From d001e271730921def34ee1b0d314fba17aae627f Mon Sep 17 00:00:00 2001
From: A4-Tacks <wdsjxhno1001@163.com>
Date: Sat, 12 Jul 2025 23:47:59 +0800
Subject: [PATCH] Fix assoc type where clause position

---
 .../src/completions/item_list/trait_impl.rs   | 53 +++++++++++++++++--
 crates/ide-completion/src/tests/item_list.rs  | 27 ++++++++++
 2 files changed, 75 insertions(+), 5 deletions(-)

diff --git a/crates/ide-completion/src/completions/item_list/trait_impl.rs b/crates/ide-completion/src/completions/item_list/trait_impl.rs
index 092219a058a1..975c2f02259e 100644
--- a/crates/ide-completion/src/completions/item_list/trait_impl.rs
+++ b/crates/ide-completion/src/completions/item_list/trait_impl.rs
@@ -37,6 +37,7 @@ use ide_db::{
     SymbolKind, documentation::HasDocs, path_transform::PathTransform,
     syntax_helpers::prettify_macro_expansion, traits::get_missing_assoc_items,
 };
+use syntax::ast::HasGenericParams;
 use syntax::{
     AstNode, SmolStr, SyntaxElement, SyntaxKind, T, TextRange, ToSmolStr,
     ast::{self, HasGenericArgs, HasTypeBounds, edit_in_place::AttrsOwnerEdit, make},
@@ -388,6 +389,12 @@ fn add_type_alias_impl(
             {
                 end
             } else if let Some(end) = transformed_ty.eq_token().map(|tok| tok.text_range().start())
+            {
+                end
+            } else if let Some(end) = transformed_ty
+                .where_clause()
+                .and_then(|wc| wc.where_token())
+                .map(|tok| tok.text_range().start())
             {
                 end
             } else if let Some(end) =
@@ -400,17 +407,29 @@ fn add_type_alias_impl(
 
             let len = end - start;
             let mut decl = transformed_ty.syntax().text().slice(..len).to_string();
-            if !decl.ends_with(' ') {
-                decl.push(' ');
-            }
-            decl.push_str("= ");
+            decl.truncate(decl.trim_end().len());
+            decl.push_str(" = ");
+
+            let wc = transformed_ty
+                .where_clause()
+                .map(|wc| {
+                    let ws = wc
+                        .where_token()
+                        .and_then(|it| it.prev_token())
+                        .filter(|token| token.kind() == SyntaxKind::WHITESPACE)
+                        .map(|token| token.to_string())
+                        .unwrap_or_else(|| " ".into());
+                    format!("{ws}{wc}")
+                })
+                .unwrap_or_default();
 
             match ctx.config.snippet_cap {
                 Some(cap) => {
-                    let snippet = format!("{decl}$0;");
+                    let snippet = format!("{decl}$0{wc};");
                     item.snippet_edit(cap, TextEdit::replace(replacement_range, snippet));
                 }
                 None => {
+                    decl.push_str(&wc);
                     item.text_edit(TextEdit::replace(replacement_range, decl));
                 }
             };
@@ -1437,6 +1456,30 @@ trait Tr<'b> {
 impl<'b> Tr<'b> for () {
     type Ty<'a: 'b, T: Copy, const C: usize> = $0;
 }
+"#,
+        );
+    }
+    #[test]
+    fn includes_where_clause() {
+        check_edit(
+            "type Ty",
+            r#"
+trait Tr {
+    type Ty where Self: Copy;
+}
+
+impl Tr for () {
+    $0
+}
+"#,
+            r#"
+trait Tr {
+    type Ty where Self: Copy;
+}
+
+impl Tr for () {
+    type Ty = $0 where Self: Copy;
+}
 "#,
         );
     }
diff --git a/crates/ide-completion/src/tests/item_list.rs b/crates/ide-completion/src/tests/item_list.rs
index 179d66936026..ac32649d4ffb 100644
--- a/crates/ide-completion/src/tests/item_list.rs
+++ b/crates/ide-completion/src/tests/item_list.rs
@@ -458,6 +458,33 @@ type O = $0;
         r"
 struct A;
 trait B {
+type O<'a>
+where
+Self: 'a;
+}
+impl B for A {
+$0
+}
+",
+        r#"
+struct A;
+trait B {
+type O<'a>
+where
+Self: 'a;
+}
+impl B for A {
+type O<'a> = $0
+where
+Self: 'a;
+}
+"#,
+    );
+    check_edit(
+        "type O",
+        r"
+struct A;
+trait B {
 type O: ?Sized = u32;
 }
 impl B for A {