extend unused_parens lint to break/return ()

src/librustc_lint/unused.rs

@@ -332,6 +332,7 @@ impl EarlyLintPass for UnusedParens {
             WhileLet(_, ref cond, ..) => (cond, "`while let` head expression", true),
             ForLoop(_, ref cond, ..) => (cond, "`for` head expression", true),
             Match(ref head, _) => (head, "`match` head expression", true),
+            Break(_, Some(ref value)) => (value, "`break` value", false),
             Ret(Some(ref value)) => (value, "`return` value", false),
             Assign(_, ref value) => (value, "assigned value", false),
             AssignOp(.., ref value) => (value, "assigned value", false),
@@ -368,6 +369,34 @@ impl EarlyLintPass for UnusedParens {
                 return;
             }
         };
+        match e.node {
+            Ret(Some(ref value)) |
+            Break(_, Some(ref value)) => {
+                if let Tup(ref vals) = value.node {
+                    if vals.is_empty() {
+                        if e.span.ctxt().outer().expn_info()
+                            .map_or(false, |info| info.call_site.ctxt().outer()
+                                    .expn_info().is_some()) {
+                                return;
+                        }
+                        let mut err = cx.struct_span_lint(
+                            UNUSED_PARENS,
+                            value.span,
+                            "unnecessary parentheses",
+                        );
+                        err.span_suggestion_short_with_applicability(
+                            value.span,
+                            "remove these parentheses",
+                            String::from(""),
+                            Applicability::MachineApplicable,
+                        );
+                        err.emit();
+                        return;
+                    }
+                }
+            }
+            _ => ()
+        }
         self.check_unused_parens_core(cx, &value, msg, struct_lit_needs_parens);
     }
 

src/librustc_typeck/check/regionck.rs

@@ -107,7 +107,7 @@ use rustc::hir::{self, PatKind};
 macro_rules! ignore_err {
     ($e:expr) => (match $e { Ok(e) => e, Err(_) => {
         debug!("ignoring mem-categorization error!");
-        return ()
+        return;
     }})
 }
 

src/test/ui/lint/unused_parens_break_return.rs

@@ -0,0 +1,26 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: --error-format pretty-json -Zunstable-options
+// compile-pass
+
+// The output for humans should just highlight the whole span without showing
+// the suggested replacement, but we also want to test that suggested
+// replacement only removes one set of parentheses, rather than naïvely
+// stripping away any starting or ending parenthesis characters—hence this
+// test of the JSON error format.
+
+#![warn(unused_parens)]
+fn main() {
+    loop {
+        break();
+    }
+    return();
+}

src/test/ui/lint/unused_parens_break_return.stderr

@@ -0,0 +1,176 @@
+{
+  "message": "unnecessary parentheses",
+  "code": {
+    "code": "unused_parens",
+    "explanation": null
+  },
+  "level": "warning",
+  "spans": [
+    {
+      "file_name": "$DIR/unused_parens_break_return.rs",
+      "byte_start": 941,
+      "byte_end": 943,
+      "line_start": 23,
+      "line_end": 23,
+      "column_start": 14,
+      "column_end": 16,
+      "is_primary": true,
+      "text": [
+        {
+          "text": "        break();",
+          "highlight_start": 14,
+          "highlight_end": 16
+        }
+      ],
+      "label": null,
+      "suggested_replacement": null,
+      "suggestion_applicability": null,
+      "expansion": null
+    }
+  ],
+  "children": [
+    {
+      "message": "lint level defined here",
+      "code": null,
+      "level": "note",
+      "spans": [
+        {
+          "file_name": "$DIR/unused_parens_break_return.rs",
+          "byte_start": 889,
+          "byte_end": 902,
+          "line_start": 20,
+          "line_end": 20,
+          "column_start": 9,
+          "column_end": 22,
+          "is_primary": true,
+          "text": [
+            {
+              "text": "#![warn(unused_parens)]",
+              "highlight_start": 9,
+              "highlight_end": 22
+            }
+          ],
+          "label": null,
+          "suggested_replacement": null,
+          "suggestion_applicability": null,
+          "expansion": null
+        }
+      ],
+      "children": [],
+      "rendered": null
+    },
+    {
+      "message": "remove these parentheses",
+      "code": null,
+      "level": "help",
+      "spans": [
+        {
+          "file_name": "$DIR/unused_parens_break_return.rs",
+          "byte_start": 941,
+          "byte_end": 943,
+          "line_start": 23,
+          "line_end": 23,
+          "column_start": 14,
+          "column_end": 16,
+          "is_primary": true,
+          "text": [
+            {
+              "text": "        break();",
+              "highlight_start": 14,
+              "highlight_end": 16
+            }
+          ],
+          "label": null,
+          "suggested_replacement": "",
+          "suggestion_applicability": "MachineApplicable",
+          "expansion": null
+        }
+      ],
+      "children": [],
+      "rendered": null
+    }
+  ],
+  "rendered": "warning: unnecessary parentheses
+  --> $DIR/unused_parens_break_return.rs:23:14
+   |
+LL |         break();
+   |              ^^ help: remove these parentheses
+   |
+note: lint level defined here
+  --> $DIR/unused_parens_break_return.rs:20:9
+   |
+LL | #![warn(unused_parens)]
+   |         ^^^^^^^^^^^^^
+
+"
+}
+{
+  "message": "unnecessary parentheses",
+  "code": {
+    "code": "unused_parens",
+    "explanation": null
+  },
+  "level": "warning",
+  "spans": [
+    {
+      "file_name": "$DIR/unused_parens_break_return.rs",
+      "byte_start": 961,
+      "byte_end": 963,
+      "line_start": 25,
+      "line_end": 25,
+      "column_start": 11,
+      "column_end": 13,
+      "is_primary": true,
+      "text": [
+        {
+          "text": "    return();",
+          "highlight_start": 11,
+          "highlight_end": 13
+        }
+      ],
+      "label": null,
+      "suggested_replacement": null,
+      "suggestion_applicability": null,
+      "expansion": null
+    }
+  ],
+  "children": [
+    {
+      "message": "remove these parentheses",
+      "code": null,
+      "level": "help",
+      "spans": [
+        {
+          "file_name": "$DIR/unused_parens_break_return.rs",
+          "byte_start": 961,
+          "byte_end": 963,
+          "line_start": 25,
+          "line_end": 25,
+          "column_start": 11,
+          "column_end": 13,
+          "is_primary": true,
+          "text": [
+            {
+              "text": "    return();",
+              "highlight_start": 11,
+              "highlight_end": 13
+            }
+          ],
+          "label": null,
+          "suggested_replacement": "",
+          "suggestion_applicability": "MachineApplicable",
+          "expansion": null
+        }
+      ],
+      "children": [],
+      "rendered": null
+    }
+  ],
+  "rendered": "warning: unnecessary parentheses
+  --> $DIR/unused_parens_break_return.rs:25:11
+   |
+LL |     return();
+   |           ^^ help: remove these parentheses
+
+"
+}