From 08277e4eccaf326c82feaa4f1f5f4a8e1f8bd143 Mon Sep 17 00:00:00 2001
From: Simon Friis Vindum <simonfv@gmail.com>
Date: Thu, 29 May 2025 15:31:17 +0200
Subject: [PATCH] Rust: Refactor type equality

---
 .../codeql/rust/internal/TypeInference.qll    | 109 +++++++-----------
 1 file changed, 43 insertions(+), 66 deletions(-)

diff --git a/rust/ql/lib/codeql/rust/internal/TypeInference.qll b/rust/ql/lib/codeql/rust/internal/TypeInference.qll
index fcacfd5d3dad..8399bde8aa80 100644
--- a/rust/ql/lib/codeql/rust/internal/TypeInference.qll
+++ b/rust/ql/lib/codeql/rust/internal/TypeInference.qll
@@ -207,81 +207,58 @@ private Type inferAssignmentOperationType(AstNode n, TypePath path) {
 }
 
 /**
- * Holds if the type of `n1` at `path1` is the same as the type of `n2` at
- * `path2` and type information should propagate in both directions through the
- * type equality.
+ * Holds if the type tree of `n1` at `prefix1` should be equal to the type tree
+ * of `n2` at `prefix2` and type information should propagate in both directions
+ * through the type equality.
  */
-bindingset[path1]
-bindingset[path2]
-private predicate typeEquality(AstNode n1, TypePath path1, AstNode n2, TypePath path2) {
-  exists(Variable v |
-    path1 = path2 and
-    n1 = v.getAnAccess()
-  |
-    n2 = v.getPat()
+private predicate typeEquality(AstNode n1, TypePath prefix1, AstNode n2, TypePath prefix2) {
+  prefix1.isEmpty() and
+  prefix2.isEmpty() and
+  (
+    exists(Variable v | n1 = v.getAnAccess() |
+      n2 = v.getPat()
+      or
+      n2 = v.getParameter().(SelfParam)
+    )
     or
-    n2 = v.getParameter().(SelfParam)
-  )
-  or
-  exists(LetStmt let |
-    let.getPat() = n1 and
-    let.getInitializer() = n2 and
-    path1 = path2
-  )
-  or
-  n1 = n2.(ParenExpr).getExpr() and
-  path1 = path2
-  or
-  n1 = n2.(BlockExpr).getStmtList().getTailExpr() and
-  path1 = path2
-  or
-  n1 = n2.(IfExpr).getABranch() and
-  path1 = path2
-  or
-  n1 = n2.(MatchExpr).getAnArm().getExpr() and
-  path1 = path2
-  or
-  exists(BreakExpr break |
-    break.getExpr() = n1 and
-    break.getTarget() = n2.(LoopExpr) and
-    path1 = path2
-  )
-  or
-  exists(AssignmentExpr be |
-    n1 = be.getLhs() and
-    n2 = be.getRhs() and
-    path1 = path2
-  )
-}
-
-bindingset[path1]
-private predicate typeEqualityLeft(AstNode n1, TypePath path1, AstNode n2, TypePath path2) {
-  typeEquality(n1, path1, n2, path2)
-  or
-  n2 =
-    any(DerefExpr pe |
-      pe.getExpr() = n1 and
-      path1.isCons(TRefTypeParameter(), path2)
+    exists(LetStmt let |
+      let.getPat() = n1 and
+      let.getInitializer() = n2
     )
-}
-
-bindingset[path2]
-private predicate typeEqualityRight(AstNode n1, TypePath path1, AstNode n2, TypePath path2) {
-  typeEquality(n1, path1, n2, path2)
-  or
-  n2 =
-    any(DerefExpr pe |
-      pe.getExpr() = n1 and
-      path1 = TypePath::cons(TRefTypeParameter(), path2)
+    or
+    n1 = n2.(ParenExpr).getExpr()
+    or
+    n1 = n2.(BlockExpr).getStmtList().getTailExpr()
+    or
+    n1 = n2.(IfExpr).getABranch()
+    or
+    n1 = n2.(MatchExpr).getAnArm().getExpr()
+    or
+    exists(BreakExpr break |
+      break.getExpr() = n1 and
+      break.getTarget() = n2.(LoopExpr)
+    )
+    or
+    exists(AssignmentExpr be |
+      n1 = be.getLhs() and
+      n2 = be.getRhs()
     )
+  )
+  or
+  n1 = n2.(DerefExpr).getExpr() and
+  prefix1 = TypePath::singleton(TRefTypeParameter()) and
+  prefix2.isEmpty()
 }
 
 pragma[nomagic]
 private Type inferTypeEquality(AstNode n, TypePath path) {
-  exists(AstNode n2, TypePath path2 | result = inferType(n2, path2) |
-    typeEqualityRight(n, path, n2, path2)
+  exists(TypePath prefix1, AstNode n2, TypePath prefix2, TypePath suffix |
+    result = inferType(n2, prefix2.appendInverse(suffix)) and
+    path = prefix1.append(suffix)
+  |
+    typeEquality(n, prefix1, n2, prefix2)
     or
-    typeEqualityLeft(n2, path2, n, path)
+    typeEquality(n2, prefix2, n, prefix1)
   )
 }