Add status fish-path

Retrieves the fully resolved path to the currently executing fish binary
(regardless of PATH). Can be used to ensure that the same fish is
launched again from a script.

`get_executable_path()` moved from fish binary to libfish, also cleaned
up some duplicated (but differing!) definitions of PATH_MAX (which was
used by that function) in the process.

doc_src/status.txt

@@ -12,6 +12,7 @@ status is-no-job-control
 status is-full-job-control
 status is-interactive-job-control
 status filename
+status fish-path
 status function
 status line-number
 status stack-trace
@@ -44,6 +45,8 @@ The following operations (sub-commands) are available:
 
 - `filename` prints the filename of the currently running script. Also `current-filename`, `-f` or `--current-filename`.
 
+- `fish-path` prints the absolute path to the currently executing instance of fish.
+
 - `function` prints the name of the currently called function if able, when missing displays "Not a
   function" (or equivalent translated string). Also `current-function`, `-u` or `--current-function`.
 

src/builtin_status.cpp

@@ -21,6 +21,7 @@ enum status_cmd_t {
     STATUS_CURRENT_CMD = 1,
     STATUS_FEATURES,
     STATUS_FILENAME,
+    STATUS_FISH_PATH,
     STATUS_FUNCTION,
     STATUS_IS_BLOCK,
     STATUS_IS_BREAKPOINT,
@@ -45,6 +46,7 @@ const enum_map<status_cmd_t> status_enum_map[] = {
     {STATUS_LINE_NUMBER, L"current-line-number"},
     {STATUS_FEATURES, L"features"},
     {STATUS_FILENAME, L"filename"},
+    {STATUS_FISH_PATH, L"fish-path"},
     {STATUS_FUNCTION, L"function"},
     {STATUS_IS_BLOCK, L"is-block"},
     {STATUS_IS_BREAKPOINT, L"is-breakpoint"},
@@ -103,6 +105,7 @@ static const struct woption long_options[] = {{L"help", no_argument, NULL, 'h'},
           {L"current-filename", no_argument, NULL, 'f'},
           {L"current-line-number", no_argument, NULL, 'n'},
           {L"filename", no_argument, NULL, 'f'},
+          {L"fish-path", no_argument, NULL, STATUS_FISH_PATH},
           {L"is-block", no_argument, NULL, 'b'},
           {L"is-command-substitution", no_argument, NULL, 'c'},
           {L"is-full-job-control", no_argument, NULL, STATUS_IS_FULL_JOB_CTRL},
@@ -169,6 +172,12 @@ static int parse_cmd_opts(status_cmd_opts_t &opts, int *optind,  //!OCLINT(high
                 }
                 break;
             }
+            case STATUS_FISH_PATH: {
+                if (!set_status_cmd(cmd, opts, STATUS_FISH_PATH, streams)) {
+                    return STATUS_CMD_ERROR;
+                }
+                break;
+            }
             case 'L': {
                 opts.level = fish_wcstoi(w.woptarg);
                 if (opts.level < 0 || errno == ERANGE) {
@@ -418,6 +427,12 @@ int builtin_status(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
             streams.out.push_back(L'\n');
             break;
         }
+        case STATUS_FISH_PATH: {
+            CHECK_FOR_UNEXPECTED_STATUS_ARGS(opts.status_cmd)
+            streams.out.append(str2wcstring(get_executable_path("fish")).c_str());
+            streams.out.push_back(L'\n');
+            break;
+        }
     }
 
     return retval;

src/common.cpp

@@ -30,6 +30,10 @@
 #include <sys/ioctl.h>
 #endif
 
+#ifdef __FreeBSD__
+#include <sys/sysctl.h>
+#endif
+
 #include <algorithm>
 #include <memory>  // IWYU pragma: keep
 #include <type_traits>
@@ -2248,3 +2252,49 @@ bool valid_func_name(const wcstring &str) {
     if (str.find_first_of(L'/') != wcstring::npos) return false;
     return true;
 }
+
+/// Return the path to the current executable. This needs to be realpath'd.
+std::string get_executable_path(const char *argv0) {
+    char buff[PATH_MAX];
+
+#if __APPLE__
+    // On OS X use it's proprietary API to get the path to the executable.
+    // This is basically grabbing exec_path after argc, argv, envp, ...: for us
+    // https://opensource.apple.com/source/adv_cmds/adv_cmds-163/ps/print.c
+    uint32_t buffSize = sizeof buff;
+    if (_NSGetExecutablePath(buff, &buffSize) == 0) return std::string(buff);
+#elif __FreeBSD__
+    // FreeBSD does not have /proc by default, but it can be mounted as procfs via the
+    // Linux compatibility layer. Per sysctl(3), passing in a process ID of -1 returns
+    // the value for the current process.
+    size_t buff_size = sizeof buff;
+    int name[] = { CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1 };
+    int result = sysctl(name, sizeof(name) / sizeof(int), buff, &buff_size, nullptr, 0);
+    if (result != 0) {
+        wperror(L"sysctl KERN_PROC_PATHNAME");
+    }
+    else {
+        return std::string(buff);
+    }
+#else
+    // On other unixes, fall back to the Linux-ish /proc/ directory
+    ssize_t len;
+    len = readlink("/proc/self/exe", buff, sizeof buff - 1);  // Linux
+    if (len == -1) {
+        len = readlink("/proc/curproc/file", buff, sizeof buff - 1);  // other BSDs
+        if (len == -1) {
+            len = readlink("/proc/self/path/a.out", buff, sizeof buff - 1);  // Solaris
+        }
+    }
+    if (len > 0) {
+        buff[len] = '\0';
+        return std::string(buff);
+    }
+#endif
+
+    // Just return argv0, which probably won't work (i.e. it's not an absolute path or a path
+    // relative to the working directory, but instead something the caller found via $PATH). We'll
+    // eventually fall back to the compile time paths.
+    return std::string(argv0 ? argv0 : "");
+}
+

