Highlight %self as an operator

src/fish_tests.cpp

@@ -2472,7 +2472,6 @@ static void test_complete() {
     do_test(completions.at(1).completion == L"zero");
     do_test((completions.at(1).flags & COMPLETE_NO_SPACE) != 0);
 
-
     // Test wraps.
     do_test(comma_join(complete_get_wrap_targets(L"wrapper1")) == L"");
     complete_add_wrapper(L"wrapper1", L"wrapper2");
@@ -4086,6 +4085,13 @@ static void test_highlighting() {
         {L"end", highlight_spec_command},
     });
 
+    highlight_tests.push_back({
+        {L"echo", highlight_spec_command},
+        {L"%self", highlight_spec_operator},
+        {L"not%self", highlight_spec_param},
+        {L"self%not", highlight_spec_param},
+    });
+
     // Verify variables and wildcards in commands using /bin/cat.
     env_set(L"VARIABLE_IN_COMMAND", ENV_LOCAL, {L"a"});
     env_set(L"VARIABLE_IN_COMMAND2", ENV_LOCAL, {L"at"});

src/highlight.cpp

@@ -444,6 +444,12 @@ static void color_string_internal(const wcstring &buffstr, highlight_spec_t base
     const size_t buff_len = buffstr.size();
     std::fill(colors, colors + buff_len, base_color);
 
+    // Hacky support for %self which must be an unquoted literal argument.
+    if (buffstr == PROCESS_EXPAND_SELF_STR) {
+        std::fill_n(colors, wcslen(PROCESS_EXPAND_SELF_STR), highlight_spec_operator);
+        return;
+    }
+
     enum { e_unquoted, e_single_quoted, e_double_quoted } mode = e_unquoted;
     int bracket_count = 0;
     for (size_t in_pos = 0; in_pos < buff_len; in_pos++) {
@@ -692,8 +698,8 @@ class highlighter_t {
 
    public:
     // Constructor
-    highlighter_t(const wcstring &str, size_t pos, const env_vars_snapshot_t &ev,
-                  wcstring wd, bool can_do_io)
+    highlighter_t(const wcstring &str, size_t pos, const env_vars_snapshot_t &ev, wcstring wd,
+                  bool can_do_io)
         : buff(str),
           cursor_pos(pos),
           vars(ev),