Fix panic for doc attributes on where predicates

compiler/rustc_attr_parsing/src/attributes/doc.rs

@@ -701,6 +701,9 @@ impl DocParser {
                 for i in items.mixed() {
                     match i {
                         MetaItemOrLitParser::MetaItemParser(mip) => {
+                            if self.nb_doc_attrs == 0 {
+                                self.attribute.first_span = cx.attr_span;
+                            }
                             self.nb_doc_attrs += 1;
                             self.parse_single_doc_attr_item(cx, mip);
                         }

compiler/rustc_attr_parsing/src/target_checking.rs

@@ -292,15 +292,16 @@ impl<'sess, S: Stage> AttributeParser<'sess, S> {
         // in where clauses. After that, this function would become useless.
         let spans = attrs
             .into_iter()
-            // FIXME: We shouldn't need to special-case `doc`!
-            .filter(|attr| {
-                matches!(
-                    attr,
-                    Attribute::Parsed(AttributeKind::DocComment { .. } | AttributeKind::Doc(_))
-                        | Attribute::Unparsed(_)
-                )
+            .filter_map(|attr| {
+                match attr {
+                    Attribute::Parsed(AttributeKind::DocComment { span, .. }) => Some(*span),
+                    // FIXME: We shouldn't need to special-case `doc`!
+                    Attribute::Parsed(AttributeKind::Doc(attr)) => Some(attr.first_span),
+                    // Checked during attribute parsing target checking
+                    Attribute::Parsed(_) => None,
+                    Attribute::Unparsed(attr) => Some(attr.span),
+                }
             })
-            .map(|attr| attr.span())
             .collect::<Vec<_>>();
         if !spans.is_empty() {
             self.dcx()

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -544,6 +544,8 @@ pub struct CfgHideShow {
 
 #[derive(Clone, Debug, Default, HashStable_Generic, Decodable, PrintAttribute)]
 pub struct DocAttribute {
+    pub first_span: Span,
+
     pub aliases: FxIndexMap<Symbol, Span>,
     pub hidden: Option<Span>,
     // Because we need to emit the error if there is more than one `inline` attribute on an item
@@ -581,6 +583,7 @@ pub struct DocAttribute {
 impl<E: rustc_span::SpanEncoder> rustc_serialize::Encodable<E> for DocAttribute {
     fn encode(&self, encoder: &mut E) {
         let DocAttribute {
+            first_span,
             aliases,
             hidden,
             inline,
@@ -603,6 +606,7 @@ impl<E: rustc_span::SpanEncoder> rustc_serialize::Encodable<E> for DocAttribute
             test_attrs,
             no_crate_inject,
         } = self;
+        rustc_serialize::Encodable::<E>::encode(first_span, encoder);
         rustc_serialize::Encodable::<E>::encode(aliases, encoder);
         rustc_serialize::Encodable::<E>::encode(hidden, encoder);
 

compiler/rustc_passes/src/check_attr.rs

@@ -1027,6 +1027,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
     /// [`check_doc_inline`]: Self::check_doc_inline
     fn check_doc_attrs(&self, attr: &DocAttribute, hir_id: HirId, target: Target) {
         let DocAttribute {
+            first_span: _,
             aliases,
             // valid pretty much anywhere, not checked here?
             // FIXME: should we?

src/librustdoc/clean/mod.rs

@@ -2780,6 +2780,7 @@ fn add_without_unwanted_attributes<'hir>(
             hir::Attribute::Parsed(AttributeKind::Doc(box d)) => {
                 // Remove attributes from `normal` that should not be inherited by `use` re-export.
                 let DocAttribute {
+                    first_span: _,
                     aliases,
                     hidden,
                     inline,

src/librustdoc/json/conversions.rs

@@ -960,6 +960,7 @@ fn maybe_from_hir_attr(attr: &hir::Attribute, item_id: ItemId, tcx: TyCtxt<'_>)
             }
 
             let DocAttribute {
+                first_span: _,
                 aliases,
                 hidden,
                 inline,

tests/ui/attributes/where-doc.rs

@@ -0,0 +1,34 @@
+#![feature(where_clause_attrs)]
+#![allow(invalid_doc_attributes)]
+
+fn test()
+where
+#[doc(alias = ":(")]
+//~^ ERROR most attributes are not supported in `where` clauses
+//~| ERROR `#[doc(alias = "...")]` isn't allowed on where predicate
+():,
+
+#[doc(hidden)]
+//~^ ERROR most attributes are not supported in `where` clauses
+():,
+
+#[doc = ""]
+//~^ ERROR most attributes are not supported in `where` clauses
+():,
+
+// == That the doc attributes below don't trigger the error is a bug
+#[doc()]
+():,
+
+#[doc(5)]
+():,
+
+#[doc]
+():,
+
+#[doc = 5]
+():,
+
+{ }
+
+fn main() {}

tests/ui/attributes/where-doc.stderr

@@ -0,0 +1,32 @@
+error: most attributes are not supported in `where` clauses
+  --> $DIR/where-doc.rs:6:1
+   |
+LL | #[doc(alias = ":(")]
+   | ^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/where-doc.rs:11:1
+   |
+LL | #[doc(hidden)]
+   | ^^^^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: most attributes are not supported in `where` clauses
+  --> $DIR/where-doc.rs:15:1
+   |
+LL | #[doc = ""]
+   | ^^^^^^^^^^^
+   |
+   = help: only `#[cfg]` and `#[cfg_attr]` are supported
+
+error: `#[doc(alias = "...")]` isn't allowed on where predicate
+  --> $DIR/where-doc.rs:6:15
+   |
+LL | #[doc(alias = ":(")]
+   |               ^^^^
+
+error: aborting due to 4 previous errors
+