[lldb] Fix that log enable's -f parameter causes LLDB to crash when it can't open the log file

[teemperor]

Summary

We didn't do anything with the llvm::Error we get from Open, so when we end up in the
error case we just crash due to the llvm::Error sanity check. Also add the missing newline
behind the error message so it no longer messes with the next (lldb) prompt.

[max-kudr]

@teemperor LLDB Windows buildbot is failing after last commit: Build 18298.

Please revert or fix.

[teemperor]

In D85970#2221899, @max-kudr wrote:

@teemperor LLDB Windows buildbot is failing after last commit: Build 18298.

Please revert or fix.

Already fixed in c6cc566c8a95bb39c65f7b39649e804809fc8701, next build should be green again.

lldb/source/Core/Debugger.cpp

if (pos != m_log_streams.end())
       log_stream_sp = pos->second.lock();
     if (!log_stream_sp) {
       File::OpenOptions flags =
           File::eOpenOptionWrite | File::eOpenOptionCanCreate;
       if (log_options & LLDB_LOG_OPTION_APPEND)
         flags |= File::eOpenOptionAppend;
       else
         flags |= File::eOpenOptionTruncate;
-      auto file = FileSystem::Instance().Open(
+      llvm::Expected<FileUP> file = FileSystem::Instance().Open(
           FileSpec(log_file), flags, lldb::eFilePermissionsFileDefault, false);
       if (!file) {
-        // FIXME: This gets garbled when called from the log command.
-        error_stream << "Unable to open log file: " << log_file;
+        error_stream << "Unable to open log file '" << log_file
+                     << "': " << llvm::toString(file.takeError()) << "\n";
         return false;
       }
 
       log_stream_sp = std::make_shared<llvm::raw_fd_ostream>(
           (*file)->GetDescriptor(), should_close, unbuffered);
       m_log_streams[log_file] = log_stream_sp;
     }
   }

lldb/test/API/commands/log/invalid-args/TestInvalidArgsLog.py

class InvalidArgsLogTestCase(TestBase):
     def test_enable_empty(self):
         self.expect("log enable", error=True,
                     substrs=["error: log enable takes a log channel and one or more log types."])
 
     @no_debug_info_test
     def test_disable_empty(self):
         self.expect("log disable", error=True,
                     substrs=["error: log disable takes a log channel and one or more log types."])
+
+    @no_debug_info_test
+    def test_enable_empty(self):
+        self.expect("log enable lldb all -f this/is/not/a/valid/path", error=True,
+                    substrs=["Unable to open log file 'this/is/not/a/valid/path': No such file or directory\n"])