commandline --cursor: respect transient command line

We have logic to prevent "commandline --cursor 123" inside "complete
-C" from setting the transient commandline's cursor.

But reading this cursor ("commandline --cursor")
is fine and expected to work by completion scripts.

I don't expect there is a use case for setting the cursor while
computing completions, so let's make that an error for now.
Could revisit that.

Closes #11993

CHANGELOG.rst

@@ -32,6 +32,7 @@ Deprecations and removed features
 Scripting improvements
 ----------------------
 - New :ref:`status language <status-language>` commands allow showing and modifying language settings for fish messages without having to modify environment variables.
+- When using a noninteractive fish instance to compute completions, ``commandline --cursor`` no works as expected instead of throwing an error (:issue:`11993`).
 
 Interactive improvements
 ------------------------

po/de.po

@@ -767,6 +767,10 @@ msgstr "%s: realpath fehlgeschlagen: %s\n"
 msgid "%s: scope can be only one of: universal function global local\n"
 msgstr ""
 
+#, c-format
+msgid "%s: setting cursor while evaluating 'complete --arguments' is not yet supported"
+msgstr ""
+
 #, c-format
 msgid "%s: stdin is closed\n"
 msgstr "%s: stdin ist geschlossen\n"

po/en.po

@@ -765,6 +765,10 @@ msgstr ""
 msgid "%s: scope can be only one of: universal function global local\n"
 msgstr ""
 
+#, c-format
+msgid "%s: setting cursor while evaluating 'complete --arguments' is not yet supported"
+msgstr ""
+
 #, c-format
 msgid "%s: stdin is closed\n"
 msgstr ""

po/fr.po

@@ -896,6 +896,10 @@ msgstr ""
 msgid "%s: scope can be only one of: universal function global local\n"
 msgstr ""
 
+#, c-format
+msgid "%s: setting cursor while evaluating 'complete --arguments' is not yet supported"
+msgstr ""
+
 #, c-format
 msgid "%s: stdin is closed\n"
 msgstr ""

po/pl.po

@@ -761,6 +761,10 @@ msgstr ""
 msgid "%s: scope can be only one of: universal function global local\n"
 msgstr ""
 
+#, c-format
+msgid "%s: setting cursor while evaluating 'complete --arguments' is not yet supported"
+msgstr ""
+
 #, c-format
 msgid "%s: stdin is closed\n"
 msgstr ""

po/pt_BR.po

@@ -766,6 +766,10 @@ msgstr ""
 msgid "%s: scope can be only one of: universal function global local\n"
 msgstr ""
 
+#, c-format
+msgid "%s: setting cursor while evaluating 'complete --arguments' is not yet supported"
+msgstr ""
+
 #, c-format
 msgid "%s: stdin is closed\n"
 msgstr ""

po/sv.po

@@ -762,6 +762,10 @@ msgstr ""
 msgid "%s: scope can be only one of: universal function global local\n"
 msgstr ""
 
+#, c-format
+msgid "%s: setting cursor while evaluating 'complete --arguments' is not yet supported"
+msgstr ""
+
 #, c-format
 msgid "%s: stdin is closed\n"
 msgstr ""

po/zh_CN.po

@@ -788,6 +788,10 @@ msgstr "%s: realpath 失败：%s\n"
 msgid "%s: scope can be only one of: universal function global local\n"
 msgstr "%s: 范围只能是：universal（通用）function（函数）global（全局）local（局域）\n"
 
+#, c-format
+msgid "%s: setting cursor while evaluating 'complete --arguments' is not yet supported"
+msgstr ""
+
 #, c-format
 msgid "%s: stdin is closed\n"
 msgstr "%s: stdin 已关闭\n"

po/zh_TW.po

@@ -761,6 +761,10 @@ msgstr "%s：realpath 失敗：%s\n"
 msgid "%s: scope can be only one of: universal function global local\n"
 msgstr "%s：作用域只能是以下之一：universal、function、global、local\n"
 
+#, c-format
+msgid "%s: setting cursor while evaluating 'complete --arguments' is not yet supported"
+msgstr ""
+
 #, c-format
 msgid "%s: stdin is closed\n"
 msgstr "%s：stdin 已關閉\n"

src/builtins/commandline.rs

@@ -616,8 +616,7 @@ pub fn commandline(parser: &Parser, streams: &mut IoStreams, args: &mut [&wstr])
 
     // At this point we have (nearly) exhausted the options which always operate on the true command
     // line. Now we respect the possibility of a transient command line due to evaluating a wrapped
-    // completion. Don't do this in cursor_mode: it makes no sense to move the cursor based on a
-    // transient commandline.
+    // completion.
     let current_buffer;
     let current_cursor_pos;
     let transient;
@@ -632,7 +631,15 @@ pub fn commandline(parser: &Parser, streams: &mut IoStreams, args: &mut [&wstr])
     } else if let Some(override_buffer) = &override_buffer {
         current_buffer = override_buffer;
         current_cursor_pos = current_buffer.len();
-    } else if parser.libdata().transient_commandline.is_some() && !cursor_mode {
+    } else if parser.libdata().transient_commandline.is_some() {
+        if cursor_mode && positional_args != 0 {
+            streams.err.append(wgettext_fmt!(
+                "%s: setting cursor while evaluating 'complete --arguments' is not yet supported",
+                cmd
+            ));
+            builtin_print_error_trailer(parser, streams.err, cmd);
+            return Err(STATUS_CMD_ERROR);
+        }
         transient = parser.libdata().transient_commandline.clone().unwrap();
         current_buffer = &transient;
         current_cursor_pos = transient.len();

tests/checks/complete.fish

@@ -686,3 +686,8 @@ complete somewrapper3
 # CHECK: complete somewrapper3
 # CHECK: complete somewrapper3
 # CHECK: complete somewrapper3 --wraps wrapped1
+
+complete command-line-aware-completions -xa "(commandline --cursor; commandline --current-process)"
+complete -C"command-line-aware-completions "
+# CHECK: 31
+# CHECK: command-line-aware-completions