Auto merge of #52488 - nikomatsakis:nll-issue-48071-universe-and-sub, r=pnkfelix

introduce universes to NLL type check

This branch aims to fix #48071 and also advance chalk integration a bit at the same time. It re-implements the subtyping/type-equating check so that NLL doesn't "piggy back" on the subtyping code of the old type checker.

This new code uses the "universe-based" approach to handling higher-ranked lifetimes, which sidesteps some of the limitations of the current "leak-based" scheme. This avoids the ICE in #48071.

At the same time, I aim for this to potentially be a kind of optimization. This NLL code is (currently) not cached, but it also generates constraints without doing as much instantiation, substitution, and folding. Right now, though, it still piggy backs on the `relate_tys` trait, which is a bit unfortunate -- it means we are doing more hashing and things than we have to. I want to measure the see the perf. Refactoring that trait is something I'd prefer to leave for follow-up work.

r? @pnkfelix -- but I want to measure perf etc first

Author: bors

src/Cargo.lock

@@ -87,7 +87,7 @@ dependencies = [
 
 [[package]]
 name = "atty"
-version = "0.2.11"
+version = "0.2.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "libc 0.2.42 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -187,7 +187,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 name = "cargo"
 version = "0.30.0"
 dependencies = [
- "atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "atty 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "bufstream 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "clap 2.32.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "core-foundation 0.6.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -303,7 +303,7 @@ version = "2.32.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "ansi_term 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "atty 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "strsim 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "textwrap 0.10.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -622,7 +622,7 @@ name = "env_logger"
 version = "0.5.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "atty 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "humantime 1.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1844,7 +1844,7 @@ name = "rustc-ap-rustc_errors"
 version = "182.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "atty 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-ap-rustc_data_structures 182.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-ap-serialize 182.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-ap-syntax_pos 182.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2097,7 +2097,7 @@ dependencies = [
 name = "rustc_errors"
 version = "0.0.0"
 dependencies = [
- "atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)",
+ "atty 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc_data_structures 0.0.0",
  "serialize 0.0.0",
  "syntax_pos 0.0.0",
@@ -3056,7 +3056,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum ansi_term 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "ee49baf6cb617b853aa8d93bf420db2383fab46d314482ca2803b40d5fde979b"
 "checksum arrayvec 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)" = "a1e964f9e24d588183fcb43503abda40d288c8657dfc27311516ce2f05675aef"
 "checksum assert_cli 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "98589b0e465a6c510d95fceebd365bb79bedece7f6e18a480897f2015f85ec51"
-"checksum atty 0.2.11 (registry+https://github.com/rust-lang/crates.io-index)" = "9a7d5b8723950951411ee34d271d99dddcc2035a16ab25310ea2c8cfd4369652"
+"checksum atty 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)" = "2fc4a1aa4c24c0718a250f0681885c1af91419d242f29eb8f2ab28502d80dbd1"
 "checksum backtrace 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)" = "89a47830402e9981c5c41223151efcced65a0510c13097c769cede7efb34782a"
 "checksum backtrace-sys 0.1.23 (registry+https://github.com/rust-lang/crates.io-index)" = "bff67d0c06556c0b8e6b5f090f0eac52d950d9dfd1d35ba04e4ca3543eaf6a7e"
 "checksum bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "aad18937a628ec6abcd26d1489012cc0e18c21798210f491af69ded9b881106d"

src/librustc/dep_graph/graph.rs

@@ -39,7 +39,6 @@ pub struct DepGraph {
     fingerprints: Lrc<Lock<IndexVec<DepNodeIndex, Fingerprint>>>
 }
 
-
 newtype_index!(DepNodeIndex);
 
 impl DepNodeIndex {

src/librustc/infer/higher_ranked/mod.rs

@@ -617,6 +617,18 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         debug!("leak_check: skol_map={:?}",
                skol_map);
 
+        // If the user gave `-Zno-leak-check`, then skip the leak
+        // check completely. This is wildly unsound and also not
+        // unlikely to cause an ICE or two. It is intended for use
+        // only during a transition period, in which the MIR typeck
+        // uses the "universe-style" check, and the rest of typeck
+        // uses the more conservative leak check.  Since the leak
+        // check is more conservative, we can't test the
+        // universe-style check without disabling it.
+        if self.tcx.sess.opts.debugging_opts.no_leak_check {
+            return Ok(());
+        }
+
         let new_vars = self.region_vars_confined_to_snapshot(snapshot);
         for (&skol_br, &skol) in skol_map {
             // The inputs to a skolemized variable can only

src/librustc/infer/mod.rs

@@ -377,7 +377,23 @@ pub enum NLLRegionVariableOrigin {
     // elsewhere. This origin indices we've got one of those.
     FreeRegion,
 
