Improve error priorities in case of using static class as a generic argument (#36203) (#37613)

src/Compilers/CSharp/Portable/Binder/Semantics/OverloadResolution/OverloadResolutionResult.cs

@@ -289,26 +289,29 @@ private static ThreeState TryGetBestResult(ArrayBuilder<MemberResolutionResult<T
                 return;
             }
 
-            // Otherwise, if there is any such method that has a bad argument conversion or out/ref mismatch 
-            // then the first such method found is the best bad method.
+            // Otherwise, if there is any such method where type inference succeeded but inferred
+            // type arguments that violate the constraints on the method, then the first such method is
+            // the best bad method.
 
-            if (HadBadArguments(diagnostics, binder, name, arguments, symbols, location, binder.Flags, isMethodGroupConversion))
+            if (HadConstraintFailure(location, diagnostics))
             {
                 return;
             }
 
             // Since we didn't return...
-            AssertNone(MemberResolutionKind.BadArgumentConversion);
+            AssertNone(MemberResolutionKind.ConstraintFailure);
 
-            // Otherwise, if there is any such method where type inference succeeded but inferred
-            // type arguments that violate the constraints on the method, then the first such method is 
-            // the best bad method.
+            // Otherwise, if there is any such method that has a bad argument conversion or out/ref mismatch
+            // then the first such method found is the best bad method.
 
-            if (HadConstraintFailure(location, diagnostics))
+            if (HadBadArguments(diagnostics, binder, name, arguments, symbols, location, binder.Flags, isMethodGroupConversion))
             {
                 return;
             }
 
+            // Since we didn't return...
+            AssertNone(MemberResolutionKind.BadArgumentConversion);
+
             // Otherwise, if there is any such method where type inference succeeded but inferred
             // a parameter type that violates its own constraints then the first such method is 
             // the best bad method.

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

@@ -2816,12 +2816,12 @@ static void Main()
                 ReturnedValue: 
                   IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: ?) (Syntax: 'x')
 ", new DiagnosticDescription[] {
-                // file.cs(9,18): error CS1929: 'string' does not contain a definition for 'Cast' and the best extension method overload 'Queryable.Cast<GC>(IQueryable)' requires a receiver of type 'IQueryable'
+                // file.cs(9,31): error CS0718: 'GC': static types cannot be used as type arguments
                 //         var q2 = string.Empty.Cast<GC>().Select(x => x);
-                Diagnostic(ErrorCode.ERR_BadInstanceArgType, "string.Empty").WithArguments("string", "Cast", "System.Linq.Queryable.Cast<System.GC>(System.Linq.IQueryable)", "System.Linq.IQueryable").WithLocation(9, 18),
-                // file.cs(10,41): error CS1929: 'string' does not contain a definition for 'Cast' and the best extension method overload 'Queryable.Cast<GC>(IQueryable)' requires a receiver of type 'IQueryable'
+                Diagnostic(ErrorCode.ERR_GenericArgIsStaticClass, "Cast<GC>").WithArguments("System.GC").WithLocation(9, 31),
+                // file.cs(10,28): error CS0718: 'GC': static types cannot be used as type arguments
                 //         var q1 = /*<bind>*/from GC x in string.Empty select x/*</bind>*/;
-                Diagnostic(ErrorCode.ERR_BadInstanceArgType, "string.Empty").WithArguments("string", "Cast", "System.Linq.Queryable.Cast<System.GC>(System.Linq.IQueryable)", "System.Linq.IQueryable").WithLocation(10, 41)
+                Diagnostic(ErrorCode.ERR_GenericArgIsStaticClass, "from GC x in string.Empty").WithArguments("System.GC").WithLocation(10, 28)
             });
         }
 

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

@@ -10488,6 +10488,26 @@ static void Main()
                 new ErrorDescription[] { new ErrorDescription { Code = (int)ErrorCode.ERR_AnonMethGrpInForEach, Line = 7, Column = 27 } });
         }
 
+        [Fact]
+        [WorkItem(36203, "https://github.com/dotnet/roslyn/issues/36203")]
+        public void CS0452_GenericConstraintError_HasHigherPriorityThanMethodOverloadError()
+        {
+            var code = @"
+class Code
+{
+    void GenericMethod<T>(int i) where T: class => throw null;
+    void GenericMethod<T>(string s) => throw null;
+
+    void IncorrectMethodCall()
+    {
+        GenericMethod<int>(1);
+    }
+}";
+            CreateCompilation(code).VerifyDiagnostics(
+                // (9,9): error CS0452: The type 'int' must be a reference type in order to use it as parameter 'T' in the generic type or method 'Code.GenericMethod<T>(int)'
+                Diagnostic(ErrorCode.ERR_RefConstraintNotSatisfied, "GenericMethod<int>").WithArguments("Code.GenericMethod<T>(int)", "T", "int").WithLocation(9, 9));
+        }
+
         [Fact]
         public void CS0457ERR_AmbigUDConv()
         {
@@ -11413,6 +11433,28 @@ public static void Main()
                 new ErrorDescription[] { new ErrorDescription { Code = (int)ErrorCode.ERR_ConvertToStaticClass, Line = 12, Column = 34 } });
         }
 
+        [Fact]
+        [WorkItem(36203, "https://github.com/dotnet/roslyn/issues/36203")]
+        public void CS0718_StaticClassError_HasHigherPriorityThanMethodOverloadError()
+        {
+            var code = @"
+static class StaticClass { }
+
+class Code
+{
+    void GenericMethod<T>(int i) => throw null;
+    void GenericMethod<T>(string s) => throw null;
+
+    void IncorrectMethodCall()
+    {
+        GenericMethod<StaticClass>(1);
+    }
+}";
+            CreateCompilation(code).VerifyDiagnostics(
+                // (11,9): error CS0718: 'StaticClass': static types cannot be used as type arguments
+                Diagnostic(ErrorCode.ERR_GenericArgIsStaticClass, "GenericMethod<StaticClass>").WithArguments("StaticClass").WithLocation(11, 9));
+        }
+
         [Fact]
         public void CS0723ERR_VarDeclIsStaticClass_Locals()
         {