Auto merge of #61613 - sinkuu:impl_trait_inline, r=ollie27

Support `impl Trait` in inlined documentation

`impl Trait` in argument position was not properly rendered when inlined from other crates. ([a live example on docs.rs](https://docs.rs/libp2p/0.8.1/libp2p/floodsub/struct.Floodsub.html#method.unsubscribe))

![old](https://user-images.githubusercontent.com/7091080/59089838-14ba9900-8946-11e9-830b-53b317bdecb4.png)
↓
![new](https://user-images.githubusercontent.com/7091080/59089844-16845c80-8946-11e9-9fe3-8998af9d73ce.png)

Author: bors

src/librustdoc/clean/inline.rs

@@ -217,8 +217,9 @@ fn build_external_function(cx: &DocContext<'_>, did: DefId) -> clean::Function {
     };
 
     let predicates = cx.tcx.predicates_of(did);
-    let generics = (cx.tcx.generics_of(did), &predicates).clean(cx);
-    let decl = (did, sig).clean(cx);
+    let (generics, decl) = clean::enter_impl_trait(cx, || {
+        ((cx.tcx.generics_of(did), &predicates).clean(cx), (did, sig).clean(cx))
+    });
     let (all_types, ret_types) = clean::get_all_types(&generics, &decl, cx);
     clean::Function {
         decl,
@@ -372,7 +373,9 @@ pub fn build_impl(cx: &DocContext<'_>, did: DefId, attrs: Option<Attrs<'_>>,
                     None
                 }
             }).collect::<Vec<_>>(),
-            (tcx.generics_of(did), &predicates).clean(cx),
+            clean::enter_impl_trait(cx, || {
+                (tcx.generics_of(did), &predicates).clean(cx)
+            }),
         )
     };
     let polarity = tcx.impl_polarity(did);

src/librustdoc/clean/mod.rs

@@ -45,7 +45,7 @@ use std::cell::RefCell;
 use std::sync::Arc;
 use std::u32;
 
-use crate::core::{self, DocContext};
+use crate::core::{self, DocContext, ImplTraitParam};
 use crate::doctree;
 use crate::html::render::{cache, ExternalLocation};
 use crate::html::item_type::ItemType;
@@ -1540,7 +1540,7 @@ impl Clean<GenericParamDef> for ty::GenericParamDef {
             ty::GenericParamDefKind::Lifetime => {
                 (self.name.to_string(), GenericParamDefKind::Lifetime)
             }
-            ty::GenericParamDefKind::Type { has_default, .. } => {
+            ty::GenericParamDefKind::Type { has_default, synthetic, .. } => {
                 cx.renderinfo.borrow_mut().external_param_names
                              .insert(self.def_id, self.name.clean(cx));
                 let default = if has_default {
@@ -1552,7 +1552,7 @@ impl Clean<GenericParamDef> for ty::GenericParamDef {
                     did: self.def_id,
                     bounds: vec![], // These are filled in from the where-clauses.
                     default,
-                    synthetic: None,
+                    synthetic,
                 })
             }
             ty::GenericParamDefKind::Const { .. } => {
@@ -1641,7 +1641,7 @@ impl Clean<Generics> for hir::Generics {
                 match param.kind {
                     GenericParamDefKind::Lifetime => unreachable!(),
                     GenericParamDefKind::Type { did, ref bounds, .. } => {
-                        cx.impl_trait_bounds.borrow_mut().insert(did, bounds.clone());
+                        cx.impl_trait_bounds.borrow_mut().insert(did.into(), bounds.clone());
                     }
                     GenericParamDefKind::Const { .. } => unreachable!(),
                 }
@@ -1693,26 +1693,123 @@ impl<'a, 'tcx> Clean<Generics> for (&'a ty::Generics,
                                     &'a &'tcx ty::GenericPredicates<'tcx>) {
     fn clean(&self, cx: &DocContext<'_>) -> Generics {
         use self::WherePredicate as WP;
+        use std::collections::BTreeMap;
 
         let (gens, preds) = *self;
 
