First version of the lint

CHANGELOG.md

@@ -2185,6 +2185,7 @@ Released 2018-09-13
 [`same_item_push`]: https://rust-lang.github.io/rust-clippy/master/index.html#same_item_push
 [`search_is_some`]: https://rust-lang.github.io/rust-clippy/master/index.html#search_is_some
 [`self_assignment`]: https://rust-lang.github.io/rust-clippy/master/index.html#self_assignment
+[`semicolon_if_nothing_returned`]: https://rust-lang.github.io/rust-clippy/master/index.html#semicolon_if_nothing_returned
 [`serde_api_misuse`]: https://rust-lang.github.io/rust-clippy/master/index.html#serde_api_misuse
 [`shadow_reuse`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_reuse
 [`shadow_same`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_same

clippy_lints/src/lib.rs

@@ -310,6 +310,7 @@ mod regex;
 mod repeat_once;
 mod returns;
 mod self_assignment;
+mod semicolon_if_nothing_returned;
 mod serde_api;
 mod shadow;
 mod single_component_path_imports;
@@ -876,6 +877,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &returns::LET_AND_RETURN,
         &returns::NEEDLESS_RETURN,
         &self_assignment::SELF_ASSIGNMENT,
+        &semicolon_if_nothing_returned::SEMICOLON_IF_NOTHING_RETURNED,
         &serde_api::SERDE_API_MISUSE,
         &shadow::SHADOW_REUSE,
         &shadow::SHADOW_SAME,
@@ -1237,6 +1239,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| box manual_unwrap_or::ManualUnwrapOr);
     store.register_late_pass(|| box manual_ok_or::ManualOkOr);
     store.register_late_pass(|| box float_equality_without_abs::FloatEqualityWithoutAbs);
+    store.register_late_pass(|| box semicolon_if_nothing_returned::SemicolonIfNothingReturned);
     store.register_late_pass(|| box async_yields_async::AsyncYieldsAsync);
     let disallowed_methods = conf.disallowed_methods.iter().cloned().collect::<FxHashSet<_>>();
     store.register_late_pass(move || box disallowed_method::DisallowedMethod::new(&disallowed_methods));
@@ -1364,6 +1367,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&ranges::RANGE_PLUS_ONE),
         LintId::of(&redundant_else::REDUNDANT_ELSE),
         LintId::of(&ref_option_ref::REF_OPTION_REF),
+        LintId::of(&semicolon_if_nothing_returned::SEMICOLON_IF_NOTHING_RETURNED),
         LintId::of(&shadow::SHADOW_UNRELATED),
         LintId::of(&strings::STRING_ADD_ASSIGN),
         LintId::of(&trait_bounds::TRAIT_DUPLICATION_IN_BOUNDS),

clippy_lints/src/semicolon_if_nothing_returned.rs

@@ -0,0 +1,58 @@
+use crate::utils::{match_def_path, paths, span_lint_and_then, sugg};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::*;
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+declare_clippy_lint! {
+    /// **What it does:**
+    ///
+    /// **Why is this bad?**
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust
+    /// // example code where clippy issues a warning
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// // example code which does not raise clippy warning
+    /// ```
+    pub SEMICOLON_IF_NOTHING_RETURNED,
+    pedantic,
+    "default lint description"
+}
+
+declare_lint_pass!(SemicolonIfNothingReturned => [SEMICOLON_IF_NOTHING_RETURNED]);
+
+impl LateLintPass<'_> for SemicolonIfNothingReturned {
+    fn check_block(&mut self, cx: &LateContext<'tcx>, block: &'tcx Block<'tcx>) {
+        if_chain! {
+            if let Some(expr) = block.expr;
+            let t_expr = cx.typeck_results().expr_ty(expr);
+            if t_expr.is_unit();
+            then {
+                let sugg = sugg::Sugg::hir(cx, &expr, "..");
+                let suggestion = format!("{0};", sugg);
+                span_lint_and_then(
+                    cx,
+                    SEMICOLON_IF_NOTHING_RETURNED,
+                    expr.span,
+                    "add `;` to terminate block",
+                    | diag | {
+                        diag.span_suggestion(
+                            expr.span,
+                            "add `;`",
+                            suggestion,
+                            Applicability::MaybeIncorrect,
+                        );
+                    }
+                )
+            }
+        }
+    }
+}

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
+