1 files changed, 59 insertions, 0 deletions
diff --git a/compiler/rustc_builtin_macros/src/cfg_accessible.rs b/compiler/rustc_builtin_macros/src/cfg_accessible.rs
new file mode 100644
index 00000000000..75f4b077640
--- /dev/null
+++ b/compiler/rustc_builtin_macros/src/cfg_accessible.rs
@@ -0,0 +1,59 @@
+//! Implementation of the `#[cfg_accessible(path)]` attribute macro.
+
+use rustc_ast as ast;
+use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, MultiItemModifier};
+use rustc_feature::AttributeTemplate;
+use rustc_parse::validate_attr;
+use rustc_span::symbol::sym;
+use rustc_span::Span;
+
+crate struct Expander;
+
+fn validate_input<'a>(ecx: &mut ExtCtxt<'_>, mi: &'a ast::MetaItem) -> Option<&'a ast::Path> {
+    match mi.meta_item_list() {
+        None => {}
+        Some([]) => ecx.span_err(mi.span, "`cfg_accessible` path is not specified"),
+        Some([_, .., l]) => ecx.span_err(l.span(), "multiple `cfg_accessible` paths are specified"),
+        Some([nmi]) => match nmi.meta_item() {
+            None => ecx.span_err(nmi.span(), "`cfg_accessible` path cannot be a literal"),
+            Some(mi) => {
+                if !mi.is_word() {
+                    ecx.span_err(mi.span, "`cfg_accessible` path cannot accept arguments");
+                }
+                return Some(&mi.path);
+            }
+        },
+    }
+    None
+}
+
+impl MultiItemModifier for Expander {
+    fn expand(
+        &self,
+        ecx: &mut ExtCtxt<'_>,
+        _span: Span,
+        meta_item: &ast::MetaItem,
+        item: Annotatable,
+    ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
+        let template = AttributeTemplate { list: Some("path"), ..Default::default() };
+        let attr = &ecx.attribute(meta_item.clone());
+        validate_attr::check_builtin_attribute(
+            &ecx.sess.parse_sess,
+            attr,
+            sym::cfg_accessible,
+            template,
+        );
+
+        let path = match validate_input(ecx, meta_item) {
+            Some(path) => path,
+            None => return ExpandResult::Ready(Vec::new()),
+        };
+
+        let failure_msg = "cannot determine whether the path is accessible or not";
+        match ecx.resolver.cfg_accessible(ecx.current_expansion.id, path) {
+            Ok(true) => ExpandResult::Ready(vec![item]),
+            Ok(false) => ExpandResult::Ready(Vec::new()),
+            Err(_) => ExpandResult::Retry(item, failure_msg.into()),
+        }
+    }
+}