tests: prevent enormous output spew in test-lfs-largefiles.t

This test currently fails on Python 3, but in a super-slow way. Adding
this `head` invocation costs us nothing, but will prevent failures in
this area from being super expensive.

Differential Revision: https://phab.mercurial-scm.org/D2600

tests/test-lfs-largefiles.t

@@ -1,354 +1,357
 This tests the interaction between the largefiles and lfs extensions, and
 conversion from largefiles -> lfs.
 
   $ cat >> $HGRCPATH << EOF
   > [extensions]
   > largefiles =
   > 
   > [lfs]
   > # standin files are 41 bytes.  Stay bigger for clarity.
   > threshold = 42
   > EOF
 
 Setup a repo with a normal file and a largefile, above and below the lfs
 threshold to test lfconvert.  *.txt start life as a normal file; *.bin start as
 an lfs/largefile.
 
   $ hg init largefiles
   $ cd largefiles
   $ echo 'normal' > normal.txt
   $ echo 'normal above lfs threshold 0000000000000000000000000' > lfs.txt
   $ hg ci -Am 'normal.txt'
   adding lfs.txt
   adding normal.txt
   $ echo 'largefile' > large.bin
   $ echo 'largefile above lfs threshold 0000000000000000000000' > lfs.bin
   $ hg add --large large.bin lfs.bin
   $ hg ci -m 'add largefiles'
 
   $ cat >> $HGRCPATH << EOF
   > [extensions]
   > lfs =
   > EOF
 
 Add an lfs file and normal file that collide with files on the other branch.
 large.bin is added as a normal file, and is named as such only to clash with the
 largefile on the other branch.
 
   $ hg up -q '.^'
   $ echo 'below lfs threshold' > large.bin
   $ echo 'lfs above the lfs threshold for length 0000000000000' > lfs.bin
   $ hg ci -Am 'add with lfs extension'
   adding large.bin
   adding lfs.bin
   created new head
 
   $ hg log -G
   @  changeset:   2:e989d0fa3764
   |  tag:         tip
   |  parent:      0:29361292f54d
   |  user:        test
   |  date:        Thu Jan 01 00:00:00 1970 +0000
   |  summary:     add with lfs extension
   |
   | o  changeset:   1:6513aaab9ca0
   |/   user:        test
   |    date:        Thu Jan 01 00:00:00 1970 +0000
   |    summary:     add largefiles
   |
   o  changeset:   0:29361292f54d
      user:        test
      date:        Thu Jan 01 00:00:00 1970 +0000
      summary:     normal.txt
   
 --------------------------------------------------------------------------------
 Merge largefiles into lfs branch
 
 The largefiles extension will prompt to use the normal or largefile when merged
 into the lfs files.  `hg manifest` will show standins if present.  They aren't,
 because largefiles merge doesn't merge content.  If it did, selecting (n)ormal
 would convert to lfs on commit, if appropriate.
 
 BUG: Largefiles isn't running the merge tool, like when two lfs files are
 merged.  This is probably by design, but it should probably at least prompt if
 content should be taken from (l)ocal or (o)ther as well.
 
   $ hg --config ui.interactive=True merge 6513aaab9ca0 <<EOF
   > n
   > n
   > EOF
   remote turned local normal file large.bin into a largefile
   use (l)argefile or keep (n)ormal file? n
   remote turned local normal file lfs.bin into a largefile
   use (l)argefile or keep (n)ormal file? n
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
   $ hg ci -m 'merge lfs with largefiles -> normal'
   $ hg manifest
   large.bin
   lfs.bin
   lfs.txt
   normal.txt
 
 The merged lfs.bin resolved to lfs because the (n)ormal option was picked.  The
 lfs.txt file is unchanged by the merge, because it was added before lfs was
 enabled, and the content didn't change.
   $ hg debugdata lfs.bin 0
   version https://git-lfs.github.com/spec/v1
   oid sha256:81c7492b2c05e130431f65a87651b54a30c5da72c99ce35a1e9b9872a807312b
   size 53
   x-is-binary 0
   $ hg debugdata lfs.txt 0
   normal above lfs threshold 0000000000000000000000000
 
 Another filelog entry is NOT made by the merge, so nothing is committed as lfs.
   $ hg log -r . -T '{join(lfs_files, ", ")}\n'
   
 
 Replay the last merge, but pick (l)arge this time.  The manifest will show any
 standins.
 
