From d077b8a7e080ffddda6c88c07d927dc54c8cde33 Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Sat, 22 May 2021 02:30:03 +0200
Subject: Work around non-unique AttrIds

---
 crates/hir_def/src/nameres/collector.rs    | 30 ++++++++++++++++++++++--------
 crates/hir_def/src/nameres/tests/macros.rs | 18 +++++++++++++++++-
 2 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index 9b108bfe7..014ea4de4 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -16,6 +16,7 @@ use hir_expand::{
     FragmentKind, HirFileId, MacroCallId, MacroCallKind, MacroDefId, MacroDefKind,
 };
 use hir_expand::{InFile, MacroCallLoc};
+use itertools::Itertools;
 use rustc_hash::{FxHashMap, FxHashSet};
 use syntax::ast;
 
@@ -1516,14 +1517,27 @@ impl ModCollector<'_, '_> {
     fn resolve_attributes(&mut self, attrs: &Attrs, mod_item: ModItem) -> Result<(), ()> {
         let mut ignore_up_to =
             self.def_collector.skip_attrs.get(&InFile::new(self.file_id, mod_item)).copied();
-        for attr in attrs.iter().skip_while(|attr| match ignore_up_to {
-            Some(id) if attr.id == id => {
-                ignore_up_to = None;
-                true
-            }
-            Some(_) => true,
-            None => false,
-        }) {
+        let iter = attrs
+            .iter()
+            .dedup_by(|a, b| {
+                // FIXME: this should not be required, all attributes on an item should have a
+                // unique ID!
+                // Still, this occurs because `#[cfg_attr]` can "expand" to multiple attributes:
+                //     #[cfg_attr(not(off), unresolved, unresolved)]
+                //     struct S;
+                // We should come up with a different way to ID attributes.
+                a.id == b.id
+            })
+            .skip_while(|attr| match ignore_up_to {
+                Some(id) if attr.id == id => {
+                    ignore_up_to = None;
+                    true
+                }
+                Some(_) => true,
+                None => false,
+            });
+
+        for attr in iter {
             if attr.path.as_ident() == Some(&hir_expand::name![derive]) {
                 self.collect_derive(attr, mod_item);
             } else if self.is_builtin_or_registered_attr(&attr.path) {
diff --git a/crates/hir_def/src/nameres/tests/macros.rs b/crates/hir_def/src/nameres/tests/macros.rs
index 133b2d818..3065efd65 100644
--- a/crates/hir_def/src/nameres/tests/macros.rs
+++ b/crates/hir_def/src/nameres/tests/macros.rs
@@ -737,6 +737,7 @@ fn unresolved_attributes_fall_back_track_per_file_moditems() {
 
 #[test]
 fn unresolved_attrs_extern_block_hang() {
+    // Regression test for https://github.com/rust-analyzer/rust-analyzer/issues/8905
     check(
         r#"
 #[unresolved]
@@ -790,7 +791,22 @@ fn derive() {}
             crate
             S: t v
         "#]],
-    )
+    );
+}
+
+#[test]
+fn unresolved_attr_with_cfg_attr_hang() {
+    // Another regression test for https://github.com/rust-analyzer/rust-analyzer/issues/8905
+    check(
+        r#"
+#[cfg_attr(not(off), unresolved, unresolved)]
+struct S;
+        "#,
+        expect![[r#"
+            crate
+            S: t v
+        "#]],
+    );
 }
 
 #[test]
-- 
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