fix: auto import trait if needed

Author: Young-Flash

Cargo.toml

@@ -12,7 +12,7 @@ authors = ["rust-analyzer team"]
 [profile.dev]
 # Disabling debug info speeds up builds a bunch,
 # and we don't rely on it for debugging that much.
-debug = 0
+debug = 2
 
 [profile.dev.package]
 # These speed up local tests.

crates/ide-assists/src/handlers/unqualify_method_call.rs

@@ -1,3 +1,4 @@
+use ide_db::imports::insert_use::ImportScope;
 use syntax::{
     ast::{self, make, AstNode, HasArgList},
     TextRange,
@@ -17,6 +18,8 @@ use crate::{AssistContext, AssistId, AssistKind, Assists};
 // ```
 // ->
 // ```
+// use std::ops::Add;
+//
 // fn main() {
 //     1.add(2);
 // }
@@ -76,10 +79,49 @@ pub(crate) fn unqualify_method_call(acc: &mut Assists, ctx: &AssistContext<'_>)
                 edit.insert(close, ")");
             }
             edit.replace(replace_comma, format!(".{method_name}("));
+            add_import(&path, ctx, edit);
         },
     )
 }
 
+fn add_import(
+    path: &ast::Path,
+    ctx: &AssistContext<'_>,
+    edit: &mut ide_db::source_change::SourceChangeBuilder,
+) {
+    let qualifier = path.qualifier().unwrap();
+
+    // for `<i32 as std::ops::Add>`
+    let path_type =
+        qualifier.segment().unwrap().syntax().children().filter_map(ast::PathType::cast).last();
+    let import = match path_type {
+        Some(it) => it.path().unwrap(),
+        None => qualifier,
+    };
+
+    // in case for `<_>`
+    match import.coloncolon_token() {
+        Some(_) => (),
+        None => {
+            return;
+        }
+    }
+
+    let scope = ide_db::imports::insert_use::ImportScope::find_insert_use_container(
+        path.syntax(),
+        &ctx.sema,
+    );
+
+    if let Some(scope) = scope {
+        let scope = match scope {
+            ImportScope::File(it) => ImportScope::File(edit.make_mut(it)),
+            ImportScope::Module(it) => ImportScope::Module(edit.make_mut(it)),
+            ImportScope::Block(it) => ImportScope::Block(edit.make_mut(it)),
+        };
+        ide_db::imports::insert_use::insert_use(&scope, import, &ctx.config.insert_use);
+    }
+}
+
 fn needs_parens_as_receiver(expr: &ast::Expr) -> bool {
     // Make `(expr).dummy()`
     let dummy_call = make::expr_method_call(
@@ -127,6 +169,8 @@ fn f() { S.f(S); }"#,
 //- minicore: add
 fn f() { <u32 as core::ops::Add>::$0add(2, 2); }"#,
             r#"
+use core::ops::Add;
+
 fn f() { 2.add(2); }"#,
         );
 
@@ -136,6 +180,8 @@ fn f() { 2.add(2); }"#,
 //- minicore: add
 fn f() { core::ops::Add::$0add(2, 2); }"#,
             r#"
+use core::ops::Add;
+
 fn f() { 2.add(2); }"#,
         );
 
@@ -179,6 +225,8 @@ impl core::ops::Deref for S {
 }
 fn f() { core::ops::Deref::$0deref(&S); }"#,
             r#"
+use core::ops::Deref;
+
 struct S;
 impl core::ops::Deref for S {
     type Target = S;

crates/ide-assists/src/tests/generated.rs

@@ -2948,6 +2948,8 @@ fn main() {
 mod std { pub mod ops { pub trait Add { fn add(self, _: Self) {} } impl Add for i32 {} } }
 "#####,
         r#####"
+use std::ops::Add;
+
 fn main() {
     1.add(2);
 }