Allow condition in GILStatNode

Cython/Compiler/Nodes.py

@@ -7794,10 +7794,12 @@ class GILStatNode(NogilTryFinallyStatNode):
     #
     #   state   string   'gil' or 'nogil'
 
+    child_attrs = ["body", "condition", "finally_clause", "finally_except_clause"]
     state_temp = None
 
-    def __init__(self, pos, state, body):
+    def __init__(self, pos, state, body, condition=None):
         self.state = state
+        self.condition = condition
         self.create_state_temp_if_needed(pos, state, body)
         TryFinallyStatNode.__init__(
             self, pos,

Cython/Compiler/Optimize.py

@@ -4688,6 +4688,30 @@ class ConstantFolding(Visitor.VisitorTransform, SkipDeclarations):
             return None
         return node
 
+    def visit_GILStatNode(self, node):
+        self.visitchildren(node)
+        if node.condition is None:
+            return node
+
+        if node.condition.has_constant_result():
+            # Condition is True - Modify node to be a normal
+            # GILStatNode with condition=None
+            if node.condition.constant_result:
+                node.condition = None
+
+            # Condition is False - the body of the GILStatNode
+            # should run without changing changing the state of the gil
+            # return the body of the GILStatNode
+            else:
+                return node.body
+
+        # If condition is not constant we keep the GILStatNode as it is.
+        # Either it will later become constant (e.g. a `numeric is int`
+        # expression in a fused typed function) and then when ConstantFolding
+        # runs again it will be handled or a later transform (i.e. GilCheck)
+        # will raise an error
+        return node
+
     # in the future, other nodes can have their own handler method here
     # that can replace them with a constant result node
 

Cython/Compiler/ParseTreeTransforms.py

@@ -2915,6 +2915,11 @@ class GilCheck(VisitorTransform):
         return node
 
     def visit_GILStatNode(self, node):
+        if node.condition is not None:
+            error(node.pos, "Non-constant condition in a "
+                            "`with %s(<condition>)` statement" % node.state)
+            return node
+
         if self.nogil and node.nogil_check:
             node.nogil_check()
 

Cython/Compiler/Parsing.py

@@ -2055,12 +2055,20 @@ def p_with_items(s, is_async=False):
             s.error("with gil/nogil cannot be async")
         state = s.systring
         s.next()
+
+        # support conditional gil/nogil
+        condition = None
+        if s.sy == '(':
+            s.next()
+            condition = p_test(s)
+            s.expect(')')
+
         if s.sy == ',':
             s.next()
             body = p_with_items(s)
         else:
             body = p_suite(s)
-        return Nodes.GILStatNode(pos, state=state, body=body)
+        return Nodes.GILStatNode(pos, state=state, body=body, condition=condition)
     else:
         manager = p_test(s)
         target = None