Add unused_trait_names tests

4 files changed, 646 insertions, 0 deletions

diff --git a/clippy_lints/src/attrs/useless_attribute.rs b/clippy_lints/src/attrs/useless_attribute.rs
index 67ba605a59f..1296b59f2e1 100644
--- a/clippy_lints/src/attrs/useless_attribute.rs
+++ b/clippy_lints/src/attrs/useless_attribute.rs
@@ -51,6 +51,7 @@ pub(super) fn check(cx: &LateContext<'_>, item: &Item<'_>, attrs: &[Attribute])
                                         | "module_name_repetitions"
                                         | "single_component_path_imports"
                                         | "disallowed_types"
+                                        | "unused_trait_names"
                                 )
                             }) {
                                 return;
diff --git a/tests/ui/unused_trait_names.fixed b/tests/ui/unused_trait_names.fixed
new file mode 100644
index 00000000000..7dfd0db65aa
--- /dev/null
+++ b/tests/ui/unused_trait_names.fixed
@@ -0,0 +1,286 @@
+//@aux-build:proc_macros.rs
+
+#![allow(unused)]
+#![warn(clippy::unused_trait_names)]
+#![feature(decl_macro)]
+
+extern crate proc_macros;
+
+fn main() {}
+
+fn bad() {
+    use std::any::Any as _;
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn good() {
+    use std::any::Any as _;
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn used_good() {
+    use std::any::Any;
+
+    println!("{:?}", Any::type_id("foo"));
+    println!("{:?}", "foo".type_id());
+}
+
+fn multi_bad() {
+    use std::any::{self, Any as _, TypeId};
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn multi_good() {
+    use std::any::{self, Any as _, TypeId};
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn renamed_bad() {
+    use std::any::Any as _;
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn multi_renamed_bad() {
+    use std::any::{Any as _, TypeId as MyTypeId};
+
+    println!("{:?}", "foo".type_id());
+}
+
+mod pub_good {
+    pub use std::any::Any;
+
+    fn foo() {
+        println!("{:?}", "foo".type_id());
+    }
+}
+
+mod used_mod_good {
+    use std::any::Any;
+
+    fn foo() {
+        println!("{:?}", Any::type_id("foo"));
+    }
+}
+
+mod mod_import_bad {
+    fn mod_import_bad() {
+        use std::any::Any as _;
+
+        println!("{:?}", "foo".type_id());
+    }
+}
+
+mod nested_mod_used_good1 {
+    use std::any::Any;
+
+    mod foo {
+        fn foo() {
+            super::Any::type_id("foo");
+        }
+    }
+}
+
+mod nested_mod_used_good2 {
+    use std::any::Any;
+
+    mod foo {
+        use super::Any;
+
+        fn foo() {
+            Any::type_id("foo");
+        }
+    }
+}
+
+mod nested_mod_used_good3 {
+    use std::any::Any;
+
+    mod foo {
+        use crate::nested_mod_used_good3::Any;
+
+        fn foo() {
+            println!("{:?}", Any::type_id("foo"));
+        }
+    }
+}
+
+mod nested_mod_used_bad {
+    use std::any::Any as _;
+
+    fn bar() {
+        println!("{:?}", "foo".type_id());
+    }
+
+    mod foo {
+        use std::any::Any;
+
+        fn foo() {
+            println!("{:?}", Any::type_id("foo"));
+        }
+    }
+}
+
+// More complex example where `use std::any::Any;` should be anonymised but `use std::any::Any as
+// MyAny;` should not as it is used by a sub module. Even though if you removed `use std::any::Any;`
+// the code would still compile.
+mod nested_mod_used_bad1 {
+    use std::any::Any as _;
+
+    use std::any::Any as MyAny;
+
+    fn baz() {
+        println!("{:?}", "baz".type_id());
+    }
+
+    mod foo {
+        use crate::nested_mod_used_bad1::MyAny;
+
+        fn foo() {
+            println!("{:?}", MyAny::type_id("foo"));
+        }
+    }
+}
+
+// Example of nested import with an unused import to try and trick it
+mod nested_mod_used_good5 {
+    use std::any::Any;
+
+    mod foo {
+        use std::any::Any;
+
+        fn baz() {
+            println!("{:?}", "baz".type_id());
+        }
+
+        mod bar {
+            use crate::nested_mod_used_good5::foo::Any;
+
+            fn foo() {
+                println!("{:?}", Any::type_id("foo"));
+            }
+        }
+    }
+}
+
+mod simple_trait {
+    pub trait MyTrait {
+        fn do_things(&self);
+    }
+
+    pub struct MyStruct;
+
+    impl MyTrait for MyStruct {
+        fn do_things(&self) {}
+    }
+}
+
+// Underscore imports were stabilized in 1.33
+#[clippy::msrv = "1.32"]
+fn msrv_1_32() {
+    use simple_trait::{MyStruct, MyTrait};
+    MyStruct.do_things();
+}
+
+#[clippy::msrv = "1.33"]
+fn msrv_1_33() {
+    use simple_trait::{MyStruct, MyTrait as _};
+    MyStruct.do_things();
+}
+
+mod lint_inside_macro_expansion_bad {
+    macro_rules! foo {
+        () => {
+            use std::any::Any as _;
+            fn bar() {
+                "bar".type_id();
+            }
+        };
+    }
+
+    foo!();
+}
+
+mod macro_and_trait_same_name {
+    pub macro Foo() {}
+    pub trait Foo {
+        fn bar(&self);
+    }
+    impl Foo for () {
+        fn bar(&self) {}
+    }
+}
+
+fn call_macro_and_trait_good() {
+    // importing trait and macro but only using macro by path won't allow us to change this to
+    // `use macro_and_trait_same_name::Foo as _;`
+    use macro_and_trait_same_name::Foo;
+    Foo!();
+    ().bar();
+}
+
+proc_macros::external!(
+    fn ignore_inside_external_proc_macro() {
+        use std::any::Any;
+        "foo".type_id();
+    }
+);
+
+proc_macros::with_span!(
+    span
+
+    fn ignore_inside_with_span_proc_macro() {
+        use std::any::Any;
+        "foo".type_id();
+    }
+);
+
+// This should warn the import is unused but should not trigger unused_trait_names
+#[warn(unused)]
+mod unused_import {
+    
+}
+
+#[allow(clippy::unused_trait_names)]
+fn allow_lint_fn() {
+    use std::any::Any;
+
+    "foo".type_id();
+}
+
+#[allow(clippy::unused_trait_names)]
+mod allow_lint_mod {
+    use std::any::Any;
+
+    fn foo() {
+        "foo".type_id();
+    }
+}
+
+mod allow_lint_import {
+    #[allow(clippy::unused_trait_names)]
+    use std::any::Any;
+
+    fn foo() {
+        "foo".type_id();
+    }
+}
+
+// Limitation: Suggests `use std::any::Any as _::{self};` which looks weird
+// fn use_trait_self_good() {
+//     use std::any::Any::{self};
+//     "foo".type_id();
+// }
+
+// Limitation: Suggests `use std::any::{Any as _, Any as _};`
+// mod repeated_renamed {
+//     use std::any::{Any, Any as MyAny};
+
+//     fn foo() {
+//         "foo".type_id();
+//     }
+// }
diff --git a/tests/ui/unused_trait_names.rs b/tests/ui/unused_trait_names.rs
new file mode 100644
index 00000000000..ce44eedbc79
--- /dev/null
+++ b/tests/ui/unused_trait_names.rs
@@ -0,0 +1,286 @@
+//@aux-build:proc_macros.rs
+
+#![allow(unused)]
+#![warn(clippy::unused_trait_names)]
+#![feature(decl_macro)]
+
+extern crate proc_macros;
+
+fn main() {}
+
+fn bad() {
+    use std::any::Any;
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn good() {
+    use std::any::Any as _;
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn used_good() {
+    use std::any::Any;
+
+    println!("{:?}", Any::type_id("foo"));
+    println!("{:?}", "foo".type_id());
+}
+
+fn multi_bad() {
+    use std::any::{self, Any, TypeId};
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn multi_good() {
+    use std::any::{self, Any as _, TypeId};
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn renamed_bad() {
+    use std::any::Any as MyAny;
+
+    println!("{:?}", "foo".type_id());
+}
+
+fn multi_renamed_bad() {
+    use std::any::{Any as MyAny, TypeId as MyTypeId};
+
+    println!("{:?}", "foo".type_id());
+}
+
+mod pub_good {
+    pub use std::any::Any;
+
+    fn foo() {
+        println!("{:?}", "foo".type_id());
+    }
+}
+
+mod used_mod_good {
+    use std::any::Any;
+
+    fn foo() {
+        println!("{:?}", Any::type_id("foo"));
+    }
+}
+
+mod mod_import_bad {
+    fn mod_import_bad() {
+        use std::any::Any;
+
+        println!("{:?}", "foo".type_id());
+    }
+}
+
+mod nested_mod_used_good1 {
+    use std::any::Any;
+
+    mod foo {
+        fn foo() {
+            super::Any::type_id("foo");
+        }
+    }
+}
+
+mod nested_mod_used_good2 {
+    use std::any::Any;
+
+    mod foo {
+        use super::Any;
+
+        fn foo() {
+            Any::type_id("foo");
+        }
+    }
+}
+
+mod nested_mod_used_good3 {
+    use std::any::Any;
+
+    mod foo {
+        use crate::nested_mod_used_good3::Any;
+
+        fn foo() {
+            println!("{:?}", Any::type_id("foo"));
+        }
+    }
+}
+
+mod nested_mod_used_bad {
+    use std::any::Any;
+
+    fn bar() {
+        println!("{:?}", "foo".type_id());
+    }
+
+    mod foo {
+        use std::any::Any;
+
+        fn foo() {
+            println!("{:?}", Any::type_id("foo"));
+        }
+    }
+}
+
+// More complex example where `use std::any::Any;` should be anonymised but `use std::any::Any as
+// MyAny;` should not as it is used by a sub module. Even though if you removed `use std::any::Any;`
+// the code would still compile.
+mod nested_mod_used_bad1 {
+    use std::any::Any;
+
+    use std::any::Any as MyAny;
+
+    fn baz() {
+        println!("{:?}", "baz".type_id());
+    }
+
+    mod foo {
+        use crate::nested_mod_used_bad1::MyAny;
+
+        fn foo() {
+            println!("{:?}", MyAny::type_id("foo"));
+        }
+    }
+}
+
+// Example of nested import with an unused import to try and trick it
+mod nested_mod_used_good5 {
+    use std::any::Any;
+
+    mod foo {
+        use std::any::Any;
+
+        fn baz() {
+            println!("{:?}", "baz".type_id());
+        }
+
+        mod bar {
+            use crate::nested_mod_used_good5::foo::Any;
+
+            fn foo() {
+                println!("{:?}", Any::type_id("foo"));
+            }
+        }
+    }
+}
+
+mod simple_trait {
+    pub trait MyTrait {
+        fn do_things(&self);
+    }
+
+    pub struct MyStruct;
+
+    impl MyTrait for MyStruct {
+        fn do_things(&self) {}
+    }
+}
+
+// Underscore imports were stabilized in 1.33
+#[clippy::msrv = "1.32"]
+fn msrv_1_32() {
+    use simple_trait::{MyStruct, MyTrait};
+    MyStruct.do_things();
+}
+
+#[clippy::msrv = "1.33"]
+fn msrv_1_33() {
+    use simple_trait::{MyStruct, MyTrait};
+    MyStruct.do_things();
+}
+
+mod lint_inside_macro_expansion_bad {
+    macro_rules! foo {
+        () => {
+            use std::any::Any;
+            fn bar() {
+                "bar".type_id();
+            }
+        };
+    }
+
+    foo!();
+}
+
+mod macro_and_trait_same_name {
+    pub macro Foo() {}
+    pub trait Foo {
+        fn bar(&self);
+    }
+    impl Foo for () {
+        fn bar(&self) {}
+    }
+}
+
+fn call_macro_and_trait_good() {
+    // importing trait and macro but only using macro by path won't allow us to change this to
+    // `use macro_and_trait_same_name::Foo as _;`
+    use macro_and_trait_same_name::Foo;
+    Foo!();
+    ().bar();
+}
+
+proc_macros::external!(
