Improve definite-assignment behavior in error cases for switch and is-pattern

Also reduce cascaded diagnostics in attribute argument binding.
Fixes #9154

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

@@ -1187,7 +1187,7 @@ private TypedConstant VisitArrayCreation(BoundArrayCreation node, DiagnosticBag
 
                 if (typedConstantKind == TypedConstantKind.Error)
                 {
-                    if (!curArgumentHasErrors)
+                    if (!curArgumentHasErrors && !attrHasErrors)
                     {
                         Binder.Error(diagnostics, ErrorCode.ERR_BadAttributeArgument, node.Syntax);
                         attrHasErrors = true;

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

@@ -727,16 +727,6 @@ private BoundExpression BindConditionalLogicalOperator(BinaryExpressionSyntax no
 
             Debug.Assert(kind == BinaryOperatorKind.LogicalAnd || kind == BinaryOperatorKind.LogicalOr);
 
-            // If either operand is bad, don't try to do binary operator overload resolution; that will just
-            // make cascading errors.  
-
-            if (left.HasAnyErrors || right.HasAnyErrors)
-            {
-                // NOTE: no candidate user-defined operators.
-                return new BoundBinaryOperator(node, kind, left, right, ConstantValue.NotAvailable, methodOpt: null,
-                    resultKind: LookupResultKind.Empty, type: GetBinaryOperatorErrorType(kind, diagnostics, node), hasErrors: true);
-            }
-
             // Let's take an easy out here. The vast majority of the time the operands will
             // both be bool. This is the only situation in which the expression can be a 
             // constant expression, so do the folding now if we can.
@@ -751,6 +741,16 @@ private BoundExpression BindConditionalLogicalOperator(BinaryExpressionSyntax no
                     resultKind: LookupResultKind.Viable, type: left.Type, hasErrors: constantValue != null && constantValue.IsBad);
             }
 
+            // If either operand is bad, don't try to do binary operator overload resolution; that will just
+            // make cascading errors.
+
+            if (left.HasAnyErrors || right.HasAnyErrors)
+            {
+                // NOTE: no candidate user-defined operators.
+                return new BoundBinaryOperator(node, kind, left, right, ConstantValue.NotAvailable, methodOpt: null,
+                    resultKind: LookupResultKind.Empty, type: GetBinaryOperatorErrorType(kind, diagnostics, node), hasErrors: true);
+            }
+
             if (left.HasDynamicType() || right.HasDynamicType())
             {
                 return BindDynamicBinaryOperator(node, kind, left, right, diagnostics);

src/Compilers/CSharp/Portable/FlowAnalysis/PreciseAbstractFlowPass.cs

@@ -2764,6 +2764,11 @@ public override BoundNode VisitSwitchExpression(BoundSwitchExpression node)
                 SetState(dispatchState.Clone());
                 VisitPattern(node.Expression, arm.Pattern);
                 SetState(StateWhenTrue);
+                if (arm.Pattern.HasErrors)
+                {
+                    // suppress definite assignment errors on broken switch arms
+                    SetUnreachable();
+                }
                 if (arm.Guard != null)
                 {
                     VisitCondition(arm.Guard);

src/Compilers/CSharp/Test/Emit/Attributes/AttributeTests.cs

@@ -6577,12 +6577,9 @@ public class A : Attribute
 class C<T, U> { public enum E {} }";
 
             CreateCompilation(source).VerifyDiagnostics(
-                // (7,31): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
-                // [A(new object[] { default(E), default(E) })]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "default(E)").WithLocation(7, 31),
                 // (7,19): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 // [A(new object[] { default(E), default(E) })]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "default(E)").WithLocation(7, 19));
+                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "default(E)").WithLocation(7, 19)
         }
 
         [Fact]