   $ hg up -Cq e989d0fa3764
 
   $ hg --config ui.interactive=True merge 6513aaab9ca0 <<EOF
   > l
   > l
   > EOF
   remote turned local normal file large.bin into a largefile
   use (l)argefile or keep (n)ormal file? l
   remote turned local normal file lfs.bin into a largefile
   use (l)argefile or keep (n)ormal file? l
   getting changed largefiles
   2 largefiles updated, 0 removed
   2 files updated, 0 files merged, 2 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
   $ hg ci -m 'merge lfs with largefiles -> large'
   created new head
   $ hg manifest
   .hglf/large.bin
   .hglf/lfs.bin
   lfs.txt
   normal.txt
 
 --------------------------------------------------------------------------------
 Merge lfs into largefiles branch
 
   $ hg up -Cq 6513aaab9ca0
   $ hg --config ui.interactive=True merge e989d0fa3764 <<EOF
   > n
   > n
   > EOF
   remote turned local largefile large.bin into a normal file
   keep (l)argefile or use (n)ormal file? n
   remote turned local largefile lfs.bin into a normal file
   keep (l)argefile or use (n)ormal file? n
   getting changed largefiles
   0 largefiles updated, 0 removed
   2 files updated, 0 files merged, 2 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
   $ hg ci -m 'merge largefiles with lfs -> normal'
   created new head
   $ hg manifest
   large.bin
   lfs.bin
   lfs.txt
   normal.txt
 
 The merged lfs.bin got converted to lfs because the (n)ormal option was picked.
 The lfs.txt file is unchanged by the merge, because it was added before lfs was
 enabled.
   $ hg debugdata lfs.bin 0
   version https://git-lfs.github.com/spec/v1
   oid sha256:81c7492b2c05e130431f65a87651b54a30c5da72c99ce35a1e9b9872a807312b
   size 53
   x-is-binary 0
   $ hg debugdata lfs.txt 0
   normal above lfs threshold 0000000000000000000000000
 
 Another filelog entry is NOT made by the merge, so nothing is committed as lfs.
   $ hg log -r . -T '{join(lfs_files, ", ")}\n'
   
 
 Replay the last merge, but pick (l)arge this time.  The manifest will show the
 standins.
 
   $ hg up -Cq 6513aaab9ca0
 
   $ hg --config ui.interactive=True merge e989d0fa3764 <<EOF
   > l
   > l
   > EOF
   remote turned local largefile large.bin into a normal file
   keep (l)argefile or use (n)ormal file? l
   remote turned local largefile lfs.bin into a normal file
   keep (l)argefile or use (n)ormal file? l
   0 files updated, 0 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)
   $ hg ci -m 'merge largefiles with lfs -> large'
   created new head
   $ hg manifest
   .hglf/large.bin
   .hglf/lfs.bin
   lfs.txt
   normal.txt
 
 --------------------------------------------------------------------------------
 
 When both largefiles and lfs are configured to add by size, the tie goes to
 largefiles since it hooks cmdutil.add() and lfs hooks the filelog write in the
 commit.  By the time the commit occurs, the tracked file is smaller than the
 threshold (assuming it is > 41, so the standins don't become lfs objects).
 
   $ $PYTHON -c 'import sys ; sys.stdout.write("y\n" * 1048576)' > large_by_size.bin
   $ hg --config largefiles.minsize=1 ci -Am 'large by size'
   adding large_by_size.bin as a largefile
   $ hg manifest
   .hglf/large.bin
   .hglf/large_by_size.bin
   .hglf/lfs.bin
   lfs.txt
   normal.txt
 
   $ hg rm large_by_size.bin
   $ hg ci -m 'remove large_by_size.bin'
 
 Largefiles doesn't do anything special with diff, so it falls back to diffing
 the standins.  Extdiff also is standin based comparison.  Diff and extdiff both
 work on the original file for lfs objects.
 
 Largefile -> lfs transition
   $ hg diff -r 1 -r 3
   diff -r 6513aaab9ca0 -r dcc5ce63e252 .hglf/large.bin
   --- a/.hglf/large.bin	Thu Jan 01 00:00:00 1970 +0000
   +++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
   @@ -1,1 +0,0 @@
   -cef9a458373df9b0743a0d3c14d0c66fb19b8629
   diff -r 6513aaab9ca0 -r dcc5ce63e252 .hglf/lfs.bin
   --- a/.hglf/lfs.bin	Thu Jan 01 00:00:00 1970 +0000
   +++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
   @@ -1,1 +0,0 @@
   -557fb6309cef935e1ac2c8296508379e4b15a6e6
   diff -r 6513aaab9ca0 -r dcc5ce63e252 large.bin
   --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
   +++ b/large.bin	Thu Jan 01 00:00:00 1970 +0000
   @@ -0,0 +1,1 @@
   +below lfs threshold
   diff -r 6513aaab9ca0 -r dcc5ce63e252 lfs.bin
   --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
   +++ b/lfs.bin	Thu Jan 01 00:00:00 1970 +0000
   @@ -0,0 +1,1 @@
   +lfs above the lfs threshold for length 0000000000000
 
