Auto merge of #42049 - Mark-Simulacrum:rollup, r=Mark-Simulacrum

Rollup of 5 pull requests

- Successful merges: #41937, #41957, #42017, #42039, #42046
- Failed merges:

Author: bors

src/doc/book

@@ -39,10 +39,12 @@ use super::sub::Sub;
 use super::InferCtxt;
 use super::{MiscVariable, TypeTrace};
 
+use hir::def_id::DefId;
 use ty::{IntType, UintType};
 use ty::{self, Ty, TyCtxt};
 use ty::error::TypeError;
 use ty::relate::{self, Relate, RelateResult, TypeRelation};
+use ty::subst::Substs;
 use traits::{Obligation, PredicateObligations};
 
 use syntax::ast;
@@ -336,6 +338,23 @@ impl<'cx, 'gcx, 'tcx> TypeRelation<'cx, 'gcx, 'tcx> for Generalizer<'cx, 'gcx, '
         Ok(ty::Binder(self.relate(a.skip_binder(), b.skip_binder())?))
     }
 
+    fn relate_item_substs(&mut self,
+                          item_def_id: DefId,
+                          a_subst: &'tcx Substs<'tcx>,
+                          b_subst: &'tcx Substs<'tcx>)
+                          -> RelateResult<'tcx, &'tcx Substs<'tcx>>
+    {
+        if self.ambient_variance == ty::Variance::Invariant {
+            // Avoid fetching the variance if we are in an invariant
+            // context; no need, and it can induce dependency cycles
+            // (e.g. #41849).
+            relate::relate_substs(self, None, a_subst, b_subst)
+        } else {
+            let opt_variances = self.tcx().variances_of(item_def_id);
+            relate::relate_substs(self, Some(&opt_variances), a_subst, b_subst)
+        }
+    }
+
     fn relate_with_variance<T: Relate<'tcx>>(&mut self,
                                              variance: ty::Variance,
                                              a: &T,

src/doc/reference

@@ -592,7 +592,7 @@ macro_rules! define_map_struct {
      output: $output:tt) => {
         define_map_struct! {
             tcx: $tcx,
-            ready: ([pub] $attrs $name),
+            ready: ([] $attrs $name),
             input: ($($input)*),
             output: $output
         }

src/librustc/infer/combine.rs

@@ -324,7 +324,9 @@ fn write_mir_sig(tcx: TyCtxt, src: MirSource, mir: &Mir, w: &mut Write)
         MirSource::Promoted(_, i) => write!(w, "{:?} in", i)?
     }
 
-    write!(w, " {}", tcx.node_path_str(src.item_id()))?;
+    item_path::with_forced_impl_filename_line(|| { // see notes on #41697 elsewhere
+        write!(w, " {}", tcx.node_path_str(src.item_id()))
+    })?;
 
     if let MirSource::Fn(_) = src {
         write!(w, "(")?;

src/librustc/ty/maps.rs

@@ -249,6 +249,45 @@ pub fn coerce_unsized_info<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                     return err_info;
                 }
 
