1 files changed, 353 insertions, 0 deletions

diff --git a/crates/ra_hir_ty/src/method_resolution.rs b/crates/ra_hir_ty/src/method_resolution.rs
new file mode 100644
index 000000000..ee1936b0e
--- /dev/null
+++ b/crates/ra_hir_ty/src/method_resolution.rs
@@ -0,0 +1,353 @@
+//! This module is concerned with finding methods that a given type provides.
+//! For details about how this works in rustc, see the method lookup page in the
+//! [rustc guide](https://rust-lang.github.io/rustc-guide/method-lookup.html)
+//! and the corresponding code mostly in librustc_typeck/check/method/probe.rs.
+use std::sync::Arc;
+
+use arrayvec::ArrayVec;
+use hir_def::{
+    lang_item::LangItemTarget, resolver::Resolver, type_ref::Mutability, AssocItemId, AstItemDef,
+    FunctionId, HasModule, ImplId, TraitId,
+};
+use hir_expand::name::Name;
+use ra_db::CrateId;
+use ra_prof::profile;
+use rustc_hash::FxHashMap;
+
+use crate::{
+    autoderef,
+    db::HirDatabase,
+    primitive::{FloatBitness, Uncertain},
+    utils::all_super_traits,
+    Canonical, ImplTy, InEnvironment, TraitEnvironment, TraitRef, Ty, TypeCtor,
+};
+
+/// This is used as a key for indexing impls.
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum TyFingerprint {
+    Apply(TypeCtor),
+}
+
+impl TyFingerprint {
+    /// Creates a TyFingerprint for looking up an impl. Only certain types can
+    /// have impls: if we have some `struct S`, we can have an `impl S`, but not
+    /// `impl &S`. Hence, this will return `None` for reference types and such.
+    fn for_impl(ty: &Ty) -> Option<TyFingerprint> {
+        match ty {
+            Ty::Apply(a_ty) => Some(TyFingerprint::Apply(a_ty.ctor)),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct CrateImplBlocks {
+    impls: FxHashMap<TyFingerprint, Vec<ImplId>>,
+    impls_by_trait: FxHashMap<TraitId, Vec<ImplId>>,
+}
+
+impl CrateImplBlocks {
+    pub(crate) fn impls_in_crate_query(
+        db: &impl HirDatabase,
+        krate: CrateId,
+    ) -> Arc<CrateImplBlocks> {
+        let _p = profile("impls_in_crate_query");
+        let mut res =
+            CrateImplBlocks { impls: FxHashMap::default(), impls_by_trait: FxHashMap::default() };
+
+        let crate_def_map = db.crate_def_map(krate);
+        for (_module_id, module_data) in crate_def_map.modules.iter() {
+            for &impl_id in module_data.impls.iter() {
+                match db.impl_ty(impl_id) {
+                    ImplTy::TraitRef(tr) => {
+                        res.impls_by_trait.entry(tr.trait_).or_default().push(impl_id);
+                    }
+                    ImplTy::Inherent(self_ty) => {
+                        if let Some(self_ty_fp) = TyFingerprint::for_impl(&self_ty) {
+                            res.impls.entry(self_ty_fp).or_default().push(impl_id);
+                        }
+                    }
+                }
+            }
+        }
+
+        Arc::new(res)
+    }
+    pub fn lookup_impl_blocks(&self, ty: &Ty) -> impl Iterator<Item = ImplId> + '_ {
+        let fingerprint = TyFingerprint::for_impl(ty);
+        fingerprint.and_then(|f| self.impls.get(&f)).into_iter().flatten().copied()
+    }
+
+    pub fn lookup_impl_blocks_for_trait(&self, tr: TraitId) -> impl Iterator<Item = ImplId> + '_ {
+        self.impls_by_trait.get(&tr).into_iter().flatten().copied()
+    }
+
+    pub fn all_impls<'a>(&'a self) -> impl Iterator<Item = ImplId> + 'a {
+        self.impls.values().chain(self.impls_by_trait.values()).flatten().copied()
+    }
+}
+
+impl Ty {
+    pub fn def_crates(
+        &self,
+        db: &impl HirDatabase,
+        cur_crate: CrateId,
+    ) -> Option<ArrayVec<[CrateId; 2]>> {
+        // Types like slice can have inherent impls in several crates, (core and alloc).
+        // The corresponding impls are marked with lang items, so we can use them to find the required crates.
