Auto merge of rust-lang#89572 - Manishearth:rollup-obz5ycp, r=Manishearth

Rollup of 10 pull requests

Successful merges:

 - rust-lang#88706 (Normalize associated type projections when checking return type of main)
 - rust-lang#88828 (Use `libc::sigaction()` instead of `sys::signal()` to prevent a deadlock)
 - rust-lang#88871 (Fix suggestion for nested struct patterns)
 - rust-lang#89317 (Move generic error message to separate branches)
 - rust-lang#89351 (for signed wrapping remainder, do not compare lhs with MIN)
 - rust-lang#89442 (Add check for duplicated doc aliases)
 - rust-lang#89502 (Fix Lower/UpperExp formatting for integers and precision zero)
 - rust-lang#89523 (Make `proc_macro_derive_resolution_fallback` a future-breakage lint)
 - rust-lang#89532 (Document behavior of  `MaybeLiveLocals` regarding enums and field-senstivity)
 - rust-lang#89546 (Make an initial guess for metadata size to reduce buffer resizes)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_lint_defs/src/builtin.rs

@@ -1960,6 +1960,7 @@ declare_lint! {
     "detects proc macro derives using inaccessible names from parent modules",
     @future_incompatible = FutureIncompatibleInfo {
         reference: "issue #83583 <https://github.com/rust-lang/rust/issues/83583>",
+        reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
     };
 }
 

compiler/rustc_metadata/src/locator.rs

@@ -740,7 +740,9 @@ fn get_metadata_section(
             // Header is okay -> inflate the actual metadata
             let compressed_bytes = &buf[header_len..];
             debug!("inflating {} bytes of compressed metadata", compressed_bytes.len());
-            let mut inflated = Vec::new();
+            // Assume the decompressed data will be at least the size of the compressed data, so we
+            // don't have to grow the buffer as much.
+            let mut inflated = Vec::with_capacity(compressed_bytes.len());
             match FrameDecoder::new(compressed_bytes).read_to_end(&mut inflated) {
                 Ok(_) => rustc_erase_owner!(OwningRef::new(inflated).map_owner_box()),
                 Err(_) => {

compiler/rustc_mir_dataflow/src/impls/liveness.rs

@@ -11,6 +11,37 @@ use crate::{AnalysisDomain, Backward, GenKill, GenKillAnalysis};
 /// exist. See [this `mir-dataflow` test][flow-test] for an example. You almost never want to use
 /// this analysis without also looking at the results of [`MaybeBorrowedLocals`].
 ///
+/// ## Field-(in)sensitivity
+///
+/// As the name suggests, this analysis is field insensitive. If a projection of a variable `x` is
+/// assigned to (e.g. `x.0 = 42`), it does not "define" `x` as far as liveness is concerned. In fact,
+/// such an assignment is currently marked as a "use" of `x` in an attempt to be maximally
+/// conservative.
+///
+/// ## Enums and `SetDiscriminant`
+///
+/// Assigning a literal value to an `enum` (e.g. `Option<i32>`), does not result in a simple
+/// assignment of the form `_1 = /*...*/` in the MIR. For example, the following assignment to `x`:
+///
+/// ```
+/// x = Some(4);
+/// ```
+///
+/// compiles to this MIR
+///
+/// ```
+/// ((_1 as Some).0: i32) = const 4_i32;
+/// discriminant(_1) = 1;
+/// ```
+///
+/// However, `MaybeLiveLocals` **does** mark `x` (`_1`) as "killed" after a statement like this.
+/// That's because it treats the `SetDiscriminant` operation as a definition of `x`, even though
+/// the writes that actually initialized the locals happened earlier.
+///
+/// This makes `MaybeLiveLocals` unsuitable for certain classes of optimization normally associated
+/// with a live variables analysis, notably dead-store elimination. It's a dirty hack, but it works
+/// okay for the generator state transform (currently the main consumuer of this analysis).
+///
 /// [`MaybeBorrowedLocals`]: super::MaybeBorrowedLocals
 /// [flow-test]: https://github.com/rust-lang/rust/blob/a08c47310c7d49cbdc5d7afb38408ba519967ecd/src/test/ui/mir-dataflow/liveness-ptr.rs
 /// [liveness]: https://en.wikipedia.org/wiki/Live_variable_analysis

