[lldb] Support a Stable ABI LLDB_PYTHON_EXT_SUFFIX (llvm#166269)

When building against the Python Stable API, we should use the `abi3`
ABI tag. Otherwise, Python will refuse to import the native shared
object. This PR adds support for generating a stable ABI compatible
suffix when `LLDB_ENABLE_PYTHON_LIMITED_API` is set.

Previously, on Darwin when building against Python 3.14, you would end
up with `_lldb.cpython-314-darwin.so`. Now, when using the stable ABI,
you get `_lldb.abi3.so` instead. A different version of the Python
interpreter will not consider loading the former, but will load the
latter.

Author: JDevlieghere

lldb/CMakeLists.txt

@@ -62,11 +62,16 @@ if (LLDB_ENABLE_PYTHON)
   set(cachestring_LLDB_PYTHON_EXT_SUFFIX
     "Filename extension for native code python modules")
 
+  if (LLDB_ENABLE_PYTHON_LIMITED_API)
+    set(stable_abi "--stable-abi")
+  endif()
+
   foreach(var LLDB_PYTHON_RELATIVE_PATH LLDB_PYTHON_EXE_RELATIVE_PATH LLDB_PYTHON_EXT_SUFFIX)
     if(NOT DEFINED ${var} AND NOT CMAKE_CROSSCOMPILING)
       execute_process(
         COMMAND ${Python3_EXECUTABLE}
           ${CMAKE_CURRENT_SOURCE_DIR}/bindings/python/get-python-config.py
+          ${stable_abi}
           ${var}
         OUTPUT_VARIABLE value
         OUTPUT_STRIP_TRAILING_WHITESPACE)

lldb/bindings/python/get-python-config.py

@@ -18,6 +18,9 @@ def relpath_nodots(path, base):
 def main():
     parser = argparse.ArgumentParser(description="extract cmake variables from python")
     parser.add_argument("variable_name")
+    parser.add_argument(
+        "--stable-abi", action="store_true", help="Target the Stable C ABI"
+    )
     args = parser.parse_args()
     if args.variable_name == "LLDB_PYTHON_RELATIVE_PATH":
         # LLDB_PYTHON_RELATIVE_PATH is the relative path from lldb's prefix
@@ -68,7 +71,10 @@ def main():
                     print("sys.prefix:", sys.prefix, file=sys.stderr)
                     sys.exit(1)
     elif args.variable_name == "LLDB_PYTHON_EXT_SUFFIX":
-        print(sysconfig.get_config_var("EXT_SUFFIX"))
+        if args.stable_abi:
+            print(".abi3%s" % sysconfig.get_config_var("SHLIB_SUFFIX"))
+        else:
+            print(sysconfig.get_config_var("EXT_SUFFIX"))
     else:
         parser.error(f"unknown variable {args.variable_name}")