No diagnostic message when Generic is called with no args (microsoft#1305)

* No diagnostic message when Generic is called with no args

Author: CTrando

src/Analysis/Ast/Impl/Analyzer/Evaluation/ExpressionEval.Generics.cs

@@ -125,7 +125,10 @@ private IReadOnlyList<IMember> EvaluateIndex(IndexExpression expr) {
                 }
             } else {
                 var index = GetValueFromExpression(expr.Index);
-                indices.Add(index ?? UnknownType);
+                // Don't count null indexes as arguments
+                if (index != null) {
+                    indices.Add(index);
+                }
             }
             return indices;
         }

src/Analysis/Ast/Impl/Analyzer/Evaluation/ExpressionEval.cs

@@ -184,6 +184,10 @@ public IMember GetValueFromExpression(Expression expr, LookupOptions options = L
                 case NamedExpression namedExpr:
                     m = GetValueFromExpression(namedExpr.Value);
                     break;
+                // indexing with nothing, e.g Generic[]
+                case ErrorExpression error:
+                    m = null;
+                    break;
                 default:
                     m = GetValueFromBinaryOp(expr) ?? GetConstantFromLiteral(expr, options);
                     break;

src/Analysis/Ast/Test/LintGenericTests.cs

@@ -80,7 +80,26 @@ public async Task GenericDuplicateArguments(string decl) {
         public async Task GenericArgumentsNoDiagnosticOnValid(string decl) {
             string code = GenericSetup + decl;
             var analysis = await GetAnalysisAsync(code);
-            analysis.Diagnostics.Should().HaveCount(0);
+            analysis.Diagnostics.Should().BeEmpty();
+        }
+
+        [TestMethod, Priority(0)]
+        public async Task GenericNoArgumentsNoDiagnostic() {
+            string code = GenericSetup + @"
+x = Generic[]
+";
+            var analysis = await GetAnalysisAsync(code);
+            analysis.Diagnostics.Should().BeEmpty();
+        }
+
+
+        [TestMethod, Priority(0)]
+        public async Task GenericArgumentSpaceNoDiagnostic() {
+            string code = GenericSetup + @"
+x = Generic[  ]
+";
+            var analysis = await GetAnalysisAsync(code);
+            analysis.Diagnostics.Should().BeEmpty();
         }
     }
 }