new behaviour in git merge

Hi all,

I am not sure when this started, but I think git has changed its behaviour when merging. As you all know, I do a lot of merging of trees for linux-next each day. Today I noticed that when I merge a tree, sometimes the timestamps are modified for files that are not modified on one side of the merge. It is not consistent and it is not all the files that are modified on the HEAD side (relative to the merge-base).

For example, today when I merged the drm tree:

$ git merge drm/drm-next
Auto-merging drivers/gpu/drm/drm_info.c
Removing drivers/gpu/drm/i830/Makefile
Removing drivers/gpu/drm/i830/i830_dma.c
Removing drivers/gpu/drm/i830/i830_drv.c
Removing drivers/gpu/drm/i830/i830_drv.h
Removing drivers/gpu/drm/i830/i830_irq.c
Auto-merging drivers/gpu/drm/i915/i915_drv.c
Auto-merging drivers/gpu/drm/i915/i915_drv.h
Auto-merging drivers/gpu/drm/i915/intel_sdvo.c
Auto-merging drivers/gpu/drm/radeon/atombios_crtc.c
Auto-merging drivers/gpu/drm/radeon/evergreen_blit_kms.c
Auto-merging drivers/gpu/drm/radeon/r600.c
Auto-merging drivers/gpu/drm/radeon/r600_blit_kms.c
Auto-merging drivers/gpu/drm/radeon/r600_cs.c
Auto-merging drivers/gpu/drm/radeon/r600d.h
Auto-merging drivers/gpu/drm/radeon/radeon_device.c
Auto-merging drivers/gpu/drm/radeon/radeon_display.c
Auto-merging drivers/gpu/drm/radeon/radeon_mode.h
Auto-merging drivers/gpu/drm/radeon/radeon_ttm.c
Auto-merging drivers/gpu/drm/radeon/rv770.c
Removing include/drm/i830_drm.h
Merge made by recursive.
 drivers/gpu/drm/Kconfig                     |   47 +-
 drivers/gpu/drm/Makefile                    |    3 +-
 drivers/gpu/drm/drm_crtc.c                  |   33 +
 drivers/gpu/drm/drm_drv.c                   |   48 +-
 drivers/gpu/drm/drm_edid.c                  |   19 +-
 drivers/gpu/drm/drm_edid_modes.h            |    4 +-
 drivers/gpu/drm/drm_fb_helper.c             |    5 +
 drivers/gpu/drm/drm_gem.c                   |    5 +-
 drivers/gpu/drm/drm_hashtab.c               |   27 +-
 drivers/gpu/drm/drm_info.c                  |   27 +-
 drivers/gpu/drm/drm_ioctl.c                 |  115 +--
 drivers/gpu/drm/drm_irq.c                   |   14 +-
 drivers/gpu/drm/drm_mm.c                    |  570 ++++++-----
 drivers/gpu/drm/drm_modes.c                 |    6 +-
 drivers/gpu/drm/drm_pci.c                   |  205 ++++-
