Prohibit #[default] in invalid places

compiler/rustc_builtin_macros/src/deriving/default.rs

@@ -2,6 +2,7 @@ use crate::deriving::generic::ty::*;
 use crate::deriving::generic::*;
 
 use rustc_ast::ptr::P;
+use rustc_ast::walk_list;
 use rustc_ast::EnumDef;
 use rustc_ast::VariantData;
 use rustc_ast::{Expr, MetaItem};
@@ -19,6 +20,8 @@ pub fn expand_deriving_default(
     item: &Annotatable,
     push: &mut dyn FnMut(Annotatable),
 ) {
+    item.visit_with(&mut DetectNonVariantDefaultAttr { cx });
+
     let inline = cx.meta_word(span, sym::inline);
     let attrs = vec![cx.attribute(inline)];
     let trait_def = TraitDef {
@@ -184,7 +187,10 @@ fn extract_default_variant<'a>(
     };
 
     if !matches!(variant.data, VariantData::Unit(..)) {
-        cx.struct_span_err(variant.ident.span, "`#[default]` may only be used on unit variants")
+        cx.struct_span_err(
+            variant.ident.span,
+            "the `#[default]` attribute may only be used on unit enum variants",
+        )
         .help("consider a manual implementation of `Default`")
         .emit();
 
@@ -253,3 +259,31 @@ fn validate_default_attribute(
     }
     Ok(())
 }
+
+struct DetectNonVariantDefaultAttr<'a, 'b> {
+    cx: &'a ExtCtxt<'b>,
+}
+
+impl<'a, 'b> rustc_ast::visit::Visitor<'a> for DetectNonVariantDefaultAttr<'a, 'b> {
+    fn visit_attribute(&mut self, attr: &'a rustc_ast::Attribute) {
+        if attr.has_name(kw::Default) {
+            self.cx
+                .struct_span_err(
+                    attr.span,
+                    "the `#[default]` attribute may only be used on unit enum variants",
+                )
+                .emit();
+        }
+
+        rustc_ast::visit::walk_attribute(self, attr);
+    }
+    fn visit_variant(&mut self, v: &'a rustc_ast::Variant) {
+        self.visit_ident(v.ident);
+        self.visit_vis(&v.vis);
+        self.visit_variant_data(&v.data);
+        walk_list!(self, visit_anon_const, &v.disr_expr);
+        for attr in &v.attrs {
+            rustc_ast::visit::walk_attribute(self, attr);
+        }
+    }
+}

src/test/ui/macros/macros-nonfatal-errors.rs

@@ -5,8 +5,40 @@
 
 #![feature(asm, llvm_asm)]
 #![feature(trace_macros, concat_idents)]
+#![feature(stmt_expr_attributes, arbitrary_enum_discriminant)]
 #![feature(derive_default_enum)]
 
+#[derive(Default)]
+struct DefaultInnerAttrStruct {
+    #[default] //~ ERROR the `#[default]` attribute may only be used on unit enum variants
+    foo: (),
+}
+
+#[derive(Default)]
+struct DefaultInnerAttrTupleStruct(#[default] ());
+//~^ ERROR the `#[default]` attribute may only be used on unit enum variants
+
+#[derive(Default)]
+#[default] //~ ERROR the `#[default]` attribute may only be used on unit enum variants
+struct DefaultOuterAttrStruct {}
+
+#[derive(Default)]
+#[default] //~ ERROR the `#[default]` attribute may only be used on unit enum variants
+enum DefaultOuterAttrEnum {
+    #[default]
+    Foo,
+}
+
+#[rustfmt::skip] // needs some work to handle this case
+#[repr(u8)]
+#[derive(Default)]
+enum AttrOnInnerExpression {
+    Foo = #[default] 0, //~ ERROR the `#[default]` attribute may only be used on unit enum variants
+    Bar([u8; #[default] 1]), //~ ERROR the `#[default]` attribute may only be used on unit enum variants
+    #[default]
+    Baz,
+}
+
 #[derive(Default)] //~ ERROR no default declared
 enum NoDeclaredDefault {
     Foo,
@@ -50,7 +82,7 @@ enum ManyDefaultAttrs {
 #[derive(Default)]
 enum DefaultHasFields {
     #[default]
-    Foo {}, //~ ERROR `#[default]` may only be used on unit variants
+    Foo {}, //~ ERROR the `#[default]` attribute may only be used on unit enum variants
     Bar,
 }
 

