Emit an error if shww/hide the same cfg on a same item

Author: GuillaumeGomez

src/librustdoc/clean/types.rs

@@ -7,7 +7,7 @@ use arrayvec::ArrayVec;
 use rustc_abi::{ExternAbi, VariantIdx};
 use rustc_ast::ast::{LitKind, MetaItemInner, MetaItemKind};
 use rustc_attr_parsing::{AttributeKind, ConstStability, Deprecation, Stability, StableSince};
-use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_hir::def::{CtorKind, DefKind, Res};
 use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE, LocalDefId};
 use rustc_hir::lang_items::LangItem;
@@ -1030,17 +1030,50 @@ impl Default for CfgInfo {
     }
 }
 
-fn handle_auto_cfg_hide_show(cfg_info: &mut CfgInfo, sub_attr: &MetaItemInner, is_show: bool) {
+fn show_hide_show_conflict_error(
+    tcx: TyCtxt<'_>,
+    item_span: rustc_span::Span,
+    previous: rustc_span::Span,
+) {
+    tcx.sess
+        .dcx()
+        .struct_span_err(
+            item_span,
+            format!(
+                "same `cfg` was in `auto_cfg(hide(...))` and `auto_cfg(show(...))` on the same item"
+            ),
+        )
+        .span_note(previous, "first change was here");
+}
+
+fn handle_auto_cfg_hide_show(
+    tcx: TyCtxt<'_>,
+    cfg_info: &mut CfgInfo,
+    sub_attr: &MetaItemInner,
+    is_show: bool,
+    new_show_attrs: &mut FxHashMap<(Symbol, Option<Symbol>), rustc_span::Span>,
+    new_hide_attrs: &mut FxHashMap<(Symbol, Option<Symbol>), rustc_span::Span>,
+) {
     if let MetaItemInner::MetaItem(item) = sub_attr
         && let MetaItemKind::List(items) = &item.kind
     {
         for item in items {
-            // Errors should already have been reported in `rustc_passes::check_attr`.
-            if let Ok(cfg) = Cfg::parse(item) {
+            // Cfg parsing errors should already have been reported in `rustc_passes::check_attr`.
+            if let Ok(Cfg::Cfg(key, value)) = Cfg::parse(item) {
                 if is_show {
-                    cfg_info.hidden_cfg.remove(&cfg);
+                    if let Some(span) = new_hide_attrs.get(&(key, value)) {
+                        show_hide_show_conflict_error(tcx, item.span(), *span);
+                    } else {
+                        new_hide_attrs.insert((key, value), item.span());
+                    }
+                    cfg_info.hidden_cfg.remove(&Cfg::Cfg(key, value));
                 } else {
-                    cfg_info.hidden_cfg.insert(cfg);
+                    if let Some(span) = new_show_attrs.get(&(key, value)) {
+                        show_hide_show_conflict_error(tcx, item.span(), *span);
+                    } else {
+                        new_show_attrs.insert((key, value), item.span());
+                    }
+                    cfg_info.hidden_cfg.insert(Cfg::Cfg(key, value));
                 }
             }
         }
@@ -1061,6 +1094,8 @@ pub(crate) fn extract_cfg_from_attrs<'a, I: Iterator<Item = &'a hir::Attribute>
         Some(item)
     }
 
+    let mut new_show_attrs = FxHashMap::default();
+    let mut new_hide_attrs = FxHashMap::default();
     let mut enable_auto_cfg = true;
     let mut cfg = Cfg::True;
 
@@ -1172,9 +1207,12 @@ pub(crate) fn extract_cfg_from_attrs<'a, I: Iterator<Item = &'a hir::Attribute>
                                     && (ident.name == sym::show || ident.name == sym::hide)
                                 {
                                     handle_auto_cfg_hide_show(
+                                        tcx,
                                         cfg_info,
                                         &sub_attr,
                                         ident.name == sym::show,
+                                        &mut new_show_attrs,
+                                        &mut new_hide_attrs,
                                     );
                                 }
                             }