add iter_over_hash_type lint

tests/ui/iter_over_hash_type.rs

@@ -0,0 +1,44 @@
+//@aux-build:proc_macros.rs
+
+#![warn(clippy::iter_over_hash_type)]
+use std::collections::{HashMap, HashSet};
+
+extern crate proc_macros;
+
+fn main() {
+    let hash_set = HashSet::<i32>::new();
+    let hash_map = HashMap::<i32, i32>::new();
+    let vec = Vec::<i32>::new();
+
+    for x in &hash_set {
+        let _ = x;
+    }
+    for x in hash_set.iter() {
+        let _ = x;
+    }
+    for x in hash_set {
+        let _ = x;
+    }
+    for (x, y) in &hash_map {
+        let _ = (x, y);
+    }
+    for x in hash_map.keys() {
+        let _ = x;
+    }
+    for x in hash_map.values() {
+        let _ = x;
+    }
+
+    // shouldnt fire
+    for x in &vec {
+        let _ = x;
+    }
+    for x in vec {
+        let _ = x;
+    }
+
+    // should not lint, this comes from an external crate
+    proc_macros::external! {
+      for _ in HashMap::<i32, i32>::new() {}
+    }
+}

tests/ui/iter_over_hash_type.stderr

@@ -0,0 +1,53 @@
+error: iterating over unordered hash-based type
+  --> $DIR/iter_over_hash_type.rs:13:5
+   |
+LL | /     for x in &hash_set {
+LL | |         let _ = x;
+LL | |     }
+   | |_____^
+   |
+   = note: `-D clippy::iter-over-hash-type` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::iter_over_hash_type)]`
+
+error: iterating over unordered hash-based type
+  --> $DIR/iter_over_hash_type.rs:16:5
+   |
+LL | /     for x in hash_set.iter() {
+LL | |         let _ = x;
+LL | |     }
+   | |_____^
+
+error: iterating over unordered hash-based type
+  --> $DIR/iter_over_hash_type.rs:19:5
+   |
+LL | /     for x in hash_set {
+LL | |         let _ = x;
+LL | |     }
+   | |_____^
+
+error: iterating over unordered hash-based type
+  --> $DIR/iter_over_hash_type.rs:22:5
+   |
+LL | /     for (x, y) in &hash_map {
+LL | |         let _ = (x, y);
+LL | |     }
+   | |_____^
+
+error: iterating over unordered hash-based type
+  --> $DIR/iter_over_hash_type.rs:25:5
+   |
+LL | /     for x in hash_map.keys() {
+LL | |         let _ = x;
+LL | |     }
+   | |_____^
+
+error: iterating over unordered hash-based type
+  --> $DIR/iter_over_hash_type.rs:28:5
+   |
+LL | /     for x in hash_map.values() {
+LL | |         let _ = x;
+LL | |     }
+   | |_____^
+
+error: aborting due to 6 previous errors
+