[lldb] Change the implementation of Status to store an llvm::Error (NFC) (#106774)

(based on a conversation I had with @labath yesterday in
https://github.com/llvm/llvm-project/pull/106442)

Most APIs that currently vend a Status would be better served by
returning llvm::Expected<> instead. If possibles APIs should be
refactored to avoid Status. The only legitimate long-term uses of Status
are objects that need to store an error for a long time (which should be
questioned as a design decision, too).

This patch makes the transition to llvm::Error easier by making the
places that cannot switch to llvm::Error explicit: They are marked with
a call to Status::clone(). Every other API can and should be refactored
to use llvm::Expected. In the end Status should only be used in very few
places.

Whenever an unchecked Error is dropped by Status it logs this to the
verbose API channel.

Implementation notes:

This patch introduces two new kinds of error_category as well as new
llvm::Error types. Here is the mapping of lldb::ErrorType to
llvm::Errors:
```
   (eErrorTypeInvalid)
   eErrorTypeGeneric      llvm::StringError
   eErrorTypePOSIX        llvm::ECError
   eErrorTypeMachKernel   MachKernelError
   eErrorTypeExpression   llvm::ErrorList<ExpressionError>
   eErrorTypeWin32        Win32Error
```

Relanding with built-in cloning support for llvm::ECError, and support
for initializing a Windows error with a NO_ERROR error code.

1 files changed, 19 insertions, 10 deletions

diff --git a/lldb/source/Plugins/ScriptInterpreter/Python/PythonDataObjects.cpp b/lldb/source/Plugins/ScriptInterpreter/Python/PythonDataObjects.cpp
index 24cf3430..90ccd10 100644
--- a/lldb/source/Plugins/ScriptInterpreter/Python/PythonDataObjects.cpp
+++ b/lldb/source/Plugins/ScriptInterpreter/Python/PythonDataObjects.cpp
@@ -1108,9 +1108,10 @@ public:
         py_error = Status::FromError(r.takeError());
     }
     base_error = Base::Close();
+    // Cloning since the wrapped exception may still reference the PyThread.
     if (py_error.Fail())
-      return py_error;
-    return base_error;
+      return py_error.Clone();
+    return base_error.Clone();
   };
 
   PyObject *GetPythonObject() const {
@@ -1196,7 +1197,8 @@ public:
       return Flush();
     auto r = m_py_obj.CallMethod("close");
     if (!r)
-      return Status::FromError(r.takeError());
+      // Cloning since the wrapped exception may still reference the PyThread.
+      return Status::FromError(r.takeError()).Clone();
     return Status();
   }
 
@@ -1204,7 +1206,8 @@ public:
     GIL takeGIL;
     auto r = m_py_obj.CallMethod("flush");
     if (!r)
-      return Status::FromError(r.takeError());
+      // Cloning since the wrapped exception may still reference the PyThread.
+      return Status::FromError(r.takeError()).Clone();
     return Status();
   }
 
@@ -1240,7 +1243,8 @@ public:
     PyObject *pybuffer_p = PyMemoryView_FromMemory(
         const_cast<char *>((const char *)buf), num_bytes, PyBUF_READ);
     if (!pybuffer_p)
-      return Status::FromError(llvm::make_error<PythonException>());
+      // Cloning since the wrapped exception may still reference the PyThread.
+      return Status::FromError(llvm::make_error<PythonException>()).Clone();
     auto pybuffer = Take<PythonObject>(pybuffer_p);
     num_bytes = 0;
     auto bytes_written = As<long long>(m_py_obj.CallMethod("write", pybuffer));
@@ -1260,7 +1264,8 @@ public:
     auto pybuffer_obj =
         m_py_obj.CallMethod("read", (unsigned long long)num_bytes);
     if (!pybuffer_obj)
-      return Status::FromError(pybuffer_obj.takeError());
+      // Cloning since the wrapped exception may still reference the PyThread.
+      return Status::FromError(pybuffer_obj.takeError()).Clone();
     num_bytes = 0;
     if (pybuffer_obj.get().IsNone()) {
       // EOF
@@ -1269,7 +1274,8 @@ public:
     }
     auto pybuffer = PythonBuffer::Create(pybuffer_obj.get());
     if (!pybuffer)
-      return Status::FromError(pybuffer.takeError());
+      // Cloning since the wrapped exception may still reference the PyThread.
+      return Status::FromError(pybuffer.takeError()).Clone();
     memcpy(buf, pybuffer.get().get().buf, pybuffer.get().get().len);
     num_bytes = pybuffer.get().get().len;
     return Status();
@@ -1300,7 +1306,8 @@ public:
     auto bytes_written =
         As<long long>(m_py_obj.CallMethod("write", pystring.get()));
     if (!bytes_written)
-      return Status::FromError(bytes_written.takeError());
+      // Cloning since the wrapped exception may still reference the PyThread.
+      return Status::FromError(bytes_written.takeError()).Clone();
     if (bytes_written.get() < 0)
       return Status::FromErrorString(
           ".write() method returned a negative number!");
@@ -1321,14 +1328,16 @@ public:
     auto pystring = As<PythonString>(
         m_py_obj.CallMethod("read", (unsigned long long)num_chars));
     if (!pystring)
-      return Status::FromError(pystring.takeError());
+      // Cloning since the wrapped exception may still reference the PyThread.
+      return Status::FromError(pystring.takeError()).Clone();
     if (pystring.get().IsNone()) {
       // EOF
       return Status();
     }
     auto stringref = pystring.get().AsUTF8();
     if (!stringref)
-      return Status::FromError(stringref.takeError());
+      // Cloning since the wrapped exception may still reference the PyThread.
+      return Status::FromError(stringref.takeError()).Clone();
     num_bytes = stringref.get().size();
     memcpy(buf, stringref.get().begin(), num_bytes);
     return Status();