Merge pull request #22203 from VSadov/relaxedEscape

Relaxed escape rules for spans

src/Compilers/CSharp/Portable/Binder/Binder_Operators.cs

@@ -3629,20 +3629,20 @@ private BoundExpression BindConditionalOperator(ConditionalExpressionSyntax node
             {
                 var currentScope = this.LocalScopeDepth;
 
-                // ref-escape must agree on both branches.
-                uint whenTrueEscape = GetRefEscape(trueExpr, currentScope);
-                uint whenFalseEscape = GetRefEscape(falseExpr, currentScope);
+                // val-escape must agree on both branches.
+                uint whenTrueEscape = GetValEscape(trueExpr, currentScope);
+                uint whenFalseEscape = GetValEscape(falseExpr, currentScope);
 
                 if (whenTrueEscape != whenFalseEscape)
                 {
                     // ask the one with narrower escape, for the wider - hopefully the errors will make the violation easier to fix.
                     if (whenTrueEscape < whenFalseEscape)
                     {
-                        CheckRefEscape(falseExpr.Syntax, falseExpr, currentScope, whenTrueEscape, checkingReceiver: false, diagnostics: diagnostics);
+                        CheckValEscape(falseExpr.Syntax, falseExpr, currentScope, whenTrueEscape, checkingReceiver: false, diagnostics: diagnostics);
                     }
                     else
                     {
-                        CheckRefEscape(trueExpr.Syntax, trueExpr, currentScope, whenFalseEscape, checkingReceiver: false, diagnostics: diagnostics);
+                        CheckValEscape(trueExpr.Syntax, trueExpr, currentScope, whenFalseEscape, checkingReceiver: false, diagnostics: diagnostics);
                     }
 
                     diagnostics.Add(ErrorCode.ERR_MismatchedRefEscapeInTernary, node.Location);

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_ConditionalOperator.cs

@@ -49,11 +49,21 @@ public override BoundNode VisitConditionalOperator(BoundConditionalOperator node
             ConstantValue conditionConstantValue = rewrittenCondition.ConstantValue;
             if (conditionConstantValue == ConstantValue.True)
             {
-                return EnsureNotAssignableIfUsedAsMethodReceiver(rewrittenConsequence);
+                if (!isRef)
+                {
+                    rewrittenConsequence = EnsureNotAssignableIfUsedAsMethodReceiver(rewrittenConsequence);
+                }
+
+                return rewrittenConsequence;
             }
             else if (conditionConstantValue == ConstantValue.False)
             {
-                return EnsureNotAssignableIfUsedAsMethodReceiver(rewrittenAlternative);
+                if (!isRef)
+                {
+                    rewrittenAlternative = EnsureNotAssignableIfUsedAsMethodReceiver(rewrittenAlternative);
+                }
+
+                return rewrittenAlternative;
             }
             else
             {

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenRefConditionalOperatorTests.cs

@@ -662,10 +662,7 @@ static void Main()
             comp.VerifyEmitDiagnostics(
                 // (15,27): error CS8168: Cannot return local 'local1' by reference because it is not a ref local
                 //         return ref b? ref local1: ref local2;
-                Diagnostic(ErrorCode.ERR_RefReturnLocal, "local1").WithArguments("local1").WithLocation(15, 27),
-                // (15,20): error CS8156: An expression cannot be used in this context because it may not be returned by reference
-                //         return ref b? ref local1: ref local2;
-                Diagnostic(ErrorCode.ERR_RefReturnLvalueExpected, "b? ref local1: ref local2").WithLocation(15, 20)
+                Diagnostic(ErrorCode.ERR_RefReturnLocal, "local1").WithArguments("local1").WithLocation(15, 27)
                );
         }
 
@@ -696,10 +693,7 @@ static void Main()
             comp.VerifyEmitDiagnostics(
                 // (14,37): error CS8168: Cannot return local 'local2' by reference because it is not a ref local
                 //         return ref b? ref val1: ref local2;
-                Diagnostic(ErrorCode.ERR_RefReturnLocal, "local2").WithArguments("local2").WithLocation(14, 37),
-                // (14,20): error CS8351: Branches of a ref ternary operator cannot refer to variables with incompatible declaration scopes.
-                //         return ref b? ref val1: ref local2;
-                Diagnostic(ErrorCode.ERR_MismatchedRefEscapeInTernary, "b? ref val1: ref local2").WithLocation(14, 20)
+                Diagnostic(ErrorCode.ERR_RefReturnLocal, "local2").WithArguments("local2").WithLocation(14, 37)
                );
         }
 
