git-archive --format=zip: add symlink support

Add symlink support to ZIP file creation, and a few tests.

This implementation sets the "version made by" field
(creator_version) to Unix for symlinks, only; regular files and
directories are still marked as originating from FAT/VFAT/NTFS.

Also set "external file attributes" (attr2) to 0 for regular
files and 16 for directories (FAT attribute), and to the file
mode for symlinks.

We could always set the creator_version to Unix and include the
mode, but then Info-ZIP unzip would set the mode of the extracted
files to *exactly* the value stored in attr2.  The FAT trick
makes it apply the umask instead.  Note: FAT has no executable
bit, so this information is not stored in the ZIP file.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <junkio@cox.net>

t/t5000-tar-tree.sh

@@ -26,6 +26,7 @@ commit id embedding:
 
 . ./test-lib.sh
 TAR=${TAR:-tar}
+UNZIP=${UNZIP:-unzip}
 
 test_expect_success \
     'populate workdir' \
@@ -95,4 +96,38 @@ test_expect_success \
     'validate file contents with prefix' \
     'diff -r a c/prefix/a'
 
+test_expect_success \
+    'git-archive --format=zip' \
+    'git-archive --format=zip HEAD >d.zip'
+
+test_expect_success \
+    'extract ZIP archive' \
+    '(mkdir d && cd d && $UNZIP ../d.zip)'
+
+test_expect_success \
+    'validate filenames' \
+    '(cd d/a && find .) | sort >d.lst &&
+     diff a.lst d.lst'
+
+test_expect_success \
+    'validate file contents' \
+    'diff -r a d/a'
+
+test_expect_success \
+    'git-archive --format=zip with prefix' \
+    'git-archive --format=zip --prefix=prefix/ HEAD >e.zip'
+
+test_expect_success \
+    'extract ZIP archive with prefix' \
+    '(mkdir e && cd e && $UNZIP ../e.zip)'
+
+test_expect_success \
+    'validate filenames with prefix' \
+    '(cd e/prefix/a && find .) | sort >e.lst &&
+     diff a.lst e.lst'
+
+test_expect_success \
+    'validate file contents with prefix' \
+    'diff -r a e/prefix/a'
+
 test_done