14 files changed, 969 insertions, 7 deletions

diff --git a/crates/ra_hir/Cargo.toml b/crates/ra_hir/Cargo.toml
index 61650cee9..594176337 100644
--- a/crates/ra_hir/Cargo.toml
+++ b/crates/ra_hir/Cargo.toml
@@ -16,3 +16,6 @@ ra_syntax = { path = "../ra_syntax" }
 ra_editor = { path = "../ra_editor" }
 ra_db = { path = "../ra_db" }
 test_utils = { path = "../test_utils" }
+
+[dev-dependencies]
+flexi_logger = "0.10.0"
diff --git a/crates/ra_hir/src/db.rs b/crates/ra_hir/src/db.rs
index 62cf9ab17..d94f75857 100644
--- a/crates/ra_hir/src/db.rs
+++ b/crates/ra_hir/src/db.rs
@@ -14,6 +14,7 @@ use crate::{
     function::FnId,
     module::{ModuleId, ModuleTree, ModuleSource,
     nameres::{ItemMap, InputModuleItems}},
+    ty::{InferenceResult, Ty},
 };
 
 salsa::query_group! {
@@ -30,6 +31,16 @@ pub trait HirDatabase: SyntaxDatabase
         use fn query_definitions::fn_syntax;
     }
 
+    fn infer(fn_id: FnId) -> Cancelable<Arc<InferenceResult>> {
+        type InferQuery;
+        use fn query_definitions::infer;
+    }
+
+    fn type_for_def(def_id: DefId) -> Cancelable<Ty> {
+        type TypeForDefQuery;
+        use fn query_definitions::type_for_def;
+    }
+
     fn file_items(file_id: FileId) -> Arc<SourceFileItems> {
         type SourceFileItemsQuery;
         use fn query_definitions::file_items;
diff --git a/crates/ra_hir/src/function.rs b/crates/ra_hir/src/function.rs
index 2925beb16..d36477b48 100644
--- a/crates/ra_hir/src/function.rs
+++ b/crates/ra_hir/src/function.rs
@@ -5,12 +5,13 @@ use std::{
     sync::Arc,
 };
 
+use ra_db::Cancelable;
 use ra_syntax::{
     TextRange, TextUnit,
     ast::{self, AstNode, DocCommentsOwner, NameOwner},
 };
 
-use crate::{ DefId, HirDatabase };
+use crate::{ DefId, HirDatabase, ty::InferenceResult, Module };
 
 pub use self::scope::FnScopes;
 
@@ -18,7 +19,7 @@ pub use self::scope::FnScopes;
 pub struct FnId(pub(crate) DefId);
 
 pub struct Function {
-    fn_id: FnId,
+    pub(crate) fn_id: FnId,
 }
 
 impl Function {
@@ -27,6 +28,10 @@ impl Function {
         Function { fn_id }
     }
 
+    pub fn syntax(&self, db: &impl HirDatabase) -> ast::FnDefNode {
+        db.fn_syntax(self.fn_id)
+    }
+
     pub fn scopes(&self, db: &impl HirDatabase) -> Arc<FnScopes> {
         db.fn_scopes(self.fn_id)
     }
@@ -35,6 +40,15 @@ impl Function {
         let syntax = db.fn_syntax(self.fn_id);
         FnSignatureInfo::new(syntax.borrowed())
     }
+
+    pub fn infer(&self, db: &impl HirDatabase) -> Cancelable<Arc<InferenceResult>> {
+        db.infer(self.fn_id)
+    }
+
+    pub fn module(&self, db: &impl HirDatabase) -> Cancelable<Module> {
+        let loc = self.fn_id.0.loc(db);
+        Module::new(db, loc.source_root_id, loc.module_id)
+    }
 }
 
 #[derive(Debug, Clone)]
diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index f56214b47..a0d99a84d 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -25,10 +25,11 @@ pub mod source_binder;
 mod krate;
 mod module;
 mod function;
+mod ty;
 
 use std::ops::Index;
 
-use ra_syntax::{SyntaxNodeRef, SyntaxNode};
+use ra_syntax::{SyntaxNodeRef, SyntaxNode, SyntaxKind};
 use ra_db::{LocationIntener, SourceRootId, FileId, Cancelable};
 
 use crate::{
@@ -66,6 +67,23 @@ pub struct DefLoc {
     source_item_id: SourceItemId,
 }
 
+impl DefKind {
+    pub(crate) fn for_syntax_kind(kind: SyntaxKind) -> Option<DefKind> {
+        match kind {
+            SyntaxKind::FN_DEF => Some(DefKind::Function),
+            SyntaxKind::MODULE => Some(DefKind::Module),
+            // These define items, but don't have their own DefKinds yet:
+            SyntaxKind::STRUCT_DEF => Some(DefKind::Item),
+            SyntaxKind::ENUM_DEF => Some(DefKind::Item),
+            SyntaxKind::TRAIT_DEF => Some(DefKind::Item),
+            SyntaxKind::TYPE_DEF => Some(DefKind::Item),
+            SyntaxKind::CONST_DEF => Some(DefKind::Item),
+            SyntaxKind::STATIC_DEF => Some(DefKind::Item),
+            _ => None,
+        }
+    }
+}
+
 impl DefId {
     pub(crate) fn loc(self, db: &impl AsRef<LocationIntener<DefLoc, DefId>>) -> DefLoc {
         db.as_ref().id2loc(self)
diff --git a/crates/ra_hir/src/mock.rs b/crates/ra_hir/src/mock.rs
index 9423e6571..b5a997170 100644
--- a/crates/ra_hir/src/mock.rs
+++ b/crates/ra_hir/src/mock.rs
@@ -8,7 +8,7 @@ use test_utils::{parse_fixture, CURSOR_MARKER, extract_offset};
 
 use crate::{db, DefId, DefLoc};
 
