Merge pull request #40078 from hborla/wrong-nil-coalescing-favoring

[CSGen] Don't walk into `??` in `LinkedExprAnalyzer`.

Author: hborla

include/swift/AST/Identifier.h

@@ -122,6 +122,10 @@ class Identifier {
            is(">") || is("<=") || is(">=");
   }
 
+  bool isNilCoalescingOperator() const {
+    return is("??");
+  }
+
   /// isOperatorStartCodePoint - Return true if the specified code point is a
   /// valid start of an operator.
   static bool isOperatorStartCodePoint(uint32_t C) {

lib/Sema/CSGen.cpp

@@ -212,7 +212,15 @@ namespace {
         return { false, expr };
       }
 
-      if (isa<BinaryExpr>(expr)) {
+      if (auto *binaryExpr = dyn_cast<BinaryExpr>(expr)) {
+        if (auto *overload = dyn_cast<OverloadedDeclRefExpr>(binaryExpr->getFn())) {
+          // Don't walk into nil coalescing operators. Attempting to favor
+          // based on operand types is wrong for this operator.
+          auto identifier = overload->getDecls().front()->getBaseIdentifier();
+          if (identifier.isNilCoalescingOperator())
+            return { false, expr };
+        }
+
         LTI.binaryExprs.push_back(dyn_cast<BinaryExpr>(expr));
       }  
 
@@ -367,7 +375,7 @@ namespace {
 
       return true;
     }
-    
+
     return false;
   }
 

test/Constraints/nil-coalescing-favoring.swift

@@ -0,0 +1,14 @@
+// RUN: %target-swift-frontend -dump-ast %s | %FileCheck %s
+
+struct B {
+  static var _none: B { B() }
+}
+
+struct A {
+  init(_ other: B) {}
+  // CHECK: constructor_decl{{.*}}interface type='(A.Type) -> (B?) -> A'
+  init(_ other: B?) {
+    // CHECK: dot_syntax_call_expr type='(B) -> A'
+    self.init(other ?? ._none)
+  }
+}