 drivers/gpu/drm/drm_platform.c              |   75 ++-
 drivers/gpu/drm/drm_stub.c                  |   21 +-
 drivers/gpu/drm/drm_usb.c                   |  117 ++
 drivers/gpu/drm/i810/i810_dma.c             |   18 +-
 drivers/gpu/drm/i810/i810_drv.c             |   20 +-
 drivers/gpu/drm/i830/Makefile               |    8 -
 drivers/gpu/drm/i830/i830_dma.c             | 1560 ---------------------------
 drivers/gpu/drm/i830/i830_drv.c             |  107 --
 drivers/gpu/drm/i830/i830_drv.h             |  295 -----
 drivers/gpu/drm/i830/i830_irq.c             |  186 ----
 drivers/gpu/drm/i915/i915_drv.c             |   23 +-
 drivers/gpu/drm/i915/i915_drv.h             |    7 +
 drivers/gpu/drm/i915/i915_gem.c             |  103 ++-
 drivers/gpu/drm/i915/intel_sdvo.c           |    2 +-
 drivers/gpu/drm/mga/mga_dma.c               |    2 +-
 drivers/gpu/drm/mga/mga_drv.c               |   13 +-
 drivers/gpu/drm/nouveau/nouveau_drv.c       |   21 +-
 drivers/gpu/drm/nouveau/nouveau_mem.c       |    2 +-
 drivers/gpu/drm/nouveau/nouveau_object.c    |    2 +-
 drivers/gpu/drm/nouveau/nouveau_sgdma.c     |   31 +-
 drivers/gpu/drm/nouveau/nouveau_state.c     |    4 +-
 drivers/gpu/drm/nouveau/nv17_tv.c           |    4 +-
 drivers/gpu/drm/nouveau/nv17_tv.h           |    2 +-
 drivers/gpu/drm/nouveau/nv17_tv_modes.c     |    2 +-
 drivers/gpu/drm/nouveau/nv50_instmem.c      |    4 +-
 drivers/gpu/drm/nouveau/nvc0_instmem.c      |    2 +-
 drivers/gpu/drm/r128/r128_drv.c             |   14 +-
 drivers/gpu/drm/radeon/atombios_crtc.c      |    8 +-
 drivers/gpu/drm/radeon/evergreen_blit_kms.c |    2 +-
 drivers/gpu/drm/radeon/r600.c               |    2 +-
 drivers/gpu/drm/radeon/r600_audio.c         |    1 +
 drivers/gpu/drm/radeon/r600_blit_kms.c      |    2 +-
 drivers/gpu/drm/radeon/r600_cs.c            |  353 ++++--
 drivers/gpu/drm/radeon/r600_hdmi.c          |    1 +
 drivers/gpu/drm/radeon/r600d.h              |    5 +
 drivers/gpu/drm/radeon/radeon.h             |   90 +--
 drivers/gpu/drm/radeon/radeon_asic.h        |   77 ++-
 drivers/gpu/drm/radeon/radeon_benchmark.c   |    4 +-
 drivers/gpu/drm/radeon/radeon_cp.c          |    4 +-
 drivers/gpu/drm/radeon/radeon_cs.c          |    2 +-
 drivers/gpu/drm/radeon/radeon_device.c      |    4 +-
 drivers/gpu/drm/radeon/radeon_display.c     |    4 +-
 drivers/gpu/drm/radeon/radeon_drv.c         |   49 +-
