cmake auto clone rocksdb (#60)

Summary:
We require passing `ROCKSDB_DIR` to cmake command, which is not easy to use. Update cmake script to make it clone rocksdb (currently pointing to pingcap/rocksdb tikv-3.0 branch) to make development use easier.

Test Plan:
local test + travis

.travis.yml

@@ -57,7 +57,6 @@ install:
         fi
       done
     fi
-  - git clone --depth=1 --branch=tikv-3.0 https://github.com/pingcap/rocksdb.git
   - export CTEST_OUTPUT_ON_FAILURE=1
   - if [ "${COMPILER}" == gcc7 ]; then
       CC=gcc-7;

CMakeLists.txt

@@ -2,6 +2,26 @@ cmake_minimum_required(VERSION 3.0)
 project(titan)
 enable_language(CXX)
 enable_language(C)
+find_package(Git)
+
+if (NOT ROCKSDB_GIT_REPO)
+  set(ROCKSDB_GIT_REPO "https://github.com/pingcap/rocksdb.git")
+endif()
+
+if (NOT ROCKSDB_GIT_BRANCH)
+  set(ROCKSDB_GIT_BRANCH "tikv-3.0")
+endif()
+
+if (NOT DEFINED ROCKSDB_DIR)
+  if (GIT_FOUND)
+    if (WIN32)
+      execute_process(COMMAND $ENV{COMSPEC} /C ${GIT_EXECUTABLE} clone --branch=${ROCKSDB_GIT_BRANCH} ${ROCKSDB_GIT_REPO})
+    else()
+      execute_process(COMMAND ${GIT_EXECUTABLE} clone --branch=${ROCKSDB_GIT_BRANCH} ${ROCKSDB_GIT_REPO})
+    endif()
+    set(ROCKSDB_DIR "${CMAKE_BINARY_DIR}/rocksdb")
+  endif()
+endif()
 
 if (NOT DEFINED ROCKSDB_DIR)
   message(FATAL_ERROR "ROCKSDB_DIR is not defined.")
@@ -31,7 +51,6 @@ if (CMAKE_BUILD_TYPE STREQUAL "Release")
   set(WITH_TITAN_TESTS OFF)
 endif()
 
-find_package(Git)
 if(GIT_FOUND AND EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/.git")
   if(WIN32)
     execute_process(COMMAND $ENV{COMSPEC} /C ${GIT_EXECUTABLE} rev-parse HEAD OUTPUT_VARIABLE GIT_SHA)

README.md

@@ -15,9 +15,14 @@ and provide the path to Titan build script.
 # To build:
 mkdir -p build
 cd build
-cmake .. -DROCKSDB_DIR=<rocksdb_source_dir>
+cmake ..
 make -j<n>
 
+# To specify custom rocksdb
+cmake .. -DROCKSDB_DIR=<rocksdb_source_dir>
+# or
+cmake .. -DROCKSDB_GIT_REPO=<git_repo> -DROCKSDB_GIT_BRANCH=<branch>
+
 # Build static lib (i.e. libtitan.a) only:
 make titan -j<n>
 

scripts/travis-make.sh

 #!/bin/bash
 
 set -ev
-cmake . -L -DROCKSDB_DIR=./rocksdb -DTRAVIS=ON ${BUILD_OPT} ${SANITIZER_OPT} ${TOOLS_OPT} ${COVERAGE_OPT}
+cmake . -L -DTRAVIS=ON ${BUILD_OPT} ${SANITIZER_OPT} ${TOOLS_OPT} ${COVERAGE_OPT}
 make -j4
 ctest -R titan