fix diagnostic highlighting and message

Some language servers report diagnostics with empty ranges, start and
end are at the same line and character, which currently results in
no highlighting at all.

Since the end of a LSP range is exclusive we always subtract 1 from
it which results in invalid ranges when the server has sent an empty one.
Introduce a check to fix this special case.

`textDocument/publishDiagnostics` doesn't always have a `code` field,
resulting in `diagnostic.code` being nil and so it is replaced with
`diagnostic` in those cases.

1 files changed, 13 insertions, 2 deletions

diff --git a/init.lua b/init.lua
index 222bd49..c7be0f3 100644
--- a/init.lua
+++ b/init.lua
@@ -575,9 +575,19 @@ local function lspc_highlight_diagnostics(win, diagnostics, style)
   for _, diagnostic in ipairs(diagnostics) do
     if lspc.highlight_diagnostics == 'range' then
       local range = diagnostic.vis_range
+
+      -- LSP ranges use an exclusive finish
+      local finish = range.finish - 1
+
+      -- In some instances the range defined by the diagnostic starts
+      -- and ends at the same position. Highlight the exact position.
+      if range.finish == range.start then
+        finish = range.finish
+      end
+
       -- make sure to highlight only ranges which actually contain the diagnostic
       if diagnostic.content == win.file:content(range) then
-        win:style(style, range.start, range.finish - 1)
+        win:style(style, range.start, finish)
       end
 
     elseif lspc.highlight_diagnostics == 'line' then
@@ -1339,7 +1349,8 @@ local function lspc_show_diagnostic(ls, win, line)
   for _, diagnostic in ipairs(diagnostics_to_show) do
     diagnostics_msg = diagnostics_msg ..
                           string.format(diagnostics_fmt, diagnostic.start.line,
-                                        diagnostic.start.col, diagnostic.code, diagnostic.message)
+                                        diagnostic.start.col, diagnostic.code or 'diagnostic',
+                                        diagnostic.message)
   end
 
   if diagnostics_msg ~= '' then