+                            .to_scalar()?
+                            .assert_bits(discr_val.layout.size);
+                        // Check if this is in the range that indicates an actual discriminant.
+                        if variant_index_relative <= u128::from(variants_end - variants_start) {
+                            let variant_index_relative = u32::try_from(variant_index_relative)
+                                .expect("we checked that this fits into a u32");
+                            // Then computing the absolute variant idx should not overflow any more.
+                            let variant_index = variants_start
+                                .checked_add(variant_index_relative)
+                                .expect("oveflow computing absolute variant idx");
+                            assert!((variant_index as usize) < rval.layout.ty
                                 .ty_adt_def()
                                 .expect("tagged layout for non adt")
                                 .variants.len());
-                            (adjusted_discr, VariantIdx::from_usize(index))
+                            (u128::from(variant_index), VariantIdx::from_u32(variant_index))
                         } else {
-                            (dataful_variant.as_u32() as u128, dataful_variant)
+                            (u128::from(dataful_variant.as_u32()), dataful_variant)
                         }
                     },
                 }

src/librustc_mir/interpret/place.rs

@@ -8,7 +8,9 @@ use std::hash::Hash;
 use rustc::mir;
 use rustc::mir::interpret::truncate;
 use rustc::ty::{self, Ty};
-use rustc::ty::layout::{self, Size, Align, LayoutOf, TyLayout, HasDataLayout, VariantIdx};
+use rustc::ty::layout::{
+    self, Size, Align, LayoutOf, TyLayout, HasDataLayout, VariantIdx, PrimitiveExt
+};
 use rustc::ty::TypeFoldable;
 
 use super::{
@@ -1027,7 +1029,7 @@ where
             }
             layout::Variants::Multiple {
                 discr_kind: layout::DiscriminantKind::Tag,
-                ref discr,
+                discr: ref discr_layout,
                 discr_index,
                 ..
             } => {
@@ -1038,7 +1040,7 @@ where
                 // raw discriminants for enums are isize or bigger during
                 // their computation, but the in-memory tag is the smallest possible
                 // representation
-                let size = discr.value.size(self);
+                let size = discr_layout.value.size(self);
                 let discr_val = truncate(discr_val, size);
 
                 let discr_dest = self.place_field(dest, discr_index as u64)?;
@@ -1050,22 +1052,32 @@ where
                     ref niche_variants,
                     niche_start,
                 },
+                discr: ref discr_layout,
                 discr_index,
                 ..
             } => {
                 assert!(
                     variant_index.as_usize() < dest.layout.ty.ty_adt_def().unwrap().variants.len(),
                 );
                 if variant_index != dataful_variant {
-                    let niche_dest =
-                        self.place_field(dest, discr_index as u64)?;
-                    let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
-                    let niche_value = (niche_value as u128)
-                        .wrapping_add(niche_start);
-                    self.write_scalar(
-                        Scalar::from_uint(niche_value, niche_dest.layout.size),
-                        niche_dest
+                    let variants_start = niche_variants.start().as_u32();
+                    let variant_index_relative = variant_index.as_u32()
+                        .checked_sub(variants_start)
+                        .expect("overflow computing relative variant idx");
+                    // We need to use machine arithmetic when taking into account `niche_start`:
+                    // discr_val = variant_index_relative + niche_start_val
+                    let discr_layout = self.layout_of(discr_layout.value.to_int_ty(*self.tcx))?;
+                    let niche_start_val = ImmTy::from_uint(niche_start, discr_layout);
+                    let variant_index_relative_val =
+                        ImmTy::from_uint(variant_index_relative, discr_layout);
+                    let discr_val = self.binary_op(
+                        mir::BinOp::Add,
+                        variant_index_relative_val,
+                        niche_start_val,
                     )?;
+                    // Write result.
+                    let niche_dest = self.place_field(dest, discr_index as u64)?;
+                    self.write_immediate(*discr_val, niche_dest)?;
                 }
             }
         }

src/librustc_typeck/check/_match.rs

@@ -43,7 +43,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // If there are no arms, that is a diverging match; a special case.
         if arms.is_empty() {
-            self.diverges.set(self.diverges.get() | Diverges::Always);
+            self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
             return tcx.types.never;
         }
 
@@ -69,7 +69,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // warnings).
             match all_pats_diverge {
                 Diverges::Maybe => Diverges::Maybe,
-                Diverges::Always | Diverges::WarnedAlways => Diverges::WarnedAlways,
+                Diverges::Always { .. } | Diverges::WarnedAlways => Diverges::WarnedAlways,
             }
         }).collect();
 
@@ -167,6 +167,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             prior_arm_ty = Some(arm_ty);
         }
 