+        // Don't populate `cx.impl_trait_bounds` before `clean`ning `where` clauses,
+        // since `Clean for ty::Predicate` would consume them.
+        let mut impl_trait = BTreeMap::<ImplTraitParam, Vec<GenericBound>>::default();
+
         // Bounds in the type_params and lifetimes fields are repeated in the
         // predicates field (see rustc_typeck::collect::ty_generics), so remove
         // them.
-        let stripped_typarams = gens.params.iter().filter_map(|param| match param.kind {
-            ty::GenericParamDefKind::Lifetime => None,
-            ty::GenericParamDefKind::Type { .. } => {
-                if param.name.as_symbol() == kw::SelfUpper {
-                    assert_eq!(param.index, 0);
-                    return None;
+        let stripped_typarams = gens.params.iter()
+            .filter_map(|param| match param.kind {
+                ty::GenericParamDefKind::Lifetime => None,
+                ty::GenericParamDefKind::Type { synthetic, .. } => {
+                    if param.name.as_symbol() == kw::SelfUpper {
+                        assert_eq!(param.index, 0);
+                        return None;
+                    }
+                    if synthetic == Some(hir::SyntheticTyParamKind::ImplTrait) {
+                        impl_trait.insert(param.index.into(), vec![]);
+                        return None;
+                    }
+                    Some(param.clean(cx))
+                }
+                ty::GenericParamDefKind::Const { .. } => None,
+            }).collect::<Vec<GenericParamDef>>();
+
+        // param index -> [(DefId of trait, associated type name, type)]
+        let mut impl_trait_proj =
+            FxHashMap::<u32, Vec<(DefId, String, Ty<'tcx>)>>::default();
+
+        let where_predicates = preds.predicates.iter()
+            .flat_map(|(p, _)| {
+                let mut projection = None;
+                let param_idx = (|| {
+                    if let Some(trait_ref) = p.to_opt_poly_trait_ref() {
+                        if let ty::Param(param) = trait_ref.self_ty().sty {
+                            return Some(param.index);
+                        }
+                    } else if let Some(outlives) = p.to_opt_type_outlives() {
+                        if let ty::Param(param) = outlives.skip_binder().0.sty {
+                            return Some(param.index);
+                        }
+                    } else if let ty::Predicate::Projection(p) = p {
+                        if let ty::Param(param) = p.skip_binder().projection_ty.self_ty().sty {
+                            projection = Some(p);
+                            return Some(param.index);
+                        }
+                    }
+
+                    None
+                })();
+
+                if let Some(param_idx) = param_idx {
+                    if let Some(b) = impl_trait.get_mut(&param_idx.into()) {
+                        let p = p.clean(cx)?;
+
+                        b.extend(
+                            p.get_bounds()
+                                .into_iter()
+                                .flatten()
+                                .cloned()
+                                .filter(|b| !b.is_sized_bound(cx))
+                        );
+
+                        let proj = projection
+                            .map(|p| (p.skip_binder().projection_ty.clean(cx), p.skip_binder().ty));
+                        if let Some(((_, trait_did, name), rhs)) =
+                            proj.as_ref().and_then(|(lhs, rhs)| Some((lhs.projection()?, rhs)))
+                        {
+                            impl_trait_proj
+                                .entry(param_idx)
+                                .or_default()
+                                .push((trait_did, name.to_string(), rhs));
+                        }
+
+                        return None;
+                    }
+                }
+
+                Some(p)
+            })
+            .collect::<Vec<_>>();
+
+        for (param, mut bounds) in impl_trait {
+            // Move trait bounds to the front.
+            bounds.sort_by_key(|b| if let GenericBound::TraitBound(..) = b {
+                false
+            } else {
+                true
+            });
+
+            if let crate::core::ImplTraitParam::ParamIndex(idx) = param {
+                if let Some(proj) = impl_trait_proj.remove(&idx) {
+                    for (trait_did, name, rhs) in proj {
+                        simplify::merge_bounds(
+                            cx,
+                            &mut bounds,
+                            trait_did,
+                            &name,
+                            &rhs.clean(cx),
+                        );
+                    }
                 }
-                Some(param.clean(cx))
+            } else {
+                unreachable!();
             }
-            ty::GenericParamDefKind::Const { .. } => None,
-        }).collect::<Vec<GenericParamDef>>();
 
