Merge branch 'bw/git-clang-format'

"make style" runs git-clang-format to help developers by pointing
out coding style issues.

* bw/git-clang-format:
Makefile: add style build rule
clang-format: outline the git project's coding style

diff --combined Makefile
index ed5960e6b378a982fb770f428324ba8fec0ba8c6,8e5b2df999b08420c038c05cdc7feb88530a0ab3..ed4ca438bd9c6ddab51f78cb4b620f02a7e12eed
--- 1/Makefile
--- 2/Makefile
+++ b/Makefile
@@@ -162,11 -162,6 +162,11 @@@ all:
  # algorithm. This is slower, but may detect attempted collision attacks.
  # Takes priority over other *_SHA1 knobs.
  #
 +# Define DC_SHA1_EXTERNAL in addition to DC_SHA1 if you want to build / link
 +# git with the external SHA1 collision-detect library.
 +# Without this option, i.e. the default behavior is to build git with its
 +# own built-in code (or submodule).
 +#
  # Define DC_SHA1_SUBMODULE in addition to DC_SHA1 to use the
  # sha1collisiondetection shipped as a submodule instead of the
  # non-submodule copy in sha1dc/. This is an experimental option used
@@@ -660,7 -655,6 +660,7 @@@ TEST_PROGRAMS_NEED_X += test-parse-opti
  TEST_PROGRAMS_NEED_X += test-path-utils
  TEST_PROGRAMS_NEED_X += test-prio-queue
  TEST_PROGRAMS_NEED_X += test-read-cache
 +TEST_PROGRAMS_NEED_X += test-write-cache
  TEST_PROGRAMS_NEED_X += test-ref-store
  TEST_PROGRAMS_NEED_X += test-regex
  TEST_PROGRAMS_NEED_X += test-revision-walking
@@@ -822,7 -816,6 +822,7 @@@ LIB_OBJS += notes-merge.
  LIB_OBJS += notes-utils.o
  LIB_OBJS += object.o
  LIB_OBJS += oidset.o
 +LIB_OBJS += packfile.o
  LIB_OBJS += pack-bitmap.o
  LIB_OBJS += pack-bitmap-write.o
  LIB_OBJS += pack-check.o
@@@ -849,7 -842,6 +849,7 @@@ LIB_OBJS += reflog-walk.
  LIB_OBJS += refs.o
  LIB_OBJS += refs/files-backend.o
  LIB_OBJS += refs/iterator.o
 +LIB_OBJS += refs/packed-backend.o
  LIB_OBJS += refs/ref-cache.o
  LIB_OBJS += ref-filter.o
  LIB_OBJS += remote.o
@@@ -1041,9 -1033,6 +1041,9 @@@ BASIC_CFLAGS += -fno-omit-frame-pointe
  ifneq ($(filter undefined,$(SANITIZERS)),)
  BASIC_CFLAGS += -DNO_UNALIGNED_LOADS
  endif
 +ifneq ($(filter leak,$(SANITIZERS)),)
 +BASIC_CFLAGS += -DSUPPRESS_ANNOTATED_LEAKS
 +endif
  endif
  
  ifndef sysconfdir
@@@ -1483,15 -1472,6 +1483,15 @@@ ifdef APPLE_COMMON_CRYPT
        BASIC_CFLAGS += -DSHA1_APPLE
  else
        DC_SHA1 := YesPlease
 +      BASIC_CFLAGS += -DSHA1_DC
 +      LIB_OBJS += sha1dc_git.o
 +ifdef DC_SHA1_EXTERNAL
 +      ifdef DC_SHA1_SUBMODULE
 +$(error Only set DC_SHA1_EXTERNAL or DC_SHA1_SUBMODULE, not both)
 +      endif
 +      BASIC_CFLAGS += -DDC_SHA1_EXTERNAL
 +      EXTLIBS += -lsha1detectcoll
 +else
  ifdef DC_SHA1_SUBMODULE
        LIB_OBJS += sha1collisiondetection/lib/sha1.o
        LIB_OBJS += sha1collisiondetection/lib/ubc_check.o
@@@ -1501,15 -1481,17 +1501,15 @@@ els
        LIB_OBJS += sha1dc/ubc_check.o
  endif
        BASIC_CFLAGS += \
 -              -DSHA1_DC \
                -DSHA1DC_NO_STANDARD_INCLUDES \
                -DSHA1DC_INIT_SAFE_HASH_DEFAULT=0 \
                -DSHA1DC_CUSTOM_INCLUDE_SHA1_C="\"cache.h\"" \
 -              -DSHA1DC_CUSTOM_TRAILING_INCLUDE_SHA1_C="\"sha1dc_git.c\"" \
 -              -DSHA1DC_CUSTOM_TRAILING_INCLUDE_SHA1_H="\"sha1dc_git.h\"" \
                -DSHA1DC_CUSTOM_INCLUDE_UBC_CHECK_C="\"git-compat-util.h\""
  endif
  endif
  endif
  endif
 +endif
  
  ifdef SHA1_MAX_BLOCK_SIZE
        LIB_OBJS += compat/sha1-chunked.o
@@@ -2055,6 -2037,7 +2055,6 @@@ XDIFF_OBJS += xdiff/xhistogram.
  
  VCSSVN_OBJS += vcs-svn/line_buffer.o
  VCSSVN_OBJS += vcs-svn/sliding_window.o
 -VCSSVN_OBJS += vcs-svn/repo_tree.o
  VCSSVN_OBJS += vcs-svn/fast_export.o
  VCSSVN_OBJS += vcs-svn/svndiff.o
  VCSSVN_OBJS += vcs-svn/svndump.o
@@@ -2457,6 -2440,10 +2457,10 @@@ $(SP_OBJ): %.sp: %.c GIT-CFLAGS FORC
  .PHONY: sparse $(SP_OBJ)
  sparse: $(SP_OBJ)
  
+ .PHONY: style
+ style:
+       git clang-format --style file --diff --extensions c,h
+ 
  check: common-cmds.h
        @if sparse; \
        then \