feat(diagnostic): add `suffix` option to `open_float()` (#21130)

Closes #18687

This introduces a `suffix` option to `vim.diagnostic.open_float()` (and
consequently `vim.diagnostic.config()`) that appends some text to each
diagnostic in the float.

It accepts the same types as `prefix`. For multiline diagnostics, the suffix is
only appended to the last line. By default, the suffix will render the
diagnostic error code, if any.

1 files changed, 55 insertions, 9 deletions

diff --git a/test/functional/lua/diagnostic_spec.lua b/test/functional/lua/diagnostic_spec.lua
index 116a541358..816b359725 100644
--- a/test/functional/lua/diagnostic_spec.lua
+++ b/test/functional/lua/diagnostic_spec.lua
@@ -16,7 +16,7 @@ describe('vim.diagnostic', function()
     exec_lua [[
       require('vim.diagnostic')
 
-      function make_diagnostic(msg, x1, y1, x2, y2, severity, source)
+      function make_diagnostic(msg, x1, y1, x2, y2, severity, source, code)
         return {
           lnum = x1,
           col = y1,
@@ -25,23 +25,24 @@ describe('vim.diagnostic', function()
           message = msg,
           severity = severity,
           source = source,
+          code = code,
         }
       end
 
-      function make_error(msg, x1, y1, x2, y2, source)
-        return make_diagnostic(msg, x1, y1, x2, y2, vim.diagnostic.severity.ERROR, source)
+      function make_error(msg, x1, y1, x2, y2, source, code)
+        return make_diagnostic(msg, x1, y1, x2, y2, vim.diagnostic.severity.ERROR, source, code)
       end
 
-      function make_warning(msg, x1, y1, x2, y2, source)
-        return make_diagnostic(msg, x1, y1, x2, y2, vim.diagnostic.severity.WARN, source)
+      function make_warning(msg, x1, y1, x2, y2, source, code)
+        return make_diagnostic(msg, x1, y1, x2, y2, vim.diagnostic.severity.WARN, source, code)
       end
 
-      function make_info(msg, x1, y1, x2, y2, source)
-        return make_diagnostic(msg, x1, y1, x2, y2, vim.diagnostic.severity.INFO, source)
+      function make_info(msg, x1, y1, x2, y2, source, code)
+        return make_diagnostic(msg, x1, y1, x2, y2, vim.diagnostic.severity.INFO, source, code)
       end
 
-      function make_hint(msg, x1, y1, x2, y2, source)
-        return make_diagnostic(msg, x1, y1, x2, y2, vim.diagnostic.severity.HINT, source)
+      function make_hint(msg, x1, y1, x2, y2, source, code)
+        return make_diagnostic(msg, x1, y1, x2, y2, vim.diagnostic.severity.HINT, source, code)
       end
 
       function count_diagnostics(bufnr, severity, namespace)
@@ -1780,6 +1781,51 @@ end)
         pcall_err(exec_lua, [[ vim.diagnostic.open_float({ prefix = 42 }) ]]))
     end)
 
+    it('can add a suffix to diagnostics', function()
+      -- Default is to render the diagnostic error code
+      eq({'1. Syntax error [code-x]', '2. Some warning [code-y]'}, exec_lua [[
+        local diagnostics = {
+          make_error("Syntax error", 0, 1, 0, 3, nil, "code-x"),
+          make_warning("Some warning", 1, 1, 1, 3, nil, "code-y"),
+        }
+        vim.api.nvim_win_set_buf(0, diagnostic_bufnr)
+        vim.diagnostic.set(diagnostic_ns, diagnostic_bufnr, diagnostics)
+        local float_bufnr, winnr = vim.diagnostic.open_float({header = false, scope = "buffer"})
+        local lines = vim.api.nvim_buf_get_lines(float_bufnr, 0, -1, false)
+        vim.api.nvim_win_close(winnr, true)
+        return lines
+      ]])
+
+      eq({'1. Syntax error', '2. Some warning'}, exec_lua [[
+        local diagnostics = {
+          make_error("Syntax error", 0, 1, 0, 3, nil, "code-x"),
+          make_warning("Some warning", 1, 1, 1, 3, nil, "code-y"),
+        }
+        vim.api.nvim_win_set_buf(0, diagnostic_bufnr)
+        vim.diagnostic.set(diagnostic_ns, diagnostic_bufnr, diagnostics)
+        local float_bufnr, winnr = vim.diagnostic.open_float({header = false, scope = "buffer", suffix = ""})
+        local lines = vim.api.nvim_buf_get_lines(float_bufnr, 0, -1, false)
+        vim.api.nvim_win_close(winnr, true)
+        return lines
+      ]])
+
+      -- Suffix is rendered on the last line of a multiline diagnostic
+      eq({'1. Syntax error', '   More context [code-x]'}, exec_lua [[
+        local diagnostics = {
+          make_error("Syntax error\nMore context", 0, 1, 0, 3, nil, "code-x"),
+        }
+        vim.api.nvim_win_set_buf(0, diagnostic_bufnr)
+        vim.diagnostic.set(diagnostic_ns, diagnostic_bufnr, diagnostics)
+        local float_bufnr, winnr = vim.diagnostic.open_float({header = false, scope = "buffer"})
+        local lines = vim.api.nvim_buf_get_lines(float_bufnr, 0, -1, false)
+        vim.api.nvim_win_close(winnr, true)
+        return lines
+      ]])
+
+      eq(".../diagnostic.lua:0: suffix: expected string|table|function, got number",
+        pcall_err(exec_lua, [[ vim.diagnostic.open_float({ suffix = 42 }) ]]))
+    end)
+
     it('works with the old signature', function()
       eq({'1. Syntax error'}, exec_lua [[
         local diagnostics = {