-        let mut where_predicates = preds.predicates.iter()
-            .flat_map(|(p, _)| p.clean(cx))
+            cx.impl_trait_bounds.borrow_mut().insert(param, bounds);
+        }
+
+        // Now that `cx.impl_trait_bounds` is populated, we can process
+        // remaining predicates which could contain `impl Trait`.
+        let mut where_predicates = where_predicates
+            .into_iter()
+            .flat_map(|p| p.clean(cx))
             .collect::<Vec<_>>();
 
         // Type parameters and have a Sized bound by default unless removed with
@@ -2613,6 +2710,21 @@ impl Type {
             _ => false,
         }
     }
+
+    pub fn projection(&self) -> Option<(&Type, DefId, &str)> {
+        let (self_, trait_, name) = match self {
+            QPath { ref self_type, ref trait_, ref name } => {
+                (self_type, trait_, name)
+            }
+            _ => return None,
+        };
+        let trait_did = match **trait_ {
+            ResolvedPath { did, .. } => did,
+            _ => return None,
+        };
+        Some((&self_, trait_did, name))
+    }
+
 }
 
 impl GetDefId for Type {
@@ -2791,7 +2903,7 @@ impl Clean<Type> for hir::Ty {
                     if let Some(new_ty) = cx.ty_substs.borrow().get(&did).cloned() {
                         return new_ty;
                     }
-                    if let Some(bounds) = cx.impl_trait_bounds.borrow_mut().remove(&did) {
+                    if let Some(bounds) = cx.impl_trait_bounds.borrow_mut().remove(&did.into()) {
                         return ImplTrait(bounds);
                     }
                 }
@@ -3082,7 +3194,13 @@ impl<'tcx> Clean<Type> for Ty<'tcx> {
 
             ty::Projection(ref data) => data.clean(cx),
 
-            ty::Param(ref p) => Generic(p.name.to_string()),
+            ty::Param(ref p) => {
+                if let Some(bounds) = cx.impl_trait_bounds.borrow_mut().remove(&p.index.into()) {
+                    ImplTrait(bounds)
+                } else {
+                    Generic(p.name.to_string())
+                }
+            }
 
             ty::Opaque(def_id, substs) => {
                 // Grab the "TraitA + TraitB" from `impl TraitA + TraitB`,

src/librustdoc/clean/simplify.rs

@@ -53,58 +53,21 @@ pub fn where_clauses(cx: &DocContext<'_>, clauses: Vec<WP>) -> Vec<WP> {
     // Look for equality predicates on associated types that can be merged into
     // general bound predicates
     equalities.retain(|&(ref lhs, ref rhs)| {
-        let (self_, trait_, name) = match *lhs {
-            clean::QPath { ref self_type, ref trait_, ref name } => {
-                (self_type, trait_, name)
-            }
-            _ => return true,
-        };
-        let generic = match **self_ {
-            clean::Generic(ref s) => s,
-            _ => return true,
+        let (self_, trait_did, name) = if let Some(p) = lhs.projection() {
+            p
+        } else {
+            return true;
         };
-        let trait_did = match **trait_ {
-            clean::ResolvedPath { did, .. } => did,
+        let generic = match self_ {
+            clean::Generic(s) => s,
             _ => return true,
         };
         let bounds = match params.get_mut(generic) {
             Some(bound) => bound,
             None => return true,
         };
-        !bounds.iter_mut().any(|b| {
-            let trait_ref = match *b {
-                clean::GenericBound::TraitBound(ref mut tr, _) => tr,
-                clean::GenericBound::Outlives(..) => return false,
-            };
-            let (did, path) = match trait_ref.trait_ {
-                clean::ResolvedPath { did, ref mut path, ..} => (did, path),
-                _ => return false,
-            };
-            // If this QPath's trait `trait_did` is the same as, or a supertrait
-            // of, the bound's trait `did` then we can keep going, otherwise
-            // this is just a plain old equality bound.
-            if !trait_is_same_or_supertrait(cx, did, trait_did) {
-                return false
-            }
-            let last = path.segments.last_mut().expect("segments were empty");
-            match last.args {
-                PP::AngleBracketed { ref mut bindings, .. } => {
-                    bindings.push(clean::TypeBinding {
-                        name: name.clone(),
-                        kind: clean::TypeBindingKind::Equality {
-                            ty: rhs.clone(),
-                        },
-                    });
-                }
-                PP::Parenthesized { ref mut output, .. } => {
-                    assert!(output.is_none());
-                    if *rhs != clean::Type::Tuple(Vec::new()) {
-                        *output = Some(rhs.clone());
-                    }
-                }
-            };
-            true
-        })
+
+        merge_bounds(cx, bounds, trait_did, name, rhs)
     });
 