 drivers/gpu/drm/radeon/radeon_fb.c          |   12 +-
 drivers/gpu/drm/radeon/radeon_gart.c        |   38 +-
 drivers/gpu/drm/radeon/radeon_gem.c         |   96 ++-
 drivers/gpu/drm/radeon/radeon_kms.c         |    4 +-
 drivers/gpu/drm/radeon/radeon_legacy_crtc.c |    4 +-
 drivers/gpu/drm/radeon/radeon_mode.h        |    1 +
 drivers/gpu/drm/radeon/radeon_object.c      |   28 +-
 drivers/gpu/drm/radeon/radeon_object.h      |    7 +-
 drivers/gpu/drm/radeon/radeon_ring.c        |    4 +-
 drivers/gpu/drm/radeon/radeon_test.c        |    4 +-
 drivers/gpu/drm/radeon/radeon_ttm.c         |   10 +-
 drivers/gpu/drm/radeon/rv770.c              |    2 +-
 drivers/gpu/drm/savage/savage_drv.c         |   14 +-
 drivers/gpu/drm/sis/sis_drv.c               |   13 +-
 drivers/gpu/drm/tdfx/tdfx_drv.c             |   13 +-
 drivers/gpu/drm/ttm/ttm_agp_backend.c       |    3 +-
 drivers/gpu/drm/ttm/ttm_bo.c                |    3 +-
 drivers/gpu/drm/ttm/ttm_page_alloc.c        |   34 +-
 drivers/gpu/drm/ttm/ttm_tt.c                |   12 +-
 drivers/gpu/drm/via/via_drv.c               |   13 +-
 drivers/gpu/drm/vmwgfx/vmwgfx_buffer.c      |    3 +-
 drivers/gpu/drm/vmwgfx/vmwgfx_drv.c         |   23 +-
 drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c         |    5 +-
 include/drm/Kbuild                          |    1 -
 include/drm/drm.h                           |    4 +
 include/drm/drmP.h                          |  120 ++-
 include/drm/drm_crtc.h                      |   13 +-
 include/drm/drm_hashtab.h                   |    6 +-
 include/drm/drm_mm.h                        |   49 +-
 include/drm/drm_mode.h                      |   29 +
 include/drm/drm_usb.h                       |   15 +
 include/drm/i830_drm.h                      |  342 ------
 include/drm/ttm/ttm_bo_driver.h             |    6 +-
 include/drm/ttm/ttm_page_alloc.h            |    8 +-
 92 files changed, 1755 insertions(+), 3565 deletions(-)
 create mode 100644 drivers/gpu/drm/drm_usb.c
 delete mode 100644 drivers/gpu/drm/i830/Makefile
 delete mode 100644 drivers/gpu/drm/i830/i830_dma.c
 delete mode 100644 drivers/gpu/drm/i830/i830_drv.c
 delete mode 100644 drivers/gpu/drm/i830/i830_drv.h
 delete mode 100644 drivers/gpu/drm/i830/i830_irq.c
 create mode 100644 include/drm/drm_usb.h
 delete mode 100644 include/drm/i830_drm.h

