Merge pull request #2975 from aaudiber/lint-identity-into-iter

Lint using identity into_iter conversion

Author: phansch

clippy_lints/src/identity_conversion.rs

@@ -5,7 +5,7 @@ use syntax::ast::NodeId;
 use crate::utils::{in_macro, match_def_path, match_trait_method, same_tys, snippet, span_lint_and_then};
 use crate::utils::{opt_def_id, paths, resolve_node};
 
-/// **What it does:** Checks for always-identical `Into`/`From` conversions.
+/// **What it does:** Checks for always-identical `Into`/`From`/`IntoIter` conversions.
 ///
 /// **Why is this bad?** Redundant code.
 ///
@@ -19,7 +19,7 @@ use crate::utils::{opt_def_id, paths, resolve_node};
 declare_clippy_lint! {
     pub IDENTITY_CONVERSION,
     complexity,
-    "using always-identical `Into`/`From` conversions"
+    "using always-identical `Into`/`From`/`IntoIter` conversions"
 }
 
 #[derive(Default)]
@@ -67,6 +67,16 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for IdentityConversion {
                         });
                     }
                 }
+                if match_trait_method(cx, e, &paths::INTO_ITERATOR) && &*name.ident.as_str() == "into_iter" {
+                    let a = cx.tables.expr_ty(e);
+                    let b = cx.tables.expr_ty(&args[0]);
+                    if same_tys(cx, a, b) {
+                        let sugg = snippet(cx, args[0].span, "<expr>").into_owned();
+                        span_lint_and_then(cx, IDENTITY_CONVERSION, e.span, "identical conversion", |db| {
+                            db.span_suggestion(e.span, "consider removing `.into_iter()`", sugg);
+                        });
+                    }
+                }
             },
 
             ExprKind::Call(ref path, ref args) => if let ExprKind::Path(ref qpath) = path.node {

tests/ui/identity_conversion.rs

@@ -32,9 +32,12 @@ fn main() {
     {
         let _: String = "foo".into();
         let _ = String::from("foo");
+        let _ = "".lines().into_iter();
     }
 
     let _: String = "foo".to_string().into();
     let _: String = From::from("foo".to_string());
     let _ = String::from("foo".to_string());
+    let _ = "".lines().into_iter();
+    let _ = vec![1, 2, 3].into_iter().into_iter();
 }

tests/ui/identity_conversion.stderr

@@ -23,22 +23,34 @@ error: identical conversion
    |                      ^^^^^^^^^^^ help: consider removing `.into()`: `0i32`
 
 error: identical conversion
-  --> $DIR/identity_conversion.rs:37:21
+  --> $DIR/identity_conversion.rs:38:21
    |
-37 |     let _: String = "foo".to_string().into();
+38 |     let _: String = "foo".to_string().into();
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into()`: `"foo".to_string()`
 
 error: identical conversion
-  --> $DIR/identity_conversion.rs:38:21
+  --> $DIR/identity_conversion.rs:39:21
    |
-38 |     let _: String = From::from("foo".to_string());
+39 |     let _: String = From::from("foo".to_string());
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `From::from()`: `"foo".to_string()`
 
 error: identical conversion
-  --> $DIR/identity_conversion.rs:39:13
+  --> $DIR/identity_conversion.rs:40:13
    |
-39 |     let _ = String::from("foo".to_string());
+40 |     let _ = String::from("foo".to_string());
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `String::from()`: `"foo".to_string()`
 
-error: aborting due to 6 previous errors
+error: identical conversion
+  --> $DIR/identity_conversion.rs:41:13
+   |
+41 |     let _ = "".lines().into_iter();
+   |             ^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into_iter()`: `"".lines()`
+
+error: identical conversion
+  --> $DIR/identity_conversion.rs:42:13
+   |
+42 |     let _ = vec![1, 2, 3].into_iter().into_iter();
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider removing `.into_iter()`: `vec![1, 2, 3].into_iter()`
+
+error: aborting due to 8 previous errors