Rollup of 10 pull requests

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -6,9 +6,10 @@ use rustc_hir::def::{DefKind, Namespace};
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_hir::{Body, Expr, ExprKind, FnRetTy, HirId, Local, Pat};
 use rustc_middle::hir::map::Map;
+use rustc_middle::infer::unify_key::ConstVariableOriginKind;
 use rustc_middle::ty::print::Print;
 use rustc_middle::ty::subst::{GenericArg, GenericArgKind};
-use rustc_middle::ty::{self, DefIdTree, Ty};
+use rustc_middle::ty::{self, DefIdTree, InferConst, Ty};
 use rustc_span::source_map::DesugaringKind;
 use rustc_span::symbol::kw;
 use rustc_span::Span;
@@ -569,14 +570,26 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             local_visitor.visit_expr(expr);
         }
 
+        let mut param_name = None;
+        let span = if let ty::ConstKind::Infer(InferConst::Var(vid)) = ct.val {
+            let origin = self.inner.borrow_mut().const_unification_table().probe_value(vid).origin;
+            if let ConstVariableOriginKind::ConstParameterDefinition(param) = origin.kind {
+                param_name = Some(param);
+            }
+            origin.span
+        } else {
+            local_visitor.target_span
+        };
+
         let error_code = error_code.into();
-        let mut err = self.tcx.sess.struct_span_err_with_code(
-            local_visitor.target_span,
-            "type annotations needed",
-            error_code,
-        );
+        let mut err =
+            self.tcx.sess.struct_span_err_with_code(span, "type annotations needed", error_code);
 
-        err.note("unable to infer the value of a const parameter");
+        if let Some(param_name) = param_name {
+            err.note(&format!("cannot infer the value of the const parameter `{}`", param_name));
+        } else {
+            err.note("unable to infer the value of a const parameter");
+        }
 
         err
     }

compiler/rustc_middle/src/infer/unify_key.rs

@@ -124,6 +124,7 @@ pub struct ConstVariableOrigin {
 pub enum ConstVariableOriginKind {
     MiscVariable,
     ConstInference,
+    // FIXME(const_generics): Consider storing the `DefId` of the param here.
     ConstParameterDefinition(Symbol),
     SubstitutionPlaceholder,
 }

compiler/rustc_middle/src/mir/mod.rs

@@ -2285,8 +2285,8 @@ impl<'tcx> Debug for Rvalue<'tcx> {
 /// Constants
 ///
 /// Two constants are equal if they are the same constant. Note that
-/// this does not necessarily mean that they are "==" in Rust -- in
-/// particular one must be wary of `NaN`!
+/// this does not necessarily mean that they are `==` in Rust -- in
+/// particular, one must be wary of `NaN`!
 
 #[derive(Clone, Copy, PartialEq, TyEncodable, TyDecodable, HashStable)]
 pub struct Constant<'tcx> {

compiler/rustc_middle/src/ty/context.rs

@@ -66,8 +66,8 @@ use std::mem;
 use std::ops::{Bound, Deref};
 use std::sync::Arc;
 
-/// A type that is not publicly constructable. This prevents people from making `TyKind::Error`
-/// except through `tcx.err*()`, which are in this module.
+/// A type that is not publicly constructable. This prevents people from making [`TyKind::Error`]s
+/// except through the error-reporting functions on a [`tcx`][TyCtxt].
 #[derive(Copy, Clone, Debug, Eq, Hash, PartialEq, PartialOrd, Ord)]
 #[derive(TyEncodable, TyDecodable, HashStable)]
 pub struct DelaySpanBugEmitted(());

compiler/rustc_middle/src/ty/diagnostics.rs

@@ -202,33 +202,59 @@ pub fn suggest_constraining_type_param(
         //    Suggestion:
         //      fn foo<T>(t: T) where T: Foo, T: Bar {... }
         //                                          - insert: `, T: Zar`
+        //
+        // Additionally, there may be no `where` clause whatsoever in the case that this was
+        // reached because the generic parameter has a default:
+        //
+        //    Message:
+        //      trait Foo<T=()> {... }
+        //             - help: consider further restricting this type parameter with `where T: Zar`
+        //
+        //    Suggestion:
+        //      trait Foo<T=()> where T: Zar {... }
+        //                     - insert: `where T: Zar`
 