+                // Here we are considering a case of converting
+                // `S<P0...Pn>` to S<Q0...Qn>`. As an example, let's imagine a struct `Foo<T, U>`,
+                // which acts like a pointer to `U`, but carries along some extra data of type `T`:
+                //
+                //     struct Foo<T, U> {
+                //         extra: T,
+                //         ptr: *mut U,
+                //     }
+                //
+                // We might have an impl that allows (e.g.) `Foo<T, [i32; 3]>` to be unsized
+                // to `Foo<T, [i32]>`. That impl would look like:
+                //
+                //   impl<T, U: Unsize<V>, V> CoerceUnsized<Foo<T, V>> for Foo<T, U> {}
+                //
+                // Here `U = [i32; 3]` and `V = [i32]`. At runtime,
+                // when this coercion occurs, we would be changing the
+                // field `ptr` from a thin pointer of type `*mut [i32;
+                // 3]` to a fat pointer of type `*mut [i32]` (with
+                // extra data `3`).  **The purpose of this check is to
+                // make sure that we know how to do this conversion.**
+                //
+                // To check if this impl is legal, we would walk down
+                // the fields of `Foo` and consider their types with
+                // both substitutes. We are looking to find that
+                // exactly one (non-phantom) field has changed its
+                // type, which we will expect to be the pointer that
+                // is becoming fat (we could probably generalize this
+                // to mutiple thin pointers of the same type becoming
+                // fat, but we don't). In this case:
+                //
+                // - `extra` has type `T` before and type `T` after
+                // - `ptr` has type `*mut U` before and type `*mut V` after
+                //
+                // Since just one field changed, we would then check
+                // that `*mut U: CoerceUnsized<*mut V>` is implemented
+                // (in other words, that we know how to do this
+                // conversion). This will work out because `U:
+                // Unsize<V>`, and we have a builtin rule that `*mut
+                // U` can be coerced to `*mut V` if `U: Unsize<V>`.
                 let fields = &def_a.struct_variant().fields;
                 let diff_fields = fields.iter()
                     .enumerate()
@@ -260,8 +299,16 @@ pub fn coerce_unsized_info<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                             return None;
                         }
 
-                        // Ignore fields that aren't significantly changed
-                        if let Ok(ok) = infcx.sub_types(false, &cause, b, a) {
+                        // Ignore fields that aren't changed; it may
+                        // be that we could get away with subtyping or
+                        // something more accepting, but we use
+                        // equality because we want to be able to
+                        // perform this check without computing
+                        // variance where possible. (This is because
+                        // we may have to evaluate constraint
+                        // expressions in the course of execution.)
+                        // See e.g. #41936.
+                        if let Ok(ok) = infcx.eq_types(false, &cause, b, a) {
                             if ok.obligations.is_empty() {
                                 return None;
                             }

src/librustc_mir/util/pretty.rs

@@ -715,7 +715,7 @@ impl Stmt {
             StmtKind::Mac(mac) => StmtKind::Mac(mac.map(|(mac, _style, attrs)| {
                 (mac, MacStmtStyle::Semicolon, attrs)
             })),
-            node @ _ => node,
+            node => node,
         };
         self
     }
@@ -1076,16 +1076,16 @@ impl LitKind {
     pub fn is_unsuffixed(&self) -> bool {
         match *self {
             // unsuffixed variants
-            LitKind::Str(..) => true,
-            LitKind::ByteStr(..) => true,
-            LitKind::Byte(..) => true,
-            LitKind::Char(..) => true,
-            LitKind::Int(_, LitIntType::Unsuffixed) => true,
-            LitKind::FloatUnsuffixed(..) => true,
+            LitKind::Str(..) |
+            LitKind::ByteStr(..) |
+            LitKind::Byte(..) |
+            LitKind::Char(..) |
+            LitKind::Int(_, LitIntType::Unsuffixed) |
+            LitKind::FloatUnsuffixed(..) |
             LitKind::Bool(..) => true,
             // suffixed variants
-            LitKind::Int(_, LitIntType::Signed(..)) => false,
-            LitKind::Int(_, LitIntType::Unsigned(..)) => false,
+            LitKind::Int(_, LitIntType::Signed(..)) |
+            LitKind::Int(_, LitIntType::Unsigned(..)) |
             LitKind::Float(..) => false,
         }
     }

src/librustc_typeck/coherence/builtin.rs

@@ -112,15 +112,15 @@ impl NestedMetaItem {
     /// Returns the MetaItem if self is a NestedMetaItemKind::MetaItem.
     pub fn meta_item(&self) -> Option<&MetaItem> {
         match self.node {
-            NestedMetaItemKind::MetaItem(ref item) => Some(&item),
+            NestedMetaItemKind::MetaItem(ref item) => Some(item),
             _ => None
         }
     }
 