+        // If all of the arms in the `match` diverge,
+        // and we're dealing with an actual `match` block
+        // (as opposed to a `match` desugared from something else'),
+        // we can emit a better note. Rather than pointing
+        // at a diverging expression in an arbitrary arm,
+        // we can point at the entire `match` expression
+        if let (Diverges::Always { .. }, hir::MatchSource::Normal) = (all_arms_diverge, match_src) {
+            all_arms_diverge = Diverges::Always {
+                span: expr.span,
+                custom_note: Some(
+                    "any code following this `match` expression is unreachable, as all arms diverge"
+                )
+            };
+        }
+
         // We won't diverge unless the discriminant or all arms diverge.
         self.diverges.set(discrim_diverges | all_arms_diverge);
 
@@ -176,7 +191,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// When the previously checked expression (the scrutinee) diverges,
     /// warn the user about the match arms being unreachable.
     fn warn_arms_when_scrutinee_diverges(&self, arms: &'tcx [hir::Arm], source: hir::MatchSource) {
-        if self.diverges.get().always() {
+        if self.diverges.get().is_always() {
             use hir::MatchSource::*;
             let msg = match source {
                 IfDesugar { .. } | IfLetDesugar { .. } => "block in `if` expression",

src/librustc_typeck/check/expr.rs

@@ -170,7 +170,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // Any expression that produces a value of type `!` must have diverged
         if ty.is_never() {
-            self.diverges.set(self.diverges.get() | Diverges::Always);
+            self.diverges.set(self.diverges.get() | Diverges::always(expr.span));
         }
 
         // Record the type, which applies it effects.

src/librustc_typeck/check/mod.rs

@@ -450,7 +450,20 @@ pub enum Diverges {
 
     /// Definitely known to diverge and therefore
     /// not reach the next sibling or its parent.
-    Always,
+    Always {
+        /// The `Span` points to the expression
+        /// that caused us to diverge
+        /// (e.g. `return`, `break`, etc).
+        span: Span,
+        /// In some cases (e.g. a `match` expression
+        /// where all arms diverge), we may be
+        /// able to provide a more informative
+        /// message to the user.
+        /// If this is `None`, a default messsage
+        /// will be generated, which is suitable
+        /// for most cases.
+        custom_note: Option<&'static str>
+    },
 
     /// Same as `Always` but with a reachability
     /// warning already emitted.
@@ -486,8 +499,22 @@ impl ops::BitOrAssign for Diverges {
 }
 
 impl Diverges {
-    fn always(self) -> bool {
-        self >= Diverges::Always
+    /// Creates a `Diverges::Always` with the provided `span` and the default note message.
+    fn always(span: Span) -> Diverges {
+        Diverges::Always {
+            span,
+            custom_note: None
+        }
+    }
+
+    fn is_always(self) -> bool {
+        // Enum comparison ignores the
+        // contents of fields, so we just
+        // fill them in with garbage here.
+        self >= Diverges::Always {
+            span: DUMMY_SP,
+            custom_note: None
+        }
     }
 }
 
@@ -2307,17 +2334,25 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Produces warning on the given node, if the current point in the
     /// function is unreachable, and there hasn't been another warning.
     fn warn_if_unreachable(&self, id: hir::HirId, span: Span, kind: &str) {
-        if self.diverges.get() == Diverges::Always &&
+        // FIXME: Combine these two 'if' expressions into one once
+        // let chains are implemented
+        if let Diverges::Always { span: orig_span, custom_note } = self.diverges.get() {
             // If span arose from a desugaring of `if` or `while`, then it is the condition itself,
             // which diverges, that we are about to lint on. This gives suboptimal diagnostics.
             // Instead, stop here so that the `if`- or `while`-expression's block is linted instead.
-            !span.is_desugaring(DesugaringKind::CondTemporary) {
-            self.diverges.set(Diverges::WarnedAlways);
+            if !span.is_desugaring(DesugaringKind::CondTemporary) {
+                self.diverges.set(Diverges::WarnedAlways);
 
-            debug!("warn_if_unreachable: id={:?} span={:?} kind={}", id, span, kind);
+                debug!("warn_if_unreachable: id={:?} span={:?} kind={}", id, span, kind);
 
-            let msg = format!("unreachable {}", kind);
-            self.tcx().lint_hir(lint::builtin::UNREACHABLE_CODE, id, span, &msg);
+                let msg = format!("unreachable {}", kind);
+                self.tcx().struct_span_lint_hir(lint::builtin::UNREACHABLE_CODE, id, span, &msg)
+                    .span_note(
+                        orig_span,
+                        custom_note.unwrap_or("any code following this expression is unreachable")
+                    )
+                    .emit();
+            }
         }
     }
 
@@ -3825,7 +3860,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 //
                 // #41425 -- label the implicit `()` as being the
                 // "found type" here, rather than the "expected type".
-                if !self.diverges.get().always() {
+                if !self.diverges.get().is_always() {
                     // #50009 -- Do not point at the entire fn block span, point at the return type
                     // span, as it is the cause of the requirement, and
                     // `consider_hint_about_removing_semicolon` will point at the last expression