-        let mut param_spans = Vec::new();
+        if matches!(param.kind, hir::GenericParamKind::Type { default: Some(_), .. })
+            && generics.where_clause.predicates.len() == 0
+        {
+            // Suggest a bound, but there is no existing `where` clause *and* the type param has a
+            // default (`<T=Foo>`), so we suggest adding `where T: Bar`.
+            err.span_suggestion_verbose(
+                generics.where_clause.tail_span_for_suggestion(),
+                &msg_restrict_type_further,
+                format!(" where {}: {}", param_name, constraint),
+                Applicability::MachineApplicable,
+            );
+        } else {
+            let mut param_spans = Vec::new();
 
-        for predicate in generics.where_clause.predicates {
-            if let WherePredicate::BoundPredicate(WhereBoundPredicate {
-                span, bounded_ty, ..
-            }) = predicate
-            {
-                if let TyKind::Path(QPath::Resolved(_, path)) = &bounded_ty.kind {
-                    if let Some(segment) = path.segments.first() {
-                        if segment.ident.to_string() == param_name {
-                            param_spans.push(span);
+            for predicate in generics.where_clause.predicates {
+                if let WherePredicate::BoundPredicate(WhereBoundPredicate {
+                    span,
+                    bounded_ty,
+                    ..
+                }) = predicate
+                {
+                    if let TyKind::Path(QPath::Resolved(_, path)) = &bounded_ty.kind {
+                        if let Some(segment) = path.segments.first() {
+                            if segment.ident.to_string() == param_name {
+                                param_spans.push(span);
+                            }
                         }
                     }
                 }
             }
-        }
 
-        match &param_spans[..] {
-            &[&param_span] => suggest_restrict(param_span.shrink_to_hi()),
-            _ => {
-                err.span_suggestion_verbose(
-                    generics.where_clause.tail_span_for_suggestion(),
-                    &msg_restrict_type_further,
-                    format!(", {}: {}", param_name, constraint),
-                    Applicability::MachineApplicable,
-                );
+            match &param_spans[..] {
+                &[&param_span] => suggest_restrict(param_span.shrink_to_hi()),
+                _ => {
+                    err.span_suggestion_verbose(
+                        generics.where_clause.tail_span_for_suggestion(),
+                        &msg_restrict_type_further,
+                        format!(", {}: {}", param_name, constraint),
+                        Applicability::MachineApplicable,
+                    );
+                }
             }
         }
 

compiler/rustc_middle/src/ty/sty.rs

@@ -1233,13 +1233,13 @@ rustc_index::newtype_index! {
     /// particular, imagine a type like this:
     ///
     ///     for<'a> fn(for<'b> fn(&'b isize, &'a isize), &'a char)
-    ///     ^          ^            |        |         |
-    ///     |          |            |        |         |
-    ///     |          +------------+ 0      |         |
-    ///     |                                |         |
-    ///     +--------------------------------+ 1       |
-    ///     |                                          |
-    ///     +------------------------------------------+ 0
+    ///     ^          ^            |          |           |
+    ///     |          |            |          |           |
+    ///     |          +------------+ 0        |           |
+    ///     |                                  |           |
+    ///     +----------------------------------+ 1         |
+    ///     |                                              |
+    ///     +----------------------------------------------+ 0
     ///
     /// In this type, there are two binders (the outer fn and the inner
     /// fn). We need to be able to determine, for any given region, which

compiler/rustc_mir/src/monomorphize/partitioning/default.rs

@@ -11,6 +11,7 @@ use rustc_middle::ty::print::characteristic_def_id_of_type;
 use rustc_middle::ty::{self, DefIdTree, InstanceDef, TyCtxt};
 use rustc_span::symbol::Symbol;
 
+use super::PartitioningCx;
 use crate::monomorphize::collector::InliningMap;
 use crate::monomorphize::partitioning::merging;
 use crate::monomorphize::partitioning::{
@@ -22,35 +23,36 @@ pub struct DefaultPartitioning;
 impl<'tcx> Partitioner<'tcx> for DefaultPartitioning {
     fn place_root_mono_items(
         &mut self,
-        tcx: TyCtxt<'tcx>,
+        cx: &PartitioningCx<'_, 'tcx>,
         mono_items: &mut dyn Iterator<Item = MonoItem<'tcx>>,
     ) -> PreInliningPartitioning<'tcx> {
         let mut roots = FxHashSet::default();
         let mut codegen_units = FxHashMap::default();
-        let is_incremental_build = tcx.sess.opts.incremental.is_some();
+        let is_incremental_build = cx.tcx.sess.opts.incremental.is_some();
         let mut internalization_candidates = FxHashSet::default();
 
         // Determine if monomorphizations instantiated in this crate will be made
         // available to downstream crates. This depends on whether we are in
         // share-generics mode and whether the current crate can even have
         // downstream crates.
-        let export_generics = tcx.sess.opts.share_generics() && tcx.local_crate_exports_generics();
+        let export_generics =
+            cx.tcx.sess.opts.share_generics() && cx.tcx.local_crate_exports_generics();
 
-        let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx);
+        let cgu_name_builder = &mut CodegenUnitNameBuilder::new(cx.tcx);
         let cgu_name_cache = &mut FxHashMap::default();
 
         for mono_item in mono_items {
-            match mono_item.instantiation_mode(tcx) {
+            match mono_item.instantiation_mode(cx.tcx) {
                 InstantiationMode::GloballyShared { .. } => {}
                 InstantiationMode::LocalCopy => continue,
             }
 
-            let characteristic_def_id = characteristic_def_id_of_mono_item(tcx, mono_item);
+            let characteristic_def_id = characteristic_def_id_of_mono_item(cx.tcx, mono_item);
             let is_volatile = is_incremental_build && mono_item.is_generic_fn();
 
             let codegen_unit_name = match characteristic_def_id {
                 Some(def_id) => compute_codegen_unit_name(
-                    tcx,
+                    cx.tcx,
                     cgu_name_builder,
                     def_id,
                     is_volatile,
@@ -65,7 +67,7 @@ impl<'tcx> Partitioner<'tcx> for DefaultPartitioning {
 
             let mut can_be_internalized = true;
             let (linkage, visibility) = mono_item_linkage_and_visibility(
-                tcx,
+                cx.tcx,
                 &mono_item,
                 &mut can_be_internalized,
                 export_generics,
@@ -97,17 +99,16 @@ impl<'tcx> Partitioner<'tcx> for DefaultPartitioning {
 
     fn merge_codegen_units(
         &mut self,
-        tcx: TyCtxt<'tcx>,
+        cx: &PartitioningCx<'_, 'tcx>,
         initial_partitioning: &mut PreInliningPartitioning<'tcx>,
-        target_cgu_count: usize,
     ) {
-        merging::merge_codegen_units(tcx, initial_partitioning, target_cgu_count);
+        merging::merge_codegen_units(cx, initial_partitioning);
     }
 
     fn place_inlined_mono_items(
         &mut self,
+        cx: &PartitioningCx<'_, 'tcx>,
         initial_partitioning: PreInliningPartitioning<'tcx>,
-        inlining_map: &InliningMap<'tcx>,
     ) -> PostInliningPartitioning<'tcx> {
         let mut new_partitioning = Vec::new();
         let mut mono_item_placements = FxHashMap::default();
@@ -124,7 +125,7 @@ impl<'tcx> Partitioner<'tcx> for DefaultPartitioning {
             // Collect all items that need to be available in this codegen unit.
             let mut reachable = FxHashSet::default();
             for root in old_codegen_unit.items().keys() {
-                follow_inlining(*root, inlining_map, &mut reachable);
+                follow_inlining(*root, cx.inlining_map, &mut reachable);
             }
 