compiler/rustc_passes/src/check_attr.rs

@@ -9,7 +9,7 @@ use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::TyCtxt;
 
 use rustc_ast::{ast, AttrStyle, Attribute, Lit, LitKind, NestedMetaItem};
-use rustc_data_structures::stable_set::FxHashSet;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::{pluralize, struct_span_err, Applicability};
 use rustc_feature::{AttributeType, BUILTIN_ATTRIBUTE_MAP};
 use rustc_hir as hir;
@@ -66,6 +66,7 @@ impl CheckAttrVisitor<'tcx> {
         target: Target,
         item: Option<ItemLike<'_>>,
     ) {
+        let mut doc_aliases = FxHashMap::default();
         let mut is_valid = true;
         let mut specified_inline = None;
         let mut seen = FxHashSet::default();
@@ -79,7 +80,13 @@ impl CheckAttrVisitor<'tcx> {
                 sym::track_caller => {
                     self.check_track_caller(hir_id, &attr.span, attrs, span, target)
                 }
-                sym::doc => self.check_doc_attrs(attr, hir_id, target, &mut specified_inline),
+                sym::doc => self.check_doc_attrs(
+                    attr,
+                    hir_id,
+                    target,
+                    &mut specified_inline,
+                    &mut doc_aliases,
+                ),
                 sym::no_link => self.check_no_link(hir_id, &attr, span, target),
                 sym::export_name => self.check_export_name(hir_id, &attr, span, target),
                 sym::rustc_layout_scalar_valid_range_start
@@ -512,6 +519,7 @@ impl CheckAttrVisitor<'tcx> {
         hir_id: HirId,
         target: Target,
         is_list: bool,
+        aliases: &mut FxHashMap<String, Span>,
     ) -> bool {
         let tcx = self.tcx;
         let err_fn = move |span: Span, msg: &str| {
@@ -582,17 +590,38 @@ impl CheckAttrVisitor<'tcx> {
         if &*item_name.as_str() == doc_alias {
             return err_fn(meta.span(), "is the same as the item's name");
         }
+        let span = meta.span();
+        if let Err(entry) = aliases.try_insert(doc_alias.to_owned(), span) {
+            self.tcx.struct_span_lint_hir(UNUSED_ATTRIBUTES, hir_id, span, |lint| {
+                lint.build("doc alias is duplicated")
+                    .span_label(*entry.entry.get(), "first defined here")
+                    .emit();
+            });
+        }
         true
     }
 
-    fn check_doc_alias(&self, meta: &NestedMetaItem, hir_id: HirId, target: Target) -> bool {
+    fn check_doc_alias(
+        &self,
+        meta: &NestedMetaItem,
+        hir_id: HirId,
+        target: Target,
+        aliases: &mut FxHashMap<String, Span>,
+    ) -> bool {
         if let Some(values) = meta.meta_item_list() {
             let mut errors = 0;
             for v in values {
                 match v.literal() {
                     Some(l) => match l.kind {
                         LitKind::Str(s, _) => {
-                            if !self.check_doc_alias_value(v, &s.as_str(), hir_id, target, true) {
+                            if !self.check_doc_alias_value(
+                                v,
+                                &s.as_str(),
+                                hir_id,
+                                target,
+                                true,
+                                aliases,
+                            ) {
                                 errors += 1;
                             }
                         }
@@ -621,7 +650,7 @@ impl CheckAttrVisitor<'tcx> {
             }
             errors == 0
         } else if let Some(doc_alias) = meta.value_str().map(|s| s.to_string()) {
-            self.check_doc_alias_value(meta, &doc_alias, hir_id, target, false)
+            self.check_doc_alias_value(meta, &doc_alias, hir_id, target, false, aliases)
         } else {
             self.tcx
                 .sess
@@ -858,6 +887,7 @@ impl CheckAttrVisitor<'tcx> {
         hir_id: HirId,
         target: Target,
         specified_inline: &mut Option<(bool, Span)>,
+        aliases: &mut FxHashMap<String, Span>,
     ) -> bool {
         let mut is_valid = true;
 
