feat(diagnostic): add format option to setloclist/setqflist (#33977)

runtime/doc/diagnostic.txt

@@ -923,6 +923,11 @@ setloclist({opts})                               *vim.diagnostic.setloclist()*
                   "Diagnostics".
                 • {severity}? (`vim.diagnostic.SeverityFilter`) See
                   |diagnostic-severity|.
+                • {format}? (`fun(diagnostic:vim.Diagnostic): string?`) A
+                  function that takes a diagnostic as input and returns a
+                  string or nil. If the return value is nil, the diagnostic is
+                  not displayed in the location list. Else the output text is
+                  used to display the diagnostic.
 
 setqflist({opts})                                 *vim.diagnostic.setqflist()*
     Add all diagnostics to the quickfix list.
@@ -938,6 +943,11 @@ setqflist({opts})                                 *vim.diagnostic.setqflist()*
                   title, it's updated. If not, a new quickfix list is created.
                 • {severity}? (`vim.diagnostic.SeverityFilter`) See
                   |diagnostic-severity|.
+                • {format}? (`fun(diagnostic:vim.Diagnostic): string?`) A
+                  function that takes a diagnostic as input and returns a
+                  string or nil. If the return value is nil, the diagnostic is
+                  not displayed in the quickfix list. Else the output text is
+                  used to display the diagnostic.
 
                                                        *vim.diagnostic.show()*
 show({namespace}, {bufnr}, {diagnostics}, {opts})

runtime/doc/news.txt

@@ -126,7 +126,9 @@ DEFAULTS
 
 DIAGNOSTICS
 
-• todo
+• |vim.diagnostic.setloclist()| and |vim.diagnostic.setqflist()| now support a
+  `format` function to modify (or filter) diagnostics before being set in the
+  location/quickfix list.
 
 EDITOR
 

runtime/lua/vim/diagnostic.lua

@@ -909,6 +909,9 @@ local function set_list(loclist, opts)
   -- Don't clamp line numbers since the quickfix list can already handle line
   -- numbers beyond the end of the buffer
   local diagnostics = get_diagnostics(bufnr, opts --[[@as vim.diagnostic.GetOpts]], false)
+  if opts.format then
+    diagnostics = reformat_diagnostics(opts.format, diagnostics)
+  end
   local items = M.toqflist(diagnostics)
   local qf_id = nil
   if loclist then
@@ -2361,6 +2364,11 @@ end
 ---
 --- See |diagnostic-severity|.
 --- @field severity? vim.diagnostic.SeverityFilter
+---
+--- A function that takes a diagnostic as input and returns a string or nil.
+--- If the return value is nil, the diagnostic is not displayed in the quickfix list.
+--- Else the output text is used to display the diagnostic.
+--- @field format? fun(diagnostic:vim.Diagnostic): string?
 
 --- Add all diagnostics to the quickfix list.
 ---
@@ -2389,6 +2397,11 @@ end
 ---
 --- See |diagnostic-severity|.
 --- @field severity? vim.diagnostic.SeverityFilter
+---
+--- A function that takes a diagnostic as input and returns a string or nil.
+--- If the return value is nil, the diagnostic is not displayed in the location list.
+--- Else the output text is used to display the diagnostic.
+--- @field format? fun(diagnostic:vim.Diagnostic): string?
 
 --- Add buffer diagnostics to the location list.
 ---

test/functional/lua/diagnostic_spec.lua

@@ -3448,6 +3448,32 @@ describe('vim.diagnostic', function()
       eq(1, #loc_list)
       eq('Error here!', loc_list[1].text)
     end)
+
+    it('supports format function', function()
+      local loc_list = exec_lua(function()
+        vim.api.nvim_win_set_buf(0, _G.diagnostic_bufnr)
+
+        vim.diagnostic.set(_G.diagnostic_ns, _G.diagnostic_bufnr, {
+          _G.make_error('Error', 1, 1, 1, 1, 'foo_ls'),
+          _G.make_error('Another error', 2, 2, 2, 2, 'foo_ls'),
+        })
+
+        vim.diagnostic.setloclist({
+          format = function(diagnostic)
+            if diagnostic.lnum > 1 then
+              return nil
+            end
+
+            return string.format('%s: %s', diagnostic.source, diagnostic.message)
+          end,
+        })
+
+        return vim.fn.getloclist(0)
+      end)
+
+      eq(1, #loc_list)
+      eq('foo_ls: Error', loc_list[1].text)
+    end)
   end)
 
   describe('setqflist()', function()
@@ -3516,6 +3542,32 @@ describe('vim.diagnostic', function()
 
       neq(0, qf_winid)
     end)
+
+    it('supports format function', function()
+      local qf_list = exec_lua(function()
+        vim.api.nvim_win_set_buf(0, _G.diagnostic_bufnr)
+
+        vim.diagnostic.set(_G.diagnostic_ns, _G.diagnostic_bufnr, {
+          _G.make_error('Error', 1, 1, 1, 1, 'foo_ls'),
+          _G.make_error('Another error', 2, 2, 2, 2, 'foo_ls'),
+        })
+
+        vim.diagnostic.setqflist({
+          format = function(diagnostic)
+            if diagnostic.lnum > 1 then
+              return nil
+            end
+
+            return string.format('%s: %s', diagnostic.source, diagnostic.message)
+          end,
+        })
+
+        return vim.fn.getqflist()
+      end)
+
+      eq(1, #qf_list)
+      eq('foo_ls: Error', qf_list[1].text)
+    end)
   end)
 
   describe('match()', function()