+    fn ignore_inside_external_proc_macro() {
+        use std::any::Any;
+        "foo".type_id();
+    }
+);
+
+proc_macros::with_span!(
+    span
+
+    fn ignore_inside_with_span_proc_macro() {
+        use std::any::Any;
+        "foo".type_id();
+    }
+);
+
+// This should warn the import is unused but should not trigger unused_trait_names
+#[warn(unused)]
+mod unused_import {
+    use std::any::Any;
+}
+
+#[allow(clippy::unused_trait_names)]
+fn allow_lint_fn() {
+    use std::any::Any;
+
+    "foo".type_id();
+}
+
+#[allow(clippy::unused_trait_names)]
+mod allow_lint_mod {
+    use std::any::Any;
+
+    fn foo() {
+        "foo".type_id();
+    }
+}
+
+mod allow_lint_import {
+    #[allow(clippy::unused_trait_names)]
+    use std::any::Any;
+
+    fn foo() {
+        "foo".type_id();
+    }
+}
+
+// Limitation: Suggests `use std::any::Any as _::{self};` which looks weird
+// fn use_trait_self_good() {
+//     use std::any::Any::{self};
+//     "foo".type_id();
+// }
+
+// Limitation: Suggests `use std::any::{Any as _, Any as _};`
+// mod repeated_renamed {
+//     use std::any::{Any, Any as MyAny};
+
+//     fn foo() {
+//         "foo".type_id();
+//     }
+// }
diff --git a/tests/ui/unused_trait_names.stderr b/tests/ui/unused_trait_names.stderr
new file mode 100644
index 00000000000..f59d8f58a17
--- /dev/null
+++ b/tests/ui/unused_trait_names.stderr
@@ -0,0 +1,73 @@
+error: unused import: `std::any::Any`
+  --> tests/ui/unused_trait_names.rs:245:9
+   |
+LL |     use std::any::Any;
+   |         ^^^^^^^^^^^^^
+   |
+   = note: `-D unused-imports` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(unused_imports)]`
+
+error: importing trait that is only used anonymously
+  --> tests/ui/unused_trait_names.rs:12:19
+   |
+LL |     use std::any::Any;
+   |                   ^^^ help: use: `Any as _`
+   |
+   = note: `-D clippy::unused-trait-names` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::unused_trait_names)]`
+
+error: importing trait that is only used anonymously
+  --> tests/ui/unused_trait_names.rs:31:26
+   |
+LL |     use std::any::{self, Any, TypeId};
+   |                          ^^^ help: use: `Any as _`
+
+error: importing trait that is only used anonymously
+  --> tests/ui/unused_trait_names.rs:43:19
+   |
+LL |     use std::any::Any as MyAny;
+   |                   ^^^^^^^^^^^^ help: use: `Any as _`
+
+error: importing trait that is only used anonymously
+  --> tests/ui/unused_trait_names.rs:49:20
+   |
+LL |     use std::any::{Any as MyAny, TypeId as MyTypeId};
+   |                    ^^^^^^^^^^^^ help: use: `Any as _`
+
+error: importing trait that is only used anonymously
+  --> tests/ui/unused_trait_names.rs:72:23
+   |
+LL |         use std::any::Any;
+   |                       ^^^ help: use: `Any as _`
+
+error: importing trait that is only used anonymously
+  --> tests/ui/unused_trait_names.rs:113:19
+   |
+LL |     use std::any::Any;
+   |                   ^^^ help: use: `Any as _`
+
+error: importing trait that is only used anonymously
+  --> tests/ui/unused_trait_names.rs:132:19
+   |
+LL |     use std::any::Any;
+   |                   ^^^ help: use: `Any as _`
+
+error: importing trait that is only used anonymously
+  --> tests/ui/unused_trait_names.rs:191:34
+   |
+LL |     use simple_trait::{MyStruct, MyTrait};
+   |                                  ^^^^^^^ help: use: `MyTrait as _`
+
+error: importing trait that is only used anonymously
+  --> tests/ui/unused_trait_names.rs:198:27
+   |
+LL |             use std::any::Any;
+   |                           ^^^ help: use: `Any as _`
+...
+LL |     foo!();
+   |     ------ in this macro invocation
+   |
+   = note: this error originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 10 previous errors
+