+        macro_rules! lang_item_crate {
+        ($($name:expr),+ $(,)?) => {{
+            let mut v = ArrayVec::<[LangItemTarget; 2]>::new();
+            $(
+                v.extend(db.lang_item(cur_crate, $name.into()));
+            )+
+            v
+        }};
+    }
+
+        let lang_item_targets = match self {
+            Ty::Apply(a_ty) => match a_ty.ctor {
+                TypeCtor::Adt(def_id) => {
+                    return Some(std::iter::once(def_id.module(db).krate).collect())
+                }
+                TypeCtor::Bool => lang_item_crate!("bool"),
+                TypeCtor::Char => lang_item_crate!("char"),
+                TypeCtor::Float(Uncertain::Known(f)) => match f.bitness {
+                    // There are two lang items: one in libcore (fXX) and one in libstd (fXX_runtime)
+                    FloatBitness::X32 => lang_item_crate!("f32", "f32_runtime"),
+                    FloatBitness::X64 => lang_item_crate!("f64", "f64_runtime"),
+                },
+                TypeCtor::Int(Uncertain::Known(i)) => lang_item_crate!(i.ty_to_string()),
+                TypeCtor::Str => lang_item_crate!("str_alloc", "str"),
+                TypeCtor::Slice => lang_item_crate!("slice_alloc", "slice"),
+                TypeCtor::RawPtr(Mutability::Shared) => lang_item_crate!("const_ptr"),
+                TypeCtor::RawPtr(Mutability::Mut) => lang_item_crate!("mut_ptr"),
+                _ => return None,
+            },
+            _ => return None,
+        };
+        let res = lang_item_targets
+            .into_iter()
+            .filter_map(|it| match it {
+                LangItemTarget::ImplBlockId(it) => Some(it),
+                _ => None,
+            })
+            .map(|it| it.module(db).krate)
+            .collect();
+        Some(res)
+    }
+}
+/// Look up the method with the given name, returning the actual autoderefed
+/// receiver type (but without autoref applied yet).
+pub(crate) fn lookup_method(
+    ty: &Canonical<Ty>,
+    db: &impl HirDatabase,
+    name: &Name,
+    resolver: &Resolver,
+) -> Option<(Ty, FunctionId)> {
+    iterate_method_candidates(ty, db, resolver, Some(name), LookupMode::MethodCall, |ty, f| match f
+    {
+        AssocItemId::FunctionId(f) => Some((ty.clone(), f)),
+        _ => None,
+    })
+}
+
+/// Whether we're looking up a dotted method call (like `v.len()`) or a path
+/// (like `Vec::new`).
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum LookupMode {
+    /// Looking up a method call like `v.len()`: We only consider candidates
+    /// that have a `self` parameter, and do autoderef.
+    MethodCall,
+    /// Looking up a path like `Vec::new` or `Vec::default`: We consider all
+    /// candidates including associated constants, but don't do autoderef.
+    Path,
+}
+
+// This would be nicer if it just returned an iterator, but that runs into
+// lifetime problems, because we need to borrow temp `CrateImplBlocks`.
+// FIXME add a context type here?
+pub fn iterate_method_candidates<T>(
+    ty: &Canonical<Ty>,
+    db: &impl HirDatabase,
+    resolver: &Resolver,
+    name: Option<&Name>,
+    mode: LookupMode,
+    mut callback: impl FnMut(&Ty, AssocItemId) -> Option<T>,
+) -> Option<T> {
+    let krate = resolver.krate()?;
+    match mode {
+        LookupMode::MethodCall => {
+            // For method calls, rust first does any number of autoderef, and then one
+            // autoref (i.e. when the method takes &self or &mut self). We just ignore
+            // the autoref currently -- when we find a method matching the given name,
+            // we assume it fits.
+
+            // Also note that when we've got a receiver like &S, even if the method we
+            // find in the end takes &self, we still do the autoderef step (just as
+            // rustc does an autoderef and then autoref again).
