fix(diagnostic): clamp line numbers in display layer (#15729)

Some parts of LSP need to use cached diagnostics as sent from the LSP
server unmodified. Rather than fixing invalid line numbers when
diagnostics are first set, fix them when they are displayed to the user
(e.g. in show() or one of the get_next/get_prev family of functions).

runtime/lua/vim/diagnostic.lua

@@ -222,26 +222,14 @@ local function diagnostic_lines(diagnostics)
 end
 
 ---@private
-local function set_diagnostic_cache(namespace, diagnostics, bufnr)
+local function set_diagnostic_cache(namespace, bufnr, diagnostics)
-  local buf_line_count = vim.api.nvim_buf_line_count(bufnr)
   for _, diagnostic in ipairs(diagnostics) do
-    if diagnostic.severity == nil then
+    diagnostic.severity = diagnostic.severity and to_severity(diagnostic.severity) or M.severity.ERROR
-      diagnostic.severity = M.severity.ERROR
+    diagnostic.end_lnum = diagnostic.end_lnum or diagnostic.lnum
-    end
+    diagnostic.end_col = diagnostic.end_col or diagnostic.col
-
     diagnostic.namespace = namespace
     diagnostic.bufnr = bufnr
-
-    if buf_line_count > 0 then
-      diagnostic.lnum = math.max(math.min(
-        diagnostic.lnum, buf_line_count - 1
-      ), 0)
-      diagnostic.end_lnum = math.max(math.min(
-        diagnostic.end_lnum, buf_line_count - 1
-      ), 0)
-    end
   end
-
   diagnostic_cache[bufnr][namespace] = diagnostics
 end
 
@@ -403,13 +391,28 @@ local function set_list(loclist, opts)
   end
 end
 
+---@private
+local function clamp_line_numbers(bufnr, diagnostics)
+  local buf_line_count = vim.api.nvim_buf_line_count(bufnr)
+  if buf_line_count == 0 then
+    return
+  end
+
+  for _, diagnostic in ipairs(diagnostics) do
+    diagnostic.lnum = math.max(math.min(diagnostic.lnum, buf_line_count - 1), 0)
+    diagnostic.end_lnum = math.max(math.min(diagnostic.end_lnum, buf_line_count - 1), 0)
+  end
+end
+
 ---@private
 local function next_diagnostic(position, search_forward, bufnr, opts, namespace)
   position[1] = position[1] - 1
-  bufnr = bufnr or vim.api.nvim_get_current_buf()
+  bufnr = get_bufnr(bufnr)
   local wrap = vim.F.if_nil(opts.wrap, true)
   local line_count = vim.api.nvim_buf_line_count(bufnr)
-  opts.namespace = namespace
+  local diagnostics = M.get(bufnr, vim.tbl_extend("keep", opts, {namespace = namespace}))
+  clamp_line_numbers(bufnr, diagnostics)
+  local line_diagnostics = diagnostic_lines(diagnostics)
   for i = 0, line_count do
     local offset = i * (search_forward and 1 or -1)
     local lnum = position[1] + offset
@@ -419,9 +422,7 @@ local function next_diagnostic(position, search_forward, bufnr, opts, namespace)
       end
       lnum = (lnum + line_count) % line_count
     end
-    opts.lnum = lnum
+    if line_diagnostics[lnum] and not vim.tbl_isempty(line_diagnostics[lnum]) then
-    local line_diagnostics = M.get(bufnr, opts)
-    if line_diagnostics and not vim.tbl_isempty(line_diagnostics) then
       local sort_diagnostics, is_next
       if search_forward then
         sort_diagnostics = function(a, b) return a.col < b.col end
@@ -430,15 +431,15 @@ local function next_diagnostic(position, search_forward, bufnr, opts, namespace)
         sort_diagnostics = function(a, b) return a.col > b.col end
         is_next = function(diagnostic) return diagnostic.col < position[2] end
       end
-      table.sort(line_diagnostics, sort_diagnostics)
+      table.sort(line_diagnostics[lnum], sort_diagnostics)
       if i == 0 then
-        for _, v in pairs(line_diagnostics) do
+        for _, v in pairs(line_diagnostics[lnum]) do
           if is_next(v) then
             return v
           end
         end
       else
-        return line_diagnostics[1]
+        return line_diagnostics[lnum][1]
       end
     end
   end
@@ -466,7 +467,6 @@ local function diagnostic_move_pos(opts, pos)
   end
 end
 
-
 -- }}}
 
 -- Public API {{{
@@ -566,7 +566,7 @@ function M.set(namespace, bufnr, diagnostics, opts)
     })
   end
 
-  set_diagnostic_cache(namespace, diagnostics, bufnr)
+  set_diagnostic_cache(namespace, bufnr, diagnostics)
 
   if vim.api.nvim_buf_is_loaded(bufnr) then
     M.show(namespace, bufnr, diagnostics, opts)
@@ -983,6 +983,8 @@ function M.show(namespace, bufnr, diagnostics, opts)
     end
   end
 
+  clamp_line_numbers(bufnr, diagnostics)
+
   if opts.underline then
     M._set_underline(namespace, bufnr, diagnostics, opts.underline)
   end
@@ -1029,7 +1031,9 @@ function M.show_position_diagnostics(opts, bufnr, position)
     position[2] >= diag.col and
     (position[2] <= diag.end_col or position[1] < diag.end_lnum)
   end
-  local position_diagnostics = vim.tbl_filter(match_position_predicate, M.get(bufnr, opts))
+  local diagnostics = M.get(bufnr, opts)
+  clamp_line_numbers(bufnr, diagnostics)
+  local position_diagnostics = vim.tbl_filter(match_position_predicate, diagnostics)
   table.sort(position_diagnostics, function(a, b) return a.severity < b.severity end)
   return show_diagnostics(opts, position_diagnostics)
 end
@@ -1049,9 +1053,11 @@ function M.show_line_diagnostics(opts, bufnr, lnum)
 
   opts = opts or {}
   opts.focus_id = "line_diagnostics"
-  opts.lnum = lnum or (vim.api.nvim_win_get_cursor(0)[1] - 1)
   bufnr = get_bufnr(bufnr)
-  local line_diagnostics = M.get(bufnr, opts)
+  local diagnostics = M.get(bufnr, opts)
+  clamp_line_numbers(bufnr, diagnostics)
+  lnum = lnum or (vim.api.nvim_win_get_cursor(0)[1] - 1)
+  local line_diagnostics = diagnostic_lines(diagnostics)[lnum]
   return show_diagnostics(opts, line_diagnostics)
 end
 

test/functional/lua/diagnostic_spec.lua

@@ -842,6 +842,18 @@ describe('vim.diagnostic', function()
         return #vim.api.nvim_buf_get_lines(popup_bufnr, 0, -1, false)
       ]])
     end)
+
+    it('clamps diagnostic line numbers within the valid range', function()
+      eq(1, exec_lua [[
+        local diagnostics = {
+          make_error("Syntax error", 6, 0, 6, 0),
+        }
+        vim.api.nvim_win_set_buf(0, diagnostic_bufnr)
+        vim.diagnostic.set(diagnostic_ns, diagnostic_bufnr, diagnostics)
+        local popup_bufnr, winnr = vim.diagnostic.show_line_diagnostics({show_header = false}, diagnostic_bufnr, 5)
+        return #vim.api.nvim_buf_get_lines(popup_bufnr, 0, -1, false)
+      ]])
+    end)
   end)
 
   describe('set_signs()', function()