fix(_comp_compgen): do not inherit -a for explicitly specified var

bash_completion

@@ -520,8 +520,8 @@ _comp_compgen__error_fallback()
 # @since 2.12
 _comp_compgen()
 {
-    local _append=${_comp_compgen__append-}
-    local _var=${_comp_compgen__var-COMPREPLY}
+    local _append=
+    local _var=
     local _cur=${_comp_compgen__cur-${cur-}}
     local _dir=""
     local _ifs=$' \t\n' _has_ifs=""
@@ -592,6 +592,11 @@ _comp_compgen()
         printf 'usage: %s [-alR|-F SEP|-v ARR|-c CUR] -- ARGS...' "$FUNCNAME" >&2
         return 2
     fi
+    if [[ ! $_var ]]; then
+        # Inherit _append and _var only when -v var is unspecified.
+        _var=${_comp_compgen__var-COMPREPLY}
+        [[ $_append ]] || _append=${_comp_compgen__append-}
+    fi
 
     if [[ $1 != -* ]]; then
         # usage: _comp_compgen [options] NAME args

test/t/unit/test_unit_compgen.py

@@ -43,6 +43,13 @@ def functions(self, bash):
             "_comp_compgen_gen8() { local -a arr=(x y z); _comp_compgen -U arr -- -W '\"${arr[@]}\"'; }",
         )
 
+        # test_9_inherit_a
+        assert_bash_exec(
+            bash,
+            '_comp_compgen_gen9sub() { local -a gen=(00); _comp_compgen -v gen -- -W 11; _comp_compgen_set "${gen[@]}"; }; '
+            "_comp_compgen_gen9() { _comp_compgen_gen9sub; _comp_compgen -a gen9sub; }",
+        )
+
     def test_1_basic(self, bash, functions):
         output = assert_bash_exec(
             bash, "_comp__test_words 12 34 56 ''", want_output=True
@@ -158,3 +165,9 @@ def test_8_option_U(self, bash, functions):
             bash, "_comp__test_compgen gen8", want_output=True
         )
         assert output.strip() == "<x><y><z>"
+
+    def test_9_inherit_a(self, bash, functions):
+        output = assert_bash_exec(
+            bash, "_comp__test_compgen gen9", want_output=True
+        )
+        assert output.strip() == "<11><11>"