Then the timestamps on all these files were updated (this is the list of files rsync has decided to copy - I checked and the timestamps are indeed modified):

Documentation/devicetree/booting-without-of.txt Documentation/devicetree/bindings/eeprom.txt Documentation/devicetree/bindings/marvell.txt Documentation/devicetree/bindings/xilinx.txt Documentation/devicetree/bindings/ata/fsl-sata.txt Documentation/devicetree/bindings/gpio/8xxx_gpio.txt Documentation/devicetree/bindings/gpio/gpio.txt Documentation/devicetree/bindings/gpio/led.txt Documentation/devicetree/bindings/i2c/fsl-i2c.txt Documentation/devicetree/bindings/mmc/fsl-esdhc.txt Documentation/devicetree/bindings/mmc/mmc-spi-slot.txt Documentation/devicetree/bindings/mtd/fsl-upm-nand.txt Documentation/devicetree/bindings/mtd/mtd-physmap.txt Documentation/devicetree/bindings/net/fsl-tsec-phy.txt Documentation/devicetree/bindings/net/mdio-gpio.txt Documentation/devicetree/bindings/net/phy.txt Documentation/devicetree/bindings/net/can/mpc5xxx-mscan.txt Documentation/devicetree/bindings/net/can/sja1000.txt Documentation/devicetree/bindings/pci/83xx-512x-pci.txt Documentation/devicetree/bindings/powerpc/4xx/cpm.txt Documentation/devicetree/bindings/powerpc/4xx/emac.txt Documentation/devicetree/bindings/powerpc/4xx/ndfc.txt Documentation/devicetree/bindings/powerpc/4xx/ppc440spe-adma.txt Documentation/devicetree/bindings/powerpc/4xx/reboot.txt Documentation/devicetree/bindings/powerpc/fsl/board.txt Documentation/devicetree/bindings/powerpc/fsl/diu.txt Documentation/devicetree/bindings/powerpc/fsl/dma.txt Documentation/devicetree/bindings/powerpc/fsl/ecm.txt Documentation/devicetree/bindings/powerpc/fsl/gtm.txt Documentation/devicetree/bindings/powerpc/fsl/guts.txt Documentation/devicetree/bindings/powerpc/fsl/lbc.txt Documentation/devicetree/bindings/powerpc/fsl/mcm.txt Documentation/devicetree/bindings/powerpc/fsl/mcu-mpc8349emitx.txt Documentation/devicetree/bindings/powerpc/fsl/mpc5121-psc.txt Documentation/devicetree/bindings/powerpc/fsl/mpc5200.txt Documentation/devicetree/bindings/powerpc/fsl/mpic.txt Documentation/devicetree/bindings/powerpc/fsl/msi-pic.txt Documentation/devicetree/bindings/powerpc/fsl/pmc.txt Documentation/devicetree/bindings/powerpc/fsl/sec.txt Documentation/devicetree/bindings/powerpc/fsl/ssi.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/gpio.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/network.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/serial.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm/brg.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm/i2c.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm/pic.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/cpm/usb.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/firmware.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/par_io.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/pincfg.