Handle methods with an immediate negation in the non-minimal boolean lint, fixes #1930.

clippy_lints/src/booleans.rs

@@ -44,6 +44,13 @@
     "boolean expressions that contain terminals which can be eliminated"
 }
 
+const METHODS_WITH_NEGATION: [(&str, &str); 4] = [
+    ("is_some", "is_none"),
+    ("is_none", "is_some"),
+    ("is_err", "is_ok"),
+    ("is_ok", "is_err"),
+];
+
 #[derive(Copy, Clone)]
 pub struct NonminimalBool;
 
@@ -396,6 +403,28 @@ fn bool_expr(&self, e: &Expr) {
             }
         }
     }
+
+    fn handle_method_call_in_not(&mut self, e: &'tcx Expr, inner: &'tcx Expr) {
+        if let ExprMethodCall(ref path, _, _) = inner.node {
+            METHODS_WITH_NEGATION.iter().for_each(|&(method, negation_method)| {
+                if method == path.name.as_str() {
+                    span_lint_and_then(
+                        self.cx,
+                        NONMINIMAL_BOOL,
+                        e.span,
+                        "this boolean expression can be simplified",
+                        |db| {
+                            db.span_suggestion(
+                                e.span,
+                                "try",
+                                negation_method.to_owned()
+                            );
+                        }
+                    )
+                }
+            })
+        }
+    }
 }
 
 impl<'a, 'tcx> Visitor<'tcx> for NonminimalBoolVisitor<'a, 'tcx> {
@@ -406,6 +435,7 @@ fn visit_expr(&mut self, e: &'tcx Expr) {
         match e.node {
             ExprBinary(binop, _, _) if binop.node == BiOr || binop.node == BiAnd => self.bool_expr(e),
             ExprUnary(UnNot, ref inner) => if self.cx.tables.node_types()[inner.hir_id].is_bool() {
+                self.handle_method_call_in_not(e, inner);
                 self.bool_expr(e);
             } else {
                 walk_expr(self, e);

tests/ui/booleans.rs

@@ -38,3 +38,17 @@ fn equality_stuff() {
     let _ = a > b && a == b;
     let _ = a != b || !(a != b || c == d);
 }
+
+#[allow(unused, many_single_char_names)]
+fn methods_with_negation() {
+    let a: Option<i32> = unimplemented!();
+    let b: Result<i32, i32> = unimplemented!();
+    let _ = a.is_some();
+    let _ = !a.is_some();
+    let _ = a.is_none();
+    let _ = !a.is_none();
+    let _ = b.is_err();
+    let _ = !b.is_err();
+    let _ = b.is_ok();
+    let _ = !b.is_ok();
+}

tests/ui/booleans.stderr

@@ -130,3 +130,27 @@ help: try
 39 |     let _ = !(a == b && c == d);
    |             ^^^^^^^^^^^^^^^^^^^
 
+error: this boolean expression can be simplified
+  --> $DIR/booleans.rs:47:13
+   |
+47 |     let _ = !a.is_some();
+   |             ^^^^^^^^^^^^ help: try: `is_none`
+
+error: this boolean expression can be simplified
+  --> $DIR/booleans.rs:49:13
+   |
+49 |     let _ = !a.is_none();
+   |             ^^^^^^^^^^^^ help: try: `is_some`
+
+error: this boolean expression can be simplified
+  --> $DIR/booleans.rs:51:13
+   |
+51 |     let _ = !b.is_err();
+   |             ^^^^^^^^^^^ help: try: `is_ok`
+
+error: this boolean expression can be simplified
+  --> $DIR/booleans.rs:53:13
+   |
+53 |     let _ = !b.is_ok();
+   |             ^^^^^^^^^^ help: try: `is_err`
+