Add Basic Function Return Type Analysis (#22747)

1. Considering functions, I have to change the node type from single value to a set. Because python function is allowed to return different types. The set represent all possible types

2. I added scope_name and scope_type for AstVarScope, because in python functions, variable may have different scope. For example:

```
a = 3
def foo(b):
    a = 9
    return a + b
```

the `a` in `foo` is different to the `a` out of `foo`. Similar to class field. The scope_name will help me to know the function name when static analysis finds a `return` sentence.

python/paddle/fluid/tests/unittests/test_ast_transformer_static_analysis.py

@@ -42,7 +42,7 @@ def func_to_test2(x):
         return x
 
 
-result_var_type2 = {'m': NodeVarType.INT}
+result_var_type2 = {'m': {NodeVarType.INT}}
 
 
 def func_to_test3():
@@ -59,16 +59,16 @@ def func_to_test3():
 
 
 result_var_type3 = {
-    'a': NodeVarType.INT,
-    'b': NodeVarType.FLOAT,
-    'c': NodeVarType.FLOAT,
-    'd': NodeVarType.FLOAT,
-    'e': NodeVarType.BOOLEAN,
-    'f': NodeVarType.INT,
-    'g': NodeVarType.STRING,
-    'h': NodeVarType.NONE,
-    'i': NodeVarType.BOOLEAN,
-    'j': NodeVarType.UNKNOWN
+    'a': {NodeVarType.INT},
+    'b': {NodeVarType.FLOAT},
+    'c': {NodeVarType.FLOAT},
+    'd': {NodeVarType.FLOAT},
+    'e': {NodeVarType.BOOLEAN},
+    'f': {NodeVarType.INT},
+    'g': {NodeVarType.STRING},
+    'h': {NodeVarType.NONE},
+    'i': {NodeVarType.BOOLEAN},
+    'j': {NodeVarType.UNKNOWN}
 }
 
 
@@ -81,15 +81,48 @@ def func_to_test4():
 
 
 result_var_type4 = {
-    'a': NodeVarType.NUMPY_NDARRAY,
-    'b': NodeVarType.NUMPY_NDARRAY,
-    'c': NodeVarType.TENSOR,
-    'd': NodeVarType.TENSOR
+    'a': {NodeVarType.NUMPY_NDARRAY},
+    'b': {NodeVarType.NUMPY_NDARRAY},
+    'c': {NodeVarType.TENSOR},
+    'd': {NodeVarType.TENSOR}
 }
 
-test_funcs = [func_to_test1, func_to_test2, func_to_test3, func_to_test4]
+
+def func_to_test5():
+    def inner_int_func():
+        return 1
+
+    def inner_bool_float_func(x):
+        a = 1.0
+        if x > 0:
+            return a
+        return False
+
+    def inner_unknown_func(x):
+        return x
+
+    a = inner_int_func()
+    b = inner_bool_float_func(3)
+    c = inner_unknown_func(None)
+    d = paddle.fluid.data('x', [1, 2])
+
+
+result_var_type5 = {
+    'a': {NodeVarType.INT},
+    'b': {NodeVarType.FLOAT, NodeVarType.BOOLEAN},
+    'c': {NodeVarType.UNKNOWN},
+    'd': {NodeVarType.PADDLE_RETURN_TYPES},
+    'inner_int_func': {NodeVarType.INT},
+    'inner_bool_float_func': {NodeVarType.FLOAT, NodeVarType.BOOLEAN},
+    'inner_unknown_func': {NodeVarType.UNKNOWN},
+}
+
+test_funcs = [
+    func_to_test1, func_to_test2, func_to_test3, func_to_test4, func_to_test5
+]
 result_var_type = [
-    result_var_type1, result_var_type2, result_var_type3, result_var_type4
+    result_var_type1, result_var_type2, result_var_type3, result_var_type4,
+    result_var_type5
 ]
 
 
@@ -117,7 +150,7 @@ class TestStaticAnalysis(unittest.TestCase):
             self._check_wrapper(wrapper_root, node_to_wrapper_map)
 
     def test_var_env(self):
-        for i in range(4):
+        for i in range(5):
             func = test_funcs[i]
             var_type = result_var_type[i]
             test_source_code = inspect.getsource(func)
@@ -125,6 +158,11 @@ class TestStaticAnalysis(unittest.TestCase):
             print(gast.dump(ast_root))
             visitor = StaticAnalysisVisitor(ast_root)
             var_env = visitor.get_var_env()
+
+            # There must be 1 sub scope for the test function
+            self.assertEqual(1, len(var_env.cur_scope.sub_scopes))
+            var_env.cur_scope = var_env.cur_scope.sub_scopes[0]
+
             scope_var_type = var_env.get_scope_var_type()
             self.assertEqual(len(scope_var_type), len(var_type))
             for name in scope_var_type: