4 files changed, 70 insertions, 1 deletions

diff --git a/crates/hir_def/src/diagnostics.rs b/crates/hir_def/src/diagnostics.rs
index fcfbbbad3..53cf1aca1 100644
--- a/crates/hir_def/src/diagnostics.rs
+++ b/crates/hir_def/src/diagnostics.rs
@@ -86,3 +86,28 @@ impl Diagnostic for UnresolvedImport {
         true
     }
 }
+
+// Diagnostic: unconfigured-code
+//
+// This diagnostic is shown for code with inactive `#[cfg]` attributes.
+#[derive(Debug)]
+pub struct UnconfiguredCode {
+    pub file: HirFileId,
+    pub node: SyntaxNodePtr,
+}
+
+impl Diagnostic for UnconfiguredCode {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("unconfigured-code")
+    }
+    fn message(&self) -> String {
+        // FIXME: say *why* it is configured out
+        "configured out".to_string()
+    }
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file, self.node.clone())
+    }
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+}
diff --git a/crates/hir_def/src/item_tree.rs b/crates/hir_def/src/item_tree.rs
index 8a1121bbd..7eb388bae 100644
--- a/crates/hir_def/src/item_tree.rs
+++ b/crates/hir_def/src/item_tree.rs
@@ -672,6 +672,24 @@ impl ModItem {
     pub fn downcast<N: ItemTreeNode>(self) -> Option<FileItemTreeId<N>> {
         N::id_from_mod_item(self)
     }
+
+    pub fn ast_id(&self, tree: &ItemTree) -> FileAstId<ast::Item> {
+        match self {
+            ModItem::Import(it) => tree[it.index].ast_id().upcast(),
+            ModItem::ExternCrate(it) => tree[it.index].ast_id().upcast(),
+            ModItem::Function(it) => tree[it.index].ast_id().upcast(),
+            ModItem::Struct(it) => tree[it.index].ast_id().upcast(),
+            ModItem::Union(it) => tree[it.index].ast_id().upcast(),
+            ModItem::Enum(it) => tree[it.index].ast_id().upcast(),
+            ModItem::Const(it) => tree[it.index].ast_id().upcast(),
+            ModItem::Static(it) => tree[it.index].ast_id().upcast(),
+            ModItem::Trait(it) => tree[it.index].ast_id().upcast(),
+            ModItem::Impl(it) => tree[it.index].ast_id().upcast(),
+            ModItem::TypeAlias(it) => tree[it.index].ast_id().upcast(),
+            ModItem::Mod(it) => tree[it.index].ast_id().upcast(),
+            ModItem::MacroCall(it) => tree[it.index].ast_id().upcast(),
+        }
+    }
 }
 
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
diff --git a/crates/hir_def/src/nameres.rs b/crates/hir_def/src/nameres.rs
index 3d04f81c6..8bb3a659f 100644
--- a/crates/hir_def/src/nameres.rs
+++ b/crates/hir_def/src/nameres.rs
@@ -286,7 +286,7 @@ mod diagnostics {
     use hir_expand::diagnostics::DiagnosticSink;
     use hir_expand::hygiene::Hygiene;
     use hir_expand::InFile;
-    use syntax::{ast, AstPtr};
+    use syntax::{ast, AstPtr, SyntaxNodePtr};
 
     use crate::path::ModPath;
     use crate::{db::DefDatabase, diagnostics::*, nameres::LocalModuleId, AstId};
@@ -298,6 +298,8 @@ mod diagnostics {
         UnresolvedExternCrate { ast: AstId<ast::ExternCrate> },
 
         UnresolvedImport { ast: AstId<ast::Use>, index: usize },
+
+        UnconfiguredCode { ast: InFile<SyntaxNodePtr> },
     }
 
     #[derive(Debug, PartialEq, Eq)]
@@ -336,6 +338,13 @@ mod diagnostics {
             Self { in_module: container, kind: DiagnosticKind::UnresolvedImport { ast, index } }
         }
 
+        pub(super) fn unconfigured_code(
+            container: LocalModuleId,
+            ast: InFile<SyntaxNodePtr>,
+        ) -> Self {
+            Self { in_module: container, kind: DiagnosticKind::UnconfiguredCode { ast } }
+        }
+
         pub(super) fn add_to(
             &self,
             db: &dyn DefDatabase,
@@ -385,6 +394,10 @@ mod diagnostics {
                         sink.push(UnresolvedImport { file: ast.file_id, node: AstPtr::new(&tree) });
                     }
                 }
+
+                DiagnosticKind::UnconfiguredCode { ast } => {
+                    sink.push(UnconfiguredCode { file: ast.file_id, node: ast.value.clone() });
+                }
             }
         }
     }
diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index c8cd04264..bff8edb62 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -913,6 +913,7 @@ impl ModCollector<'_, '_> {
         for &item in items {
             let attrs = self.item_tree.attrs(item.into());
             if !self.is_cfg_enabled(attrs) {
+                self.emit_unconfigured_diagnostic(item);
                 continue;
             }
             let module =
@@ -1323,6 +1324,18 @@ impl ModCollector<'_, '_> {
     fn is_cfg_enabled(&self, attrs: &Attrs) -> bool {
         attrs.is_cfg_enabled(self.def_collector.cfg_options)
     }
+
+    fn emit_unconfigured_diagnostic(&mut self, item: ModItem) {
+        let ast_id = item.ast_id(self.item_tree);
+        let id_map = self.def_collector.db.ast_id_map(self.file_id);
+        let syntax_ptr = id_map.get(ast_id).syntax_node_ptr();
+
+        let ast_node = InFile::new(self.file_id, syntax_ptr);
+        self.def_collector
+            .def_map
+            .diagnostics
+            .push(DefDiagnostic::unconfigured_code(self.module_id, ast_node));
+    }
 }
 
 fn is_macro_rules(path: &ModPath) -> bool {