Diagnostics not found for buffer on Windows #343
Description
It seems that buffer-file-name on Windows makes the leading drive letter lowercase (c:/foo), while diagnostics reported by servers could have the drive letter uppercase (file:///C:/foo). Since equal is used to test equality inside the hash for diagnostics in lsp-mode, diagnostics won't be found when looking for buffer-file-name in the diagnostics hash. Since this is Windows-specific behavior and ignoring case would be an issue on operating systems where case-sensitivity is an issue, I think this should be an extra case to handle specially when trying to find diagnostics for a buffer.