 lfs -> largefiles transition
   $ hg diff -r 2 -r 6
   diff -r e989d0fa3764 -r 95e1e80325c8 .hglf/large.bin
   --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
   +++ b/.hglf/large.bin	Thu Jan 01 00:00:00 1970 +0000
   @@ -0,0 +1,1 @@
   +cef9a458373df9b0743a0d3c14d0c66fb19b8629
   diff -r e989d0fa3764 -r 95e1e80325c8 .hglf/lfs.bin
   --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
   +++ b/.hglf/lfs.bin	Thu Jan 01 00:00:00 1970 +0000
   @@ -0,0 +1,1 @@
   +557fb6309cef935e1ac2c8296508379e4b15a6e6
   diff -r e989d0fa3764 -r 95e1e80325c8 large.bin
   --- a/large.bin	Thu Jan 01 00:00:00 1970 +0000
   +++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
   @@ -1,1 +0,0 @@
   -below lfs threshold
   diff -r e989d0fa3764 -r 95e1e80325c8 lfs.bin
   --- a/lfs.bin	Thu Jan 01 00:00:00 1970 +0000
   +++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
   @@ -1,1 +0,0 @@
   -lfs above the lfs threshold for length 0000000000000
 
 A largefiles repo can be converted to lfs.  The lfconvert command uses the
 convert extension under the hood with --to-normal.  So the --config based
 parameters are available, but not --authormap, --branchmap, etc.
 
   $ cd ..
   $ hg lfconvert --to-normal largefiles nolargefiles 2>&1
   initializing destination nolargefiles
   0 additional largefiles cached
   scanning source...
   sorting...
   converting...
   8 normal.txt
   7 add largefiles
   6 add with lfs extension
   5 merge lfs with largefiles -> normal
   4 merge lfs with largefiles -> large
   3 merge largefiles with lfs -> normal
   2 merge largefiles with lfs -> large
   1 large by size
   0 remove large_by_size.bin
   $ cd nolargefiles
 
 The requirement is added to the destination repo, and the extension is enabled
 locally.
 
   $ cat .hg/requires
   dotencode
   fncache
   generaldelta
   lfs
   revlogv1
   store
   $ hg config --debug extensions | grep lfs
   $TESTTMP/nolargefiles/.hg/hgrc:*: extensions.lfs= (glob)
 
   $ hg log -r 'all()' -G -T '{rev} {join(lfs_files, ", ")} ({desc})\n'
   o  8 large_by_size.bin (remove large_by_size.bin)
   |
   o  7 large_by_size.bin (large by size)
   |
   o    6  (merge largefiles with lfs -> large)
   |\
   +---o  5  (merge largefiles with lfs -> normal)
   | |/
   +---o  4 lfs.bin (merge lfs with largefiles -> large)
   | |/
   +---o  3  (merge lfs with largefiles -> normal)
   | |/
   | o  2 lfs.bin (add with lfs extension)
   | |
   o |  1 lfs.bin (add largefiles)
   |/
   o  0 lfs.txt (normal.txt)
   
   $ hg debugdata lfs.bin 0
   version https://git-lfs.github.com/spec/v1
   oid sha256:2172a5bd492dd41ec533b9bb695f7691b6351719407ac797f0ccad5348c81e62
   size 53
   x-is-binary 0
   $ hg debugdata lfs.bin 1
   version https://git-lfs.github.com/spec/v1
   oid sha256:81c7492b2c05e130431f65a87651b54a30c5da72c99ce35a1e9b9872a807312b
   size 53
   x-is-binary 0
   $ hg debugdata lfs.bin 2
   version https://git-lfs.github.com/spec/v1
   oid sha256:2172a5bd492dd41ec533b9bb695f7691b6351719407ac797f0ccad5348c81e62
   size 53
   x-is-binary 0
   $ hg debugdata lfs.bin 3
   abort: invalid revision identifier 3
   [255]
 
 No diffs when comparing merge and p1 that kept p1's changes.  Diff of lfs to
 largefiles no longer operates in standin files.
 
-  $ hg diff -r 2:3
+This `head -n 20` looks dumb (since we expect no output), but if something
+breaks you can get 1048576 lines of +y in the output, which takes a looooooong
+time to print.
+  $ hg diff -r 2:3 | head -n 20
   $ hg diff -r 2:6
   diff -r e989d0fa3764 -r 752e3a0d8488 large.bin
   --- a/large.bin	Thu Jan 01 00:00:00 1970 +0000
   +++ b/large.bin	Thu Jan 01 00:00:00 1970 +0000
   @@ -1,1 +1,1 @@
   -below lfs threshold
   +largefile
   diff -r e989d0fa3764 -r 752e3a0d8488 lfs.bin
   --- a/lfs.bin	Thu Jan 01 00:00:00 1970 +0000
   +++ b/lfs.bin	Thu Jan 01 00:00:00 1970 +0000
   @@ -1,1 +1,1 @@
   -lfs above the lfs threshold for length 0000000000000
   +largefile above lfs threshold 0000000000000000000000