12 files changed, 151 insertions, 129 deletions

diff --git a/Cargo.lock b/Cargo.lock
index fe09e4afe..a69aef199 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -268,7 +268,6 @@ dependencies = [
 name = "completion"
 version = "0.0.0"
 dependencies = [
- "assists",
  "base_db",
  "call_info",
  "expect-test",
diff --git a/crates/assists/src/handlers/add_missing_impl_members.rs b/crates/assists/src/handlers/add_missing_impl_members.rs
index 4c400f287..b82fb30ad 100644
--- a/crates/assists/src/handlers/add_missing_impl_members.rs
+++ b/crates/assists/src/handlers/add_missing_impl_members.rs
@@ -1,4 +1,5 @@
 use hir::HasSource;
+use ide_db::traits::{get_missing_assoc_items, resolve_target_trait};
 use syntax::{
     ast::{
         self,
@@ -11,7 +12,7 @@ use syntax::{
 use crate::{
     assist_context::{AssistContext, Assists},
     ast_transform::{self, AstTransform, QualifyPaths, SubstituteTypeParams},
-    utils::{get_missing_assoc_items, render_snippet, resolve_target_trait, Cursor},
+    utils::{render_snippet, Cursor},
     AssistId, AssistKind,
 };
 
diff --git a/crates/assists/src/handlers/replace_if_let_with_match.rs b/crates/assists/src/handlers/replace_if_let_with_match.rs
index 79097621e..9a49c48c1 100644
--- a/crates/assists/src/handlers/replace_if_let_with_match.rs
+++ b/crates/assists/src/handlers/replace_if_let_with_match.rs
@@ -7,10 +7,8 @@ use syntax::{
     AstNode,
 };
 
-use crate::{
-    utils::{unwrap_trivial_block, TryEnum},
-    AssistContext, AssistId, AssistKind, Assists,
-};
+use crate::{utils::unwrap_trivial_block, AssistContext, AssistId, AssistKind, Assists};
+use ide_db::ty_filter::TryEnum;
 
 // Assist: replace_if_let_with_match
 //
diff --git a/crates/assists/src/handlers/replace_let_with_if_let.rs b/crates/assists/src/handlers/replace_let_with_if_let.rs
index ed6d0c29b..a5bcbda24 100644
--- a/crates/assists/src/handlers/replace_let_with_if_let.rs
+++ b/crates/assists/src/handlers/replace_let_with_if_let.rs
@@ -9,7 +9,8 @@ use syntax::{
     AstNode, T,
 };
 
-use crate::{utils::TryEnum, AssistContext, AssistId, AssistKind, Assists};
+use crate::{AssistContext, AssistId, AssistKind, Assists};
+use ide_db::ty_filter::TryEnum;
 
 // Assist: replace_let_with_if_let
 //
diff --git a/crates/assists/src/handlers/replace_unwrap_with_match.rs b/crates/assists/src/handlers/replace_unwrap_with_match.rs
index 4043c219c..f547066f0 100644
--- a/crates/assists/src/handlers/replace_unwrap_with_match.rs
+++ b/crates/assists/src/handlers/replace_unwrap_with_match.rs
@@ -10,9 +10,10 @@ use syntax::{
 };
 
 use crate::{
-    utils::{render_snippet, Cursor, TryEnum},
+    utils::{render_snippet, Cursor},
     AssistContext, AssistId, AssistKind, Assists,
 };
+use ide_db::ty_filter::TryEnum;
 
 // Assist: replace_unwrap_with_match
 //
diff --git a/crates/assists/src/utils.rs b/crates/assists/src/utils.rs
index 1a6b48b45..56f925ee6 100644
--- a/crates/assists/src/utils.rs
+++ b/crates/assists/src/utils.rs
@@ -2,14 +2,13 @@
 pub(crate) mod insert_use;
 pub(crate) mod import_assets;
 
-use std::{iter, ops};
+use std::ops;
 