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/ucc.txt Documentation/devicetree/bindings/powerpc/fsl/cpm_qe/qe/usb.txt Documentation/devicetree/bindings/powerpc/nintendo/gamecube.txt Documentation/devicetree/bindings/powerpc/nintendo/wii.txt Documentation/devicetree/bindings/spi/fsl-spi.txt Documentation/devicetree/bindings/spi/spi-bus.txt Documentation/devicetree/bindings/usb/fsl-usb.txt Documentation/devicetree/bindings/usb/usb-ehci.txt Documentation/laptops/hpfall.c Documentation/misc-devices/lis3lv02d arch/arm/mach-exynos4/Kconfig arch/arm/mach-exynos4/Makefile.boot arch/arm/mach-exynos4/clock.c arch/arm/mach-exynos4/cpu.c arch/arm/mach-exynos4/cpufreq.c arch/arm/mach-exynos4/dev-audio.c arch/arm/mach-exynos4/dev-pd.c arch/arm/mach-exynos4/dev-sysmmu.c arch/arm/mach-exynos4/dma.c arch/arm/mach-exynos4/gpiolib.c arch/arm/mach-exynos4/headsmp.S arch/arm/mach-exynos4/hotplug.c arch/arm/mach-exynos4/init.c arch/arm/mach-exynos4/irq-combiner.c arch/arm/mach-exynos4/irq-eint.c arch/arm/mach-exynos4/localtimer.c arch/arm/mach-exynos4/mach-smdkc210.c arch/arm/mach-exynos4/mach-smdkv310.c arch/arm/mach-exynos4/mach-universal_c210.c arch/arm/mach-exynos4/platsmp.c arch/arm/mach-exynos4/setup-i2c0.c arch/arm/mach-exynos4/setup-i2c1.c arch/arm/mach-exynos4/setup-i2c2.c arch/arm/mach-exynos4/setup-i2c3.c arch/arm/mach-exynos4/setup-i2c4.c arch/arm/mach-exynos4/setup-i2c5.c arch/arm/mach-exynos4/setup-i2c6.c arch/arm/mach-exynos4/setup-i2c7.c arch/arm/mach-exynos4/setup-sdhci-gpio.c arch/arm/mach-exynos4/setup-sdhci.c arch/arm/mach-exynos4/time.c arch/arm/mach-exynos4/include/mach/debug-macro.S arch/arm/mach-exynos4/include/mach/entry-macro.S arch/arm/mach-exynos4/include/mach/hardware.h arch/arm/mach-exynos4/include/mach/io.h arch/arm/mach-exynos4/include/mach/irqs.h arch/arm/mach-exynos4/include/mach/memory.h arch/arm/mach-exynos4/include/mach/pwm-clock.h arch/arm/mach-exynos4/include/mach/regs-clock.h arch/arm/mach-exynos4/include/mach/regs-irq.h arch/arm/mach-exynos4/include/mach/regs-mem.h arch/arm/mach-exynos4/include/mach/regs-pmu.h arch/arm/mach-exynos4/include/mach/regs-sysmmu.h arch/arm/mach-exynos4/include/mach/smp.h arch/arm/mach-exynos4/include/mach/sysmmu.h arch/arm/mach-exynos4/include/mach/system.h arch/arm/mach-exynos4/include/mach/timex.h arch/arm/mach-exynos4/include/mach/uncompress.h arch/arm/mach-exynos4/include/mach/vmalloc.h arch/arm/mach-msm/devices-iommu.c arch/arm/mach-mx5/devices-imx50.h arch/arm/mach-vt8500/include/mach/vmalloc.h arch/arm/plat-versatile/headsmp.S arch/arm/plat-versatile/localtimer.c drivers/char/virtio_console.c deleting drivers/gpu/drm/i830/i830_irq.c deleting drivers/gpu/drm/i830/i830_drv.h deleting drivers/gpu/drm/i830/i830_drv.c deleting drivers/gpu/drm/i830/i830_dma.c deleting drivers/gpu/drm/i830/Makefile drivers/gpu/drm/Kconfig drivers/gpu/drm/Makefile drivers/gpu/drm/drm_crtc.c drivers/gpu/drm/drm_drv.c drivers/gpu/drm/drm_edid.c drivers/gpu/drm/drm_edid_modes.h drivers/gpu/drm/drm_fb_helper.c drivers/gpu/drm/drm_gem.c drivers/gpu/drm/drm_hashtab.c drivers/gpu/drm/drm_info.c drivers/gpu/drm/drm_ioctl.c drivers/gpu/drm/drm_irq.c drivers/gpu/drm/drm_mm.c drivers/gpu/drm/drm_modes.c drivers/gpu/drm/drm_pci.c drivers/gpu/drm/drm_platform.c drivers/gpu/drm/drm_stub.c drivers/gpu/drm/drm_usb.c drivers/gpu/drm/i810/i810_dma.c drivers/gpu/drm/i810/i810_drv.c drivers/gpu/drm/i915/i915_drv.c drivers/gpu/drm/i915/i915_drv.h drivers/gpu/drm/i915/i915_gem.c drivers/gpu/drm/i915/intel_sdvo.c