src/Compilers/CSharp/Test/Semantic/Semantics/OutVarTests.cs

@@ -1975,7 +1975,7 @@ class Test : System.Attribute
                 // (9,15): error CS0841: Cannot use local variable 'x4' before it is declared
                 //     [Test(p = x4 && TakeOutParam(out int x4))]
                 Diagnostic(ErrorCode.ERR_VariableUsedBeforeDeclaration, "x4").WithArguments("x4").WithLocation(9, 15),
-                // (11,40): error CS0128: A local variable named 'x5' is already defined in this scope
+                // (11,40): error CS0128: A local variable or function named 'x5' is already defined in this scope
                 //               TakeOutParam(52, out int x5) && 
                 Diagnostic(ErrorCode.ERR_LocalDuplicate, "x5").WithArguments("x5").WithLocation(11, 40),
                 // (10,15): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
@@ -1983,15 +1983,12 @@ class Test : System.Attribute
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, @"TakeOutParam(51, out int x5) && 
               TakeOutParam(52, out int x5) && 
               x5 > 0").WithLocation(10, 15),
-                // (14,37): error CS0128: A local variable named 'x6' is already defined in this scope
+                // (14,37): error CS0128: A local variable or function named 'x6' is already defined in this scope
                 //           p2 = TakeOutParam(out int x6) && x6 > 0)]
                 Diagnostic(ErrorCode.ERR_LocalDuplicate, "x6").WithArguments("x6").WithLocation(14, 37),
                 // (13,16): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 //     [Test(p1 = TakeOutParam(out int x6) && x6 > 0, 
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out int x6) && x6 > 0").WithLocation(13, 16),
-                // (14,16): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
-                //           p2 = TakeOutParam(out int x6) && x6 > 0)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out int x6) && x6 > 0").WithLocation(14, 16),
                 // (15,15): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 //     [Test(p = TakeOutParam(out int x7) && x7 > 0)]
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out int x7) && x7 > 0").WithLocation(15, 15),
@@ -2085,7 +2082,7 @@ class Test : System.Attribute
                 // (9,11): error CS0841: Cannot use local variable 'x4' before it is declared
                 //     [Test(x4 && TakeOutParam(out int x4))]
                 Diagnostic(ErrorCode.ERR_VariableUsedBeforeDeclaration, "x4").WithArguments("x4").WithLocation(9, 11),
-                // (11,36): error CS0128: A local variable named 'x5' is already defined in this scope
+                // (11,36): error CS0128: A local variable or function named 'x5' is already defined in this scope
                 //           TakeOutParam(52, out int x5) && 
                 Diagnostic(ErrorCode.ERR_LocalDuplicate, "x5").WithArguments("x5").WithLocation(11, 36),
                 // (10,11): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
@@ -2093,15 +2090,12 @@ class Test : System.Attribute
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, @"TakeOutParam(51, out int x5) && 
           TakeOutParam(52, out int x5) && 
           x5 > 0").WithLocation(10, 11),
-                // (14,32): error CS0128: A local variable named 'x6' is already defined in this scope
+                // (14,32): error CS0128: A local variable or function named 'x6' is already defined in this scope
                 //           TakeOutParam(out int x6) && x6 > 0)]
                 Diagnostic(ErrorCode.ERR_LocalDuplicate, "x6").WithArguments("x6").WithLocation(14, 32),
                 // (13,11): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 //     [Test(TakeOutParam(out int x6) && x6 > 0, 
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out int x6) && x6 > 0").WithLocation(13, 11),
-                // (14,11): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
-                //           TakeOutParam(out int x6) && x6 > 0)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out int x6) && x6 > 0").WithLocation(14, 11),
                 // (15,11): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 //     [Test(TakeOutParam(out int x7) && x7 > 0)]
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out int x7) && x7 > 0").WithLocation(15, 11),
@@ -2197,7 +2191,7 @@ class Test : System.Attribute
                 // (9,15): error CS0841: Cannot use local variable 'x4' before it is declared
                 //     [Test(p = x4 && TakeOutParam(out var x4))]
                 Diagnostic(ErrorCode.ERR_VariableUsedBeforeDeclaration, "x4").WithArguments("x4").WithLocation(9, 15),
-                // (11,40): error CS0128: A local variable named 'x5' is already defined in this scope
+                // (11,40): error CS0128: A local variable or function named 'x5' is already defined in this scope
                 //               TakeOutParam(52, out var x5) && 
                 Diagnostic(ErrorCode.ERR_LocalDuplicate, "x5").WithArguments("x5").WithLocation(11, 40),
                 // (10,15): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
@@ -2205,15 +2199,12 @@ class Test : System.Attribute
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, @"TakeOutParam(51, out var x5) && 
               TakeOutParam(52, out var x5) && 
               x5 > 0").WithLocation(10, 15),
-                // (14,37): error CS0128: A local variable named 'x6' is already defined in this scope
+                // (14,37): error CS0128: A local variable or function named 'x6' is already defined in this scope
                 //           p2 = TakeOutParam(out var x6) && x6 > 0)]
                 Diagnostic(ErrorCode.ERR_LocalDuplicate, "x6").WithArguments("x6").WithLocation(14, 37),
                 // (13,16): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 //     [Test(p1 = TakeOutParam(out var x6) && x6 > 0, 
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out var x6) && x6 > 0").WithLocation(13, 16),
-                // (14,16): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
-                //           p2 = TakeOutParam(out var x6) && x6 > 0)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out var x6) && x6 > 0").WithLocation(14, 16),
                 // (15,15): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 //     [Test(p = TakeOutParam(out var x7) && x7 > 0)]
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out var x7) && x7 > 0").WithLocation(15, 15),
@@ -2307,7 +2298,7 @@ class Test : System.Attribute
                 // (9,11): error CS0841: Cannot use local variable 'x4' before it is declared
                 //     [Test(x4 && TakeOutParam(out var x4))]
                 Diagnostic(ErrorCode.ERR_VariableUsedBeforeDeclaration, "x4").WithArguments("x4").WithLocation(9, 11),
-                // (11,36): error CS0128: A local variable named 'x5' is already defined in this scope
+                // (11,36): error CS0128: A local variable or function named 'x5' is already defined in this scope
                 //           TakeOutParam(52, out var x5) && 
                 Diagnostic(ErrorCode.ERR_LocalDuplicate, "x5").WithArguments("x5").WithLocation(11, 36),
                 // (10,11): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
@@ -2315,15 +2306,12 @@ class Test : System.Attribute
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, @"TakeOutParam(51, out var x5) && 
           TakeOutParam(52, out var x5) && 
           x5 > 0").WithLocation(10, 11),
-                // (14,32): error CS0128: A local variable named 'x6' is already defined in this scope
+                // (14,32): error CS0128: A local variable or function named 'x6' is already defined in this scope
                 //           TakeOutParam(out var x6) && x6 > 0)]
                 Diagnostic(ErrorCode.ERR_LocalDuplicate, "x6").WithArguments("x6").WithLocation(14, 32),
                 // (13,11): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 //     [Test(TakeOutParam(out var x6) && x6 > 0, 
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out var x6) && x6 > 0").WithLocation(13, 11),
-                // (14,11): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
-                //           TakeOutParam(out var x6) && x6 > 0)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out var x6) && x6 > 0").WithLocation(14, 11),
                 // (15,11): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 //     [Test(TakeOutParam(out var x7) && x7 > 0)]
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "TakeOutParam(out var x7) && x7 > 0").WithLocation(15, 11),
@@ -11472,9 +11460,6 @@ static bool TakeOutParam<T>(T y, out T x)
                 // (94,15): error CS0103: The name 'u7' does not exist in the current context
                 //         Dummy(u7); 
                 Diagnostic(ErrorCode.ERR_NameNotInContext, "u7").WithArguments("u7").WithLocation(94, 15),
-                // (88,68): error CS0165: Use of unassigned local variable 'u7'
-                //                           x > y7 && TakeOutParam(1, out var u7) && u7 == 
-                Diagnostic(ErrorCode.ERR_UseDefViolation, "u7").WithArguments("u7").WithLocation(88, 68),
                 // (102,15): error CS0103: The name 'z8' does not exist in the current context
                 //         Dummy(z8); 
                 Diagnostic(ErrorCode.ERR_NameNotInContext, "z8").WithArguments("z8").WithLocation(102, 15),
@@ -24125,10 +24110,7 @@ static bool TakeOutParam<T>(T y, out T x)
                 Diagnostic(ErrorCode.ERR_NameNotInContext, "z9").WithArguments("z9").WithLocation(82, 7),
                 // (83,7): error CS0103: The name 'u9' does not exist in the current context
                 // Dummy(u9); 
-                Diagnostic(ErrorCode.ERR_NameNotInContext, "u9").WithArguments("u9").WithLocation(83, 7),
-                // (62,62): error CS0165: Use of unassigned local variable 'u7'
-                //                     x > y7 && TakeOutParam(1, out var u7) && u7 == 
-                Diagnostic(ErrorCode.ERR_UseDefViolation, "u7").WithArguments("u7").WithLocation(62, 62)
+                Diagnostic(ErrorCode.ERR_NameNotInContext, "u9").WithArguments("u9").WithLocation(83, 7)
                     );
 