     /// Returns the Lit if self is a NestedMetaItemKind::Literal.
     pub fn literal(&self) -> Option<&Lit> {
         match self.node {
-            NestedMetaItemKind::Literal(ref lit) => Some(&lit),
+            NestedMetaItemKind::Literal(ref lit) => Some(lit),
             _ => None
         }
     }
@@ -259,7 +259,7 @@ impl MetaItem {
         match self.node {
             MetaItemKind::NameValue(ref v) => {
                 match v.node {
-                    LitKind::Str(ref s, _) => Some((*s).clone()),
+                    LitKind::Str(ref s, _) => Some(*s),
                     _ => None,
                 }
             },
@@ -1217,9 +1217,10 @@ impl LitKind {
                 Token::Literal(token::Lit::Float(symbol), Some(Symbol::intern(ty.ty_to_string())))
             }
             LitKind::FloatUnsuffixed(symbol) => Token::Literal(token::Lit::Float(symbol), None),
-            LitKind::Bool(value) => Token::Ident(Ident::with_empty_ctxt(Symbol::intern(match value {
-                true => "true",
-                false => "false",
+            LitKind::Bool(value) => Token::Ident(Ident::with_empty_ctxt(Symbol::intern(if value {
+                "true"
+            } else {
+                "false"
             }))),
         }
     }
@@ -1261,7 +1262,7 @@ impl<T: HasAttrs> HasAttrs for Spanned<T> {
 
 impl HasAttrs for Vec<Attribute> {
     fn attrs(&self) -> &[Attribute] {
-        &self
+        self
     }
     fn map_attrs<F: FnOnce(Vec<Attribute>) -> Vec<Attribute>>(self, f: F) -> Self {
         f(self)
@@ -1270,7 +1271,7 @@ impl HasAttrs for Vec<Attribute> {
 
 impl HasAttrs for ThinVec<Attribute> {
     fn attrs(&self) -> &[Attribute] {
-        &self
+        self
     }
     fn map_attrs<F: FnOnce(Vec<Attribute>) -> Vec<Attribute>>(self, f: F) -> Self {
         f(self.into()).into()

src/libsyntax/ast.rs

@@ -485,7 +485,7 @@ impl CodeMap {
         match self.span_to_snippet(sp) {
             Ok(snippet) => {
                 let snippet = snippet.split(c).nth(0).unwrap_or("").trim_right();
-                if snippet.len() > 0 && !snippet.contains('\n') {
+                if !snippet.is_empty() && !snippet.contains('\n') {
                     Span { hi: BytePos(sp.lo.0 + snippet.len() as u32), ..sp }
                 } else {
                     sp
@@ -502,7 +502,7 @@ impl CodeMap {
     pub fn get_filemap(&self, filename: &str) -> Option<Rc<FileMap>> {
         for fm in self.files.borrow().iter() {
             if filename == fm.name {
-               (self.dep_tracking_callback.borrow())(&fm);
+               (self.dep_tracking_callback.borrow())(fm);
                 return Some(fm.clone());
             }
         }

src/libsyntax/attr.rs

@@ -123,7 +123,7 @@ impl<'a> StripUnconfigured<'a> {
                 return false;
             }
 