drivers/gpu/drm/mga/mga_dma.c drivers/gpu/drm/mga/mga_drv.c drivers/gpu/drm/nouveau/nouveau_drv.c drivers/gpu/drm/nouveau/nouveau_mem.c drivers/gpu/drm/nouveau/nouveau_object.c drivers/gpu/drm/nouveau/nouveau_sgdma.c drivers/gpu/drm/nouveau/nouveau_state.c drivers/gpu/drm/nouveau/nv17_tv.c drivers/gpu/drm/nouveau/nv17_tv.h drivers/gpu/drm/nouveau/nv17_tv_modes.c drivers/gpu/drm/nouveau/nv50_instmem.c drivers/gpu/drm/nouveau/nvc0_instmem.c drivers/gpu/drm/r128/r128_drv.c drivers/gpu/drm/radeon/atombios_crtc.c drivers/gpu/drm/radeon/evergreen_blit_kms.c drivers/gpu/drm/radeon/r600.c drivers/gpu/drm/radeon/r600_audio.c drivers/gpu/drm/radeon/r600_blit_kms.c drivers/gpu/drm/radeon/r600_cs.c drivers/gpu/drm/radeon/r600_hdmi.c drivers/gpu/drm/radeon/r600d.h drivers/gpu/drm/radeon/radeon.h drivers/gpu/drm/radeon/radeon_asic.h drivers/gpu/drm/radeon/radeon_benchmark.c drivers/gpu/drm/radeon/radeon_cp.c drivers/gpu/drm/radeon/radeon_cs.c drivers/gpu/drm/radeon/radeon_device.c drivers/gpu/drm/radeon/radeon_display.c drivers/gpu/drm/radeon/radeon_drv.c drivers/gpu/drm/radeon/radeon_fb.c drivers/gpu/drm/radeon/radeon_gart.c drivers/gpu/drm/radeon/radeon_gem.c drivers/gpu/drm/radeon/radeon_kms.c drivers/gpu/drm/radeon/radeon_legacy_crtc.c drivers/gpu/drm/radeon/radeon_mode.h drivers/gpu/drm/radeon/radeon_object.c drivers/gpu/drm/radeon/radeon_object.h drivers/gpu/drm/radeon/radeon_ring.c drivers/gpu/drm/radeon/radeon_test.c drivers/gpu/drm/radeon/radeon_ttm.c drivers/gpu/drm/radeon/rv770.c drivers/gpu/drm/savage/savage_drv.c drivers/gpu/drm/sis/sis_drv.c drivers/gpu/drm/tdfx/tdfx_drv.c drivers/gpu/drm/ttm/ttm_agp_backend.c drivers/gpu/drm/ttm/ttm_bo.c drivers/gpu/drm/ttm/ttm_page_alloc.c drivers/gpu/drm/ttm/ttm_tt.c drivers/gpu/drm/via/via_drv.c drivers/gpu/drm/vmwgfx/vmwgfx_buffer.c drivers/gpu/drm/vmwgfx/vmwgfx_drv.c drivers/gpu/drm/vmwgfx/vmwgfx_ldu.c drivers/misc/lis3lv02d/lis3lv02d.c drivers/misc/lis3lv02d/lis3lv02d.h drivers/misc/lis3lv02d/lis3lv02d_i2c.c drivers/misc/lis3lv02d/lis3lv02d_spi.c drivers/net/wireless/iwlegacy/iwl-3945-debugfs.c drivers/net/wireless/iwlegacy/iwl-3945-fh.h drivers/net/wireless/iwlegacy/iwl-3945-hw.h drivers/net/wireless/iwlegacy/iwl-3945-rs.c drivers/net/wireless/iwlegacy/iwl-3945.c drivers/net/wireless/iwlegacy/iwl-3945.h drivers/net/wireless/iwlegacy/iwl-4965-debugfs.h drivers/net/wireless/iwlegacy/iwl-4965-eeprom.c drivers/net/wireless/iwlegacy/iwl-4965-hw.h drivers/net/wireless/iwlegacy/iwl-4965-led.c drivers/net/wireless/iwlegacy/iwl-4965.c drivers/net/wireless/iwlegacy/iwl3945-base.c drivers/net/wireless/rtlwifi/rtl8192c/fw_common.c drivers/net/wireless/rtlwifi/rtl8192c/fw_common.h drivers/net/wireless/rtlwifi/rtl8192cu/rf.h drivers/platform/x86/hp_accel.c drivers/scsi/fcoe/fcoe_ctlr.c drivers/watchdog/m54xx_wdt.c deleting include/drm/i830_drm.h include/drm/Kbuild include/drm/drm.h include/drm/drmP.h include/drm/drm_crtc.h include/drm/drm_hashtab.h include/drm/drm_mm.h include/drm/drm_mode.h include/drm/drm_usb.h include/drm/ttm/ttm_bo_driver.h include/drm/ttm/ttm_page_alloc.h include/linux/hid-roccat.h include/linux/i2c-tegra.h include/linux/i2c/atmel_mxt_ts.h include/media/s5p_fimc.h net/bluetooth/l2cap_core.c