-    Inferred(::mir::visit::TyContext),
+    BoundRegion(ty::UniverseIndex),
+
+    Existential,
+}
+
+impl NLLRegionVariableOrigin {
+    pub fn is_universal(self) -> bool {
+        match self {
+            NLLRegionVariableOrigin::FreeRegion => true,
+            NLLRegionVariableOrigin::BoundRegion(..) => true,
+            NLLRegionVariableOrigin::Existential => false,
+        }
+    }
+
+    pub fn is_existential(self) -> bool {
+        !self.is_universal()
+    }
 }
 
 #[derive(Copy, Clone, Debug)]
@@ -1381,6 +1397,17 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     fn universe(&self) -> ty::UniverseIndex {
         self.universe.get()
     }
+
+    /// Create and return a new subunivese of the current universe;
+    /// update `self.universe` to that new subuniverse. At present,
+    /// used only in the NLL subtyping code, which uses the new
+    /// universe-based scheme instead of the more limited leak-check
+    /// scheme.
+    pub fn create_subuniverse(&self) -> ty::UniverseIndex {
+        let u = self.universe.get().subuniverse();
+        self.universe.set(u);
+        u
+    }
 }
 
 impl<'a, 'gcx, 'tcx> TypeTrace<'tcx> {

src/librustc/lib.rs

@@ -69,6 +69,7 @@
 #![feature(trusted_len)]
 #![feature(vec_remove_item)]
 #![feature(catch_expr)]
+#![feature(step_trait)]
 #![feature(integer_atomics)]
 #![feature(test)]
 #![feature(in_band_lifetimes)]

src/librustc/mir/traversal.rs

@@ -9,7 +9,6 @@
 // except according to those terms.
 
 use rustc_data_structures::bitvec::BitVector;
-use rustc_data_structures::indexed_vec::Idx;
 
 use super::*;
 
@@ -33,7 +32,7 @@ use super::*;
 #[derive(Clone)]
 pub struct Preorder<'a, 'tcx: 'a> {
     mir: &'a Mir<'tcx>,
-    visited: BitVector,
+    visited: BitVector<BasicBlock>,
     worklist: Vec<BasicBlock>,
 }
 
@@ -58,7 +57,7 @@ impl<'a, 'tcx> Iterator for Preorder<'a, 'tcx> {
 
     fn next(&mut self) -> Option<(BasicBlock, &'a BasicBlockData<'tcx>)> {
         while let Some(idx) = self.worklist.pop() {
-            if !self.visited.insert(idx.index()) {
+            if !self.visited.insert(idx) {
                 continue;
             }
 
@@ -107,7 +106,7 @@ impl<'a, 'tcx> ExactSizeIterator for Preorder<'a, 'tcx> {}
 /// A Postorder traversal of this graph is `D B C A` or `D C B A`
 pub struct Postorder<'a, 'tcx: 'a> {
     mir: &'a Mir<'tcx>,
-    visited: BitVector,
+    visited: BitVector<BasicBlock>,
     visit_stack: Vec<(BasicBlock, Successors<'a>)>
 }
 
@@ -123,7 +122,7 @@ impl<'a, 'tcx> Postorder<'a, 'tcx> {
         let data = &po.mir[root];
 
         if let Some(ref term) = data.terminator {
-            po.visited.insert(root.index());
+            po.visited.insert(root);
             po.visit_stack.push((root, term.successors()));
             po.traverse_successor();
         }
@@ -190,8 +189,8 @@ impl<'a, 'tcx> Postorder<'a, 'tcx> {
                 break;
             };
 
-            if self.visited.insert(bb.index()) {
-                if let Some(ref term) = self.mir[bb].terminator {
+            if self.visited.insert(bb) {
+                if let Some(term) = &self.mir[bb].terminator {
                     self.visit_stack.push((bb, term.successors()));
                 }
             }

src/librustc/session/config.rs

@@ -1353,6 +1353,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
           "generate build artifacts that are compatible with linker-based LTO."),
     no_parallel_llvm: bool = (false, parse_bool, [UNTRACKED],
           "don't run LLVM in parallel (while keeping codegen-units and ThinLTO)"),
+    no_leak_check: bool = (false, parse_bool, [UNTRACKED],
+        "disables the 'leak check' for subtyping; unsound, but useful for tests"),
 }
 
 pub fn default_lib_output() -> CrateType {

src/librustc/ty/mod.rs

@@ -1481,14 +1481,27 @@ impl<'tcx> InstantiatedPredicates<'tcx> {
 /// type name in a non-zero universe is a skolemized type -- an
 /// idealized representative of "types in general" that we use for
 /// checking generic functions.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable)]
 pub struct UniverseIndex(u32);
 
 impl UniverseIndex {
     /// The root universe, where things that the user defined are
     /// visible.
     pub const ROOT: Self = UniverseIndex(0);
 