                 var tree = compilation.SyntaxTrees.Single();
@@ -32989,18 +32971,12 @@ class MyAttribute: System.Attribute
                 // (2,5): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 // [My(C.M(nameof(C.M(out int z1)), z1), z1)]
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "C.M(nameof(C.M(out int z1)), z1)").WithLocation(2, 5),
-                // (2,39): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
-                // [My(C.M(nameof(C.M(out int z1)), z1), z1)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "z1").WithLocation(2, 39),
                 // (3,16): error CS8081: Expression does not have a name.
                 // [My(C.M(nameof(C.M(out var z2)), z2), z2)]
                 Diagnostic(ErrorCode.ERR_ExpressionHasNoName, "C.M(out var z2)").WithLocation(3, 16),
                 // (3,5): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 // [My(C.M(nameof(C.M(out var z2)), z2), z2)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "C.M(nameof(C.M(out var z2)), z2)").WithLocation(3, 5),
-                // (3,39): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
-                // [My(C.M(nameof(C.M(out var z2)), z2), z2)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "z2").WithLocation(3, 39)
+                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "C.M(nameof(C.M(out var z2)), z2)").WithLocation(3, 5)
                 );
             var tree = compilation.SyntaxTrees[0];
             var model = compilation.GetSemanticModel(tree);
@@ -33043,18 +33019,12 @@ class MyAttribute: System.Attribute
                 // (2,15): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 // [assembly: My(C.M(nameof(C.M(out int z1)), z1), z1)]
                 Diagnostic(ErrorCode.ERR_BadAttributeArgument, "C.M(nameof(C.M(out int z1)), z1)").WithLocation(2, 15),
-                // (2,49): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
-                // [assembly: My(C.M(nameof(C.M(out int z1)), z1), z1)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "z1").WithLocation(2, 49),
                 // (3,26): error CS8081: Expression does not have a name.
                 // [assembly: My(C.M(nameof(C.M(out var z2)), z2), z2)]
                 Diagnostic(ErrorCode.ERR_ExpressionHasNoName, "C.M(out var z2)").WithLocation(3, 26),
                 // (3,15): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
                 // [assembly: My(C.M(nameof(C.M(out var z2)), z2), z2)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "C.M(nameof(C.M(out var z2)), z2)").WithLocation(3, 15),
-                // (3,49): error CS0182: An attribute argument must be a constant expression, typeof expression or array creation expression of an attribute parameter type
-                // [assembly: My(C.M(nameof(C.M(out var z2)), z2), z2)]
-                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "z2").WithLocation(3, 49)
+                Diagnostic(ErrorCode.ERR_BadAttributeArgument, "C.M(nameof(C.M(out var z2)), z2)").WithLocation(3, 15)
                 );
             var tree = compilation.SyntaxTrees[0];
             var model = compilation.GetSemanticModel(tree);

