[lldb] fix -print-script-interpreter-info on windows

Apparently "{sys.prefix}/bin/python3" isn't where you find the
python interpreter on windows, so the test I wrote for
-print-script-interpreter-info is failing.

We can't rely on sys.executable at runtime, because that will point
to lldb.exe not python.exe.

We can't just record sys.executable from build time, because python
could have been moved to a different location.

But it should be OK to apply relative path from sys.prefix to sys.executable
from build-time to the sys.prefix at runtime.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D113650

lldb/CMakeLists.txt

@@ -31,24 +31,28 @@ if (WIN32)
 endif()
 
 if (LLDB_ENABLE_PYTHON)
-  if (NOT CMAKE_CROSSCOMPILING)
-    execute_process(
-      COMMAND ${Python3_EXECUTABLE}
-          -c "import distutils.sysconfig; print(distutils.sysconfig.get_python_lib(True, False, ''))"
-      OUTPUT_VARIABLE LLDB_PYTHON_DEFAULT_RELATIVE_PATH
-      OUTPUT_STRIP_TRAILING_WHITESPACE)
+  set(cachestring_LLDB_PYTHON_RELATIVE_PATH
+    "Path where Python modules are installed, relative to install prefix")
+  set(cachestring_LLDB_PYTHON_EXE_RELATIVE_PATH
+    "Path to python interpreter exectuable, relative to install prefix")
 
-    file(TO_CMAKE_PATH ${LLDB_PYTHON_DEFAULT_RELATIVE_PATH} LLDB_PYTHON_DEFAULT_RELATIVE_PATH)
-  else ()
-    if ("${LLDB_PYTHON_RELATIVE_PATH}" STREQUAL "")
-      message(FATAL_ERROR
-        "Crosscompiling LLDB with Python requires manually setting
-        LLDB_PYTHON_RELATIVE_PATH.")
-    endif ()
-  endif ()
-
-  set(LLDB_PYTHON_RELATIVE_PATH ${LLDB_PYTHON_DEFAULT_RELATIVE_PATH}
-    CACHE STRING "Path where Python modules are installed, relative to install prefix")
+  foreach(var LLDB_PYTHON_RELATIVE_PATH LLDB_PYTHON_EXE_RELATIVE_PATH)
+    if(NOT DEFINED ${var} AND NOT CMAKE_CROSSCOMPILING)
+      execute_process(
+        COMMAND ${Python3_EXECUTABLE}
+          ${CMAKE_CURRENT_SOURCE_DIR}/bindings/python/get-python-config.py
+          ${var}
+        OUTPUT_VARIABLE value
+        OUTPUT_STRIP_TRAILING_WHITESPACE)
+      file(TO_CMAKE_PATH "${value}" value)
+      set(${var} ${value} CACHE STRING ${cachestring_${var}})
+    else()
+      if ("${${var}}" STREQUAL "")
+        message(FATAL_ERROR
+          "Crosscompiling LLDB with Python requires manually setting ${var}.")
+      endif()
+    endif()
+  endforeach()
 endif ()
 
 if (LLDB_ENABLE_LUA)

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

@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+
+import os
+import sys
+import argparse
+import sysconfig
+import distutils.sysconfig
+
+
+def relpath_nodots(path, base):
+    rel = os.path.normpath(os.path.relpath(path, base))
+    assert not os.path.isabs(rel)
+    parts = rel.split(os.path.sep)
+    if parts and parts[0] == '..':
+        raise ValueError(f"{path} is not under {base}")
+    return rel
+
+def main():
+    parser = argparse.ArgumentParser(description="extract cmake variables from python")
+    parser.add_argument("variable_name")
+    args = parser.parse_args()
+    if args.variable_name == "LLDB_PYTHON_RELATIVE_PATH":
+        print(distutils.sysconfig.get_python_lib(True, False, ''))
+    elif args.variable_name == "LLDB_PYTHON_EXE_RELATIVE_PATH":
+        tried = list()
+        exe = sys.executable
+        while True:
+            try:
+                print(relpath_nodots(exe, sys.prefix))
+                break
+            except ValueError:
+                tried.append(exe)
+                if os.path.islink(exe):
+                    exe = os.path.join(os.path.dirname(exe), os.readlink(exe))
+                    continue
+                else:
+                    print("Could not find a relative path to sys.executable under sys.prefix", file=sys.stderr)
+                    for e in tried:
+                        print("tried:", e, file=sys.stderr)
+                    print("sys.prefix:", sys.prefix, file=sys.stderr)
+                    sys.exit(1)
+
+    else:
+        parser.error(f"unknown variable {args.variable_name}")
+
+if __name__ == '__main__':
+    main()