-const WORKSPACE: SourceRootId = SourceRootId(0);
+pub const WORKSPACE: SourceRootId = SourceRootId(0);
 
 #[derive(Debug)]
 pub(crate) struct MockDatabase {
@@ -24,6 +24,15 @@ impl MockDatabase {
         (db, source_root)
     }
 
+    pub(crate) fn with_single_file(text: &str) -> (MockDatabase, SourceRoot, FileId) {
+        let mut db = MockDatabase::default();
+        let mut source_root = SourceRoot::default();
+        let file_id = db.add_file(&mut source_root, "/main.rs", text);
+        db.query_mut(ra_db::SourceRootQuery)
+            .set(WORKSPACE, Arc::new(source_root.clone()));
+        (db, source_root, file_id)
+    }
+
     pub(crate) fn with_position(fixture: &str) -> (MockDatabase, FilePosition) {
         let (db, _, position) = MockDatabase::from_fixture(fixture);
         let position = position.expect("expected a marker ( <|> )");
@@ -182,6 +191,8 @@ salsa::database_storage! {
             fn item_map() for db::ItemMapQuery;
             fn fn_syntax() for db::FnSyntaxQuery;
             fn submodules() for db::SubmodulesQuery;
+            fn infer() for db::InferQuery;
+            fn type_for_def() for db::TypeForDefQuery;
         }
     }
 }
diff --git a/crates/ra_hir/src/module.rs b/crates/ra_hir/src/module.rs
index cd31e8cfe..891119953 100644
--- a/crates/ra_hir/src/module.rs
+++ b/crates/ra_hir/src/module.rs
@@ -2,6 +2,7 @@ pub(super) mod imp;
 pub(super) mod nameres;
 
 use std::sync::Arc;
+use log;
 
 use ra_syntax::{
     algo::generate,
diff --git a/crates/ra_hir/src/module/nameres.rs b/crates/ra_hir/src/module/nameres.rs
index 39e891cda..0b152a406 100644
--- a/crates/ra_hir/src/module/nameres.rs
+++ b/crates/ra_hir/src/module/nameres.rs
@@ -272,13 +272,13 @@ where
                 }
             }
         }
-        // Populate explicitelly declared items, except modules
+        // Populate explicitly declared items, except modules
         for item in input.items.iter() {
             if item.kind == MODULE {
                 continue;
             }
             let def_loc = DefLoc {
-                kind: DefKind::Item,
+                kind: DefKind::for_syntax_kind(item.kind).unwrap_or(DefKind::Item),
                 source_root_id: self.source_root,
                 module_id,
                 source_item_id: SourceItemId {
diff --git a/crates/ra_hir/src/query_definitions.rs b/crates/ra_hir/src/query_definitions.rs
index efaeb1525..b654af920 100644
--- a/crates/ra_hir/src/query_definitions.rs
+++ b/crates/ra_hir/src/query_definitions.rs
@@ -11,7 +11,7 @@ use ra_syntax::{
 use ra_db::{SourceRootId, FileId, Cancelable,};
 
 use crate::{
-    SourceFileItems, SourceItemId, DefKind,
+    SourceFileItems, SourceItemId, DefKind, Function, DefId,
     db::HirDatabase,
     function::{FnScopes, FnId},
     module::{
@@ -19,6 +19,7 @@ use crate::{
         imp::Submodule,
         nameres::{InputModuleItems, ItemMap, Resolver},
     },
+    ty::{self, InferenceResult, Ty}
 };
 
 /// Resolve `FnId` to the corresponding `SyntaxNode`
@@ -35,6 +36,15 @@ pub(super) fn fn_scopes(db: &impl HirDatabase, fn_id: FnId) -> Arc<FnScopes> {
     Arc::new(res)
 }
 
