Cache function eval result per argument set (microsoft#988)

* Fix microsoft#668 (partial)

* Tests

* Revert "Tests"

This reverts commit 7ffc9db.

* Exp

* Limit concurrency

* Concurrency limit

* Drop cache after analysis

* Fix regression

* Fix test

* Cache argument eval

* Fix hash calculation

* Fix exception when there is a space before triple quote

* Fix exception

Author: Mikhail Arkhipov

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

@@ -196,7 +196,7 @@ public IMember GetValueFromFunctionType(IPythonFunctionType fn, IPythonInstance
             // make sense to evaluate stubs since they already should be annotated.
             if (fn.DeclaringModule is IDocument doc && fd?.Ast == doc.GetAnyAst()) {
                 // Stubs are coming from another module.
-                return TryEvaluateWithArguments(fn.DeclaringModule, fd, args);
+                return TryEvaluateWithArguments(fn, args);
             }
             return UnknownType;
         }
@@ -207,9 +207,26 @@ public IMember GetValueFromProperty(IPythonPropertyType p, IPythonInstance insta
             return instance.Call(p.Name, ArgumentSet.Empty);
         }
 
-        private IMember TryEvaluateWithArguments(IPythonModule module, FunctionDefinition fd, IArgumentSet args) {
+
+        private readonly Dictionary<int, IMember> _argEvalCache = new Dictionary<int, IMember>();
+
+        private IMember TryEvaluateWithArguments(IPythonFunctionType fn, IArgumentSet args) {
+            var name = fn.DeclaringType != null ? $"{fn.DeclaringModule.Name}.{fn.Name}" : fn.Name;
+            var argHash = args
+                .Arguments
+                .Select(a => a.Name.GetHashCode() ^ 397 * (a.Value?.GetHashCode() ?? 0))
+                .Aggregate(0, (current, d) => 31 * current ^ d);
+            var key = fn.DeclaringModule.Name.GetHashCode() ^ name.GetHashCode() ^ (397 * argHash);
+
+            if (_argEvalCache.TryGetValue(key, out var result)) {
+                return result;
+            }
+
+            var fd = fn.FunctionDefinition;
+            var module = fn.DeclaringModule;
+
             // Attempt to evaluate with specific arguments but prevent recursion.
-            IMember result = UnknownType;
+            result = UnknownType;
             if (fd != null && !_callEvalStack.Contains(fd)) {
                 using (OpenScope(module, fd.Parent, out _)) {
                     _callEvalStack.Push(fd);
@@ -222,6 +239,8 @@ private IMember TryEvaluateWithArguments(IPythonModule module, FunctionDefinitio
                     }
                 }
             }
+
+            _argEvalCache[key] = result;
             return result;
         }
 

src/Analysis/Ast/Impl/Modules/PythonModule.cs

@@ -496,8 +496,11 @@ private string TryGetDocFromModuleInitFile() {
                     }
 
                     if (quote != null) {
-                        // Check if it is a single-liner
-                        if (line.EndsWithOrdinal(quote) && line.IndexOf(quote, StringComparison.Ordinal) < line.LastIndexOf(quote, StringComparison.Ordinal)) {
+                        // Check if it is a single-liner, but do distinguish from """<eol>
+                        // Also, handle quadruple+ quotes.
+                        line = line.Trim();
+                        line = line.All(c => c == quote[0]) ? quote : line;
+                        if (line.EndsWithOrdinal(quote) && line.IndexOf(quote, StringComparison.Ordinal) < line.LastIndexOf(quote, StringComparison.Ordinal)) { 
                             return line.Substring(quote.Length, line.Length - 2 * quote.Length).Trim();
                         }
                         var sb = new StringBuilder();