New -n flag for string join. (#8774)

* New -n flag for string join command.

This is an argument that excludes empty result items. Fixes #8351

* New documentation for string-join.

The new argument --no-empty was added at string-join manpage.

* New completions for the new -n flag for string join.

* Remove the documentation of the new -n flag of string join0

The reason to remove this new argument in the join0 is that this flag basically doesn't make any difference in the join0.

* Refactor the validation for the string join.

The string join command was using the length of the argument, this commit changes the validation to use the empty function.

* Revert #4b56ab452

The reason for the revert is thath the build broke on the ubuntu in the Github actions.

* Revert #e72e239a1

The reason the compilation on GitHub broke is that the test was weird, it didn't even run it, Common CI systems are typically very very resource-constrained.

* Resolve conflicts in the string-join.rst.

* Resolve conflicts in the "string-join.rst".

commit #1242d0fd7 not fixed all conflicts.

doc_src/cmds/string-join.rst

@@ -18,7 +18,7 @@ Description
 
 .. BEGIN DESCRIPTION
 
-``string join`` joins its *STRING* arguments into a single string separated by *SEP*, which can be an empty string. Exit status: 0 if at least one join was performed, or 1 otherwise.
+``string join`` joins its *STRING* arguments into a single string separated by *SEP*, which can be an empty string. Exit status: 0 if at least one join was performed, or 1 otherwise. If ``-n`` or ``--no-empty`` is specified, empty strings are excluded from consideration (e.g. ``string join -n + a b "" c`` would expand to ``a+b+c`` not ``a+b++c``).
 
 ``string join0`` joins its *STRING* arguments into a single string separated by the zero byte (NUL), and adds a trailing NUL. This is most useful in conjunction with tools that accept NUL-delimited input, such as ``sort -z``. Exit status: 0 if at least one join was performed, or 1 otherwise.
 

doc_src/cmds/string.rst

@@ -10,7 +10,7 @@ Synopsis
 
     string collect [-N | --no-trim-newlines] [STRING ...]
     string escape [-n | --no-quoted] [--style=] [STRING ...]
-    string join [-q | --quiet] SEP [STRING ...]
+    string join [-q | --quiet] [-n | --no-empty] SEP [STRING ...]
     string join0 [-q | --quiet] [STRING ...]
     string length [-q | --quiet] [STRING ...]
     string lower [-q | --quiet] [STRING ...]

share/completions/string.fish

@@ -23,6 +23,7 @@ complete -f -c string -n 'test (count (commandline -opc)) -ge 2; and string matc
 
 complete -f -c string -n "test (count (commandline -opc)) -lt 2" -a join
 complete -f -c string -n "test (count (commandline -opc)) -lt 2" -a join0
+complete -f -c string -n 'test (count (commandline -opc)) -ge 2; and contains -- (commandline -opc)[2] join' -s n -l no-empty -d "Empty strings excluded"
 complete -f -c string -n "test (count (commandline -opc)) -lt 2" -a trim
 complete -f -c string -n "test (count (commandline -opc)) -ge 2; and contains -- (commandline -opc)[2] trim" -s l -l left -d "Trim only leading chars"
 complete -f -c string -n "test (count (commandline -opc)) -ge 2; and contains -- (commandline -opc)[2] trim" -s r -l right -d "Trim only trailing chars"

src/builtins/string.cpp

@@ -741,6 +741,7 @@ static int string_join_maybe0(parser_t &parser, io_streams_t &streams, int argc,
                               const wchar_t **argv, bool is_join0) {
     options_t opts;
     opts.quiet_valid = true;
+    opts.no_empty_valid = true;
     int optind;
     int retval = parse_opts(&opts, &optind, is_join0 ? 0 : 1, argc, argv, parser, streams);
     if (retval != STATUS_CMD_OK) return retval;
@@ -750,6 +751,8 @@ static int string_join_maybe0(parser_t &parser, io_streams_t &streams, int argc,
     arg_iterator_t aiter(argv, optind, streams);
     while (const wcstring *arg = aiter.nextstr()) {
         if (!opts.quiet) {
+            if (opts.no_empty && arg->empty()) continue;
+
             if (nargs > 0) {
                 streams.out.append(sep);
             }