+            let environment = TraitEnvironment::lower(db, resolver);
+            let ty = InEnvironment { value: ty.clone(), environment };
+            for derefed_ty in autoderef::autoderef(db, resolver.krate(), ty) {
+                if let Some(result) =
+                    iterate_inherent_methods(&derefed_ty, db, name, mode, krate, &mut callback)
+                {
+                    return Some(result);
+                }
+                if let Some(result) = iterate_trait_method_candidates(
+                    &derefed_ty,
+                    db,
+                    resolver,
+                    name,
+                    mode,
+                    &mut callback,
+                ) {
+                    return Some(result);
+                }
+            }
+        }
+        LookupMode::Path => {
+            // No autoderef for path lookups
+            if let Some(result) =
+                iterate_inherent_methods(&ty, db, name, mode, krate.into(), &mut callback)
+            {
+                return Some(result);
+            }
+            if let Some(result) =
+                iterate_trait_method_candidates(&ty, db, resolver, name, mode, &mut callback)
+            {
+                return Some(result);
+            }
+        }
+    }
+    None
+}
+
+fn iterate_trait_method_candidates<T>(
+    ty: &Canonical<Ty>,
+    db: &impl HirDatabase,
+    resolver: &Resolver,
+    name: Option<&Name>,
+    mode: LookupMode,
+    mut callback: impl FnMut(&Ty, AssocItemId) -> Option<T>,
+) -> Option<T> {
+    let krate = resolver.krate()?;
+    // FIXME: maybe put the trait_env behind a query (need to figure out good input parameters for that)
+    let env = TraitEnvironment::lower(db, resolver);
+    // if ty is `impl Trait` or `dyn Trait`, the trait doesn't need to be in scope
+    let inherent_trait = ty.value.inherent_trait().into_iter();
+    // if we have `T: Trait` in the param env, the trait doesn't need to be in scope
+    let traits_from_env = env
+        .trait_predicates_for_self_ty(&ty.value)
+        .map(|tr| tr.trait_)
+        .flat_map(|t| all_super_traits(db, t));
+    let traits =
+        inherent_trait.chain(traits_from_env).chain(resolver.traits_in_scope(db).into_iter());
+    'traits: for t in traits {
+        let data = db.trait_data(t);
+
+        // we'll be lazy about checking whether the type implements the
+        // trait, but if we find out it doesn't, we'll skip the rest of the
+        // iteration
+        let mut known_implemented = false;
+        for (_name, item) in data.items.iter() {
+            if !is_valid_candidate(db, name, mode, (*item).into()) {
+                continue;
+            }
+            if !known_implemented {
+                let goal = generic_implements_goal(db, env.clone(), t, ty.clone());
+                if db.trait_solve(krate.into(), goal).is_none() {
+                    continue 'traits;
+                }
+            }
+            known_implemented = true;
+            if let Some(result) = callback(&ty.value, (*item).into()) {
+                return Some(result);
+            }
+        }
+    }
+    None
+}
+
+fn iterate_inherent_methods<T>(
+    ty: &Canonical<Ty>,
+    db: &impl HirDatabase,
+    name: Option<&Name>,
+    mode: LookupMode,
+    krate: CrateId,
+    mut callback: impl FnMut(&Ty, AssocItemId) -> Option<T>,
+) -> Option<T> {
+    for krate in ty.value.def_crates(db, krate)? {
+        let impls = db.impls_in_crate(krate);
+
+        for impl_block in impls.lookup_impl_blocks(&ty.value) {
+            for &item in db.impl_data(impl_block).items.iter() {
+                if !is_valid_candidate(db, name, mode, item) {
+                    continue;
+                }
+                if let Some(result) = callback(&ty.value, item.into()) {
+                    return Some(result);
+                }
+            }
+        }
+    }
+    None
+}
+
+fn is_valid_candidate(
+    db: &impl HirDatabase,
+    name: Option<&Name>,
+    mode: LookupMode,
+    item: AssocItemId,
+) -> bool {
+    match item {
+        AssocItemId::FunctionId(m) => {
+            let data = db.function_data(m);
+            name.map_or(true, |name| &data.name == name)
+                && (data.has_self_param || mode == LookupMode::Path)
+        }
+        AssocItemId::ConstId(c) => {
+            let data = db.const_data(c);
+            name.map_or(true, |name| data.name.as_ref() == Some(name)) && (mode == LookupMode::Path)
+        }
+        _ => false,
+    }
+}
+
+pub fn implements_trait(
+    ty: &Canonical<Ty>,
+    db: &impl HirDatabase,
+    resolver: &Resolver,
+    krate: CrateId,
+    trait_: TraitId,
+) -> bool {
+    if ty.value.inherent_trait() == Some(trait_) {
+        // FIXME this is a bit of a hack, since Chalk should say the same thing
+        // anyway, but currently Chalk doesn't implement `dyn/impl Trait` yet
+        return true;
+    }
+    let env = TraitEnvironment::lower(db, resolver);
+    let goal = generic_implements_goal(db, env, trait_, ty.clone());
+    let solution = db.trait_solve(krate.into(), goal);
+
+    solution.is_some()
+}
+
+/// This creates Substs for a trait with the given Self type and type variables
+/// for all other parameters, to query Chalk with it.
+fn generic_implements_goal(
+    db: &impl HirDatabase,
+    env: Arc<TraitEnvironment>,
+    trait_: TraitId,
+    self_ty: Canonical<Ty>,
+) -> Canonical<InEnvironment<super::Obligation>> {
+    let num_vars = self_ty.num_vars;
+    let substs = super::Substs::build_for_def(db, trait_)
+        .push(self_ty.value)
+        .fill_with_bound_vars(num_vars as u32)
+        .build();
+    let num_vars = substs.len() - 1 + self_ty.num_vars;
+    let trait_ref = TraitRef { trait_, substs };
+    let obligation = super::Obligation::Trait(trait_ref);
+    Canonical { num_vars, value: InEnvironment::new(env, obligation) }
+}