I am pretty sure that git did not used to do this. Has anyone else seen this? I am running git version 1.7.4.1 from Debian unstable.

On Thu, Feb 24, 2011 at 02:33:53PM +1100, Stephen Rothwell wrote:

I don't think any such change was intentional. I couldn't reproduce with a trivial example. Can you give the commit IDs of the two heads in your example merge? I'd like to try bisecting if I can reproduce the issue.

-Peff

Hi Jeff,

On Thu, 24 Feb 2011 03:15:53 -0500 Jeff King <peff@peff.net> wrote:

I was hoping that it was not intentional :-)

I also tried a trivial example but failed to reproduce it.

In today's linux-next tree (available at git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git), commit ad11c1e8abca18872c2993b09b1abde418955b6c is just before the merge and commit a2c06ee2fe5b48a71e697bae00c6e7195fc016b6 is what was merged.

I just did this in a copy of my tree:

	git reset --hard ad11c1e8abca18872c2993b09b1abde418955b6c
	sleep 90
	git merge a2c06ee2fe5b48a71e697bae00c6e7195fc016b6

A comparison of the ls -lR ouput before and after showed a lot of changed modification times.

Several other merges showed the same problem.

Thanks for looking at this.

[+cc Elijah Newren; this is a bug that bisects to one of your commits.
 The backstory is that during a merge, many unrelated files get
 unnecessarily re-written with the same content. Read on for details.]

On Thu, Feb 24, 2011 at 08:24:54PM +1100, Stephen Rothwell wrote:

Thanks for the reproduction recipe. I was able to bisect using this script as my test:

-- >8 -- #!/bin/sh

stat() {
  git ls-files -z | xargs --null stat --format='%Y %n' | sort
}

cd linux-next &&
git reset --hard ad11c1e8abca18872c2993b09b1abde418955b6c &&
sleep 3 &&
stat >before &&
git merge a2c06ee2fe5b48a71e697bae00c6e7195fc016b6 &&
stat >after &&
comm -13 before after | cut -d' ' -f2 | sort >stat-diff &&
git diff-tree -r --name-only HEAD HEAD^ >tree-diff &&
comm -23 stat-diff tree-diff >extra-stats &&
if test -s extra-stats; then
  cat extra-stats
  echo FAIL
  exit 1
else
  echo OK
  exit 0
fi
-- 8< --

It bisects to 882fd11 (merge-recursive: Delay content merging for renames, 2010-09-20). And indeed, looking further at the files that get modified, they appear to be renames on one side of the merge, but not touched on the other side. But rather than notice that there is nothing to be done on them, we seem to update the index and write out the new entries.

The patch below makes the problem go away in your test case, but also introduces some test failures in t3509, so I'm sure there is something else going on. I'm somewhat clueless about the merge code, so I'll defer to Elijah, who wrote 882fd11, and see what he says.

-Peff

This patch series adds a simple testcase demonstrating the problem reported by Stephen Rothwell, and a fix. Unfortunately, there's a bug with the fix (hence the RFC) that makes the relevant files racily clean rather than clearly clean (i.e. 'git diff-files' will report these files as modified when it shouldn't).

I'll try to figure out how to fix the second problem in the next few days. If anyone has some hints, I'm all ears.

Elijah Newren (2):
  t6022: New test checking for unnecessary updates of renamed+modified
    files
  merge-recursive: When we detect we can skip an update, actually skip
    it

 merge-recursive.c       |    7 +++++--
 t/t6022-merge-rename.sh |   32 ++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 2 deletions(-)

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 t/t6022-merge-rename.sh |   32 ++++++++++++++++++++++++++++++++
 1 files changed, 32 insertions(+), 0 deletions(-)

In 882fd11 (merge-recursive: Delay content merging for renames 2010-09-20), the code that checked for whether we could skip updating a file in the working directory (due to the merged version matching the current copy) was moved into a separate function. In order to defer the content merging, we had to update the index with unmerged entries. As part of the move, a bug was introduced such that the message about skipping the update would be printed (if GIT_MERGE_VERBOSITY was sufficiently high) but the file would be updated in the working copy anyway.

When we detect that the file does not need to be updated in the working copy, update the index to remove the unmerged entries and then return early before updating the working copy.

STILL BROKEN: Unfortunately, this change leaves the index in a state where the renamed file is only racily clean; a 'git diff-files' will report the file as modified.

--- No Signed-off-by since it still doesn't work.

 merge-recursive.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

Hi,

On Sat, Feb 26, 2011 at 11:34 AM, Elijah Newren <newren@gmail.com> wrote:

And, of course, I forgot to include the cc's in my send-email command.
 Sorry about that, Stephen and Jeff.  Adding you on this email, at
least.