-            let mis = if !is_cfg(&attr) {
+            let mis = if !is_cfg(attr) {
                 return true;
             } else if let Some(mis) = attr.meta_item_list() {
                 mis
@@ -150,7 +150,7 @@ impl<'a> StripUnconfigured<'a> {
         // flag the offending attributes
         for attr in attrs.iter() {
             if !self.features.map(|features| features.stmt_expr_attributes).unwrap_or(true) {
-                let mut err = feature_err(&self.sess,
+                let mut err = feature_err(self.sess,
                                           "stmt_expr_attributes",
                                           attr.span,
                                           GateIssue::Language,
@@ -258,7 +258,7 @@ impl<'a> StripUnconfigured<'a> {
     pub fn configure_struct_expr_field(&mut self, field: ast::Field) -> Option<ast::Field> {
         if !self.features.map(|features| features.struct_field_attributes).unwrap_or(true) {
             if !field.attrs.is_empty() {
-                let mut err = feature_err(&self.sess,
+                let mut err = feature_err(self.sess,
                                           "struct_field_attributes",
                                           field.span,
                                           GateIssue::Language,
@@ -290,7 +290,7 @@ impl<'a> StripUnconfigured<'a> {
         for attr in attrs.iter() {
             if !self.features.map(|features| features.struct_field_attributes).unwrap_or(true) {
                 let mut err = feature_err(
-                    &self.sess,
+                    self.sess,
                     "struct_field_attributes",
                     attr.span,
                     GateIssue::Language,

src/libsyntax/codemap.rs

@@ -120,7 +120,7 @@ pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt,
 
         // URLs can be unavoidably longer than the line limit, so we allow them.
         // Allowed format is: `[name]: https://www.rust-lang.org/`
-        let is_url = |l: &str| l.starts_with('[') && l.contains("]:") && l.contains("http");
+        let is_url = |l: &str| l.starts_with("[") && l.contains("]:") && l.contains("http");
 
         if msg.lines().any(|line| line.len() > MAX_DESCRIPTION_WIDTH && !is_url(line)) {
             ecx.span_err(span, &format!(
@@ -177,7 +177,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
             if let Err(e) = output_metadata(ecx,
                                             &target_triple,
                                             &crate_name.name.as_str(),
-                                            &diagnostics) {
+                                            diagnostics) {
                 ecx.span_bug(span, &format!(
                     "error writing metadata for triple `{}` and crate `{}`, error: {}, \
                      cause: {:?}",
@@ -227,7 +227,7 @@ pub fn expand_build_diagnostic_array<'cx>(ecx: &'cx mut ExtCtxt,
 
     MacEager::items(SmallVector::many(vec![
         P(ast::Item {
-            ident: name.clone(),
+            ident: *name,
             attrs: Vec::new(),
             id: ast::DUMMY_NODE_ID,
             node: ast::ItemKind::Const(

src/libsyntax/config.rs

@@ -637,8 +637,8 @@ pub struct ExpansionData {
 }
 
 /// One of these is made during expansion and incrementally updated as we go;
-/// when a macro expansion occurs, the resulting nodes have the backtrace()
-/// -> expn_info of their expansion context stored into their span.
+/// when a macro expansion occurs, the resulting nodes have the `backtrace()
+/// -> expn_info` of their expansion context stored into their span.
 pub struct ExtCtxt<'a> {
     pub parse_sess: &'a parse::ParseSess,
     pub ecfg: expand::ExpansionConfig<'a>,
@@ -711,7 +711,7 @@ impl<'a> ExtCtxt<'a> {
                 }
                 ctxt = info.call_site.ctxt;
                 last_macro = Some(info.call_site);
-                return Some(());
+                Some(())
             }).is_none() {
                 break
             }
@@ -772,9 +772,9 @@ impl<'a> ExtCtxt<'a> {
     }
     pub fn trace_macros_diag(&self) {
         for (sp, notes) in self.expansions.iter() {
-            let mut db = self.parse_sess.span_diagnostic.span_note_diag(*sp, &"trace_macro");
+            let mut db = self.parse_sess.span_diagnostic.span_note_diag(*sp, "trace_macro");
             for note in notes {
-                db.note(&note);
+                db.note(note);
             }
             db.emit();
         }
@@ -797,7 +797,7 @@ impl<'a> ExtCtxt<'a> {
             v.push(self.ident_of(s));
         }
         v.extend(components.iter().map(|s| self.ident_of(s)));
-        return v
+        v
     }
     pub fn name_of(&self, st: &str) -> ast::Name {
         Symbol::intern(st)