     // And finally, let's reassemble everything
@@ -127,6 +90,49 @@ pub fn where_clauses(cx: &DocContext<'_>, clauses: Vec<WP>) -> Vec<WP> {
     clauses
 }
 
+pub fn merge_bounds(
+    cx: &clean::DocContext<'_>,
+    bounds: &mut Vec<clean::GenericBound>,
+    trait_did: DefId,
+    name: &str,
+    rhs: &clean::Type,
+) -> bool {
+    !bounds.iter_mut().any(|b| {
+        let trait_ref = match *b {
+            clean::GenericBound::TraitBound(ref mut tr, _) => tr,
+            clean::GenericBound::Outlives(..) => return false,
+        };
+        let (did, path) = match trait_ref.trait_ {
+            clean::ResolvedPath { did, ref mut path, ..} => (did, path),
+            _ => return false,
+        };
+        // If this QPath's trait `trait_did` is the same as, or a supertrait
+        // of, the bound's trait `did` then we can keep going, otherwise
+        // this is just a plain old equality bound.
+        if !trait_is_same_or_supertrait(cx, did, trait_did) {
+            return false
+        }
+        let last = path.segments.last_mut().expect("segments were empty");
+        match last.args {
+            PP::AngleBracketed { ref mut bindings, .. } => {
+                bindings.push(clean::TypeBinding {
+                    name: name.to_string(),
+                    kind: clean::TypeBindingKind::Equality {
+                        ty: rhs.clone(),
+                    },
+                });
+            }
+            PP::Parenthesized { ref mut output, .. } => {
+                assert!(output.is_none());
+                if *rhs != clean::Type::Tuple(Vec::new()) {
+                    *output = Some(rhs.clone());
+                }
+            }
+        };
+        true
+    })
+}
+
 pub fn ty_params(mut params: Vec<clean::GenericParamDef>) -> Vec<clean::GenericParamDef> {
     for param in &mut params {
         match param.kind {

src/librustdoc/core.rs

@@ -61,8 +61,8 @@ pub struct DocContext<'tcx> {
     pub lt_substs: RefCell<FxHashMap<DefId, clean::Lifetime>>,
     /// Table `DefId` of const parameter -> substituted const
     pub ct_substs: RefCell<FxHashMap<DefId, clean::Constant>>,
-    /// Table DefId of `impl Trait` in argument position -> bounds
-    pub impl_trait_bounds: RefCell<FxHashMap<DefId, Vec<clean::GenericBound>>>,
+    /// Table synthetic type parameter for `impl Trait` in argument position -> bounds
+    pub impl_trait_bounds: RefCell<FxHashMap<ImplTraitParam, Vec<clean::GenericBound>>>,
     pub fake_def_ids: RefCell<FxHashMap<CrateNum, DefId>>,
     pub all_fake_def_ids: RefCell<FxHashSet<DefId>>,
     /// Auto-trait or blanket impls processed so far, as `(self_ty, trait_def_id)`.
@@ -459,3 +459,23 @@ pub fn run_core(options: RustdocOptions) -> (clean::Crate, RenderInfo, RenderOpt
         })
     })
 }
+
+/// `DefId` or parameter index (`ty::ParamTy.index`) of a synthetic type parameter
+/// for `impl Trait` in argument position.
+#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub enum ImplTraitParam {
+    DefId(DefId),
+    ParamIndex(u32),
+}
+
+impl From<DefId> for ImplTraitParam {
+    fn from(did: DefId) -> Self {
+        ImplTraitParam::DefId(did)
+    }
+}
+
+impl From<u32> for ImplTraitParam {
+    fn from(idx: u32) -> Self {
+        ImplTraitParam::ParamIndex(idx)
+    }
+}