src/test/ui/macros/macros-nonfatal-errors.stderr

@@ -1,5 +1,41 @@
+error: the `#[default]` attribute may only be used on unit enum variants
+  --> $DIR/macros-nonfatal-errors.rs:13:5
+   |
+LL |     #[default]
+   |     ^^^^^^^^^^
+
+error: the `#[default]` attribute may only be used on unit enum variants
+  --> $DIR/macros-nonfatal-errors.rs:18:36
+   |
+LL | struct DefaultInnerAttrTupleStruct(#[default] ());
+   |                                    ^^^^^^^^^^
+
+error: the `#[default]` attribute may only be used on unit enum variants
+  --> $DIR/macros-nonfatal-errors.rs:22:1
+   |
+LL | #[default]
+   | ^^^^^^^^^^
+
+error: the `#[default]` attribute may only be used on unit enum variants
+  --> $DIR/macros-nonfatal-errors.rs:26:1
+   |
+LL | #[default]
+   | ^^^^^^^^^^
+
+error: the `#[default]` attribute may only be used on unit enum variants
+  --> $DIR/macros-nonfatal-errors.rs:36:11
+   |
+LL |     Foo = #[default] 0,
+   |           ^^^^^^^^^^
+
+error: the `#[default]` attribute may only be used on unit enum variants
+  --> $DIR/macros-nonfatal-errors.rs:37:14
+   |
+LL |     Bar([u8; #[default] 1]),
+   |              ^^^^^^^^^^
+
 error: no default declared
-  --> $DIR/macros-nonfatal-errors.rs:10:10
+  --> $DIR/macros-nonfatal-errors.rs:42:10
    |
 LL | #[derive(Default)]
    |          ^^^^^^^
@@ -8,7 +44,7 @@ LL | #[derive(Default)]
    = note: this error originates in the derive macro `Default` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: multiple declared defaults
-  --> $DIR/macros-nonfatal-errors.rs:16:10
+  --> $DIR/macros-nonfatal-errors.rs:48:10
    |
 LL | #[derive(Default)]
    |          ^^^^^^^
@@ -26,7 +62,7 @@ LL |     Baz,
    = note: this error originates in the derive macro `Default` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: `#[default]` attribute does not accept a value
-  --> $DIR/macros-nonfatal-errors.rs:28:5
+  --> $DIR/macros-nonfatal-errors.rs:60:5
    |
 LL |     #[default = 1]
    |     ^^^^^^^^^^^^^^
@@ -34,7 +70,7 @@ LL |     #[default = 1]
    = help: try using `#[default]`
 
 error: multiple `#[default]` attributes
-  --> $DIR/macros-nonfatal-errors.rs:36:5
+  --> $DIR/macros-nonfatal-errors.rs:68:5
    |
 LL |     #[default]
    |     ---------- `#[default]` used here
@@ -45,13 +81,13 @@ LL |     Foo,
    |
    = note: only one `#[default]` attribute is needed
 help: try removing this
-  --> $DIR/macros-nonfatal-errors.rs:35:5
+  --> $DIR/macros-nonfatal-errors.rs:67:5
    |
 LL |     #[default]
    |     ^^^^^^^^^^
 
 error: multiple `#[default]` attributes
-  --> $DIR/macros-nonfatal-errors.rs:46:5
+  --> $DIR/macros-nonfatal-errors.rs:78:5
    |
 LL |     #[default]
    |     ---------- `#[default]` used here
@@ -63,7 +99,7 @@ LL |     Foo,
    |
    = note: only one `#[default]` attribute is needed
 help: try removing these
-  --> $DIR/macros-nonfatal-errors.rs:43:5
+  --> $DIR/macros-nonfatal-errors.rs:75:5
    |
 LL |     #[default]
    |     ^^^^^^^^^^
@@ -72,8 +108,8 @@ LL |     #[default]
 LL |     #[default]
    |     ^^^^^^^^^^
 
-error: `#[default]` may only be used on unit variants
+error: the `#[default]` attribute may only be used on unit enum variants
-  --> $DIR/macros-nonfatal-errors.rs:53:5
+  --> $DIR/macros-nonfatal-errors.rs:85:5
    |
 LL |     Foo {},
    |     ^^^
@@ -81,7 +117,7 @@ LL |     Foo {},
    = help: consider a manual implementation of `Default`
 
 error: default variant must be exhaustive
-  --> $DIR/macros-nonfatal-errors.rs:61:5
+  --> $DIR/macros-nonfatal-errors.rs:93:5
    |
 LL |     #[non_exhaustive]
    |     ----------------- declared `#[non_exhaustive]` here
@@ -91,43 +127,43 @@ LL |     Foo,
    = help: consider a manual implementation of `Default`
 