+pub(super) fn infer(db: &impl HirDatabase, fn_id: FnId) -> Cancelable<Arc<InferenceResult>> {
+    let function = Function { fn_id };
+    ty::infer(db, function).map(Arc::new)
+}
+
+pub(super) fn type_for_def(db: &impl HirDatabase, def_id: DefId) -> Cancelable<Ty> {
+    ty::type_for_def(db, def_id)
+}
+
 pub(super) fn file_items(db: &impl HirDatabase, file_id: FileId) -> Arc<SourceFileItems> {
     let mut res = SourceFileItems::new(file_id);
     let source_file = db.source_file(file_id);
diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
new file mode 100644
index 000000000..c759d4c8b
--- /dev/null
+++ b/crates/ra_hir/src/ty.rs
@@ -0,0 +1,601 @@
+mod primitive;
+#[cfg(test)]
+mod tests;
+
+use std::sync::Arc;
+use std::fmt;
+
+use log;
+use rustc_hash::{FxHashMap};
+
+use ra_db::{LocalSyntaxPtr, Cancelable};
+use ra_syntax::{
+    SmolStr,
+    ast::{self, AstNode, LoopBodyOwner, ArgListOwner},
+    SyntaxNodeRef
+};
+
+use crate::{Def, DefId, FnScopes, Module, Function, Path, db::HirDatabase};
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub enum Ty {
+    /// The primitive boolean type. Written as `bool`.
+    Bool,
+
+    /// The primitive character type; holds a Unicode scalar value
+    /// (a non-surrogate code point).  Written as `char`.
+    Char,
+
+    /// A primitive signed integer type. For example, `i32`.
+    Int(primitive::IntTy),
+
+    /// A primitive unsigned integer type. For example, `u32`.
+    Uint(primitive::UintTy),
+
+    /// A primitive floating-point type. For example, `f64`.
+    Float(primitive::FloatTy),
+
+    // Structures, enumerations and unions.
+    // Adt(AdtDef, Substs),
+    /// The pointee of a string slice. Written as `str`.
+    Str,
+
+    // An array with the given length. Written as `[T; n]`.
+    // Array(Ty, ty::Const),
+    /// The pointee of an array slice.  Written as `[T]`.
+    Slice(TyRef),
+
+    // A raw pointer. Written as `*mut T` or `*const T`
+    // RawPtr(TypeAndMut<'tcx>),
+
+    // A reference; a pointer with an associated lifetime. Written as
+    // `&'a mut T` or `&'a T`.
+    // Ref(Ty<'tcx>, hir::Mutability),
+    /// A pointer to a function.  Written as `fn() -> i32`.
+    ///
+    /// For example the type of `bar` here:
+    ///
+    /// ```rust
+    /// fn foo() -> i32 { 1 }
+    /// let bar: fn() -> i32 = foo;
+    /// ```
+    FnPtr(Arc<FnSig>),
+
+    // A trait, defined with `dyn trait`.
+    // Dynamic(),
+    /// The anonymous type of a closure. Used to represent the type of
+    /// `|a| a`.
+    // Closure(DefId, ClosureSubsts<'tcx>),
+
+    /// The anonymous type of a generator. Used to represent the type of
+    /// `|a| yield a`.
+    // Generator(DefId, GeneratorSubsts<'tcx>, hir::GeneratorMovability),
+
+    /// A type representin the types stored inside a generator.
+    /// This should only appear in GeneratorInteriors.
+    // GeneratorWitness(Binder<&'tcx List<Ty<'tcx>>>),
+
+    /// The never type `!`
+    Never,
+
+    /// A tuple type.  For example, `(i32, bool)`.
+    Tuple(Vec<Ty>),
+
+    // The projection of an associated type.  For example,
+    // `<T as Trait<..>>::N`.
+    // Projection(ProjectionTy),
+
+    // Opaque (`impl Trait`) type found in a return type.
+    // The `DefId` comes either from
+    // * the `impl Trait` ast::Ty node,
+    // * or the `existential type` declaration
+    // The substitutions are for the generics of the function in question.
+    // Opaque(DefId, Substs),
+
+    // A type parameter; for example, `T` in `fn f<T>(x: T) {}
+    // Param(ParamTy),
+
+    // A placeholder type - universally quantified higher-ranked type.
+    // Placeholder(ty::PlaceholderType),
+
+    // A type variable used during type checking.
+    // Infer(InferTy),
+    /// A placeholder for a type which could not be computed; this is
+    /// propagated to avoid useless error messages.
+    Unknown,
+}
+
+type TyRef = Arc<Ty>;
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub struct FnSig {
+    input: Vec<Ty>,
+    output: Ty,
+}
+
+impl Ty {
+    pub fn new(_db: &impl HirDatabase, node: ast::TypeRef) -> Cancelable<Self> {
+        use ra_syntax::ast::TypeRef::*;
+        Ok(match node {
+            ParenType(_inner) => Ty::Unknown, // TODO
+            TupleType(_inner) => Ty::Unknown, // TODO
+            NeverType(..) => Ty::Never,
+            PathType(inner) => {
+                let path = if let Some(p) = inner.path() {
+                    p
+                } else {
+                    return Ok(Ty::Unknown);
+                };
+                if path.qualifier().is_none() {
+                    let name = path
+                        .segment()
+                        .and_then(|s| s.name_ref())
+                        .map(|n| n.text())
+                        .unwrap_or(SmolStr::new(""));
+                    if let Some(int_ty) = primitive::IntTy::from_string(&name) {
+                        Ty::Int(int_ty)
