Make sure we don't lose default struct value when formatting struct

src/tools/rustfmt/src/items.rs

@@ -1944,6 +1944,11 @@ pub(crate) fn rewrite_struct_field(
     shape: Shape,
     lhs_max_width: usize,
 ) -> RewriteResult {
+    // FIXME(default_field_values): Implement formatting.
+    if field.default.is_some() {
+        return Err(RewriteError::Unknown);
+    }
+
     if contains_skip(&field.attrs) {
         return Ok(context.snippet(field.span()).to_owned());
     }

src/tools/rustfmt/src/spanned.rs

@@ -144,6 +144,7 @@ impl Spanned for ast::GenericParam {
 
 impl Spanned for ast::FieldDef {
     fn span(&self) -> Span {
+        // FIXME(default_field_values): This needs to be adjusted.
         span_with_attrs_lo_hi!(self, self.span.lo(), self.ty.span.hi())
     }
 }

src/tools/rustfmt/tests/source/default-field-values.rs

@@ -0,0 +1,18 @@
+#![feature(default_struct_values)]
+
+// Test for now that nightly default field values are left alone for now.
+
+struct Foo {
+    default_field:    Spacing =    /* uwu */ 0,
+}
+
+struct Foo2 {
+    #[rustfmt::skip]
+    default_field:    Spacing =    /* uwu */ 0,
+}
+
+a_macro!(
+    struct Foo2 {
+        default_field:    Spacing =    /* uwu */ 0,
+    }
+);

src/tools/rustfmt/tests/target/default-field-values.rs

@@ -0,0 +1,18 @@
+#![feature(default_struct_values)]
+
+// Test for now that nightly default field values are left alone for now.
+
+struct Foo {
+    default_field:    Spacing =    /* uwu */ 0,
+}
+
+struct Foo2 {
+    #[rustfmt::skip]
+    default_field:    Spacing =    /* uwu */ 0,
+}
+
+a_macro!(
+    struct Foo2 {
+        default_field:    Spacing =    /* uwu */ 0,
+    }
+);