 error: asm template must be a string literal
-  --> $DIR/macros-nonfatal-errors.rs:66:10
+  --> $DIR/macros-nonfatal-errors.rs:98:10
    |
 LL |     asm!(invalid);
    |          ^^^^^^^
 
 error: inline assembly must be a string literal
-  --> $DIR/macros-nonfatal-errors.rs:67:15
+  --> $DIR/macros-nonfatal-errors.rs:99:15
    |
 LL |     llvm_asm!(invalid);
    |               ^^^^^^^
 
 error: concat_idents! requires ident args.
-  --> $DIR/macros-nonfatal-errors.rs:69:5
+  --> $DIR/macros-nonfatal-errors.rs:101:5
    |
 LL |     concat_idents!("not", "idents");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: argument must be a string literal
-  --> $DIR/macros-nonfatal-errors.rs:71:17
+  --> $DIR/macros-nonfatal-errors.rs:103:17
    |
 LL |     option_env!(invalid);
    |                 ^^^^^^^
 
 error: expected string literal
-  --> $DIR/macros-nonfatal-errors.rs:72:10
+  --> $DIR/macros-nonfatal-errors.rs:104:10
    |
 LL |     env!(invalid);
    |          ^^^^^^^
 
 error: expected string literal
-  --> $DIR/macros-nonfatal-errors.rs:73:10
+  --> $DIR/macros-nonfatal-errors.rs:105:10
    |
 LL |     env!(foo, abr, baz);
    |          ^^^
 
 error: environment variable `RUST_HOPEFULLY_THIS_DOESNT_EXIST` not defined
-  --> $DIR/macros-nonfatal-errors.rs:74:5
+  --> $DIR/macros-nonfatal-errors.rs:106:5
    |
 LL |     env!("RUST_HOPEFULLY_THIS_DOESNT_EXIST");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -135,7 +171,7 @@ LL |     env!("RUST_HOPEFULLY_THIS_DOESNT_EXIST");
    = note: this error originates in the macro `env` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: format argument must be a string literal
-  --> $DIR/macros-nonfatal-errors.rs:76:13
+  --> $DIR/macros-nonfatal-errors.rs:108:13
    |
 LL |     format!(invalid);
    |             ^^^^^^^
@@ -146,19 +182,19 @@ LL |     format!("{}", invalid);
    |             ^^^^^
 
 error: argument must be a string literal
-  --> $DIR/macros-nonfatal-errors.rs:78:14
+  --> $DIR/macros-nonfatal-errors.rs:110:14
    |
 LL |     include!(invalid);
    |              ^^^^^^^
 
 error: argument must be a string literal
-  --> $DIR/macros-nonfatal-errors.rs:80:18
+  --> $DIR/macros-nonfatal-errors.rs:112:18
    |
 LL |     include_str!(invalid);
    |                  ^^^^^^^
 
 error: couldn't read $DIR/i'd be quite surprised if a file with this name existed: $FILE_NOT_FOUND_MSG (os error 2)
-  --> $DIR/macros-nonfatal-errors.rs:81:5
+  --> $DIR/macros-nonfatal-errors.rs:113:5
    |
 LL |     include_str!("i'd be quite surprised if a file with this name existed");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -166,13 +202,13 @@ LL |     include_str!("i'd be quite surprised if a file with this name existed")
    = note: this error originates in the macro `include_str` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: argument must be a string literal
-  --> $DIR/macros-nonfatal-errors.rs:82:20
+  --> $DIR/macros-nonfatal-errors.rs:114:20
    |
 LL |     include_bytes!(invalid);
    |                    ^^^^^^^
 
 error: couldn't read $DIR/i'd be quite surprised if a file with this name existed: $FILE_NOT_FOUND_MSG (os error 2)
-  --> $DIR/macros-nonfatal-errors.rs:83:5
+  --> $DIR/macros-nonfatal-errors.rs:115:5
    |
 LL |     include_bytes!("i'd be quite surprised if a file with this name existed");
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -180,10 +216,10 @@ LL |     include_bytes!("i'd be quite surprised if a file with this name existed
    = note: this error originates in the macro `include_bytes` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: trace_macros! accepts only `true` or `false`
-  --> $DIR/macros-nonfatal-errors.rs:85:5
+  --> $DIR/macros-nonfatal-errors.rs:117:5
    |
 LL |     trace_macros!(invalid);
    |     ^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 21 previous errors
+error: aborting due to 27 previous errors