Feature / Bug Fix: Brain for the stdlib signal module (#1172)

* Added brain for stdlib signal module, for dynamically generated IntEnums.

* Added static definitions for Signals, Handlers and Sigmasks enums.

* Moved sys.platform checks outside of generated code.

* Added note to brain_signal docstring.

* Added unit tests for brain_signal.py.

2 files changed, 158 insertions, 0 deletions

diff --git a/astroid/brain/brain_signal.py b/astroid/brain/brain_signal.py
new file mode 100644
index 00000000..46a64139
--- /dev/null
+++ b/astroid/brain/brain_signal.py
@@ -0,0 +1,117 @@
+# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
+# For details: https://github.com/PyCQA/astroid/blob/main/LICENSE
+"""Astroid hooks for the signal library.
+
+The signal module generates the 'Signals', 'Handlers' and 'Sigmasks' IntEnums
+dynamically using the IntEnum._convert() classmethod, which modifies the module
+globals. Astroid is unable to handle this type of code.
+
+Without these hooks, the following are erroneously triggered by Pylint:
+    * E1101: Module 'signal' has no 'Signals' member (no-member)
+    * E1101: Module 'signal' has no 'Handlers' member (no-member)
+    * E1101: Module 'signal' has no 'Sigmasks' member (no-member)
+
+These enums are defined slightly differently depending on the user's operating
+system and platform. These platform differences should follow the current
+Python typeshed stdlib `signal.pyi` stub file, available at:
+
+* https://github.com/python/typeshed/blob/master/stdlib/signal.pyi
+
+Note that the enum.auto() values defined here for the Signals, Handlers and
+Sigmasks IntEnums are just dummy integer values, and do not correspond to the
+actual standard signal numbers - which may vary depending on the system.
+"""
+
+
+import sys
+
+from astroid.brain.helpers import register_module_extender
+from astroid.builder import parse
+from astroid.manager import AstroidManager
+
+
+def _signals_enums_transform():
+    """Generates the AST for 'Signals', 'Handlers' and 'Sigmasks' IntEnums."""
+    return parse(_signals_enum() + _handlers_enum() + _sigmasks_enum())
+
+
+def _signals_enum():
+    """Generates the source code for the Signals int enum."""
+    signals_enum = """
+    import enum
+    class Signals(enum.IntEnum):
+        SIGABRT   = enum.auto()
+        SIGEMT    = enum.auto()
+        SIGFPE    = enum.auto()
+        SIGILL    = enum.auto()
+        SIGINFO   = enum.auto()
+        SIGINT    = enum.auto()
+        SIGSEGV   = enum.auto()
+        SIGTERM   = enum.auto()
+    """
+    if sys.platform != "win32":
+        signals_enum += """
+        SIGALRM   = enum.auto()
+        SIGBUS    = enum.auto()
+        SIGCHLD   = enum.auto()
+        SIGCONT   = enum.auto()
+        SIGHUP    = enum.auto()
+        SIGIO     = enum.auto()
+        SIGIOT    = enum.auto()
+        SIGKILL   = enum.auto()
+        SIGPIPE   = enum.auto()
+        SIGPROF   = enum.auto()
+        SIGQUIT   = enum.auto()
+        SIGSTOP   = enum.auto()
+        SIGSYS    = enum.auto()
+        SIGTRAP   = enum.auto()
+        SIGTSTP   = enum.auto()
+        SIGTTIN   = enum.auto()
+        SIGTTOU   = enum.auto()
+        SIGURG    = enum.auto()
+        SIGUSR1   = enum.auto()
+        SIGUSR2   = enum.auto()
+        SIGVTALRM = enum.auto()
+        SIGWINCH  = enum.auto()
+        SIGXCPU   = enum.auto()
+        SIGXFSZ   = enum.auto()
+        """
+    if sys.platform == "win32":
+        signals_enum += """
+        SIGBREAK  = enum.auto()
+        """
+    if sys.platform not in ("darwin", "win32"):
+        signals_enum += """
+        SIGCLD    = enum.auto()
+        SIGPOLL   = enum.auto()
+        SIGPWR    = enum.auto()
+        SIGRTMAX  = enum.auto()
+        SIGRTMIN  = enum.auto()
+        """
+    return signals_enum
+
+
+def _handlers_enum():
+    """Generates the source code for the Handlers int enum."""
+    return """
+    import enum
+    class Handlers(enum.IntEnum):
+        SIG_DFL = enum.auto()
+        SIG_IGN = eunm.auto()
+    """
+
+
+def _sigmasks_enum():
+    """Generates the source code for the Sigmasks int enum."""
+    if sys.platform != "win32":
+        return """
+    import enum
+    class Sigmasks(enum.IntEnum):
+        SIG_BLOCK   = enum.auto()
+        SIG_UNBLOCK = enum.auto()
+        SIG_SETMASK = enum.auto()
+        """
+    return ""
+
+
+register_module_extender(AstroidManager(), "signal", _signals_enums_transform)
diff --git a/tests/unittest_brain_signal.py b/tests/unittest_brain_signal.py
new file mode 100644
index 00000000..5422ecfa
--- /dev/null
+++ b/tests/unittest_brain_signal.py
@@ -0,0 +1,41 @@
+# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
+# For details: https://github.com/PyCQA/astroid/blob/main/LICENSE
+"""Unit Tests for the signal brain module."""
+
+
+import sys
+
+import pytest
+
+from astroid import builder, nodes
+
+# Define signal enums
+ENUMS = ["Signals", "Handlers", "Sigmasks"]
+if sys.platform == "win32":
+    ENUMS.remove("Sigmasks")  # Sigmasks do not exist on Windows
+
+
+@pytest.mark.parametrize("enum_name", ENUMS)
+def test_enum(enum_name):
+    """Tests that the signal module enums are handled by the brain."""
+    # Extract node for signal module enum from code
+    node = builder.extract_node(
+        f"""
+        import signal
+        signal.{enum_name}
+        """
+    )
+
+    # Check the extracted node
+    assert isinstance(node, nodes.NodeNG)
+    node_inf = node.inferred()[0]
+    assert isinstance(node_inf, nodes.ClassDef)
+    assert node_inf.display_type() == "Class"
+    assert node_inf.is_subtype_of("enum.IntEnum")
+    assert node_inf.qname() == f"signal.{enum_name}"
+
+    # Check enum members
+    for member in node_inf.body:
+        assert isinstance(member, nodes.Assign)
+        for target in member.targets:
+            assert isinstance(target, nodes.AssignName)