+                    } else if let Some(uint_ty) = primitive::UintTy::from_string(&name) {
+                        Ty::Uint(uint_ty)
+                    } else if let Some(float_ty) = primitive::FloatTy::from_string(&name) {
+                        Ty::Float(float_ty)
+                    } else {
+                        // TODO
+                        Ty::Unknown
+                    }
+                } else {
+                    // TODO
+                    Ty::Unknown
+                }
+            }
+            PointerType(_inner) => Ty::Unknown,     // TODO
+            ArrayType(_inner) => Ty::Unknown,       // TODO
+            SliceType(_inner) => Ty::Unknown,       // TODO
+            ReferenceType(_inner) => Ty::Unknown,   // TODO
+            PlaceholderType(_inner) => Ty::Unknown, // TODO
+            FnPointerType(_inner) => Ty::Unknown,   // TODO
+            ForType(_inner) => Ty::Unknown,         // TODO
+            ImplTraitType(_inner) => Ty::Unknown,   // TODO
+            DynTraitType(_inner) => Ty::Unknown,    // TODO
+        })
+    }
+
+    pub fn unit() -> Self {
+        Ty::Tuple(Vec::new())
+    }
+}
+
+impl fmt::Display for Ty {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Ty::Bool => write!(f, "bool"),
+            Ty::Char => write!(f, "char"),
+            Ty::Int(t) => write!(f, "{}", t.ty_to_string()),
+            Ty::Uint(t) => write!(f, "{}", t.ty_to_string()),
+            Ty::Float(t) => write!(f, "{}", t.ty_to_string()),
+            Ty::Str => write!(f, "str"),
+            Ty::Slice(t) => write!(f, "[{}]", t),
+            Ty::Never => write!(f, "!"),
+            Ty::Tuple(ts) => {
+                write!(f, "(")?;
+                for t in ts {
+                    write!(f, "{},", t)?;
+                }
+                write!(f, ")")
+            }
+            Ty::FnPtr(sig) => {
+                write!(f, "fn(")?;
+                for t in &sig.input {
+                    write!(f, "{},", t)?;
+                }
+                write!(f, ") -> {}", sig.output)
+            }
+            Ty::Unknown => write!(f, "[unknown]"),
+        }
+    }
+}
+
+pub fn type_for_fn(db: &impl HirDatabase, f: Function) -> Cancelable<Ty> {
+    let syntax = f.syntax(db);
+    let node = syntax.borrowed();
+    // TODO we ignore type parameters for now
+    let input = node
+        .param_list()
+        .map(|pl| {
+            pl.params()
+                .map(|p| {
+                    p.type_ref()
+                        .map(|t| Ty::new(db, t))
+                        .unwrap_or(Ok(Ty::Unknown))
+                })
+                .collect()
+        })
+        .unwrap_or_else(|| Ok(Vec::new()))?;
+    let output = node
+        .ret_type()
+        .and_then(|rt| rt.type_ref())
+        .map(|t| Ty::new(db, t))
+        .unwrap_or(Ok(Ty::Unknown))?;
+    let sig = FnSig { input, output };
+    Ok(Ty::FnPtr(Arc::new(sig)))
+}
+
+// TODO this should probably be per namespace (i.e. types vs. values), since for
+// a tuple struct `struct Foo(Bar)`, Foo has function type as a value, but
+// defines the struct type Foo when used in the type namespace. rustc has a
+// separate DefId for the constructor, but with the current DefId approach, that
+// seems complicated.
+pub fn type_for_def(db: &impl HirDatabase, def_id: DefId) -> Cancelable<Ty> {
+    let def = def_id.resolve(db)?;
+    match def {
+        Def::Module(..) => {
+            log::debug!("trying to get type for module {:?}", def_id);
+            Ok(Ty::Unknown)
+        }
+        Def::Function(f) => type_for_fn(db, f),
+        Def::Item => {
+            log::debug!("trying to get type for item of unknown type {:?}", def_id);
+            Ok(Ty::Unknown)
+        }
+    }
+}
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+pub struct InferenceResult {
+    type_of: FxHashMap<LocalSyntaxPtr, Ty>,
+}
+
+impl InferenceResult {
+    pub fn type_of_node(&self, node: SyntaxNodeRef) -> Option<Ty> {
+        self.type_of.get(&LocalSyntaxPtr::new(node)).cloned()
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct InferenceContext<'a, D: HirDatabase> {
+    db: &'a D,
+    scopes: Arc<FnScopes>,
+    module: Module,
+    // TODO unification tables...
+    type_of: FxHashMap<LocalSyntaxPtr, Ty>,
+}
+
+impl<'a, D: HirDatabase> InferenceContext<'a, D> {
+    fn new(db: &'a D, scopes: Arc<FnScopes>, module: Module) -> Self {
+        InferenceContext {
+            type_of: FxHashMap::default(),
+            db,
+            scopes,
+            module,
+        }
+    }
+
+    fn write_ty(&mut self, node: SyntaxNodeRef, ty: Ty) {
+        self.type_of.insert(LocalSyntaxPtr::new(node), ty);
+    }
+
+    fn unify(&mut self, ty1: &Ty, ty2: &Ty) -> Option<Ty> {
+        if *ty1 == Ty::Unknown {
+            return Some(ty2.clone());
+        }
+        if *ty2 == Ty::Unknown {
+            return Some(ty1.clone());
+        }
+        if ty1 == ty2 {
+            return Some(ty1.clone());
+        }
+        // TODO implement actual unification
+        return None;
+    }
+
+    fn unify_with_coercion(&mut self, ty1: &Ty, ty2: &Ty) -> Option<Ty> {
+        // TODO implement coercion
+        self.unify(ty1, ty2)
+    }
+
+    fn infer_path_expr(&mut self, expr: ast::PathExpr) -> Cancelable<Option<Ty>> {
+        let ast_path = ctry!(expr.path());
+        let path = ctry!(Path::from_ast(ast_path));
+        if path.is_ident() {
+            // resolve locally
+            let name = ctry!(ast_path.segment().and_then(|s| s.name_ref()));
+            if let Some(scope_entry) = self.scopes.resolve_local_name(name) {
+                let ty = ctry!(self.type_of.get(&scope_entry.ptr()));
+                return Ok(Some(ty.clone()));
+            };
+        };
+
+        // resolve in module
+        let resolved = ctry!(self.module.resolve_path(self.db, path)?);
+        let ty = self.db.type_for_def(resolved)?;
+        // TODO we will need to add type variables for type parameters etc. here
+        Ok(Some(ty))
+    }
+
+    fn infer_expr(&mut self, expr: ast::Expr) -> Cancelable<Ty> {
+        let ty = match expr {
+            ast::Expr::IfExpr(e) => {
+                if let Some(condition) = e.condition() {
+                    if let Some(e) = condition.expr() {
+                        // TODO if no pat, this should be bool
+                        self.infer_expr(e)?;
+                    }
+                    // TODO write type for pat
+                };
+                let if_ty = if let Some(block) = e.then_branch() {
+                    self.infer_block(block)?
+                } else {
+                    Ty::Unknown
+                };
+                let else_ty = if let Some(block) = e.else_branch() {
+                    self.infer_block(block)?
+                } else {
+                    Ty::Unknown
+                };
+                if let Some(ty) = self.unify(&if_ty, &else_ty) {
+                    ty
+                } else {
+                    // TODO report diagnostic
+                    Ty::Unknown
+                }
+            }
+            ast::Expr::BlockExpr(e) => {
+                if let Some(block) = e.block() {
+                    self.infer_block(block)?
+                } else {
+                    Ty::Unknown
+                }
+            }
+            ast::Expr::LoopExpr(e) => {
+                if let Some(block) = e.loop_body() {
+                    self.infer_block(block)?;
+                };
+                // TODO never, or the type of the break param
+                Ty::Unknown
+            }
+            ast::Expr::WhileExpr(e) => {
+                if let Some(condition) = e.condition() {
+                    if let Some(e) = condition.expr() {
+                        // TODO if no pat, this should be bool
+                        self.infer_expr(e)?;
+                    }
+                    // TODO write type for pat
+                };
+                if let Some(block) = e.loop_body() {
+                    // TODO
+                    self.infer_block(block)?;
+                };
+                // TODO always unit?
+                Ty::Unknown
+            }
+            ast::Expr::ForExpr(e) => {
+                if let Some(expr) = e.iterable() {
+                    self.infer_expr(expr)?;
+                }
+                if let Some(_pat) = e.pat() {
+                    // TODO write type for pat
+                }
+                if let Some(block) = e.loop_body() {
+                    self.infer_block(block)?;
+                }
+                // TODO always unit?
+                Ty::Unknown
+            }
+            ast::Expr::LambdaExpr(e) => {
+                let _body_ty = if let Some(body) = e.body() {
+                    self.infer_expr(body)?
+                } else {
+                    Ty::Unknown
+                };
+                Ty::Unknown
+            }
+            ast::Expr::CallExpr(e) => {
+                let callee_ty = if let Some(e) = e.expr() {
+                    self.infer_expr(e)?
+                } else {
+                    Ty::Unknown
+                };
+                if let Some(arg_list) = e.arg_list() {
+                    for arg in arg_list.args() {
+                        // TODO unify / expect argument type
+                        self.infer_expr(arg)?;
+                    }
+                }
+                match callee_ty {
+                    Ty::FnPtr(sig) => sig.output.clone(),
+                    _ => {
+                        // not callable
+                        // TODO report an error?
+                        Ty::Unknown
+                    }
+                }
+            }
+            ast::Expr::MethodCallExpr(e) => {
+                let _receiver_ty = if let Some(e) = e.expr() {
+                    self.infer_expr(e)?