@@ -735,10 +729,7 @@ struct S1
             comp.VerifyEmitDiagnostics(
                 // (14,38): error CS8168: Cannot return local 'local2' by reference because it is not a ref local
                 //         return ref (b? ref val1: ref local2).x;
-                Diagnostic(ErrorCode.ERR_RefReturnLocal, "local2").WithArguments("local2").WithLocation(14, 38),
-                // (14,21): error CS8351: Branches of a ref ternary operator cannot refer to variables with incompatible declaration scopes.
-                //         return ref (b? ref val1: ref local2).x;
-                Diagnostic(ErrorCode.ERR_MismatchedRefEscapeInTernary, "b? ref val1: ref local2").WithLocation(14, 21)
+                Diagnostic(ErrorCode.ERR_RefReturnLocal, "local2").WithArguments("local2").WithLocation(14, 38)
                );
         }
 
@@ -773,12 +764,9 @@ struct S1
             var comp = CreateCompilationWithMscorlib45(source, options: TestOptions.ReleaseExe);
 
             comp.VerifyEmitDiagnostics(
-                // (14,46): error CS8168: Cannot return local 'local2' by reference because it is not a ref local
-                //         ref var temp = ref (b? ref val1: ref local2).x;
-                Diagnostic(ErrorCode.ERR_RefReturnLocal, "local2").WithArguments("local2").WithLocation(14, 46),
-                // (14,29): error CS8351: Branches of a ref ternary operator cannot refer to variables with incompatible declaration scopes.
-                //         ref var temp = ref (b? ref val1: ref local2).x;
-                Diagnostic(ErrorCode.ERR_MismatchedRefEscapeInTernary, "b? ref val1: ref local2").WithLocation(14, 29)
+                // (15,20): error CS8157: Cannot return 'temp' by reference because it was initialized to a value that cannot be returned by reference
+                //         return ref temp;
+                Diagnostic(ErrorCode.ERR_RefReturnNonreturnableLocal, "temp").WithArguments("temp").WithLocation(15, 20)
                );
         }
 
@@ -828,6 +816,81 @@ .maxstack  1
 ");
         }
 
+        [Fact]
+        public void TestRefConditionalSafeToReturn2()
+        {
+            var source = @"
+class C
+{
+    static void Main()
+    {
+        Test() ++;
+        System.Console.WriteLine(val1.x);
+    }
+
+    static ref int Test()
+    {
+        return ref (true? ref val1: ref val2).x;
+    }
+
+    static S1 val1;
+    static S1 val2;
+
+    struct S1
+    {
+        public int x;
+    }
+}
+";
+            var comp = CompileAndVerify(source, expectedOutput: "1", verify: false);
+            comp.VerifyDiagnostics();
+
+            comp.VerifyIL("C.Test", @"
+{
+  // Code size       11 (0xb)
+  .maxstack  1
+  IL_0000:  ldsflda    ""C.S1 C.val1""
+  IL_0005:  ldflda     ""int C.S1.x""
+  IL_000a:  ret
+}
+");
+        }
+
+        [Fact]
+        public void TestRefConditionalSafeToReturn3()
+        {
+            var source = @"
+class C
+{
+    static void Main()
+    {
+        (false? ref val1: ref val2) = (true? 1: val2);
+        (true? ref val1: ref val2) = (false? ref val1: ref val2);
+        System.Console.WriteLine(val1);
+    }
+
+    static int val1;
+    static int val2;
+}
+";
+            var comp = CompileAndVerify(source, expectedOutput: "1", verify: false);
+            comp.VerifyDiagnostics();
+
+            comp.VerifyIL("C.Main()", @"
+{
+  // Code size       27 (0x1b)
+  .maxstack  1
+  IL_0000:  ldc.i4.1
+  IL_0001:  stsfld     ""int C.val2""
+  IL_0006:  ldsfld     ""int C.val2""
+  IL_000b:  stsfld     ""int C.val1""
+  IL_0010:  ldsfld     ""int C.val1""
+  IL_0015:  call       ""void System.Console.WriteLine(int)""
+  IL_001a:  ret
+}
+");
+        }
+
         [Fact]
         public void TestRefConditionalDifferentTypes1()
         {