Rust: Context typing for constructors

Author: hvitved

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

@@ -955,7 +955,7 @@ private module ContextTyping {
      */
     bindingset[this, i, target]
     predicate isContextTypedAt(
-      ImplOrTraitItemNode i, Function target, TypePath path, FunctionPosition pos
+      ImplOrTraitItemNode i, Function target, FunctionPosition pos, TypePath path
     ) {
       exists(TypeParameter tp |
         assocFunctionReturnContextTypedAt(i, target, pos, path, tp) and
@@ -2090,6 +2090,17 @@ private module MethodCallMatchingInput implements MatchingWithEnvironmentInputSi
     }
 
     Declaration getTarget(string derefChainBorrow) { result = this.getTarget(_, derefChainBorrow) }
+
+    /**
+     * Holds if the return type of this call at `path` may have to be inferred
+     * from the context.
+     */
+    pragma[nomagic]
+    predicate isContextTypedAt(string derefChainBorrow, FunctionPosition pos, TypePath path) {
+      exists(ImplOrTraitItemNode i |
+        this.isContextTypedAt(i, this.getTarget(i, derefChainBorrow), pos, path)
+      )
+    }
   }
 }
 
@@ -2105,10 +2116,8 @@ private Type inferMethodCallType0(
     (
       result = MethodCallMatching::inferAccessType(a, derefChainBorrow, apos, path0)
       or
-      exists(ImplOrTraitItemNode i |
-        a.isContextTypedAt(i, a.getTarget(i, derefChainBorrow), path0, apos) and
-        result = TContextType()
-      )
+      a.isContextTypedAt(derefChainBorrow, apos, path0) and
+      result = TContextType()
     )
   |
     if
@@ -2585,6 +2594,35 @@ private module NonMethodCallMatchingInput implements MatchingInputSig {
     Declaration getTarget() {
       result = this.resolveCallTarget() // potential mutual recursion; resolving some associated function calls requires resolving types
     }
+
+    /**
+     * Holds if the return type of this call at `path` may have to be inferred
+     * from the context.
+     */
+    pragma[nomagic]
+    predicate isContextTypedAt(FunctionPosition pos, TypePath path) {
+      exists(ImplOrTraitItemNode i |
+        this.isContextTypedAt(i,
+          [
+            this.resolveCallTargetViaPathResolution().(NonMethodFunction),
+            this.resolveCallTargetViaTypeInference(i),
+            this.resolveTraitFunctionViaPathResolution(i)
+          ], pos, path)
+      )
+      or
+      // Tuple declarations, such as `None`, may also be context typed
+      exists(TupleDeclaration td, TypeParameter tp |
+        td = this.resolveCallTargetViaPathResolution() and
+        pos.isReturn() and
+        tp = td.getReturnType(path) and
+        not tp = td.getParameterType(_, _) and
+        // check that no explicit type arguments have been supplied for `tp`
+        not exists(TypeArgumentPosition tapos |
+          exists(this.getTypeArgument(tapos, _)) and
+          TTypeParamTypeParameter(tapos.asTypeParam()) = tp
+        )
+      )
+    }
   }
 }
 
@@ -2597,15 +2635,8 @@ private Type inferNonMethodCallType0(
   exists(NonMethodCallMatchingInput::Access a | n = a.getNodeAt(apos) |
     result = NonMethodCallMatching::inferAccessType(a, apos, path)
     or
-    exists(ImplOrTraitItemNode i |
-      a.isContextTypedAt(i,
-        [
-          a.resolveCallTargetViaPathResolution().(NonMethodFunction),
-          a.resolveCallTargetViaTypeInference(i),
-          a.resolveTraitFunctionViaPathResolution(i)
-        ], path, apos) and
-      result = TContextType()
-    )
+    a.isContextTypedAt(apos, path) and
+    result = TContextType()
   )
 }
 

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

@@ -3115,9 +3115,12 @@ inferType
 | main.rs:1370:26:1370:27 | p3 | Snd | main.rs:1310:5:1311:14 | S3 |
 | main.rs:1372:9:1372:55 | g(...) |  | file://:0:0:0:0 | () |
 | main.rs:1372:11:1372:54 | ...::PairSnd(...) |  | main.rs:1285:5:1291:5 | PairOption |
+| main.rs:1372:11:1372:54 | ...::PairSnd(...) | Fst | main.rs:1307:5:1308:14 | S2 |
 | main.rs:1372:11:1372:54 | ...::PairSnd(...) | Snd | main.rs:1285:5:1291:5 | PairOption |
+| main.rs:1372:11:1372:54 | ...::PairSnd(...) | Snd.Fst | main.rs:1307:5:1308:14 | S2 |
 | main.rs:1372:11:1372:54 | ...::PairSnd(...) | Snd.Snd | main.rs:1310:5:1311:14 | S3 |
 | main.rs:1372:31:1372:53 | ...::PairSnd(...) |  | main.rs:1285:5:1291:5 | PairOption |
+| main.rs:1372:31:1372:53 | ...::PairSnd(...) | Fst | main.rs:1307:5:1308:14 | S2 |
 | main.rs:1372:31:1372:53 | ...::PairSnd(...) | Snd | main.rs:1310:5:1311:14 | S3 |
 | main.rs:1372:51:1372:52 | S3 |  | main.rs:1310:5:1311:14 | S3 |
 | main.rs:1374:13:1374:13 | x |  | {EXTERNAL LOCATION} | Result |
@@ -3823,6 +3826,7 @@ inferType
 | main.rs:1700:21:1700:25 | input | T | main.rs:1699:20:1699:27 | T |
 | main.rs:1700:21:1700:26 | TryExpr |  | main.rs:1699:20:1699:27 | T |
 | main.rs:1701:22:1701:38 | ...::Ok(...) |  | {EXTERNAL LOCATION} | Result |
+| main.rs:1701:22:1701:38 | ...::Ok(...) | E | main.rs:1667:5:1668:14 | S1 |
 | main.rs:1701:22:1701:38 | ...::Ok(...) | T | main.rs:1699:20:1699:27 | T |
 | main.rs:1701:22:1704:10 | ... .and_then(...) |  | {EXTERNAL LOCATION} | Result |
 | main.rs:1701:22:1704:10 | ... .and_then(...) | E | main.rs:1667:5:1668:14 | S1 |
@@ -3895,6 +3899,7 @@ inferType
 | main.rs:1722:37:1722:63 | try_complex(...) | E | main.rs:1667:5:1668:14 | S1 |
 | main.rs:1722:37:1722:63 | try_complex(...) | T | main.rs:1667:5:1668:14 | S1 |
 | main.rs:1722:49:1722:62 | ...::Ok(...) |  | {EXTERNAL LOCATION} | Result |
+| main.rs:1722:49:1722:62 | ...::Ok(...) | E | main.rs:1667:5:1668:14 | S1 |
 | main.rs:1722:49:1722:62 | ...::Ok(...) | T | main.rs:1667:5:1668:14 | S1 |
 | main.rs:1722:60:1722:61 | S1 |  | main.rs:1667:5:1668:14 | S1 |
 | main.rs:1722:65:1724:9 | { ... } |  | file://:0:0:0:0 | () |