From b7a2f21d585b76aa21a9af12d1abc2dfa336785d Mon Sep 17 00:00:00 2001
From: A4-Tacks <wdsjxhno1001@163.com>
Date: Thu, 4 Sep 2025 14:57:41 +0800
Subject: [PATCH] Add cfg_attr predicate completion

Example
---
```rust
#[cfg_attr($0, must_use)]
struct Foo;
```
---
 .../src/completions/attribute.rs              |  2 +-
 crates/ide-completion/src/tests/attribute.rs  | 52 +++++++++++++++++++
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/crates/ide-completion/src/completions/attribute.rs b/crates/ide-completion/src/completions/attribute.rs
index c542e140df..e174b0c892 100644
--- a/crates/ide-completion/src/completions/attribute.rs
+++ b/crates/ide-completion/src/completions/attribute.rs
@@ -70,7 +70,7 @@ pub(crate) fn complete_known_attribute_input(
 
             lint::complete_lint(acc, ctx, colon_prefix, &existing_lints, &lints);
         }
-        ["cfg"] => cfg::complete_cfg(acc, ctx),
+        ["cfg"] | ["cfg_attr"] => cfg::complete_cfg(acc, ctx),
         ["macro_use"] => macro_use::complete_macro_use(
             acc,
             ctx,
diff --git a/crates/ide-completion/src/tests/attribute.rs b/crates/ide-completion/src/tests/attribute.rs
index 46a3630045..30e1e108c6 100644
--- a/crates/ide-completion/src/tests/attribute.rs
+++ b/crates/ide-completion/src/tests/attribute.rs
@@ -835,6 +835,58 @@ mod cfg {
         );
     }
 
+    #[test]
+    fn inside_cfg_attr() {
+        check(
+            r#"
+//- /main.rs cfg:test,dbg=false,opt_level=2
+#[cfg_attr($0)]
+"#,
+            expect![[r#"
+                ba dbg
+                ba opt_level
+                ba test
+                ba true
+            "#]],
+        );
+        check(
+            r#"
+//- /main.rs cfg:test,dbg=false,opt_level=2
+#[cfg_attr(b$0)]
+"#,
+            expect![[r#"
+                ba dbg
+                ba opt_level
+                ba test
+                ba true
+            "#]],
+        );
+        check(
+            r#"
+//- /main.rs cfg:test,dbg=false,opt_level=2
+#[cfg_attr($0, allow(deprecated))]
+"#,
+            expect![[r#"
+                ba dbg
+                ba opt_level
+                ba test
+                ba true
+            "#]],
+        );
+        check(
+            r#"
+//- /main.rs cfg:test,dbg=false,opt_level=2
+#[cfg_attr(b$0, allow(deprecated))]
+"#,
+            expect![[r#"
+                ba dbg
+                ba opt_level
+                ba test
+                ba true
+            "#]],
+        );
+    }
+
     #[test]
     fn cfg_target_endian() {
         check(