[lldb][windows] print an error if python.dll is not in the DLL search path (llvm#164893)

This is a follow up to llvm#162509.

Using the `SearchPathW` API, we can ensure that the correct version of
Python is installed before `liblldb` is loaded (and `python.dll`
subsequently). If it's not, we try to add it to the search path with the
methods introduced in llvm#162509.
If that fails or if that method is `#ifdef`'d out, we print an error
which will appear before lldb crashes due to the missing dll.

Before llvm#162509, when invoked
from Powershell, lldb would silently crash (no error message/crash
report). After llvm#162509, it
crashes without any indications that the root cause is the missing
python.dll. With this patch, we print the error before crashing.

Author: charles-zablit

lldb/CMakeLists.txt

@@ -87,6 +87,12 @@ if (LLDB_ENABLE_PYTHON)
       set(LLDB_PYTHON_EXT_SUFFIX "_d${LLDB_PYTHON_EXT_SUFFIX}")
     endif()
   endif()
+  if(TARGET Python3::Python)
+    get_target_property(_Python3_LIB_PATH Python3::Python IMPORTED_LIBRARY_LOCATION)
+    if(_Python3_LIB_PATH)
+      get_filename_component(LLDB_PYTHON_RUNTIME_LIBRARY_FILENAME "${_Python3_LIB_PATH}" NAME)
+    endif()
+  endif()
 endif ()
 
 if (LLDB_ENABLE_LUA)

lldb/tools/driver/CMakeLists.txt

@@ -37,6 +37,9 @@ add_dependencies(lldb
 if(DEFINED LLDB_PYTHON_DLL_RELATIVE_PATH)
   target_compile_definitions(lldb PRIVATE LLDB_PYTHON_DLL_RELATIVE_PATH="${LLDB_PYTHON_DLL_RELATIVE_PATH}")
 endif()
+if(DEFINED LLDB_PYTHON_RUNTIME_LIBRARY_FILENAME)
+  target_compile_definitions(lldb PRIVATE LLDB_PYTHON_RUNTIME_LIBRARY_FILENAME="${LLDB_PYTHON_RUNTIME_LIBRARY_FILENAME}")
+endif()
 
 if(LLDB_BUILD_FRAMEWORK)
   # In the build-tree, we know the exact path to the framework directory.

lldb/tools/driver/Driver.cpp

@@ -433,7 +433,8 @@ SBError Driver::ProcessArgs(const opt::InputArgList &args, bool &exiting) {
   return error;
 }
 
-#if defined(_WIN32) && defined(LLDB_PYTHON_DLL_RELATIVE_PATH)
+#ifdef _WIN32
+#ifdef LLDB_PYTHON_DLL_RELATIVE_PATH
 /// Returns the full path to the lldb.exe executable.
 inline std::wstring GetPathToExecutableW() {
   // Iterate until we reach the Windows API maximum path length (32,767).
@@ -447,30 +448,73 @@ inline std::wstring GetPathToExecutableW() {
   return L"";
 }
 
-/// Resolve the full path of the directory defined by
+/// \brief Resolve the full path of the directory defined by
 /// LLDB_PYTHON_DLL_RELATIVE_PATH. If it exists, add it to the list of DLL
 /// search directories.
-void AddPythonDLLToSearchPath() {
+/// \return `true` if the library was added to the search path.
+/// `false` otherwise.
+bool AddPythonDLLToSearchPath() {
   std::wstring modulePath = GetPathToExecutableW();
-  if (modulePath.empty()) {
-    llvm::errs() << "error: unable to find python.dll." << '\n';
-    return;
-  }
+  if (modulePath.empty())
+    return false;
 
   SmallVector<char, MAX_PATH> utf8Path;
   if (sys::windows::UTF16ToUTF8(modulePath.c_str(), modulePath.length(),
                                 utf8Path))
-    return;
+    return false;
   sys::path::remove_filename(utf8Path);
   sys::path::append(utf8Path, LLDB_PYTHON_DLL_RELATIVE_PATH);
   sys::fs::make_absolute(utf8Path);
 
   SmallVector<wchar_t, 1> widePath;
   if (sys::windows::widenPath(utf8Path.data(), widePath))
-    return;
+    return false;
 
   if (sys::fs::exists(utf8Path))
-    SetDllDirectoryW(widePath.data());
+    return SetDllDirectoryW(widePath.data());
+  return false;
+}
+#endif
+
+#ifdef LLDB_PYTHON_RUNTIME_LIBRARY_FILENAME
+/// Returns whether `python3x.dll` is in the DLL search path.
+bool IsPythonDLLInPath() {
+#define WIDEN2(x) L##x
+#define WIDEN(x) WIDEN2(x)
+  WCHAR foundPath[MAX_PATH];
+  DWORD result =
+      SearchPathW(nullptr, WIDEN(LLDB_PYTHON_RUNTIME_LIBRARY_FILENAME), nullptr,
+                  MAX_PATH, foundPath, nullptr);
+#undef WIDEN2
+#undef WIDEN
+
+  return result > 0;
+}
+#endif
+
+/// Try to setup the DLL search path for the Python Runtime Library
+/// (python3xx.dll).
+///
+/// If `LLDB_PYTHON_RUNTIME_LIBRARY_FILENAME` is set, we first check if
+/// python3xx.dll is in the search path. If it's not, we try to add it and
+/// check for it a second time.
+/// If only `LLDB_PYTHON_DLL_RELATIVE_PATH` is set, we try to add python3xx.dll
+/// to the search path python.dll is already in the search path or not.
+void SetupPythonRuntimeLibrary() {
+#ifdef LLDB_PYTHON_RUNTIME_LIBRARY_FILENAME
+  if (IsPythonDLLInPath())
+    return;
+#ifdef LLDB_PYTHON_DLL_RELATIVE_PATH
+  if (AddPythonDLLToSearchPath() && IsPythonDLLInPath())
+    return;
+#endif
+  llvm::errs() << "error: unable to find '"
+               << LLDB_PYTHON_RUNTIME_LIBRARY_FILENAME << "'.\n";
+  return;
+#elif defined(LLDB_PYTHON_DLL_RELATIVE_PATH)
+  if (!AddPythonDLLToSearchPath())
+    llvm::errs() << "error: unable to find the Python runtime library.\n";
+#endif
 }
 #endif
 
@@ -776,8 +820,8 @@ int main(int argc, char const *argv[]) {
                         "~/Library/Logs/DiagnosticReports/.\n");
 #endif
 
-#if defined(_WIN32) && defined(LLDB_PYTHON_DLL_RELATIVE_PATH)
-  AddPythonDLLToSearchPath();
+#ifdef _WIN32
+  SetupPythonRuntimeLibrary();
 #endif
 
   // Parse arguments.