Add needless_character_iteration lint

tests/ui/needless_character_iteration.fixed

@@ -0,0 +1,51 @@
+#![warn(clippy::needless_character_iteration)]
+#![allow(clippy::map_identity, clippy::unnecessary_operation)]
+
+#[derive(Default)]
+struct S {
+    field: &'static str,
+}
+
+impl S {
+    fn field(&self) -> &str {
+        self.field
+    }
+}
+
+fn magic(_: char) {}
+
+fn main() {
+    "foo".is_ascii();
+    //~^ ERROR: checking if a string is ascii using iterators
+    !"foo".is_ascii();
+    //~^ ERROR: checking if a string is ascii using iterators
+    "foo".is_ascii();
+    //~^ ERROR: checking if a string is ascii using iterators
+    !"foo".is_ascii();
+    //~^ ERROR: checking if a string is ascii using iterators
+
+    let s = String::new();
+    s.is_ascii();
+    //~^ ERROR: checking if a string is ascii using iterators
+    !"foo".to_string().is_ascii();
+    //~^ ERROR: checking if a string is ascii using iterators
+
+    "foo".is_ascii();
+    !"foo".is_ascii();
+
+    S::default().field().is_ascii();
+    //~^ ERROR: checking if a string is ascii using iterators
+
+    // Should not lint!
+    "foo".chars().all(|c| {
+        let x = c;
+        magic(x);
+        x.is_ascii()
+    });
+
+    // Should not lint!
+    "foo".chars().all(|c| c.is_ascii() && c.is_alphabetic());
+
+    // Should not lint!
+    "foo".chars().map(|c| c).all(|c| !char::is_ascii(&c));
+}

tests/ui/needless_character_iteration.rs

@@ -0,0 +1,59 @@
+#![warn(clippy::needless_character_iteration)]
+#![allow(clippy::map_identity, clippy::unnecessary_operation)]
+
+#[derive(Default)]
+struct S {
+    field: &'static str,
+}
+
+impl S {
+    fn field(&self) -> &str {
+        self.field
+    }
+}
+
+fn magic(_: char) {}
+
+fn main() {
+    "foo".chars().all(|c| c.is_ascii());
+    //~^ ERROR: checking if a string is ascii using iterators
+    "foo".chars().all(|c| !c.is_ascii());
+    //~^ ERROR: checking if a string is ascii using iterators
+    "foo".chars().all(|c| char::is_ascii(&c));
+    //~^ ERROR: checking if a string is ascii using iterators
+    "foo".chars().all(|c| !char::is_ascii(&c));
+    //~^ ERROR: checking if a string is ascii using iterators
+
+    let s = String::new();
+    s.chars().all(|c| c.is_ascii());
+    //~^ ERROR: checking if a string is ascii using iterators
+    "foo".to_string().chars().all(|c| !c.is_ascii());
+    //~^ ERROR: checking if a string is ascii using iterators
+
+    "foo".chars().all(|c| {
+        //~^ ERROR: checking if a string is ascii using iterators
+        let x = c;
+        x.is_ascii()
+    });
+    "foo".chars().all(|c| {
+        //~^ ERROR: checking if a string is ascii using iterators
+        let x = c;
+        !x.is_ascii()
+    });
+
+    S::default().field().chars().all(|x| x.is_ascii());
+    //~^ ERROR: checking if a string is ascii using iterators
+
+    // Should not lint!
+    "foo".chars().all(|c| {
+        let x = c;
+        magic(x);
+        x.is_ascii()
+    });
+
+    // Should not lint!
+    "foo".chars().all(|c| c.is_ascii() && c.is_alphabetic());
+
+    // Should not lint!
+    "foo".chars().map(|c| c).all(|c| !char::is_ascii(&c));
+}

tests/ui/needless_character_iteration.stderr

@@ -0,0 +1,67 @@
+error: checking if a string is ascii using iterators
+  --> tests/ui/needless_character_iteration.rs:18:5
+   |
+LL |     "foo".chars().all(|c| c.is_ascii());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `"foo".is_ascii()`
+   |
+   = note: `-D clippy::needless-character-iteration` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::needless_character_iteration)]`
+
+error: checking if a string is ascii using iterators
+  --> tests/ui/needless_character_iteration.rs:20:5
+   |
+LL |     "foo".chars().all(|c| !c.is_ascii());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `!"foo".is_ascii()`
+
+error: checking if a string is ascii using iterators
+  --> tests/ui/needless_character_iteration.rs:22:5
+   |
+LL |     "foo".chars().all(|c| char::is_ascii(&c));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `"foo".is_ascii()`
+
+error: checking if a string is ascii using iterators
+  --> tests/ui/needless_character_iteration.rs:24:5
+   |
+LL |     "foo".chars().all(|c| !char::is_ascii(&c));
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `!"foo".is_ascii()`
+
+error: checking if a string is ascii using iterators
+  --> tests/ui/needless_character_iteration.rs:28:5
+   |
+LL |     s.chars().all(|c| c.is_ascii());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `s.is_ascii()`
+
+error: checking if a string is ascii using iterators
+  --> tests/ui/needless_character_iteration.rs:30:5
+   |
+LL |     "foo".to_string().chars().all(|c| !c.is_ascii());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `!"foo".to_string().is_ascii()`
+
+error: checking if a string is ascii using iterators
+  --> tests/ui/needless_character_iteration.rs:33:5
+   |
+LL | /     "foo".chars().all(|c| {
+LL | |
+LL | |         let x = c;
+LL | |         x.is_ascii()
+LL | |     });
+   | |______^ help: try: `"foo".is_ascii()`
+
+error: checking if a string is ascii using iterators
+  --> tests/ui/needless_character_iteration.rs:38:5
+   |
+LL | /     "foo".chars().all(|c| {
+LL | |
+LL | |         let x = c;
+LL | |         !x.is_ascii()
+LL | |     });
+   | |______^ help: try: `!"foo".is_ascii()`
+
+error: checking if a string is ascii using iterators
+  --> tests/ui/needless_character_iteration.rs:44:5
+   |
+LL |     S::default().field().chars().all(|x| x.is_ascii());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `S::default().field().is_ascii()`
+
+error: aborting due to 9 previous errors
+