Merge pull request #21057 from hvitved/rust/fix-bad-join

Rust: Fix bad join

Author: hvitved

rust/ql/lib/codeql/rust/frameworks/stdlib/Stdlib.qll

@@ -250,6 +250,19 @@ class IndexTrait extends Trait {
   }
 }
 
+/**
+ * The [`IndexMut` trait][1].
+ *
+ * [1]: https://doc.rust-lang.org/std/ops/trait.IndexMut.html
+ */
+class IndexMutTrait extends Trait {
+  pragma[nomagic]
+  IndexMutTrait() { this.getCanonicalPath() = "core::ops::index::IndexMut" }
+
+  /** Gets the `index_mut` function. */
+  Function getIndexMutFunction() { result = this.(TraitItemNode).getAssocItem("index_mut") }
+}
+
 /**
  * The [`Box` struct][1].
  *

rust/ql/lib/codeql/rust/internal/TypeInference.qll

@@ -1839,8 +1839,8 @@ private module MethodResolution {
 
     override Trait getTrait() {
       if this.isInMutableContext()
-      then result.getCanonicalPath() = "core::ops::index::IndexMut"
-      else result.getCanonicalPath() = "core::ops::index::Index"
+      then result instanceof IndexMutTrait
+      else result instanceof IndexTrait
     }
   }