+    /// The "max universe" -- this isn't really a valid universe, but
+    /// it's useful sometimes as a "starting value" when you are
+    /// taking the minimum of a (non-empty!) set of universes.
+    pub const MAX: Self = UniverseIndex(::std::u32::MAX);
+
+    /// Creates a universe index from the given integer.  Not to be
+    /// used lightly lest you pick a bad value. But sometimes we
+    /// convert universe indicies into integers and back for various
+    /// reasons.
+    pub fn from_u32(index: u32) -> Self {
+        UniverseIndex(index)
+    }
+
     /// A "subuniverse" corresponds to being inside a `forall` quantifier.
     /// So, for example, suppose we have this type in universe `U`:
     ///
@@ -1504,6 +1517,11 @@ impl UniverseIndex {
         UniverseIndex(self.0.checked_add(1).unwrap())
     }
 
+    /// True if the names in this universe are a subset of the names in `other`.
+    pub fn is_subset_of(self, other: UniverseIndex) -> bool {
+        self.0 <= other.0
+    }
+
     pub fn as_u32(&self) -> u32 {
         self.0
     }
@@ -1513,6 +1531,12 @@ impl UniverseIndex {
     }
 }
 
+impl fmt::Debug for UniverseIndex {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        write!(fmt, "U{}", self.as_u32())
+    }
+}
+
 impl From<u32> for UniverseIndex {
     fn from(index: u32) -> Self {
         UniverseIndex(index)

src/librustc_codegen_llvm/debuginfo/create_scope_map.rs

@@ -65,7 +65,7 @@ pub fn create_mir_scopes(cx: &CodegenCx, mir: &Mir, debug_context: &FunctionDebu
     let mut has_variables = BitVector::new(mir.source_scopes.len());
     for var in mir.vars_iter() {
         let decl = &mir.local_decls[var];
-        has_variables.insert(decl.visibility_scope.index());
+        has_variables.insert(decl.visibility_scope);
     }
 
     // Instantiate all scopes.
@@ -79,7 +79,7 @@ pub fn create_mir_scopes(cx: &CodegenCx, mir: &Mir, debug_context: &FunctionDebu
 
 fn make_mir_scope(cx: &CodegenCx,
                   mir: &Mir,
-                  has_variables: &BitVector,
+                  has_variables: &BitVector<SourceScope>,
                   debug_context: &FunctionDebugContextData,
                   scope: SourceScope,
                   scopes: &mut IndexVec<SourceScope, MirDebugScope>) {
@@ -102,7 +102,7 @@ fn make_mir_scope(cx: &CodegenCx,
         return;
     };
 
-    if !has_variables.contains(scope.index()) {
+    if !has_variables.contains(scope) {
         // Do not create a DIScope if there are no variables
         // defined in this MIR Scope, to avoid debuginfo bloat.
 

src/librustc_codegen_llvm/mir/analyze.rs

@@ -22,7 +22,7 @@ use rustc::ty::layout::LayoutOf;
 use type_of::LayoutLlvmExt;
 use super::FunctionCx;
 
-pub fn non_ssa_locals<'a, 'tcx>(fx: &FunctionCx<'a, 'tcx>) -> BitVector {
+pub fn non_ssa_locals<'a, 'tcx>(fx: &FunctionCx<'a, 'tcx>) -> BitVector<mir::Local> {
     let mir = fx.mir;
     let mut analyzer = LocalAnalyzer::new(fx);
 
@@ -54,7 +54,7 @@ pub fn non_ssa_locals<'a, 'tcx>(fx: &FunctionCx<'a, 'tcx>) -> BitVector {
 struct LocalAnalyzer<'mir, 'a: 'mir, 'tcx: 'a> {
     fx: &'mir FunctionCx<'a, 'tcx>,
     dominators: Dominators<mir::BasicBlock>,
-    non_ssa_locals: BitVector,
+    non_ssa_locals: BitVector<mir::Local>,
     // The location of the first visited direct assignment to each
     // local, or an invalid location (out of bounds `block` index).
     first_assignment: IndexVec<mir::Local, Location>
@@ -90,7 +90,7 @@ impl<'mir, 'a, 'tcx> LocalAnalyzer<'mir, 'a, 'tcx> {
 
     fn not_ssa(&mut self, local: mir::Local) {
         debug!("marking {:?} as non-SSA", local);
-        self.non_ssa_locals.insert(local.index());
+        self.non_ssa_locals.insert(local);
     }
 
     fn assign(&mut self, local: mir::Local, location: Location) {