src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTests2.cs

@@ -1048,6 +1048,53 @@ public static void M(object o)
                 );
         }
 
+        [Fact]
+        public void ErroneousSwitchArmDefiniteAssignment()
+        {
+            // When a switch expression arm is erroneous, ensure that the expression is treated as unreachable (e.g. for definite assignment purposes).
+            var source =
+@"class Program2
+{
+    public static int Main() => 0;
+    public static void M(string s)
+    {
+        int i;
+        int j = s switch { ""frog"" => 1, 0 => i, _ => 2 };
+    }
+}
+";
+            var compilation = CreatePatternCompilation(source);
+            compilation.VerifyDiagnostics(
+                // (7,41): error CS0029: Cannot implicitly convert type 'int' to 'string'
+                //         int j = s switch { "frog" => 1, 0 => i, _ => 2 };
+                Diagnostic(ErrorCode.ERR_NoImplicitConv, "0").WithArguments("int", "string").WithLocation(7, 41)
+                );
+        }
+
+        [Fact, WorkItem(9154, "https://github.com/dotnet/roslyn/issues/9154")]
+        public void ErroneousIsPatternDefiniteAssignment()
+        {
+            var source =
+@"class Program2
+{
+    public static int Main() => 0;
+    void Dummy(object o) {}
+    void Test5()
+    {
+        Dummy((System.Func<object, object, bool>) ((o1, o2) => o1 is int x5 && 
+                                                               o2 is int x5 && 
+                                                               x5 > 0));
+    }
+}
+";
+            var compilation = CreatePatternCompilation(source);
+            compilation.VerifyDiagnostics(
+                // (8,74): error CS0128: A local variable or function named 'x5' is already defined in this scope
+                //                                                                o2 is int x5 && 
+                Diagnostic(ErrorCode.ERR_LocalDuplicate, "x5").WithArguments("x5").WithLocation(8, 74)
+                );
+        }
+
         // PROTOTYPE(patterns2): Need to have tests that exercise:
         // PROTOTYPE(patterns2): Building the decision tree for the var-pattern
         // PROTOTYPE(patterns2): Definite assignment for the var-pattern

src/Compilers/CSharp/Test/Semantic/Semantics/PatternMatchingTests_Global.cs

@@ -7267,10 +7267,7 @@ into g
                 Diagnostic(ErrorCode.ERR_NameNotInContext, "z9").WithArguments("z9").WithLocation(82, 7),
                 // (83,7): error CS0103: The name 'u9' does not exist in the current context
                 // Dummy(u9); 
-                Diagnostic(ErrorCode.ERR_NameNotInContext, "u9").WithArguments("u9").WithLocation(83, 7),
-                // (62,46): error CS0165: Use of unassigned local variable 'u7'
-                //                     x > y7 && 1 is var u7 && u7 == 
-                Diagnostic(ErrorCode.ERR_UseDefViolation, "u7").WithArguments("u7").WithLocation(62, 46)
+                Diagnostic(ErrorCode.ERR_NameNotInContext, "u9").WithArguments("u9").WithLocation(83, 7)
                     );
 
                 var tree = compilation.SyntaxTrees.Single();