-use hir::{Adt, Crate, Enum, Module, ScopeDef, Semantics, Trait, Type};
+use hir::{Crate, Enum, Module, ScopeDef, Semantics, Trait};
 use ide_db::RootDatabase;
 use itertools::Itertools;
-use rustc_hash::FxHashSet;
 use syntax::{
-    ast::{self, make, ArgListOwner, NameOwner},
+    ast::{self, make, ArgListOwner},
     AstNode, Direction,
     SyntaxKind::*,
     SyntaxNode, TextSize, T,
@@ -115,72 +114,6 @@ pub(crate) fn render_snippet(_cap: SnippetCap, node: &SyntaxNode, cursor: Cursor
     }
 }
 
-pub fn get_missing_assoc_items(
-    sema: &Semantics<RootDatabase>,
-    impl_def: &ast::Impl,
-) -> Vec<hir::AssocItem> {
-    // Names must be unique between constants and functions. However, type aliases
-    // may share the same name as a function or constant.
-    let mut impl_fns_consts = FxHashSet::default();
-    let mut impl_type = FxHashSet::default();
-
-    if let Some(item_list) = impl_def.assoc_item_list() {
-        for item in item_list.assoc_items() {
-            match item {
-                ast::AssocItem::Fn(f) => {
-                    if let Some(n) = f.name() {
-                        impl_fns_consts.insert(n.syntax().to_string());
-                    }
-                }
-
-                ast::AssocItem::TypeAlias(t) => {
-                    if let Some(n) = t.name() {
-                        impl_type.insert(n.syntax().to_string());
-                    }
-                }
-
-                ast::AssocItem::Const(c) => {
-                    if let Some(n) = c.name() {
-                        impl_fns_consts.insert(n.syntax().to_string());
-                    }
-                }
-                ast::AssocItem::MacroCall(_) => (),
-            }
-        }
-    }
-
-    resolve_target_trait(sema, impl_def).map_or(vec![], |target_trait| {
-        target_trait
-            .items(sema.db)
-            .iter()
-            .filter(|i| match i {
-                hir::AssocItem::Function(f) => {
-                    !impl_fns_consts.contains(&f.name(sema.db).to_string())
-                }
-                hir::AssocItem::TypeAlias(t) => !impl_type.contains(&t.name(sema.db).to_string()),
-                hir::AssocItem::Const(c) => c
-                    .name(sema.db)
-                    .map(|n| !impl_fns_consts.contains(&n.to_string()))
-                    .unwrap_or_default(),
-            })
-            .cloned()
-            .collect()
-    })
-}
-
-pub(crate) fn resolve_target_trait(
-    sema: &Semantics<RootDatabase>,
-    impl_def: &ast::Impl,
-) -> Option<hir::Trait> {
-    let ast_path =
-        impl_def.trait_().map(|it| it.syntax().clone()).and_then(ast::PathType::cast)?.path()?;
-
-    match sema.resolve_path(&ast_path) {
-        Some(hir::PathResolution::Def(hir::ModuleDef::Trait(def))) => Some(def),
-        _ => None,
-    }
-}
-
 pub(crate) fn vis_offset(node: &SyntaxNode) -> TextSize {
     node.children_with_tokens()
         .find(|it| !matches!(it.kind(), WHITESPACE | COMMENT | ATTR))
@@ -223,54 +156,6 @@ fn invert_special_case(expr: &ast::Expr) -> Option<ast::Expr> {
     }
 }
 
