Merge branch 'master' of https://github.com/fish-shell/fish-shell

src/common.cpp

@@ -71,6 +71,8 @@ static rwlock_t termsize_rwlock;
 static char *wcs2str_internal(const wchar_t *in, char *out);
 static void debug_shared(const wchar_t msg_level, const wcstring &msg);
 
+bool has_working_tty_timestamps = true;
+
 #ifdef HAVE_BACKTRACE_SYMBOLS
 // This function produces a stack backtrace with demangled function & method names. It is based on
 // https://gist.github.com/fmela/591333 but adapted to the style of the fish project.

src/common.h

@@ -21,6 +21,13 @@
 #include "fallback.h"  // IWYU pragma: keep
 #include "signal.h"    // IWYU pragma: keep
 
+// Define a symbol we can use elsewhere in our code to determine if we're being built on MS Windows
+// under Cygwin.
+#if defined(_WIN32) || defined(_WIN64) || defined(WIN32) || defined(__CYGWIN__) || \
+    defined(__WIN32__)
+#define OS_IS_CYGWIN
+#endif
+
 /// Avoid writing the type name twice in a common "static_cast-initialization". Caveat: This doesn't
 /// work with type names containing commas!
 #define CAST_INIT(type, dst, src) type dst = static_cast<type>(src)
@@ -188,6 +195,10 @@ extern const wchar_t *program_name;
 void read_ignore(int fd, void *buff, size_t count);
 void write_ignore(int fd, const void *buff, size_t count);
 
+/// Set to false at run-time if it's been determined we can't trust the last modified timestamp on
+/// the tty.
+extern bool has_working_tty_timestamps;
+
 /// This macro is used to check that an input argument is not null. It is a bit lika a non-fatal
 /// form of assert. Instead of exit-ing on failure, the current function is ended at once. The
 /// second parameter is the return value of the current function on failure.

src/fish.cpp

@@ -407,6 +407,36 @@ static int fish_parse_opt(int argc, char **argv, std::vector<std::string> *cmds)
     return optind;
 }
 
+/// Various things we need to initialize at run-time that don't really fit any of the other init
+/// routines.
+static void misc_init() {
+#ifdef OS_IS_CYGWIN
+    // MS Windows tty devices do not have either a read or write timestamp. Those respective fields
+    // of `struct stat` are always the current time. Which means we can't use them. So we assume no
+    // external program has written to the terminal behind our back. This makes multiline prompts
+    // usable. See issue #2859.
+    has_working_tty_timestamps = false;
+#else
+    // This covers Windows Subsystem for Linux (WSL).
+    int fd = open("/proc/sys/kernel/osrelease", O_RDONLY);
+    if (fd != -1) {
+        const char *magic_suffix = "Microsoft";
+        int len_magic_suffix = strlen(magic_suffix);
+        char osrelease[128] = {0};
+        int len_osrelease = read(fd, osrelease, sizeof(osrelease) - 1);
+        if (osrelease[len_osrelease - 1] == '\n') {
+            osrelease[len_osrelease - 1] = '\0';
+            len_osrelease--;
+        }
+        if (len_osrelease >= len_magic_suffix &&
+            strcmp(magic_suffix, osrelease + len_osrelease - len_magic_suffix) == 0) {
+            has_working_tty_timestamps = false;
+        }
+        close(fd);
+    }
+#endif  // OS_IS_MS_WINDOWS
+}
+
 int main(int argc, char **argv) {
     int res = 1;
     int my_optind = 0;
@@ -452,6 +482,7 @@ int main(int argc, char **argv) {
     history_init();
     // For set_color to support term256 in config.fish (issue #1022).
     update_fish_color_support();
+    misc_init();
 
     parser_t &parser = parser_t::principal_parser();
 

src/screen.cpp

@@ -347,12 +347,18 @@ static void s_save_status(screen_t *s) {
 static void s_check_status(screen_t *s) {
     fflush(stdout);
     fflush(stderr);
+    if (!has_working_tty_timestamps) {
+        // We can't reliably determine if the terminal has been written to behind our back so we
+        // just assume that hasn't happened and hope for the best. This is important for multi-line
+        // prompts to work correctly.
+        return;
+    }
 
     fstat(1, &s->post_buff_1);
     fstat(2, &s->post_buff_2);
 
-    int changed = (s->prev_buff_1.st_mtime != s->post_buff_1.st_mtime) ||
-                  (s->prev_buff_2.st_mtime != s->post_buff_2.st_mtime);
+    bool changed = (s->prev_buff_1.st_mtime != s->post_buff_1.st_mtime) ||
+                   (s->prev_buff_2.st_mtime != s->post_buff_2.st_mtime);
 
 #if defined HAVE_STRUCT_STAT_ST_MTIMESPEC_TV_NSEC
     changed = changed ||