First version of the lint

tests/ui/semicolon_if_nothing_returned.rs

@@ -0,0 +1,18 @@
+#![warn(clippy::semicolon_if_nothing_returned)]
+
+fn get_unit() {}
+
+// the functions below trigger the lint
+fn main() {
+    println!("Hello")
+}
+
+fn hello() {
+    get_unit()
+}
+
+// this is fine
+fn print_sum(a: i32, b: i32) {
+    println!("{}", a + b);
+    assert_eq!(true, false);
+}

tests/ui/semicolon_if_nothing_returned.stderr

@@ -0,0 +1,17 @@
+error: add `;` to terminate block
+  --> $DIR/semicolon_if_nothing_returned.rs:7:5
+   |
+LL |     println!("Hello")
+   |     ^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::semicolon-if-nothing-returned` implied by `-D warnings`
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: add `;` to terminate block
+  --> $DIR/semicolon_if_nothing_returned.rs:11:5
+   |
+LL |     get_unit()
+   |     ^^^^^^^^^^ help: add `;`: `get_unit();`
+
+error: aborting due to 2 previous errors
+