2 files changed, 76 insertions, 3 deletions

diff --git a/crates/ra_assists/src/lib.rs b/crates/ra_assists/src/lib.rs
index 828a8e9e8..cb124eaf0 100644
--- a/crates/ra_assists/src/lib.rs
+++ b/crates/ra_assists/src/lib.rs
@@ -9,7 +9,7 @@ mod assist_ctx;
 mod marks;
 #[cfg(test)]
 mod doc_tests;
-mod utils;
+pub mod utils;
 pub mod ast_transform;
 
 use ra_db::FileRange;
diff --git a/crates/ra_assists/src/utils.rs b/crates/ra_assists/src/utils.rs
index 0d5722295..7bc21c6e4 100644
--- a/crates/ra_assists/src/utils.rs
+++ b/crates/ra_assists/src/utils.rs
@@ -1,10 +1,83 @@
 //! Assorted functions shared by several assists.
 
 use ra_syntax::{
-    ast::{self, make},
-    T,
+    ast::{self, make, NameOwner},
+    AstNode, T,
 };
 
+use hir::db::HirDatabase;
+
+use rustc_hash::FxHashSet;
+
+pub fn get_missing_impl_items(
+    db: &impl HirDatabase,
+    analyzer: &hir::SourceAnalyzer,
+    impl_block: &ast::ImplBlock,
+) -> Vec<hir::AssocItem> {
+    // since the names are unique only to each associated type (fn/type/const),
+    // create buckets of each already implemented type that we'll use in the
+    // lookup later.
+    let mut impl_fns = FxHashSet::default();
+    let mut impl_type = FxHashSet::default();
+    let mut impl_const = FxHashSet::default();
+
+    if let Some(item_list) = impl_block.item_list() {
+        for item in item_list.impl_items() {
+            match item {
+                ast::ImplItem::FnDef(f) => {
+                    if let Some(n) = f.name() {
+                        impl_fns.insert(n.syntax().to_string());
+                    }
+                }
+
+                ast::ImplItem::TypeAliasDef(t) => {
+                    if let Some(n) = t.name() {
+                        impl_type.insert(n.syntax().to_string());
+                    }
+                }
+
+                ast::ImplItem::ConstDef(c) => {
+                    if let Some(n) = c.name() {
+                        impl_const.insert(n.syntax().to_string());
+                    }
+                }
+            }
+        }
+    }
+
+    resolve_target_trait(db, analyzer, impl_block).map_or(vec![], |target_trait| {
+        target_trait
+            .items(db)
+            .iter()
+            .filter(|i| match i {
+                hir::AssocItem::Function(f) => !impl_fns.contains(&f.name(db).to_string()),
+                hir::AssocItem::TypeAlias(t) => !impl_type.contains(&t.name(db).to_string()),
+                hir::AssocItem::Const(c) => {
+                    c.name(db).map(|n| !impl_const.contains(&n.to_string())).unwrap_or_default()
+                }
+            })
+            .map(|i| i.clone())
+            .collect()
+    })
+}
+
+fn resolve_target_trait(
+    db: &impl HirDatabase,
+    analyzer: &hir::SourceAnalyzer,
+    impl_block: &ast::ImplBlock,
+) -> Option<hir::Trait> {
+    let ast_path = impl_block
+        .target_trait()
+        .map(|it| it.syntax().clone())
+        .and_then(ast::PathType::cast)?
+        .path()?;
+
+    match analyzer.resolve_path(db, &ast_path) {
+        Some(hir::PathResolution::Def(hir::ModuleDef::Trait(def))) => Some(def),
+        _ => None,
+    }
+}
+
 pub(crate) fn invert_boolean_expression(expr: ast::Expr) -> ast::Expr {
     if let Some(expr) = invert_special_case(&expr) {
         return expr;