Revert "builtin function: remove dead code"

This reverts commit 993b977c9b.

Fixes #11912

(cherry picked from commit b7fe3190bb)

CHANGELOG.rst

@@ -1,5 +1,12 @@
-fish 4.1.2 (released October 07, 2025)
-======================================
+fish 4.1.3 (released ???)
+=========================
+
+This release fixes the following regressions identified in 4.1.0:
+
+- Crash on invalid :doc:`function <cmds/function>` call (:issue:`11912`).
+
+fish 4.1.2 (released October 7, 2025)
+=====================================
 
 This release fixes the following regressions identified in 4.1.0:
 

po/de.po

@@ -795,6 +795,10 @@ msgstr "%lsund %lu weitere Zeilen"
 msgid "%lu\n"
 msgstr ""
 
+#, c-format
+msgid "%ls: function name required"
+msgstr "%ls: Brauche Funktionsnamen"
+
 #, c-format
 msgid "%s"
 msgstr ""

po/en.po

@@ -794,6 +794,10 @@ msgstr "%lsand %lu more rows"
 msgid "%lu\n"
 msgstr ""
 
+#, c-format
+msgid "%ls: function name required"
+msgstr ""
+
 #, c-format
 msgid "%s"
 msgstr ""

po/fr.po

@@ -895,6 +895,10 @@ msgstr "%lset %lu lignes de plus"
 msgid "%lu\n"
 msgstr ""
 
+#, c-format
+msgid "%ls: function name required"
+msgstr ""
+
 #, c-format
 msgid "%s"
 msgstr ""

po/pl.po

@@ -790,6 +790,10 @@ msgstr "%lsand %lu więcej rzędów"
 msgid "%lu\n"
 msgstr ""
 
+#, c-format
+msgid "%ls: function name required"
+msgstr ""
+
 #, c-format
 msgid "%s"
 msgstr ""

po/pt_BR.po

@@ -795,6 +795,10 @@ msgstr "%lse mais %lu linhas"
 msgid "%lu\n"
 msgstr ""
 
+#, c-format
+msgid "%ls: function name required"
+msgstr ""
+
 #, c-format
 msgid "%s"
 msgstr ""

po/sv.po

@@ -791,6 +791,10 @@ msgstr "%lsoch %lu rader till"
 msgid "%lu\n"
 msgstr ""
 
+#, c-format
+msgid "%ls: function name required"
+msgstr ""
+
 #, c-format
 msgid "%s"
 msgstr ""

po/zh_CN.po

@@ -812,6 +812,10 @@ msgstr "%ls还有 %lu 行"
 msgid "%lu\n"
 msgstr "%lu\n"
 
+#, c-format
+msgid "%ls: function name required"
+msgstr "%ls: 函数名称是必须的"
+
 #, c-format
 msgid "%s"
 msgstr "%s"

src/builtins/function.rs

@@ -243,7 +243,19 @@ fn parse_cmd_opts(
     STATUS_CMD_OK
 }
 
-fn validate_function_name(function_name: &wstr, cmd: &wstr, streams: &mut IoStreams) -> c_int {
+fn validate_function_name(
+    argv: &mut [&wstr],
+    function_name: &mut WString,
+    cmd: &wstr,
+    streams: &mut IoStreams,
+) -> c_int {
+    if argv.len() < 2 {
+        streams
+            .err
+            .append(wgettext_fmt!("%ls: function name required", cmd));
+        return STATUS_INVALID_ARGS;
+    }
+    *function_name = argv[1].to_owned();
     if !valid_func_name(function_name) {
         streams.err.append(wgettext_fmt!(
             "%ls: %ls: invalid function name",
@@ -281,8 +293,8 @@ pub fn function(
     let cmd = argv[0];
 
     // A valid function name has to be the first argument.
-    let function_name = argv[1].to_owned();
-    let mut retval = validate_function_name(&function_name, cmd, streams);
+    let mut function_name = WString::new();
+    let mut retval = validate_function_name(argv, &mut function_name, cmd, streams);
     if retval != STATUS_CMD_OK {
         return retval;
     }

tests/checks/function.fish

@@ -186,4 +186,10 @@ function foo; echo before; end
 foo (functions --erase foo)
 # CHECKERR: error: Unknown function 'foo'
 
+function ()
+end
+# CHECKERR: {{.*}}/tests/checks/function.fish (line {{\d+}}): function: function name required
+# CHECKERR: function ()
+# CHECKERR: ^
+
 exit 0