Restore %self to refer to the fish pid

This brings back the %self argument. Like the original %self it only expands
if the argument is literally %self.

src/common.cpp

@@ -1040,6 +1040,7 @@ static void escape_string_script(const wchar_t *orig_in, size_t in_len, wcstring
                 case L'|':
                 case L';':
                 case L'"':
+                case L'%':
                 case L'~': {
                     bool char_is_normal = (c == L'~' && no_tilde) || (c == L'^' && no_caret) ||
                                           (c == L'?' && no_qmark);
@@ -1398,6 +1399,17 @@ static bool unescape_string_internal(const wchar_t *const input, const size_t in
                     }
                     break;
                 }
+                case L'%': {
+                    // Note that this only recognizes %self if the string is literally %self.
+                    // %self/foo will NOT match this.
+                    if (unescape_special && input_position == 0 &&
+                        !wcscmp(input, PROCESS_EXPAND_SELF_STR)) {
+                        to_append_or_none = PROCESS_EXPAND_SELF;
+                        input_position +=
+                            wcslen(PROCESS_EXPAND_SELF_STR) - 1;  // skip over 'self' part.
+                    }
+                    break;
+                }
                 case L'*': {
                     if (unescape_special) {
                         // In general, this is ANY_STRING. But as a hack, if the last appended char

src/env.cpp

@@ -924,7 +924,7 @@ void env_init(const struct config_paths_t *paths /* or NULL */) {
     wcstring version = str2wcstring(get_fish_version());
     env_set_one(L"version", ENV_GLOBAL, version);
 
-    // Set the $fish_pid variable (%self replacement)
+    // Set the $fish_pid variable.
     env_set_one(L"fish_pid", ENV_GLOBAL, to_string<long>(getpid()));
 
     // Set the $hostname variable

src/expand.cpp

@@ -56,7 +56,7 @@
 
 /// Characters which make a string unclean if they are the first character of the string. See \c
 /// expand_is_clean().
-#define UNCLEAN_FIRST L"~"
+#define UNCLEAN_FIRST L"~%"
 /// Unclean characters. See \c expand_is_clean().
 #define UNCLEAN L"$*?\\\"'({})"
 
@@ -784,6 +784,13 @@ static void expand_home_directory(wcstring &input) {
     }
 }
 
+/// Expand the %self escape. Note this can only come at the beginning of the string.
+static void expand_percent_self(wcstring &input) {
+    if (!input.empty() && input.front() == PROCESS_EXPAND_SELF) {
+        input.replace(0, 1, to_string<long>(getpid()));
+    }
+}
+
 void expand_tilde(wcstring &input) {
     // Avoid needless COW behavior by ensuring we use const at.
     const wcstring &tmp = input;
@@ -934,12 +941,13 @@ static expand_error_t expand_stage_braces(wcstring input, std::vector<completion
     return expand_braces(input, flags, out, errors);
 }
 
-static expand_error_t expand_stage_home(wcstring input, std::vector<completion_t> *out,
+static expand_error_t expand_stage_home_and_self(wcstring input, std::vector<completion_t> *out,
-                                        expand_flags_t flags, parse_error_list_t *errors) {
+                                                 expand_flags_t flags, parse_error_list_t *errors) {
     (void)errors;
     if (!(EXPAND_SKIP_HOME_DIRECTORIES & flags)) {
         expand_home_directory(input);
     }
+    expand_percent_self(input);
     append_completion(out, std::move(input));
     return EXPAND_OK;
 }
@@ -1047,7 +1055,7 @@ expand_error_t expand_string(wcstring input, std::vector<completion_t> *out_comp
 
     // Our expansion stages.
     const expand_stage_t stages[] = {expand_stage_cmdsubst, expand_stage_variables,
-                                     expand_stage_braces, expand_stage_home,
+                                     expand_stage_braces, expand_stage_home_and_self,
                                      expand_stage_wildcards};
 
     // Load up our single initial completion.

src/expand.h

@@ -61,6 +61,8 @@ class completion_t;
 enum {
     /// Character representing a home directory.
     HOME_DIRECTORY = EXPAND_RESERVED_BASE,
+    /// Character representing process expansion for %self.
+    PROCESS_EXPAND_SELF,
     /// Character representing variable expansion.
     VARIABLE_EXPAND,
     /// Character representing variable expansion into a single element.
@@ -95,6 +97,9 @@ enum expand_error_t {
     EXPAND_WILDCARD_MATCH
 };
 
+/// The string represented by PROCESS_EXPAND_SELF
+#define PROCESS_EXPAND_SELF_STR L"%self"
+
 /// Perform various forms of expansion on in, such as tilde expansion (\~USER becomes the users home
 /// directory), variable expansion (\$VAR_NAME becomes the value of the environment variable
 /// VAR_NAME), cmdsubst expansion and wildcard expansion. The results are inserted into the list

src/highlight.cpp

@@ -121,6 +121,7 @@ bool is_potential_path(const wcstring &potential_path_fragment, const wcstring_l
     for (size_t i = 0; i < path_with_magic.size(); i++) {
         wchar_t c = path_with_magic.at(i);
         switch (c) {
+            case PROCESS_EXPAND_SELF:
             case VARIABLE_EXPAND:
             case VARIABLE_EXPAND_SINGLE:
             case BRACE_BEGIN:

tests/expansion.err

@@ -8,6 +8,9 @@ fish: Invalid index value
 echo ()[d]
         ^
 
+####################
+# Percent self
+
 ####################
 # Catch your breath
 fish: $) is not a valid variable in fish.

tests/expansion.in

@@ -101,6 +101,11 @@ echo $foo[d]
 echo ()[1]
 echo ()[d]
 
+logmsg Percent self
+echo %selfNOT NOT%self \%self "%self" '%self'
+echo %self | string match -qr '^\\d+$'
+echo "All digits: $status"
+
 logmsg Catch your breath
 set paren ')'
 echo $$paren

tests/expansion.out

@@ -63,6 +63,11 @@
 0
 
 
+####################
+# Percent self
+%selfNOT NOT%self %self %self %self
+All digits: 0
+
 ####################
 # Catch your breath