git-submodule.sh: preserve stdin for the command spawned by foreach

The user-supplied command spawned by 'submodule foreach' loses its
connection to the original standard input.  Instead, it is connected to the
output of a pipe within the git-submodule script.  The user-supplied
command supplied to 'submodule foreach' is spawned within a while loop
which is being piped into.  Due to the way shells implement piping output
to a while loop, a subshell is created with its standard input attached to
the output of the pipe.  This results in all of the commands executed
within the while loop to have their stdins modified in the same way,
including the user-supplied command.

This can cause a problem if the command requires reading from stdin or if
it changes its behavior based on whether stdin is a tty or not.  For
example, this problem was noticed when trying to execute the following:

git submodule foreach git shortlog --since=two.weeks.ago

which printed a message about entering the first submodule and produced no
further output and exited with a status of zero.  In this case, shortlog
detected that it was not connected to a tty, and since no revision was
supplied as an argument, it attempted to read the list of revisions from
standard input.  Instead, it slurped up the list of submodules that was
being piped to the enclosing while loop and caused that loop to end early
without processing the remaining submodules.

Work around this behavior by saving the original standard input file
descriptor before the while loop, and restoring it when spawning the
user-supplied command.

This fixes the tests in t7407.

Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/git-submodule.sh b/git-submodule.sh
index 4fd8982894a5d135cac4b27b5b42f57c72228e7e..07dc675cef2c71e487648a4bd8cc18f4d93db917 100755 (executable)
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -285,6 +285,10 @@ cmd_foreach()
 
        toplevel=$(pwd)
 
+       # dup stdin so that it can be restored when running the external
+       # command in the subshell (and a recursive call to this function)
+       exec 3<&0
+
        module_list |
        while read mode sha1 stage path
        do
@@ -301,7 +305,7 @@ cmd_foreach()
                                then
                                        cmd_foreach "--recursive" "$@"
                                fi
-                       ) ||
+                       ) <&3 3<&- ||
                        die "Stopping at '$path'; script returned non-zero status."
                fi
        done

diff --git a/t/t7407-submodule-foreach.sh b/t/t7407-submodule-foreach.sh
index 97b7562dbfe510daa86f9888a4a5bc401c789b6c..8a74ccac5f875368d559be876feaed51dfc2af66 100755 (executable)
--- a/t/t7407-submodule-foreach.sh
+++ b/t/t7407-submodule-foreach.sh
@@ -288,7 +288,7 @@ test_expect_success 'use "update --recursive nested1" to checkout all submodules
        )
 '
 
-test_expect_failure 'command passed to foreach retains notion of stdin' '
+test_expect_success 'command passed to foreach retains notion of stdin' '
        (
                cd super &&
                git submodule foreach echo success >../expected &&
@@ -297,7 +297,7 @@ test_expect_failure 'command passed to foreach retains notion of stdin' '
        test_cmp expected actual
 '
 
-test_expect_failure 'command passed to foreach --recursive retains notion of stdin' '
+test_expect_success 'command passed to foreach --recursive retains notion of stdin' '
        (
                cd clone2 &&
                git submodule foreach --recursive echo success >../expected &&