Rust: Fix type inference inconsistency

Author: paldepind

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

@@ -324,13 +324,19 @@ private module CertainTypeInference {
       or
       // A `let` statement with a type annotation is a coercion site and hence
       // is not a certain type equality.
-      exists(LetStmt let | not let.hasTypeRepr() |
-        let.getPat() = n1 and
+      exists(LetStmt let |
+        not let.hasTypeRepr() and
+        // Due to "binding modes" the type of the pattern is not necessarily the
+        // same as the type of the initializer. The pattern being an identifier
+        // pattern is sufficient to ensure that this is not the case.
+        let.getPat().(IdentPat) = n1 and
         let.getInitializer() = n2
       )
       or
       exists(LetExpr let |
-        let.getPat() = n1 and
+        // Similarly as for let statements, we need to rule out binding modes
+        // changing the type.
+        let.getPat().(IdentPat) = n1 and
         let.getScrutinee() = n2
       )
       or
@@ -486,6 +492,11 @@ private predicate typeEquality(AstNode n1, TypePath prefix1, AstNode n2, TypePat
     or
     n1 = n2.(MatchExpr).getAnArm().getExpr()
     or
+    exists(LetExpr let |
+      n1 = let.getScrutinee() and
+      n2 = let.getPat()
+    )
+    or
     exists(MatchExpr me |
       n1 = me.getScrutinee() and
       n2 = me.getAnArm().getPat()

rust/ql/test/library-tests/type-inference/CONSISTENCY/TypeInferenceConsistency.expected

@@ -5884,7 +5884,6 @@ inferType
 | pattern_matching.rs:482:22:482:60 | MacroExpr |  | {EXTERNAL LOCATION} | Arguments |
 | pattern_matching.rs:482:50:482:60 | single_elem |  | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:487:9:487:18 | ref_tuple1 |  | file://:0:0:0:0 | & |
-| pattern_matching.rs:487:9:487:18 | ref_tuple1 |  | file://:0:0:0:0 | (T_2) |
 | pattern_matching.rs:487:9:487:18 | ref_tuple1 | &T | file://:0:0:0:0 | (T_2) |
 | pattern_matching.rs:487:9:487:18 | ref_tuple1 | &T.0(2) | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:487:9:487:18 | ref_tuple1 | &T.1(2) | {EXTERNAL LOCATION} | i32 |
@@ -5897,13 +5896,8 @@ inferType
 | pattern_matching.rs:487:36:487:41 | TupleExpr | 1(2) | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:487:37:487:37 | 1 |  | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:487:40:487:40 | 2 |  | {EXTERNAL LOCATION} | i32 |
-| pattern_matching.rs:488:12:488:17 | TuplePat |  | file://:0:0:0:0 | & |
 | pattern_matching.rs:488:12:488:17 | TuplePat |  | file://:0:0:0:0 | (T_2) |
-| pattern_matching.rs:488:12:488:17 | TuplePat | &T | file://:0:0:0:0 | (T_2) |
-| pattern_matching.rs:488:12:488:17 | TuplePat | &T.0(2) | {EXTERNAL LOCATION} | i32 |
-| pattern_matching.rs:488:12:488:17 | TuplePat | &T.1(2) | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:488:21:488:30 | ref_tuple1 |  | file://:0:0:0:0 | & |
-| pattern_matching.rs:488:21:488:30 | ref_tuple1 |  | file://:0:0:0:0 | (T_2) |
 | pattern_matching.rs:488:21:488:30 | ref_tuple1 | &T | file://:0:0:0:0 | (T_2) |
 | pattern_matching.rs:488:21:488:30 | ref_tuple1 | &T.0(2) | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:488:21:488:30 | ref_tuple1 | &T.1(2) | {EXTERNAL LOCATION} | i32 |
@@ -5916,7 +5910,6 @@ inferType
 | pattern_matching.rs:490:18:490:27 | FormatArgsExpr |  | {EXTERNAL LOCATION} | Arguments |
 | pattern_matching.rs:490:18:490:27 | MacroExpr |  | {EXTERNAL LOCATION} | Arguments |
 | pattern_matching.rs:494:9:494:18 | ref_tuple2 |  | file://:0:0:0:0 | & |
-| pattern_matching.rs:494:9:494:18 | ref_tuple2 |  | file://:0:0:0:0 | (T_2) |
 | pattern_matching.rs:494:9:494:18 | ref_tuple2 | &T | file://:0:0:0:0 | (T_2) |
 | pattern_matching.rs:494:9:494:18 | ref_tuple2 | &T.0(2) | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:494:9:494:18 | ref_tuple2 | &T.1(2) | {EXTERNAL LOCATION} | i32 |
@@ -5929,13 +5922,8 @@ inferType
 | pattern_matching.rs:494:36:494:41 | TupleExpr | 1(2) | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:494:37:494:37 | 1 |  | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:494:40:494:40 | 2 |  | {EXTERNAL LOCATION} | i32 |
-| pattern_matching.rs:495:9:495:14 | TuplePat |  | file://:0:0:0:0 | & |
 | pattern_matching.rs:495:9:495:14 | TuplePat |  | file://:0:0:0:0 | (T_2) |
-| pattern_matching.rs:495:9:495:14 | TuplePat | &T | file://:0:0:0:0 | (T_2) |
-| pattern_matching.rs:495:9:495:14 | TuplePat | &T.0(2) | {EXTERNAL LOCATION} | i32 |
-| pattern_matching.rs:495:9:495:14 | TuplePat | &T.1(2) | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:495:18:495:27 | ref_tuple2 |  | file://:0:0:0:0 | & |
-| pattern_matching.rs:495:18:495:27 | ref_tuple2 |  | file://:0:0:0:0 | (T_2) |
 | pattern_matching.rs:495:18:495:27 | ref_tuple2 | &T | file://:0:0:0:0 | (T_2) |
 | pattern_matching.rs:495:18:495:27 | ref_tuple2 | &T.0(2) | {EXTERNAL LOCATION} | i32 |
 | pattern_matching.rs:495:18:495:27 | ref_tuple2 | &T.1(2) | {EXTERNAL LOCATION} | i32 |