3 files changed, 208 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/method_resolution.rs b/crates/ra_hir/src/ty/method_resolution.rs
new file mode 100644
index 000000000..ad80aa8b6
--- /dev/null
+++ b/crates/ra_hir/src/ty/method_resolution.rs
@@ -0,0 +1,164 @@
+//! 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 rustc_hash::FxHashMap;
+
+use ra_db::{Cancelable, SourceRootId};
+
+use crate::{HirDatabase, DefId, module_tree::ModuleId, Module, Crate, Name, Function, impl_block::{ImplId, ImplBlock, ImplItem}};
+use super::Ty;
+
+/// This is used as a key for indexing impls.
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub enum TyFingerprint {
+    Adt(DefId),
+    // we'll also want to index impls for primitive types etc.
+}
+
+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::Adt { def_id, .. } => Some(TyFingerprint::Adt(*def_id)),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct CrateImplBlocks {
+    /// To make sense of the ModuleIds, we need the source root.
+    source_root_id: SourceRootId,
+    impls: FxHashMap<TyFingerprint, Vec<(ModuleId, ImplId)>>,
+}
+
+impl CrateImplBlocks {
+    pub fn lookup_impl_blocks<'a>(
+        &'a self,
+        db: &'a impl HirDatabase,
+        ty: &Ty,
+    ) -> impl Iterator<Item = Cancelable<ImplBlock>> + 'a {
+        let fingerprint = TyFingerprint::for_impl(ty);
+        fingerprint
+            .and_then(|f| self.impls.get(&f))
+            .into_iter()
+            .flat_map(|i| i.iter())
+            .map(move |(module_id, impl_id)| {
+                let module_impl_blocks = db.impls_in_module(self.source_root_id, *module_id)?;
+                Ok(ImplBlock::from_id(module_impl_blocks, *impl_id))
+            })
+    }
+
+    fn collect_recursive(&mut self, db: &impl HirDatabase, module: Module) -> Cancelable<()> {
+        let module_id = module.def_id.loc(db).module_id;
+        let module_impl_blocks = db.impls_in_module(self.source_root_id, module_id)?;
+
+        for (impl_id, impl_data) in module_impl_blocks.impls.iter() {
+            let impl_block = ImplBlock::from_id(Arc::clone(&module_impl_blocks), impl_id);
+
+            if let Some(_target_trait) = impl_data.target_trait() {
+                // ignore for now
+            } else {
+                let target_ty =
+                    Ty::from_hir(db, &module, Some(&impl_block), impl_data.target_type())?;
+                if let Some(target_ty_fp) = TyFingerprint::for_impl(&target_ty) {
+                    self.impls
+                        .entry(target_ty_fp)
+                        .or_insert_with(Vec::new)
+                        .push((module_id, impl_id));
+                }
+            }
+        }
+
+        for child in module.children(db)? {
+            self.collect_recursive(db, child)?;
+        }
+
+        Ok(())
+    }
+}
+
+pub(crate) fn impls_in_crate(
+    db: &impl HirDatabase,
+    krate: Crate,
+) -> Cancelable<Arc<CrateImplBlocks>> {
+    let crate_graph = db.crate_graph();
+    let file_id = crate_graph.crate_root(krate.crate_id);
+    let source_root_id = db.file_source_root(file_id);
+    let mut crate_impl_blocks = CrateImplBlocks {
+        source_root_id,
+        impls: FxHashMap::default(),
+    };
+    if let Some(module) = krate.root_module(db)? {
+        crate_impl_blocks.collect_recursive(db, module)?;
+    }
+    Ok(Arc::new(crate_impl_blocks))
+}
+
+fn def_crate(db: &impl HirDatabase, ty: &Ty) -> Cancelable<Option<Crate>> {
+    match ty {
+        Ty::Adt { def_id, .. } => def_id.krate(db),
+        _ => Ok(None),
+    }
+}
+
+impl Ty {
+    // TODO: cache this as a query?
+    // - if so, what signature? (TyFingerprint, Name)?
+    // - or maybe cache all names and def_ids of methods per fingerprint?
+    pub fn lookup_method(self, db: &impl HirDatabase, name: &Name) -> Cancelable<Option<DefId>> {
+        self.iterate_methods(db, |f| {
+            let sig = f.signature(db);
+            if sig.name() == name && sig.has_self_arg() {
+                Ok(Some(f.def_id()))
+            } else {
+                Ok(None)
+            }
+        })
+    }
+
+    // This would be nicer if it just returned an iterator, but that's really
+    // complicated with all the cancelable operations
+    pub fn iterate_methods<T>(
+        self,
+        db: &impl HirDatabase,
+        mut callback: impl FnMut(Function) -> Cancelable<Option<T>>,
+    ) -> Cancelable<Option<T>> {
+        // 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).
+
+        for derefed_ty in self.autoderef(db) {
+            let krate = match def_crate(db, &derefed_ty)? {
+                Some(krate) => krate,
+                None => continue,
+            };
+            let impls = db.impls_in_crate(krate)?;
+
+            for impl_block in impls.lookup_impl_blocks(db, &derefed_ty) {
+                let impl_block = impl_block?;
+                for item in impl_block.items() {
+                    match item {
+                        ImplItem::Method(f) => {
+                            if let Some(result) = callback(f.clone())? {
+                                return Ok(Some(result));
+                            }
+                        }
+                        _ => {}
+                    }
+                }
+            }
+        }
+        Ok(None)
+    }
+}
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
index 815aecda7..1c3129441 100644
--- a/crates/ra_hir/src/ty/tests.rs
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -242,6 +242,32 @@ fn test() {
     );
 }
 
+#[test]
+fn infer_inherent_method() {
+    check_inference(
+        r#"
+struct A;
+
+impl A {
+    fn foo(self, x: u32) -> i32 {}
+}
+
+mod b {
+    impl super::A {
+        fn bar(&self, x: u64) -> i64 {}
+    }
+}
+
+fn test(a: A) {
+    a.foo(1);
+    (&a).bar(1);
+    a.bar(1);
+}
+"#,
+        "inherent_method.txt",
+    );
+}
+
 fn infer(content: &str) -> String {
     let (db, _, file_id) = MockDatabase::with_single_file(content);
     let source_file = db.source_file(file_id);
diff --git a/crates/ra_hir/src/ty/tests/data/inherent_method.txt b/crates/ra_hir/src/ty/tests/data/inherent_method.txt
new file mode 100644
index 000000000..6e6f70357
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests/data/inherent_method.txt
@@ -0,0 +1,18 @@
+[32; 36) 'self': A
+[38; 39) 'x': u32
+[53; 55) '{}': ()
+[103; 107) 'self': &A
+[109; 110) 'x': u64
+[124; 126) '{}': ()
+[144; 145) 'a': A
+[150; 198) '{     ...(1); }': ()
+[156; 157) 'a': A
+[156; 164) 'a.foo(1)': i32
+[162; 163) '1': u32
+[170; 181) '(&a).bar(1)': i64
+[171; 173) '&a': &A
+[172; 173) 'a': A
+[179; 180) '1': u64
+[187; 188) 'a': A
+[187; 195) 'a.bar(1)': i64
+[193; 194) '1': u64