Auto merge of #69076 - cjgillot:split_trait, r=matthewjasper

Split librustc::{traits,infer} to their respective crates

Followup on #67953.

I tried to follow the existing module structures.

cc @eddyb
r? @Zoxc

Cargo.lock

@@ -3783,19 +3783,15 @@ dependencies = [
 name = "rustc_infer"
 version = "0.0.0"
 dependencies = [
- "fmt_macros",
  "graphviz",
  "log",
  "rustc",
  "rustc_ast",
- "rustc_attr",
  "rustc_data_structures",
- "rustc_error_codes",
  "rustc_errors",
  "rustc_hir",
  "rustc_index",
  "rustc_macros",
- "rustc_session",
  "rustc_span",
  "rustc_target",
  "smallvec 1.0.0",
@@ -3835,6 +3831,7 @@ dependencies = [
  "rustc_session",
  "rustc_span",
  "rustc_target",
+ "rustc_trait_selection",
  "rustc_traits",
  "rustc_ty",
  "rustc_typeck",
@@ -3869,6 +3866,7 @@ dependencies = [
  "rustc_session",
  "rustc_span",
  "rustc_target",
+ "rustc_trait_selection",
  "unicode-security",
 ]
 
@@ -3938,6 +3936,7 @@ dependencies = [
  "rustc_macros",
  "rustc_span",
  "rustc_target",
+ "rustc_trait_selection",
  "serialize",
  "smallvec 1.0.0",
 ]
@@ -3961,6 +3960,7 @@ dependencies = [
  "rustc_session",
  "rustc_span",
  "rustc_target",
+ "rustc_trait_selection",
  "serialize",
  "smallvec 1.0.0",
 ]
@@ -4001,6 +4001,7 @@ dependencies = [
  "rustc_session",
  "rustc_span",
  "rustc_target",
+ "rustc_trait_selection",
 ]
 
 [[package]]
@@ -4048,7 +4049,6 @@ dependencies = [
  "rustc_expand",
  "rustc_feature",
  "rustc_hir",
- "rustc_infer",
  "rustc_metadata",
  "rustc_session",
  "rustc_span",
@@ -4128,6 +4128,27 @@ version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b725dadae9fabc488df69a287f5a99c5eaf5d10853842a8a3dfac52476f544ee"
 
+[[package]]
+name = "rustc_trait_selection"
+version = "0.0.0"
+dependencies = [
+ "fmt_macros",
+ "log",
+ "rustc",
+ "rustc_ast",
+ "rustc_attr",
+ "rustc_data_structures",
+ "rustc_errors",
+ "rustc_hir",
+ "rustc_index",
+ "rustc_infer",
+ "rustc_macros",
+ "rustc_session",
+ "rustc_span",
+ "rustc_target",
+ "smallvec 1.0.0",
+]
+
 [[package]]
 name = "rustc_traits"
 version = "0.0.0"
@@ -4141,6 +4162,7 @@ dependencies = [
  "rustc_macros",
  "rustc_span",
  "rustc_target",
+ "rustc_trait_selection",
  "smallvec 1.0.0",
 ]
 
@@ -4155,6 +4177,7 @@ dependencies = [
  "rustc_infer",
  "rustc_span",
  "rustc_target",
+ "rustc_trait_selection",
 ]
 
 [[package]]
@@ -4173,6 +4196,7 @@ dependencies = [
  "rustc_infer",
  "rustc_span",
  "rustc_target",
+ "rustc_trait_selection",
  "smallvec 1.0.0",
 ]
 

src/librustc/traits/select.rs

@@ -288,3 +288,44 @@ impl<T: Clone> WithDepNode<T> {
         self.cached_value.clone()
     }
 }
+
+#[derive(Clone, Debug)]
+pub enum IntercrateAmbiguityCause {
+    DownstreamCrate { trait_desc: String, self_desc: Option<String> },
+    UpstreamCrateUpdate { trait_desc: String, self_desc: Option<String> },
+    ReservationImpl { message: String },
+}
+
+impl IntercrateAmbiguityCause {
+    /// Emits notes when the overlap is caused by complex intercrate ambiguities.
+    /// See #23980 for details.
+    pub fn add_intercrate_ambiguity_hint(&self, err: &mut rustc_errors::DiagnosticBuilder<'_>) {
+        err.note(&self.intercrate_ambiguity_hint());
+    }
+
+    pub fn intercrate_ambiguity_hint(&self) -> String {
+        match self {
+            &IntercrateAmbiguityCause::DownstreamCrate { ref trait_desc, ref self_desc } => {
+                let self_desc = if let &Some(ref ty) = self_desc {
+                    format!(" for type `{}`", ty)
+                } else {
+                    String::new()
+                };
+                format!("downstream crates may implement trait `{}`{}", trait_desc, self_desc)
+            }
+            &IntercrateAmbiguityCause::UpstreamCrateUpdate { ref trait_desc, ref self_desc } => {
+                let self_desc = if let &Some(ref ty) = self_desc {
+                    format!(" for type `{}`", ty)
+                } else {
+                    String::new()
+                };
+                format!(
+                    "upstream crates may add a new impl of trait `{}`{} \
+                     in future versions",
+                    trait_desc, self_desc
+                )
+            }
+            &IntercrateAmbiguityCause::ReservationImpl { ref message } => message.clone(),
+        }
+    }
+}

