feat(quickfix): support -q - to read 'errorfile' from stdin (#27303)

Note that this only works when stdin is a pipe.

runtime/doc/news.txt

@@ -409,6 +409,8 @@ The following changes to existing APIs or features add new behavior.
 • |nvim_open_win()| and |nvim_win_set_config()| now support opening normal (split)
   windows, and moving floating windows into split windows.
 
+• 'errorfile' (|-q|) accepts `-` as an alias for stdin.
+
 ==============================================================================
 REMOVED FEATURES                                                 *news-removed*
 

src/nvim/main.c

@@ -1016,6 +1016,7 @@ static bool edit_stdin(mparm_T *parmp)
                   && !(embedded_mode && stdin_fd <= 0)
                   && (!exmode_active || parmp->input_istext)
                   && !stdin_isatty
+                  && parmp->edit_type <= EDIT_STDIN
                   && parmp->scriptin == NULL;  // `-s -` was not given.
   return parmp->had_stdin_file || implicit;
 }

src/nvim/os/fileio.c

@@ -25,10 +25,6 @@
 #include "nvim/rbuffer_defs.h"
 #include "nvim/types_defs.h"
 
-#ifdef MSWIN
-# include "nvim/os/os_win_console.h"
-#endif
-
 #ifdef HAVE_SYS_UIO_H
 # include <sys/uio.h>
 #endif
@@ -179,17 +175,7 @@ FileDescriptor *file_open_stdin(void)
   FUNC_ATTR_MALLOC FUNC_ATTR_WARN_UNUSED_RESULT
 {
   int error;
-  int stdin_dup_fd;
+  FileDescriptor *const stdin_dup = file_open_fd_new(&error, os_open_stdin_fd(),
-  if (stdin_fd > 0) {
-    stdin_dup_fd = stdin_fd;
-  } else {
-    stdin_dup_fd = os_dup(STDIN_FILENO);
-#ifdef MSWIN
-    // Replace the original stdin with the console input handle.
-    os_replace_stdin_to_conin();
-#endif
-  }
-  FileDescriptor *const stdin_dup = file_open_fd_new(&error, stdin_dup_fd,
                                                      kFileReadOnly|kFileNonBlocking);
   assert(stdin_dup != NULL);
   if (error != 0) {

src/nvim/os/fs.c

@@ -55,6 +55,7 @@
 #ifdef MSWIN
 # include "nvim/mbyte.h"
 # include "nvim/option.h"
+# include "nvim/os/os_win_console.h"
 # include "nvim/strings.h"
 #endif
 
@@ -541,6 +542,22 @@ os_dup_dup:
   return ret;
 }
 
+/// Open the file descriptor for stdin.
+int os_open_stdin_fd(void)
+{
+  int stdin_dup_fd;
+  if (stdin_fd > 0) {
+    stdin_dup_fd = stdin_fd;
+  } else {
+    stdin_dup_fd = os_dup(STDIN_FILENO);
+#ifdef MSWIN
+    // Replace the original stdin with the console input handle.
+    os_replace_stdin_to_conin();
+#endif
+  }
+  return stdin_dup_fd;
+}
+
 /// Read from a file
 ///
 /// Handles EINTR and ENOMEM, but not other errors.

src/nvim/quickfix.c

@@ -1065,7 +1065,9 @@ static int qf_setup_state(qfstate_T *pstate, char *restrict enc, const char *res
   }
 
   if (efile != NULL
-      && (pstate->fd = os_fopen(efile, "r")) == NULL) {
+      && (pstate->fd = (strequal(efile, "-")
+                        ? fdopen(os_open_stdin_fd(), "r")
+                        : os_fopen(efile, "r"))) == NULL) {
     semsg(_(e_openerrf), efile);
     return FAIL;
   }

test/functional/ui/embed_spec.lua

@@ -3,6 +3,7 @@ local uv = vim.uv
 local helpers = require('test.functional.helpers')(after_each)
 local Screen = require('test.functional.ui.screen')
 
+local api = helpers.api
 local feed = helpers.feed
 local eq = helpers.eq
 local neq = helpers.neq
@@ -11,6 +12,7 @@ local ok = helpers.ok
 local fn = helpers.fn
 local nvim_prog = helpers.nvim_prog
 local retry = helpers.retry
+local write_file = helpers.write_file
 
 local function test_embed(ext_linegrid)
   local screen
@@ -113,26 +115,83 @@ describe('--embed UI', function()
       writer:close()
     end)
 
-    screen:expect {
+    screen:expect [[
-      grid = [[
       ^hello nvim                              |
       from external input                     |
       {1:~                                       }|*5
                                               |
-    ]],
+    ]]
-    }
 
     -- stdin (rpc input) still works
     feed 'o'
-    screen:expect {
+    screen:expect [[
-      grid = [[
       hello nvim                              |
       ^                                        |
       from external input                     |
       {1:~                                       }|*4
       {2:-- INSERT --}                            |
-    ]],
+    ]]
+  end)
+
+  it('can pass stdin to -q - #17523', function()
+    write_file(
+      'Xbadfile.c',
+      [[
+      /* some file with an error */
+      main() {
+        functionCall(arg; arg, arg);
+        return 666
+      }
+      ]]
+    )
+    finally(function()
+      os.remove('Xbadfile.c')
+    end)
+
+    local pipe = assert(uv.pipe())
+
+    local writer = assert(uv.new_pipe(false))
+    writer:open(pipe.write)
+
+    clear { args_rm = { '--headless' }, args = { '-q', '-' }, io_extra = pipe.read }
+
+    -- attach immediately after startup, for early UI
+    local screen = Screen.new(60, 8)
+    screen.rpc_async = true -- Avoid hanging. #24888
+    screen:attach { stdin_fd = 3 }
+    screen:set_default_attr_ids {
+      [1] = { bold = true, foreground = Screen.colors.Blue1 },
+      [2] = { bold = true },
     }
+
+    writer:write [[Xbadfile.c:4:12: error: expected ';' before '}' token]]
+    writer:shutdown(function()
+      writer:close()
+    end)
+
+    screen:expect [[
+      /* some file with an error */                               |
+      main() {                                                    |
+        functionCall(arg; arg, arg);                              |
+        return 66^6                                                |
+      }                                                           |
+      {1:~                                                           }|*2
+      (1 of 1): error: expected ';' before '}' token              |
+    ]]
+
+    -- stdin (rpc input) still works
+    feed 'A'
+    screen:expect [[
+      /* some file with an error */                               |
+      main() {                                                    |
+        functionCall(arg; arg, arg);                              |
+        return 666^                                                |
+      }                                                           |
+      {1:~                                                           }|*2
+      {2:-- INSERT --}                                                |
+    ]]
+
+    eq('-', api.nvim_get_option_value('errorfile', {}))
   end)
 
   it('only sets background colors once even if overridden', function()