lldb/source/Plugins/ScriptInterpreter/Python/CMakeLists.txt

@@ -3,6 +3,12 @@ if(NOT LLDB_PYTHON_RELATIVE_PATH)
 endif()
 add_definitions(-DLLDB_PYTHON_RELATIVE_LIBDIR="${LLDB_PYTHON_RELATIVE_PATH}")
 
+if(NOT LLDB_PYTHON_EXE_RELATIVE_PATH)
+  message(FATAL_ERROR "LLDB_PYTHON_EXE_RELATIVE_PATH is not set.")
+endif()
+add_definitions(-DLLDB_PYTHON_EXE_RELATIVE_PATH="${LLDB_PYTHON_EXE_RELATIVE_PATH}")
+
+
 if (LLDB_ENABLE_LIBEDIT)
   list(APPEND LLDB_LIBEDIT_LIBS ${LibEdit_LIBRARIES})
 endif()

lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp

@@ -410,30 +410,31 @@ FileSpec ScriptInterpreterPython::GetPythonDir() {
   return g_spec;
 }
 
+static const char GetInterpreterInfoScript[] = R"(
+import os
+import sys
+
+def main(lldb_python_dir, python_exe_relative_path):
+  info = {
+    "lldb-pythonpath": lldb_python_dir,
+    "language": "python",
+    "prefix": sys.prefix,
+    "executable": os.path.join(sys.prefix, python_exe_relative_path)
+  }
+  return info
+)";
+
+static const char python_exe_relative_path[] = LLDB_PYTHON_EXE_RELATIVE_PATH;
+
 StructuredData::DictionarySP ScriptInterpreterPython::GetInterpreterInfo() {
   GIL gil;
   FileSpec python_dir_spec = GetPythonDir();
   if (!python_dir_spec)
     return nullptr;
-  PythonString python_dir(python_dir_spec.GetPath());
-  PythonDictionary info(PyInitialValue::Empty);
-  llvm::Error error = info.SetItem("lldb-pythonpath", python_dir);
-  if (error)
-    return nullptr;
-  static const char script[] = R"(
-def main(info):
-  import sys
-  import os
-  name = 'python' + str(sys.version_info.major)
-  info.update({
-    "language": "python",
-    "prefix": sys.prefix,
-    "executable": os.path.join(sys.prefix, "bin", name),
-  })
-  return info
-)";
-  PythonScript get_info(script);
-  auto info_json = unwrapIgnoringErrors(As<PythonDictionary>(get_info(info)));
+  PythonScript get_info(GetInterpreterInfoScript);
+  auto info_json = unwrapIgnoringErrors(
+      As<PythonDictionary>(get_info(PythonString(python_dir_spec.GetPath()),
+                                    PythonString(python_exe_relative_path))));
   if (!info_json)
     return nullptr;
   return info_json.CreateStructuredDictionary();

lldb/test/API/functionalities/paths/TestPaths.py

@@ -51,8 +51,6 @@ class TestPaths(TestBase):
         stream = lldb.SBStream()
         self.assertTrue(info_sd.GetAsJSON(stream).Success())
         info = json.loads(stream.GetData())
-        if os.name == 'nt': #FIXME
-            return
         prefix = info['prefix']
         self.assertEqual(os.path.realpath(sys.prefix), os.path.realpath(prefix))
         self.assertEqual(