src/librustc_infer/Cargo.toml

@@ -10,18 +10,14 @@ path = "lib.rs"
 doctest = false
 
 [dependencies]
-fmt_macros = { path = "../libfmt_macros" }
 graphviz = { path = "../libgraphviz" }
 log = { version = "0.4", features = ["release_max_level_info", "std"] }
-rustc_attr = { path = "../librustc_attr" }
 rustc = { path = "../librustc" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_errors = { path = "../librustc_errors" }
-rustc_error_codes = { path = "../librustc_error_codes" }
 rustc_hir = { path = "../librustc_hir" }
 rustc_index = { path = "../librustc_index" }
 rustc_macros = { path = "../librustc_macros" }
-rustc_session = { path = "../librustc_session" }
 rustc_span = { path = "../librustc_span" }
 rustc_target = { path = "../librustc_target" }
 smallvec = { version = "1.0", features = ["union", "may_dangle"] }

src/librustc_infer/infer/canonical/query_response.rs

@@ -14,7 +14,7 @@ use crate::infer::canonical::{
 };
 use crate::infer::nll_relate::{NormalizationStrategy, TypeRelating, TypeRelatingDelegate};
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
-use crate::infer::{InferCtxt, InferCtxtBuilder, InferOk, InferResult, NLLRegionVariableOrigin};
+use crate::infer::{InferCtxt, InferOk, InferResult, NLLRegionVariableOrigin};
 use crate::traits::query::{Fallible, NoSolution};
 use crate::traits::{DomainGoal, TraitEngine};
 use crate::traits::{Obligation, ObligationCause, PredicateObligation};
@@ -26,52 +26,8 @@ use rustc::ty::{self, BoundVar, Ty, TyCtxt};
 use rustc_data_structures::captures::Captures;
 use rustc_index::vec::Idx;
 use rustc_index::vec::IndexVec;
-use rustc_span::DUMMY_SP;
 use std::fmt::Debug;
 
-impl<'tcx> InferCtxtBuilder<'tcx> {
-    /// The "main method" for a canonicalized trait query. Given the
-    /// canonical key `canonical_key`, this method will create a new
-    /// inference context, instantiate the key, and run your operation
-    /// `op`. The operation should yield up a result (of type `R`) as
-    /// well as a set of trait obligations that must be fully
-    /// satisfied. These obligations will be processed and the
-    /// canonical result created.
-    ///
-    /// Returns `NoSolution` in the event of any error.
-    ///
-    /// (It might be mildly nicer to implement this on `TyCtxt`, and
-    /// not `InferCtxtBuilder`, but that is a bit tricky right now.
-    /// In part because we would need a `for<'tcx>` sort of
-    /// bound for the closure and in part because it is convenient to
-    /// have `'tcx` be free on this function so that we can talk about
-    /// `K: TypeFoldable<'tcx>`.)
-    pub fn enter_canonical_trait_query<K, R>(
-        &mut self,
-        canonical_key: &Canonical<'tcx, K>,
-        operation: impl FnOnce(&InferCtxt<'_, 'tcx>, &mut dyn TraitEngine<'tcx>, K) -> Fallible<R>,
-    ) -> Fallible<CanonicalizedQueryResponse<'tcx, R>>
-    where
-        K: TypeFoldable<'tcx>,
-        R: Debug + TypeFoldable<'tcx>,
-        Canonical<'tcx, QueryResponse<'tcx, R>>: ArenaAllocatable,
-    {
-        self.enter_with_canonical(
-            DUMMY_SP,
-            canonical_key,
-            |ref infcx, key, canonical_inference_vars| {
-                let mut fulfill_cx = TraitEngine::new(infcx.tcx);
-                let value = operation(infcx, &mut *fulfill_cx, key)?;
-                infcx.make_canonicalized_query_response(
-                    canonical_inference_vars,
-                    value,
-                    &mut *fulfill_cx,
-                )
-            },
-        )
-    }
-}
-
 impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     /// This method is meant to be invoked as the final step of a canonical query
     /// implementation. It is given:

src/librustc_infer/infer/error_reporting/mod.rs

@@ -49,7 +49,6 @@ use super::lexical_region_resolve::RegionResolutionError;
 use super::region_constraints::GenericKind;
 use super::{InferCtxt, RegionVariableOrigin, SubregionOrigin, TypeTrace, ValuePairs};
 
