Limit size of exact collections (microsoft#913)

Fixes microsoft#877.

Limit the size of exact collections to 1000 items (when they are created from the expressions). This is set high in order to not affect potentially large `__all__` definitions.

probablepeople has a dictionary with more than 150,000 key/value pairs, which takes a very long time to process; 1000 doesn't take very long.

Author: jakebailey

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

@@ -23,6 +23,8 @@
 
 namespace Microsoft.Python.Analysis.Analyzer.Evaluation {
     internal sealed partial class ExpressionEval {
+        private const int MaxCollectionSize = 1000;
+
         public IMember GetValueFromIndex(IndexExpression expr) {
             if (expr?.Target == null) {
                 return null;
@@ -56,39 +58,39 @@ public IMember GetValueFromIndex(IndexExpression expr) {
 
         public IMember GetValueFromList(ListExpression expression) {
             var contents = new List<IMember>();
-            foreach (var item in expression.Items) {
+            foreach (var item in expression.Items.Take(MaxCollectionSize)) {
                 var value = GetValueFromExpression(item) ?? UnknownType;
                 contents.Add(value);
             }
-            return PythonCollectionType.CreateList(Module.Interpreter, contents, exact: true);
+            return PythonCollectionType.CreateList(Module.Interpreter, contents, exact: expression.Items.Count <= MaxCollectionSize);
         }
 
         public IMember GetValueFromDictionary(DictionaryExpression expression) {
             var contents = new Dictionary<IMember, IMember>();
-            foreach (var item in expression.Items) {
+            foreach (var item in expression.Items.Take(MaxCollectionSize)) {
                 var key = GetValueFromExpression(item.SliceStart) ?? UnknownType;
                 var value = GetValueFromExpression(item.SliceStop) ?? UnknownType;
                 contents[key] = value;
             }
-            return new PythonDictionary(Interpreter, contents, exact: true);
+            return new PythonDictionary(Interpreter, contents, exact: expression.Items.Count <= MaxCollectionSize);
         }
 
         private IMember GetValueFromTuple(TupleExpression expression) {
             var contents = new List<IMember>();
-            foreach (var item in expression.Items) {
+            foreach (var item in expression.Items.Take(MaxCollectionSize)) {
                 var value = GetValueFromExpression(item) ?? UnknownType;
                 contents.Add(value);
             }
-            return PythonCollectionType.CreateTuple(Module.Interpreter, contents, exact: true);
+            return PythonCollectionType.CreateTuple(Module.Interpreter, contents, exact: expression.Items.Count <= MaxCollectionSize);
         }
 
         public IMember GetValueFromSet(SetExpression expression) {
             var contents = new List<IMember>();
-            foreach (var item in expression.Items) {
+            foreach (var item in expression.Items.Take(MaxCollectionSize)) {
                 var value = GetValueFromExpression(item) ?? UnknownType;
                 contents.Add(value);
             }
-            return PythonCollectionType.CreateSet(Interpreter, contents, exact: true);
+            return PythonCollectionType.CreateSet(Interpreter, contents, exact: expression.Items.Count <= MaxCollectionSize);
         }
 
         public IMember GetValueFromGenerator(GeneratorExpression expression) {