Add test for macro expansion

Author: bluebear94

clippy_lints/src/default_box_assignments.rs

@@ -38,7 +38,7 @@ impl LateLintPass<'_> for DefaultBoxAssignments {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ Expr<'_>) {
         if let ExprKind::Assign(lhs, rhs, _) = &expr.kind {
             let lhs_ty = cx.typeck_results().expr_ty(lhs);
-            if is_box_of_default(lhs_ty, cx) && is_default_call(rhs, cx) {
+            if is_box_of_default(lhs_ty, cx) && is_default_call(rhs, cx) && !rhs.span.from_expansion() {
                 span_lint_and_then(
                     cx,
                     DEFAULT_BOX_ASSIGNMENTS,

tests/ui/default_box_assignments.fixed

@@ -1,5 +1,11 @@
 #![warn(clippy::default_box_assignments)]
 
+macro_rules! create_default {
+    () => {
+        Default::default()
+    };
+}
+
 fn main() {
     let mut b = Box::new(1u32);
     *(b) = Default::default();
@@ -11,7 +17,10 @@ fn main() {
     *b = Default::default();
     *b = u32::default();
 
-    // No lint for assigning to Box<T> where T is unsized
+    // No lint for call originating in macro
+    b = create_default!();
+
+    // No lint for assigning to Box<T> where T: !Default
     let mut b = Box::<str>::from("hi".to_string());
     b = Default::default();
 }

tests/ui/default_box_assignments.rs

@@ -1,5 +1,11 @@
 #![warn(clippy::default_box_assignments)]
 
+macro_rules! create_default {
+    () => {
+        Default::default()
+    };
+}
+
 fn main() {
     let mut b = Box::new(1u32);
     b = Default::default();
@@ -11,7 +17,10 @@ fn main() {
     *b = Default::default();
     *b = u32::default();
 
-    // No lint for assigning to Box<T> where T is unsized
+    // No lint for call originating in macro
+    b = create_default!();
+
+    // No lint for assigning to Box<T> where T: !Default
     let mut b = Box::<str>::from("hi".to_string());
     b = Default::default();
 }

tests/ui/default_box_assignments.stderr

@@ -1,5 +1,5 @@
 error: assigning `Default::default()` to `Box<T>`
-  --> tests/ui/default_box_assignments.rs:5:5
+  --> tests/ui/default_box_assignments.rs:11:5
    |
 LL |     b = Default::default();
    |     ^^^^^^^^^^^^^^^^^^^^^^ help: assign to the inner value: `*(b) = Default::default()`
@@ -9,7 +9,7 @@ LL |     b = Default::default();
    = help: to override `-D warnings` add `#[allow(clippy::default_box_assignments)]`
 
 error: assigning `Default::default()` to `Box<T>`
-  --> tests/ui/default_box_assignments.rs:7:5
+  --> tests/ui/default_box_assignments.rs:13:5
    |
 LL |     b = Box::default();
    |     ^^^^^^^^^^^^^^^^^^ help: assign to the inner value: `*(b) = Default::default()`