@@ -867,7 +897,7 @@ impl CheckAttrVisitor<'tcx> {
                     match i_meta.name_or_empty() {
                         sym::alias
                             if !self.check_attr_not_crate_level(&meta, hir_id, "alias")
-                                || !self.check_doc_alias(&meta, hir_id, target) =>
+                                || !self.check_doc_alias(&meta, hir_id, target, aliases) =>
                         {
                             is_valid = false
                         }

compiler/rustc_passes/src/lib.rs

@@ -9,8 +9,9 @@
 #![feature(in_band_lifetimes)]
 #![feature(format_args_capture)]
 #![feature(iter_zip)]
-#![feature(nll)]
+#![feature(map_try_insert)]
 #![feature(min_specialization)]
+#![feature(nll)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
 

compiler/rustc_passes/src/liveness.rs

@@ -265,21 +265,24 @@ impl IrMaps<'tcx> {
         self.capture_info_map.insert(hir_id, Rc::new(cs));
     }
 
-    fn add_from_pat(&mut self, pat: &hir::Pat<'tcx>) {
+    fn collect_shorthand_field_ids(&self, pat: &hir::Pat<'tcx>) -> HirIdSet {
         // For struct patterns, take note of which fields used shorthand
         // (`x` rather than `x: x`).
         let mut shorthand_field_ids = HirIdSet::default();
         let mut pats = VecDeque::new();
         pats.push_back(pat);
+
         while let Some(pat) = pats.pop_front() {
             use rustc_hir::PatKind::*;
             match &pat.kind {
                 Binding(.., inner_pat) => {
                     pats.extend(inner_pat.iter());
                 }
                 Struct(_, fields, _) => {
-                    let ids = fields.iter().filter(|f| f.is_shorthand).map(|f| f.pat.hir_id);
-                    shorthand_field_ids.extend(ids);
+                    let (short, not_short): (Vec<&_>, Vec<&_>) =
+                        fields.iter().partition(|f| f.is_shorthand);
+                    shorthand_field_ids.extend(short.iter().map(|f| f.pat.hir_id));
+                    pats.extend(not_short.iter().map(|f| f.pat));
                 }
                 Ref(inner_pat, _) | Box(inner_pat) => {
                     pats.push_back(inner_pat);
@@ -296,6 +299,12 @@ impl IrMaps<'tcx> {
             }
         }
 
+        return shorthand_field_ids;
+    }
+
+    fn add_from_pat(&mut self, pat: &hir::Pat<'tcx>) {
+        let shorthand_field_ids = self.collect_shorthand_field_ids(pat);
+
         pat.each_binding(|_, hir_id, _, ident| {
             self.add_live_node_for_node(hir_id, VarDefNode(ident.span, hir_id));
             self.add_variable(Local(LocalInfo {
@@ -373,15 +382,13 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
     }
 
     fn visit_param(&mut self, param: &'tcx hir::Param<'tcx>) {
+        let shorthand_field_ids = self.collect_shorthand_field_ids(param.pat);
         param.pat.each_binding(|_bm, hir_id, _x, ident| {
             let var = match param.pat.kind {
-                rustc_hir::PatKind::Struct(_, fields, _) => Local(LocalInfo {
+                rustc_hir::PatKind::Struct(..) => Local(LocalInfo {
                     id: hir_id,
                     name: ident.name,
-                    is_shorthand: fields
-                        .iter()
-                        .find(|f| f.ident == ident)
-                        .map_or(false, |f| f.is_shorthand),
+                    is_shorthand: shorthand_field_ids.contains(&hir_id),
                 }),
                 _ => Param(hir_id, ident.name),
             };