-use crate::infer::opaque_types;
 use crate::infer::{self, SuppressRegionErrors};
 use crate::traits::error_reporting::report_object_safety_error;
 use crate::traits::{
@@ -288,6 +287,86 @@ fn explain_span(tcx: TyCtxt<'tcx>, heading: &str, span: Span) -> (String, Option
     (format!("the {} at {}:{}", heading, lo.line, lo.col.to_usize() + 1), Some(span))
 }
 
+pub fn unexpected_hidden_region_diagnostic(
+    tcx: TyCtxt<'tcx>,
+    region_scope_tree: Option<&region::ScopeTree>,
+    span: Span,
+    hidden_ty: Ty<'tcx>,
+    hidden_region: ty::Region<'tcx>,
+) -> DiagnosticBuilder<'tcx> {
+    let mut err = struct_span_err!(
+        tcx.sess,
+        span,
+        E0700,
+        "hidden type for `impl Trait` captures lifetime that does not appear in bounds",
+    );
+
+    // Explain the region we are capturing.
+    if let ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReStatic | ty::ReEmpty(_) = hidden_region {
+        // Assuming regionck succeeded (*), we ought to always be
+        // capturing *some* region from the fn header, and hence it
+        // ought to be free. So under normal circumstances, we will go
+        // down this path which gives a decent human readable
+        // explanation.
+        //
+        // (*) if not, the `tainted_by_errors` flag would be set to
+        // true in any case, so we wouldn't be here at all.
+        note_and_explain_free_region(
+            tcx,
+            &mut err,
+            &format!("hidden type `{}` captures ", hidden_ty),
+            hidden_region,
+            "",
+        );
+    } else {
+        // Ugh. This is a painful case: the hidden region is not one
+        // that we can easily summarize or explain. This can happen
+        // in a case like
+        // `src/test/ui/multiple-lifetimes/ordinary-bounds-unsuited.rs`:
+        //
+        // ```
+        // fn upper_bounds<'a, 'b>(a: Ordinary<'a>, b: Ordinary<'b>) -> impl Trait<'a, 'b> {
+        //   if condition() { a } else { b }
+        // }
+        // ```
+        //
+        // Here the captured lifetime is the intersection of `'a` and
+        // `'b`, which we can't quite express.
+
+        if let Some(region_scope_tree) = region_scope_tree {
+            // If the `region_scope_tree` is available, this is being
+            // invoked from the "region inferencer error". We can at
+            // least report a really cryptic error for now.
+            note_and_explain_region(
+                tcx,
+                region_scope_tree,
+                &mut err,
+                &format!("hidden type `{}` captures ", hidden_ty),
+                hidden_region,
+                "",
+            );
+        } else {
+            // If the `region_scope_tree` is *unavailable*, this is
+            // being invoked by the code that comes *after* region
+            // inferencing. This is a bug, as the region inferencer
+            // ought to have noticed the failed constraint and invoked
+            // error reporting, which in turn should have prevented us
+            // from getting trying to infer the hidden type
+            // completely.
+            tcx.sess.delay_span_bug(
+                span,
+                &format!(
+                    "hidden type captures unexpected lifetime `{:?}` \
+                     but no region inference failure",
+                    hidden_region,
+                ),
+            );
+        }
+    }
+
+    err
+}
+
 impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     pub fn report_region_errors(
         &self,
@@ -410,7 +489,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                         span,
                     } => {
                         let hidden_ty = self.resolve_vars_if_possible(&hidden_ty);
-                        opaque_types::unexpected_hidden_region_diagnostic(
+                        unexpected_hidden_region_diagnostic(
                             self.tcx,
                             Some(region_scope_tree),
                             span,
@@ -2077,7 +2156,7 @@ impl<'tcx> ObligationCauseExt<'tcx> for ObligationCause<'tcx> {
 /// This is a bare signal of what kind of type we're dealing with. `ty::TyKind` tracks
 /// extra information about each type, but we only care about the category.
 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
-crate enum TyCategory {
+pub enum TyCategory {
     Closure,
     Opaque,
     Generator,