In the LSP diagnostics in ST3 I'm seeing "Could not build a preamble for file", but there's no diagnostics reported, even with --log-level debug and SOURCEKIT_LOGGING 3. How can I find out why clangd (which is the one reporting this error as far as I can tell) is failing?
You may get more information from clangd if you increase its own logging level as well. The clangd option is
Which you can forward through sourcekit-lsp with
-Xclangd --log -Xclangd verbose