src/common.h

@@ -106,6 +106,16 @@ static_assert(false, "Neither NAME_MAX nor MAXNAMELEN is defined!");
 #endif
 #endif
 
+// PATH_MAX may not exist.
+#ifndef PATH_MAX
+#ifdef MAXPATHLEN
+#define PATH_MAX MAXPATHLEN
+#else
+/// Fallback length of MAXPATHLEN. Hopefully a sane value.
+#define PATH_MAX 4096
+#endif
+#endif
+
 enum escape_string_style_t { STRING_STYLE_SCRIPT, STRING_STYLE_URL, STRING_STYLE_VAR };
 
 // Flags for unescape_string functions.
@@ -1007,4 +1017,7 @@ struct hash<const wcstring> {
 }  // namespace std
 #endif
 
+/// Get the absolute path to the fish executable itself
+std::string get_executable_path(const char *fallback);
+
 #endif

src/fish.cpp

@@ -54,15 +54,6 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 #include "signal.h"
 #include "wutil.h"  // IWYU pragma: keep
 
-#ifdef __FreeBSD__
-#include <sys/sysctl.h>
-#endif
-
-// PATH_MAX may not exist.
-#ifndef PATH_MAX
-#define PATH_MAX 4096
-#endif
-
 // container to hold the options specified within the command line
 class fish_cmd_opts_t {
    public:
@@ -98,51 +89,6 @@ extern "C" {
 int _NSGetExecutablePath(char *buf, uint32_t *bufsize);
 }
 
-/// Return the path to the current executable. This needs to be realpath'd.
-static std::string get_executable_path(const char *argv0) {
-    char buff[PATH_MAX];
-
-#if __APPLE__
-    // On OS X use it's proprietary API to get the path to the executable.
-    // This is basically grabbing exec_path after argc, argv, envp, ...: for us
-    // https://opensource.apple.com/source/adv_cmds/adv_cmds-163/ps/print.c
-    uint32_t buffSize = sizeof buff;
-    if (_NSGetExecutablePath(buff, &buffSize) == 0) return std::string(buff);
-#elif __FreeBSD__
-    // FreeBSD does not have /proc by default, but it can be mounted as procfs via the
-    // Linux compatibility layer. Per sysctl(3), passing in a process ID of -1 returns
-    // the value for the current process.
-    size_t buff_size = sizeof buff;
-    int name[] = { CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1 };
-    int result = sysctl(name, sizeof(name) / sizeof(int), buff, &buff_size, nullptr, 0);
-    if (result != 0) {
-        wperror(L"sysctl KERN_PROC_PATHNAME");
-    }
-    else {
-        return std::string(buff);
-    }
-#else
-    // On other unixes, fall back to the Linux-ish /proc/ directory
-    ssize_t len;
-    len = readlink("/proc/self/exe", buff, sizeof buff - 1);  // Linux
-    if (len == -1) {
-        len = readlink("/proc/curproc/file", buff, sizeof buff - 1);  // other BSDs
-        if (len == -1) {
-            len = readlink("/proc/self/path/a.out", buff, sizeof buff - 1);  // Solaris
-        }
-    }
-    if (len > 0) {
-        buff[len] = '\0';
-        return std::string(buff);
-    }
-#endif
-
-    // Just return argv0, which probably won't work (i.e. it's not an absolute path or a path
-    // relative to the working directory, but instead something the caller found via $PATH). We'll
-    // eventually fall back to the compile time paths.
-    return std::string(argv0 ? argv0 : "");
-}
-
 static struct config_paths_t determine_config_directory_paths(const char *argv0) {
     struct config_paths_t paths;
     bool done = false;

src/wutil.cpp

@@ -33,15 +33,6 @@ typedef std::string cstring;
 
 const file_id_t kInvalidFileID = {(dev_t)-1LL, (ino_t)-1LL, (uint64_t)-1LL, -1, -1, -1, -1};
 
-#ifndef PATH_MAX
-#ifdef MAXPATHLEN
-#define PATH_MAX MAXPATHLEN
-#else
-/// Fallback length of MAXPATHLEN. Hopefully a sane value.
-#define PATH_MAX 4096
-#endif
-#endif
-
 /// Map used as cache by wgettext.
 static owning_lock<std::unordered_map<wcstring, wcstring>> wgettext_map;