-#[derive(Clone, Copy)]
-pub enum TryEnum {
-    Result,
-    Option,
-}
-
-impl TryEnum {
-    const ALL: [TryEnum; 2] = [TryEnum::Option, TryEnum::Result];
-
-    pub fn from_ty(sema: &Semantics<RootDatabase>, ty: &Type) -> Option<TryEnum> {
-        let enum_ = match ty.as_adt() {
-            Some(Adt::Enum(it)) => it,
-            _ => return None,
-        };
-        TryEnum::ALL.iter().find_map(|&var| {
-            if &enum_.name(sema.db).to_string() == var.type_name() {
-                return Some(var);
-            }
-            None
-        })
-    }
-
-    pub(crate) fn happy_case(self) -> &'static str {
-        match self {
-            TryEnum::Result => "Ok",
-            TryEnum::Option => "Some",
-        }
-    }
-
-    pub(crate) fn sad_pattern(self) -> ast::Pat {
-        match self {
-            TryEnum::Result => make::tuple_struct_pat(
-                make::path_unqualified(make::path_segment(make::name_ref("Err"))),
-                iter::once(make::wildcard_pat().into()),
-            )
-            .into(),
-            TryEnum::Option => make::ident_pat(make::name("None")).into(),
-        }
-    }
-
-    fn type_name(self) -> &'static str {
-        match self {
-            TryEnum::Result => "Result",
-            TryEnum::Option => "Option",
-        }
-    }
-}
-
 /// Helps with finding well-know things inside the standard library. This is
 /// somewhat similar to the known paths infra inside hir, but it different; We
 /// want to make sure that IDE specific paths don't become interesting inside
diff --git a/crates/completion/Cargo.toml b/crates/completion/Cargo.toml
index 25192456a..8b6e80448 100644
--- a/crates/completion/Cargo.toml
+++ b/crates/completion/Cargo.toml
@@ -21,7 +21,6 @@ base_db = { path = "../base_db", version = "0.0.0" }
 ide_db = { path = "../ide_db", version = "0.0.0" }
 profile = { path = "../profile", version = "0.0.0" }
 test_utils = { path = "../test_utils", version = "0.0.0" }
-assists = { path = "../assists", version = "0.0.0" }
 call_info = { path = "../call_info", version = "0.0.0" }
 
 # completions crate should depend only on the top-level `hir` package. if you need
diff --git a/crates/completion/src/complete_postfix.rs b/crates/completion/src/complete_postfix.rs
index 700573cf2..2622f12ab 100644
--- a/crates/completion/src/complete_postfix.rs
+++ b/crates/completion/src/complete_postfix.rs
@@ -2,7 +2,7 @@
 
 mod format_like;
 
-use assists::utils::TryEnum;
+use ide_db::ty_filter::TryEnum;
 use syntax::{
     ast::{self, AstNode, AstToken},
     TextRange, TextSize,
diff --git a/crates/completion/src/complete_trait_impl.rs b/crates/completion/src/complete_trait_impl.rs
index c06af99e2..a14be9c73 100644
--- a/crates/completion/src/complete_trait_impl.rs
+++ b/crates/completion/src/complete_trait_impl.rs
@@ -31,8 +31,8 @@
 //! }
 //! ```
 
-use assists::utils::get_missing_assoc_items;
 use hir::{self, HasAttrs, HasSource};
+use ide_db::traits::get_missing_assoc_items;
 use syntax::{
     ast::{self, edit, Impl},
     display::function_declaration,
diff --git a/crates/ide_db/src/lib.rs b/crates/ide_db/src/lib.rs
index 7eff247c7..88f74265c 100644
--- a/crates/ide_db/src/lib.rs
+++ b/crates/ide_db/src/lib.rs
@@ -10,6 +10,8 @@ pub mod defs;
 pub mod search;
 pub mod imports_locator;
 pub mod source_change;
+pub mod ty_filter;
+pub mod traits;
 
 use std::{fmt, sync::Arc};
 