+                } else {
+                    Ty::Unknown
+                };
+                if let Some(arg_list) = e.arg_list() {
+                    for arg in arg_list.args() {
+                        // TODO unify / expect argument type
+                        self.infer_expr(arg)?;
+                    }
+                }
+                Ty::Unknown
+            }
+            ast::Expr::MatchExpr(e) => {
+                let _ty = if let Some(match_expr) = e.expr() {
+                    self.infer_expr(match_expr)?
+                } else {
+                    Ty::Unknown
+                };
+                if let Some(match_arm_list) = e.match_arm_list() {
+                    for arm in match_arm_list.arms() {
+                        // TODO type the bindings in pat
+                        // TODO type the guard
+                        let _ty = if let Some(e) = arm.expr() {
+                            self.infer_expr(e)?
+                        } else {
+                            Ty::Unknown
+                        };
+                    }
+                    // TODO unify all the match arm types
+                    Ty::Unknown
+                } else {
+                    Ty::Unknown
+                }
+            }
+            ast::Expr::TupleExpr(_e) => Ty::Unknown,
+            ast::Expr::ArrayExpr(_e) => Ty::Unknown,
+            ast::Expr::PathExpr(e) => self.infer_path_expr(e)?.unwrap_or(Ty::Unknown),
+            ast::Expr::ContinueExpr(_e) => Ty::Never,
+            ast::Expr::BreakExpr(_e) => Ty::Never,
+            ast::Expr::ParenExpr(e) => {
+                if let Some(e) = e.expr() {
+                    self.infer_expr(e)?
+                } else {
+                    Ty::Unknown
+                }
+            }
+            ast::Expr::Label(_e) => Ty::Unknown,
+            ast::Expr::ReturnExpr(e) => {
+                if let Some(e) = e.expr() {
+                    // TODO unify with return type
+                    self.infer_expr(e)?;
+                };
+                Ty::Never
+            }
+            ast::Expr::MatchArmList(_) | ast::Expr::MatchArm(_) | ast::Expr::MatchGuard(_) => {
+                // Can this even occur outside of a match expression?
+                Ty::Unknown
+            }
+            ast::Expr::StructLit(_e) => Ty::Unknown,
+            ast::Expr::NamedFieldList(_) | ast::Expr::NamedField(_) => {
+                // Can this even occur outside of a struct literal?
+                Ty::Unknown
+            }
+            ast::Expr::IndexExpr(_e) => Ty::Unknown,
+            ast::Expr::FieldExpr(_e) => Ty::Unknown,
+            ast::Expr::TryExpr(e) => {
+                let _inner_ty = if let Some(e) = e.expr() {
+                    self.infer_expr(e)?
+                } else {
+                    Ty::Unknown
+                };
+                Ty::Unknown
+            }
+            ast::Expr::CastExpr(e) => {
+                let _inner_ty = if let Some(e) = e.expr() {
+                    self.infer_expr(e)?
+                } else {
+                    Ty::Unknown
+                };
+                let cast_ty = e
+                    .type_ref()
+                    .map(|t| Ty::new(self.db, t))
+                    .unwrap_or(Ok(Ty::Unknown))?;
+                // TODO do the coercion...
+                cast_ty
+            }
+            ast::Expr::RefExpr(e) => {
+                let _inner_ty = if let Some(e) = e.expr() {
+                    self.infer_expr(e)?
+                } else {
+                    Ty::Unknown
+                };
+                Ty::Unknown
+            }
+            ast::Expr::PrefixExpr(e) => {
+                let _inner_ty = if let Some(e) = e.expr() {
+                    self.infer_expr(e)?
+                } else {
+                    Ty::Unknown
+                };
+                Ty::Unknown
+            }
+            ast::Expr::RangeExpr(_e) => Ty::Unknown,
+            ast::Expr::BinExpr(_e) => Ty::Unknown,
+            ast::Expr::Literal(_e) => Ty::Unknown,
+        };
+        self.write_ty(expr.syntax(), ty.clone());
+        Ok(ty)
+    }
+
+    fn infer_block(&mut self, node: ast::Block) -> Cancelable<Ty> {
+        for stmt in node.statements() {
+            match stmt {
+                ast::Stmt::LetStmt(stmt) => {
+                    let decl_ty = if let Some(type_ref) = stmt.type_ref() {
+                        Ty::new(self.db, type_ref)?
+                    } else {
+                        Ty::Unknown
+                    };
+                    let ty = if let Some(expr) = stmt.initializer() {
+                        // TODO pass expectation
+                        let expr_ty = self.infer_expr(expr)?;
+                        self.unify_with_coercion(&expr_ty, &decl_ty)
+                            .unwrap_or(decl_ty)
+                    } else {
+                        decl_ty
+                    };
+
+                    if let Some(pat) = stmt.pat() {
+                        self.write_ty(pat.syntax(), ty);
+                    };
+                }
+                ast::Stmt::ExprStmt(expr_stmt) => {
+                    if let Some(expr) = expr_stmt.expr() {
+                        self.infer_expr(expr)?;
+                    }
+                }
+            }
+        }
+        let ty = if let Some(expr) = node.expr() {
+            self.infer_expr(expr)?
+        } else {
+            Ty::unit()
+        };
+        self.write_ty(node.syntax(), ty.clone());
+        Ok(ty)
+    }
+}
+
+pub fn infer(db: &impl HirDatabase, function: Function) -> Cancelable<InferenceResult> {
+    let scopes = function.scopes(db);
+    let module = function.module(db)?;
+    let mut ctx = InferenceContext::new(db, scopes, module);
+
+    let syntax = function.syntax(db);
+    let node = syntax.borrowed();
+
+    if let Some(param_list) = node.param_list() {
+        for param in param_list.params() {
+            let pat = if let Some(pat) = param.pat() {
+                pat
+            } else {
+                continue;
+            };
+            if let Some(type_ref) = param.type_ref() {
+                let ty = Ty::new(db, type_ref)?;
+                ctx.type_of.insert(LocalSyntaxPtr::new(pat.syntax()), ty);
+            } else {
+                // TODO self param
+                ctx.type_of
+                    .insert(LocalSyntaxPtr::new(pat.syntax()), Ty::Unknown);
+            };
+        }
+    }
+
+    // TODO get Ty for node.ret_type() and pass that to infer_block as expectation
+    // (see Expectation in rustc_typeck)
+
+    if let Some(block) = node.body() {
+        ctx.infer_block(block)?;
+    }
+
+    // TODO 'resolve' the types: replace inference variables by their inferred results
+
+    Ok(InferenceResult {
+        type_of: ctx.type_of,
+    })
+}
diff --git a/crates/ra_hir/src/ty/primitive.rs b/crates/ra_hir/src/ty/primitive.rs
new file mode 100644
index 000000000..ad79b17e4
--- /dev/null
+++ b/crates/ra_hir/src/ty/primitive.rs
@@ -0,0 +1,130 @@
+use std::fmt;
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Copy)]
+pub enum IntTy {
+    Isize,
+    I8,
+    I16,
+    I32,
+    I64,
+    I128,
+}
+
+impl fmt::Debug for IntTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+impl fmt::Display for IntTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.ty_to_string())
+    }
+}
+
+impl IntTy {
+    pub fn ty_to_string(&self) -> &'static str {
+        match *self {
+            IntTy::Isize => "isize",
+            IntTy::I8 => "i8",
+            IntTy::I16 => "i16",
+            IntTy::I32 => "i32",
+            IntTy::I64 => "i64",
+            IntTy::I128 => "i128",
+        }
+    }
+
+    pub fn from_string(s: &str) -> Option<IntTy> {
+        match s {
+            "isize" => Some(IntTy::Isize),
+            "i8" => Some(IntTy::I8),
+            "i16" => Some(IntTy::I16),
+            "i32" => Some(IntTy::I32),
+            "i64" => Some(IntTy::I64),
+            "i128" => Some(IntTy::I128),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Copy)]
+pub enum UintTy {
+    Usize,
+    U8,
+    U16,
+    U32,
+    U64,
+    U128,
+}
+
+impl UintTy {
+    pub fn ty_to_string(&self) -> &'static str {
+        match *self {
+            UintTy::Usize => "usize",
+            UintTy::U8 => "u8",
+            UintTy::U16 => "u16",
+            UintTy::U32 => "u32",
+            UintTy::U64 => "u64",
+            UintTy::U128 => "u128",
+        }
+    }
+
+    pub fn from_string(s: &str) -> Option<UintTy> {
+        match s {
+            "usize" => Some(UintTy::Usize),
+            "u8" => Some(UintTy::U8),
+            "u16" => Some(UintTy::U16),
+            "u32" => Some(UintTy::U32),
+            "u64" => Some(UintTy::U64),
+            "u128" => Some(UintTy::U128),
+            _ => None,
+        }
+    }
+}
+
+impl fmt::Debug for UintTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+impl fmt::Display for UintTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.ty_to_string())
+    }
+}
+
+#[derive(Clone, PartialEq, Eq, Hash, Copy, PartialOrd, Ord)]
+pub enum FloatTy {
+    F32,
+    F64,
+}
+
+impl fmt::Debug for FloatTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(self, f)
+    }
+}
+
+impl fmt::Display for FloatTy {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.ty_to_string())
+    }
+}
+
+impl FloatTy {
+    pub fn ty_to_string(self) -> &'static str {
+        match self {
+            FloatTy::F32 => "f32",
+            FloatTy::F64 => "f64",
+        }
+    }
+
+    pub fn from_string(s: &str) -> Option<FloatTy> {
+        match s {
+            "f32" => Some(FloatTy::F32),
+            "f64" => Some(FloatTy::F64),
+            _ => None,
+        }
+    }
+}
diff --git a/crates/ra_hir/src/ty/tests.rs b/crates/ra_hir/src/ty/tests.rs
new file mode 100644
index 000000000..b6c02cd80