             let mut new_codegen_unit = CodegenUnit::new(old_codegen_unit.name());
@@ -198,9 +199,8 @@ impl<'tcx> Partitioner<'tcx> for DefaultPartitioning {
 
     fn internalize_symbols(
         &mut self,
-        _tcx: TyCtxt<'tcx>,
+        cx: &PartitioningCx<'_, 'tcx>,
         partitioning: &mut PostInliningPartitioning<'tcx>,
-        inlining_map: &InliningMap<'tcx>,
     ) {
         if partitioning.codegen_units.len() == 1 {
             // Fast path for when there is only one codegen unit. In this case we
@@ -218,7 +218,7 @@ impl<'tcx> Partitioner<'tcx> for DefaultPartitioning {
         // Build a map from every monomorphization to all the monomorphizations that
         // reference it.
         let mut accessor_map: FxHashMap<MonoItem<'tcx>, Vec<MonoItem<'tcx>>> = Default::default();
-        inlining_map.iter_accesses(|accessor, accessees| {
+        cx.inlining_map.iter_accesses(|accessor, accessees| {
             for accessee in accessees {
                 accessor_map.entry(*accessee).or_default().push(accessor);
             }

compiler/rustc_mir/src/monomorphize/partitioning/merging.rs

@@ -3,17 +3,16 @@ use std::cmp;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def_id::LOCAL_CRATE;
 use rustc_middle::mir::mono::{CodegenUnit, CodegenUnitNameBuilder};
-use rustc_middle::ty::TyCtxt;
 use rustc_span::symbol::{Symbol, SymbolStr};
 
+use super::PartitioningCx;
 use crate::monomorphize::partitioning::PreInliningPartitioning;
 
 pub fn merge_codegen_units<'tcx>(
-    tcx: TyCtxt<'tcx>,
+    cx: &PartitioningCx<'_, 'tcx>,
     initial_partitioning: &mut PreInliningPartitioning<'tcx>,
-    target_cgu_count: usize,
 ) {
-    assert!(target_cgu_count >= 1);
+    assert!(cx.target_cgu_count >= 1);
     let codegen_units = &mut initial_partitioning.codegen_units;
 
     // Note that at this point in time the `codegen_units` here may not be in a
@@ -32,7 +31,7 @@ pub fn merge_codegen_units<'tcx>(
         codegen_units.iter().map(|cgu| (cgu.name(), vec![cgu.name().as_str()])).collect();
 
     // Merge the two smallest codegen units until the target size is reached.
-    while codegen_units.len() > target_cgu_count {
+    while codegen_units.len() > cx.target_cgu_count {
         // Sort small cgus to the back
         codegen_units.sort_by_cached_key(|cgu| cmp::Reverse(cgu.size_estimate()));
         let mut smallest = codegen_units.pop().unwrap();
@@ -56,9 +55,9 @@ pub fn merge_codegen_units<'tcx>(
         );
     }
 
-    let cgu_name_builder = &mut CodegenUnitNameBuilder::new(tcx);
+    let cgu_name_builder = &mut CodegenUnitNameBuilder::new(cx.tcx);
 
-    if tcx.sess.opts.incremental.is_some() {
+    if cx.tcx.sess.opts.incremental.is_some() {
         // If we are doing incremental compilation, we want CGU names to
         // reflect the path of the source level module they correspond to.
         // For CGUs that contain the code of multiple modules because of the
@@ -84,7 +83,7 @@ pub fn merge_codegen_units<'tcx>(
 
         for cgu in codegen_units.iter_mut() {
             if let Some(new_cgu_name) = new_cgu_names.get(&cgu.name()) {
-                if tcx.sess.opts.debugging_opts.human_readable_cgu_names {
+                if cx.tcx.sess.opts.debugging_opts.human_readable_cgu_names {
                     cgu.set_name(Symbol::intern(&new_cgu_name));
                 } else {
                     // If we don't require CGU names to be human-readable, we