ENH: add tool to find functions missing types

Closes https://github.com/numpy/numpy/issues/16625.

This is ported from the numpy-stubs here:

https://github.com/numpy/numpy-stubs/blob/master/runtests.py#L94

You run

```
./tools/functions_missing_types.py <module>
```

and it will give you a list of things in that module that don't have
type annotations.

1 files changed, 129 insertions, 0 deletions

diff --git a/tools/functions_missing_types.py b/tools/functions_missing_types.py
new file mode 100755
index 000000000..a3f57ddec
--- /dev/null
+++ b/tools/functions_missing_types.py
@@ -0,0 +1,129 @@
+#!/usr/bin/env python
+import argparse
+import ast
+import importlib
+import os
+
+NUMPY_ROOT = os.path.dirname(os.path.join(
+    os.path.abspath(__file__), "..",
+))
+
+# Technically "public" functions (they don't start with an underscore)
+# that we don't want to include.
+EXCLUDE_LIST = {
+    "numpy": {
+        # Stdlib modules in the namespace by accident
+        "absolute_import",
+        "division",
+        "print_function",
+        "warnings",
+        # Accidentally public, deprecated, or shouldn't be used
+        "Tester",
+        "add_docstring",
+        "add_newdoc",
+        "add_newdoc_ufunc",
+        "core",
+        "fastCopyAndTranspose",
+        "get_array_wrap",
+        "int_asbuffer",
+        "oldnumeric",
+        "safe_eval",
+        "set_numeric_ops",
+        "test",
+        # Builtins
+        "bool",
+        "complex",
+        "float",
+        "int",
+        "long",
+        "object",
+        "str",
+        "unicode",
+        # Should use numpy_financial instead
+        "fv",
+        "ipmt",
+        "irr",
+        "mirr",
+        "nper",
+        "npv",
+        "pmt",
+        "ppmt",
+        "pv",
+        "rate",
+        # More standard names should be preferred
+        "alltrue",  # all
+        "sometrue",  # any
+    }
+}
+
+
+class FindAttributes(ast.NodeVisitor):
+    """Find top-level attributes/functions/classes a stubs file.
+
+    Do this by walking the stubs ast. See e.g.
+
+    https://greentreesnakes.readthedocs.io/en/latest/index.html
+
+    for more information on working with Python's ast.
+
+    """
+
+    def __init__(self):
+        self.attributes = set()
+
+    def visit_FunctionDef(self, node):
+        if node.name == "__getattr__":
+            # Not really a module member.
+            return
+        self.attributes.add(node.name)
+        # Do not call self.generic_visit; we are only interested in
+        # top-level functions.
+        return
+
+    def visit_ClassDef(self, node):
+        if not node.name.startswith("_"):
+            self.attributes.add(node.name)
+        return
+
+    def visit_AnnAssign(self, node):
+        self.attributes.add(node.target.id)
+
+
+def find_missing(module_name):
+    module_path = os.path.join(
+        NUMPY_ROOT,
+        module_name.replace(".", os.sep),
+        "__init__.pyi",
+    )
+
+    module = importlib.import_module(module_name)
+    module_attributes = {
+        attribute for attribute in dir(module) if not attribute.startswith("_")
+    }
+
+    if os.path.isfile(module_path):
+        with open(module_path) as f:
+            tree = ast.parse(f.read())
+        ast_visitor = FindAttributes()
+        ast_visitor.visit(tree)
+        stubs_attributes = ast_visitor.attributes
+    else:
+        # No stubs for this module yet.
+        stubs_attributes = set()
+
+    exclude_list = EXCLUDE_LIST.get(module_name, set())
+
+    missing = module_attributes - stubs_attributes - exclude_list
+    print("\n".join(sorted(missing)))
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("module")
+    args = parser.parse_args()
+
+    find_missing(args.module)
+
+
+if __name__ == "__main__":
+    main()