Prevent closure creation when all free variables are globals (#1145)

Author: BCSharp

Src/IronPython/Compiler/Ast/ClassDefinition.cs

@@ -359,4 +359,4 @@ internal override void RewriteBody(MSAst.ExpressionVisitor visitor) {
             Body = new RewrittenBodyStatement(Body, visitor.Visit(Body));
         }
     }
-}
+}

Src/IronPython/Compiler/Ast/Comprehension.cs

@@ -250,8 +250,14 @@ internal override bool ExposesLocalVariable(PythonVariable variable) {
             return MSAst.Expression.Call(null, typeof(PythonOps).GetMethod(nameof(PythonOps.GetClosureTupleFromContext)), Parent.LocalContext);
         }
 
+        internal override void AddFreeVariable(PythonVariable variable, bool accessedInScope) {
+            if (!accessedInScope) {
+                ContainsNestedFreeVariables = true;
+            }
+            base.AddFreeVariable(variable, accessedInScope);
+        }
+
         internal override bool TryBindOuter(ScopeStatement from, PythonReference reference, out PythonVariable variable) {
-            ContainsNestedFreeVariables = true;
             if (TryGetVariable(reference.Name, out variable)) {
                 Debug.Assert(variable.Kind != VariableKind.Nonlocal, "there should be no nonlocals in a comprehension");
                 variable.AccessedInNestedScope = true;
@@ -264,6 +270,7 @@ internal override bool TryBindOuter(ScopeStatement from, PythonReference referen
                     }
 
                     AddCellVariable(variable);
+                    ContainsNestedFreeVariables = true;
                 } else {
                     from.AddReferencedGlobal(reference.Name);
                 }

Src/IronPython/Compiler/Ast/FunctionDefinition.cs

@@ -185,9 +185,15 @@ internal override FunctionAttributes Flags {
             }
         }
 
+        internal override void AddFreeVariable(PythonVariable variable, bool accessedInScope) {
+            if (!accessedInScope) {
+                ContainsNestedFreeVariables = true;
+            }
+            base.AddFreeVariable(variable, accessedInScope);
+        }
+
         internal override bool TryBindOuter(ScopeStatement from, PythonReference reference, out PythonVariable variable) {
             // Functions expose their locals to direct access
-            ContainsNestedFreeVariables = true;
             if (TryGetVariable(reference.Name, out variable) && variable.Kind != VariableKind.Nonlocal) {
                 variable.AccessedInNestedScope = true;
 
@@ -199,6 +205,7 @@ internal override bool TryBindOuter(ScopeStatement from, PythonReference referen
                     }
 
                     AddCellVariable(variable);
+                    ContainsNestedFreeVariables = true;
                 } else {
                     from.AddReferencedGlobal(reference.Name);
                 }

Src/IronPython/Compiler/Ast/ScopeStatement.cs

@@ -80,7 +80,7 @@ internal bool IsClosure {
         }
 
         /// <summary>
-        /// True if an inner scope is accessing a variable defined in this scope.
+        /// True if an inner scope is accessing a non-global variable defined in this or an outer scope.
         /// </summary>
         internal bool ContainsNestedFreeVariables { get; set; }
 
@@ -184,7 +184,7 @@ internal virtual IList<string> GetVarNames() {
         }
 
 
-        internal void AddFreeVariable(PythonVariable variable, bool accessedInScope) {
+        internal virtual void AddFreeVariable(PythonVariable variable, bool accessedInScope) {
             Debug.Assert(variable?.Kind is VariableKind.Local or VariableKind.Parameter);
 
             if (_freeVars == null) {

Tests/test_function.py

@@ -1461,4 +1461,10 @@ def fn_no_closure():
                 fn_no_closure.__globals__, "name", fn_no_closure.__defaults__,
                 fn_with_closure.__closure__)
 
+    def test_ipy3_gh1143(self):
+        def f(): pass
+        self.assertIsNone(f.__closure__)
+        def g(): str
+        self.assertIsNone(g.__closure__)
+
 run_test(__name__)