add support for cfg feature attributes on expression #4063

Signed-off-by: Benjamin Coenen <5719034+bnjjj@users.noreply.github.com>

crates/ra_hir_def/src/body/lower.rs

@@ -141,6 +141,10 @@ impl ExprCollector<'_> {
 
     fn collect_expr(&mut self, expr: ast::Expr) -> ExprId {
         let syntax_ptr = AstPtr::new(&expr);
+        let attrs = self.expander.parse_attrs(&expr);
+        if !self.expander.is_cfg_enabled(&attrs) {
+            return self.missing_expr();
+        }
         match expr {
             ast::Expr::IfExpr(e) => {
                 let then_branch = self.collect_block_opt(e.then_branch());

crates/ra_hir_ty/src/tests.rs

@@ -390,6 +390,38 @@ fn no_such_field_with_feature_flag_diagnostics_on_struct_lit() {
     assert_snapshot!(diagnostics, @r###""###);
 }
 
+#[test]
+fn no_such_field_with_feature_flag_diagnostics_on_block_expr() {
+    let diagnostics = TestDB::with_files(
+        r#"
+        //- /lib.rs crate:foo cfg:feature=foo
+        struct S {
+            #[cfg(feature = "foo")]
+            foo: u32,
+            #[cfg(not(feature = "foo"))]
+            bar: u32,
+        }
+
+        impl S {
+            fn new(bar: u32) -> Self {
+                #[cfg(feature = "foo")]
+                {
+                Self { foo: bar }
+                }
+                #[cfg(not(feature = "foo"))]
+                {
+                Self { bar }
+                }
+            }
+        }
+        "#,
+    )
+    .diagnostics()
+    .0;
+
+    assert_snapshot!(diagnostics, @r###""###);
+}
+
 #[test]
 fn no_such_field_with_feature_flag_diagnostics_on_struct_fields() {
     let diagnostics = TestDB::with_files(