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests.rs
@@ -0,0 +1,134 @@
+use std::fmt::Write;
+use std::path::{PathBuf, Path};
+use std::fs;
+
+use ra_db::{SyntaxDatabase};
+use ra_syntax::ast::{self, AstNode};
+use test_utils::{project_dir, assert_eq_text, read_text};
+
+use crate::{
+    source_binder,
+    mock::MockDatabase,
+};
+
+// These tests compare the inference results for all expressions in a file
+// against snapshots of the current results. If you change something and these
+// tests fail expectedly, you can update the comparison files by deleting them
+// and running the tests again. Similarly, to add a new test, just write the
+// test here in the same pattern and it will automatically write the snapshot.
+
+#[test]
+fn infer_basics() {
+    check_inference(
+        r#"
+fn test(a: u32, b: isize, c: !, d: &str) {
+    a;
+    b;
+    c;
+    d;
+    1usize;
+    1isize;
+    "test";
+    1.0f32;
+}"#,
+        "0001_basics.txt",
+    );
+}
+
+#[test]
+fn infer_let() {
+    check_inference(
+        r#"
+fn test() {
+    let a = 1isize;
+    let b: usize = 1;
+    let c = b;
+}
+}"#,
+        "0002_let.txt",
+    );
+}
+
+#[test]
+fn infer_paths() {
+    check_inference(
+        r#"
+fn a() -> u32 { 1 }
+
+mod b {
+    fn c() -> u32 { 1 }
+}
+
+fn test() {
+    a();
+    b::c();
+}
+}"#,
+        "0003_paths.txt",
+    );
+}
+
+fn infer(content: &str) -> String {
+    let (db, _, file_id) = MockDatabase::with_single_file(content);
+    let source_file = db.source_file(file_id);
+    let mut acc = String::new();
+    for fn_def in source_file
+        .syntax()
+        .descendants()
+        .filter_map(ast::FnDef::cast)
+    {
+        let func = source_binder::function_from_source(&db, file_id, fn_def)
+            .unwrap()
+            .unwrap();
+        let inference_result = func.infer(&db).unwrap();
+        for (syntax_ptr, ty) in &inference_result.type_of {
+            let node = syntax_ptr.resolve(&source_file);
+            write!(
+                acc,
+                "{} '{}': {}\n",
+                syntax_ptr.range(),
+                ellipsize(node.text().to_string().replace("\n", " "), 15),
+                ty
+            )
+            .unwrap();
+        }
+    }
+    acc
+}
+
+fn check_inference(content: &str, data_file: impl AsRef<Path>) {
+    let data_file_path = test_data_dir().join(data_file);
+    let result = infer(content);
+
+    if !data_file_path.exists() {
+        println!("File with expected result doesn't exist, creating...\n");
+        println!("{}\n{}", content, result);
+        fs::write(&data_file_path, &result).unwrap();
+        panic!("File {:?} with expected result was created", data_file_path);
+    }
+
+    let expected = read_text(&data_file_path);
+    assert_eq_text!(&expected, &result);
+}
+
+fn ellipsize(mut text: String, max_len: usize) -> String {
+    if text.len() <= max_len {
+        return text;
+    }
+    let ellipsis = "...";
+    let e_len = ellipsis.len();
+    let mut prefix_len = (max_len - e_len) / 2;
+    while !text.is_char_boundary(prefix_len) {
+        prefix_len += 1;
+    }
+    let mut suffix_len = max_len - e_len - prefix_len;
+    while !text.is_char_boundary(text.len() - suffix_len) {
+        suffix_len += 1;
+    }
+    text.replace_range(prefix_len..text.len() - suffix_len, ellipsis);
+    text
+}
+
+fn test_data_dir() -> PathBuf {
+    project_dir().join("crates/ra_hir/src/ty/tests/data")
+}
diff --git a/crates/ra_hir/src/ty/tests/data/0001_basics.txt b/crates/ra_hir/src/ty/tests/data/0001_basics.txt
new file mode 100644
index 000000000..0c46f243a
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests/data/0001_basics.txt
@@ -0,0 +1,13 @@
+[33; 34) 'd': [unknown]
+[88; 94) '1isize': [unknown]
+[48; 49) 'a': u32
+[55; 56) 'b': isize
+[112; 118) '1.0f32': [unknown]
+[76; 82) '1usize': [unknown]
+[9; 10) 'a': u32
+[27; 28) 'c': !
+[62; 63) 'c': !
+[17; 18) 'b': isize
+[100; 106) '"test"': [unknown]
+[42; 121) '{     ...f32; }': ()
+[69; 70) 'd': [unknown]
diff --git a/crates/ra_hir/src/ty/tests/data/0002_let.txt b/crates/ra_hir/src/ty/tests/data/0002_let.txt
new file mode 100644
index 000000000..2d0d1f57b
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests/data/0002_let.txt
@@ -0,0 +1,7 @@
+[21; 22) 'a': [unknown]
+[52; 53) '1': [unknown]
+[11; 71) '{     ...= b; }': ()
+[63; 64) 'c': usize
+[25; 31) '1isize': [unknown]
+[41; 42) 'b': usize
+[67; 68) 'b': usize
diff --git a/crates/ra_hir/src/ty/tests/data/0003_paths.txt b/crates/ra_hir/src/ty/tests/data/0003_paths.txt
new file mode 100644
index 000000000..dcb5456ae
--- /dev/null
+++ b/crates/ra_hir/src/ty/tests/data/0003_paths.txt
@@ -0,0 +1,9 @@
+[15; 20) '{ 1 }': [unknown]
+[17; 18) '1': [unknown]
+[50; 51) '1': [unknown]
+[48; 53) '{ 1 }': [unknown]
+[82; 88) 'b::c()': u32
+[67; 91) '{     ...c(); }': ()
+[73; 74) 'a': fn() -> u32
+[73; 76) 'a()': u32
+[82; 86) 'b::c': fn() -> u32