diff --git a/crates/ide_db/src/traits.rs b/crates/ide_db/src/traits.rs
new file mode 100644
index 000000000..dcd61a595
--- /dev/null
+++ b/crates/ide_db/src/traits.rs
@@ -0,0 +1,78 @@
+//! Functionality for obtaining data related to traits from the DB.
+
+use crate::RootDatabase;
+use hir::Semantics;
+use rustc_hash::FxHashSet;
+use syntax::{
+    ast::{self, NameOwner},
+    AstNode,
+};
+
+/// Given the `impl` block, attempts to find the trait this `impl` corresponds to.
+pub fn resolve_target_trait(
+    sema: &Semantics<RootDatabase>,
+    impl_def: &ast::Impl,
+) -> Option<hir::Trait> {
+    let ast_path =
+        impl_def.trait_().map(|it| it.syntax().clone()).and_then(ast::PathType::cast)?.path()?;
+
+    match sema.resolve_path(&ast_path) {
+        Some(hir::PathResolution::Def(hir::ModuleDef::Trait(def))) => Some(def),
+        _ => None,
+    }
+}
+
+/// Given the `impl` block, returns the list of associated items (e.g. functions or types) that are
+/// missing in this `impl` block.
+pub fn get_missing_assoc_items(
+    sema: &Semantics<RootDatabase>,
+    impl_def: &ast::Impl,
+) -> Vec<hir::AssocItem> {
+    // Names must be unique between constants and functions. However, type aliases
+    // may share the same name as a function or constant.
+    let mut impl_fns_consts = FxHashSet::default();
+    let mut impl_type = FxHashSet::default();
+
+    if let Some(item_list) = impl_def.assoc_item_list() {
+        for item in item_list.assoc_items() {
+            match item {
+                ast::AssocItem::Fn(f) => {
+                    if let Some(n) = f.name() {
+                        impl_fns_consts.insert(n.syntax().to_string());
+                    }
+                }
+
+                ast::AssocItem::TypeAlias(t) => {
+                    if let Some(n) = t.name() {
+                        impl_type.insert(n.syntax().to_string());
+                    }
+                }
+
+                ast::AssocItem::Const(c) => {
+                    if let Some(n) = c.name() {
+                        impl_fns_consts.insert(n.syntax().to_string());
+                    }
+                }
+                ast::AssocItem::MacroCall(_) => (),
+            }
+        }
+    }
+
+    resolve_target_trait(sema, impl_def).map_or(vec![], |target_trait| {
+        target_trait
+            .items(sema.db)
+            .iter()
+            .filter(|i| match i {
+                hir::AssocItem::Function(f) => {
+                    !impl_fns_consts.contains(&f.name(sema.db).to_string())
+                }
+                hir::AssocItem::TypeAlias(t) => !impl_type.contains(&t.name(sema.db).to_string()),
+                hir::AssocItem::Const(c) => c
+                    .name(sema.db)
+                    .map(|n| !impl_fns_consts.contains(&n.to_string()))
+                    .unwrap_or_default(),
+            })
+            .cloned()
+            .collect()
+    })
+}
diff --git a/crates/ide_db/src/ty_filter.rs b/crates/ide_db/src/ty_filter.rs
new file mode 100644
index 000000000..63a945282
--- /dev/null
+++ b/crates/ide_db/src/ty_filter.rs
@@ -0,0 +1,58 @@
+//! This module contains structures for filtering the expected types.
+//! Use case for structures in this module is, for example, situation when you need to process
+//! only certain `Enum`s.
+
+use crate::RootDatabase;
+use hir::{Adt, Semantics, Type};
+use std::iter;
+use syntax::ast::{self, make};
+
+/// Enum types that implement `std::ops::Try` trait.
+#[derive(Clone, Copy)]
+pub enum TryEnum {
+    Result,
+    Option,
+}
+
+impl TryEnum {
+    const ALL: [TryEnum; 2] = [TryEnum::Option, TryEnum::Result];
+
+    /// Returns `Some(..)` if the provided type is an enum that implements `std::ops::Try`.
+    pub fn from_ty(sema: &Semantics<RootDatabase>, ty: &Type) -> Option<TryEnum> {
+        let enum_ = match ty.as_adt() {
+            Some(Adt::Enum(it)) => it,
+            _ => return None,
+        };
+        TryEnum::ALL.iter().find_map(|&var| {
+            if &enum_.name(sema.db).to_string() == var.type_name() {
+                return Some(var);
+            }
+            None
+        })
+    }
+
+    pub fn happy_case(self) -> &'static str {
+        match self {
+            TryEnum::Result => "Ok",
+            TryEnum::Option => "Some",
+        }
+    }
+
+    pub fn sad_pattern(self) -> ast::Pat {
+        match self {
+            TryEnum::Result => make::tuple_struct_pat(
+                make::path_unqualified(make::path_segment(make::name_ref("Err"))),
+                iter::once(make::wildcard_pat().into()),
+            )
+            .into(),
+            TryEnum::Option => make::ident_pat(make::name("None")).into(),
+        }
+    }
+
+    fn type_name(self) -> &'static str {
+        match self {
+            TryEnum::Result => "Result",
+            TryEnum::Option => "Option",
+        }
+    }
+}