Coverage support with LCOV and GCOV

This patch adds a `coverage` target that allows coverage statisitics to be
retrieved for the project. It requires that lcov and gcov is installed and
that the generator is unix makefiles but this can be improved upon in
future releases.

To make it work use the coverage build type:

```
cmake -DCMAKE_BUILD_TYPE=Coverage .
make coverage
```

Author: mattyclarkson

.gitignore

@@ -10,6 +10,10 @@
 *.pyc
 __pycache__
 
+# lcov
+*.lcov
+/lcov
+
 # cmake files.
 /Testing
 CMakeCache.txt

CMakeLists.txt

@@ -64,6 +64,27 @@ if (BENCHMARK_ENABLE_LTO)
   endif()
 endif()
 
+# Coverage build type
+set(CMAKE_CXX_FLAGS_COVERAGE "${CMAKE_CXX_FLAGS_DEBUG}" CACHE STRING
+  "Flags used by the C++ compiler during coverage builds."
+  FORCE)
+set(CMAKE_EXE_LINKER_FLAGS_COVERAGE
+  "${CMAKE_EXE_LINKER_FLAGS_DEBUG}" CACHE STRING
+  "Flags used for linking binaries during coverage builds."
+  FORCE)
+set(CMAKE_SHARED_LINKER_FLAGS_COVERAGE
+  "${CMAKE_SHARED_LINKER_FLAGS_DEBUG}" CACHE STRING
+  "Flags used by the shared libraries linker during coverage builds."
+  FORCE)
+mark_as_advanced(
+  CMAKE_CXX_FLAGS_COVERAGE
+  CMAKE_EXE_LINKER_FLAGS_COVERAGE
+  CMAKE_SHARED_LINKER_FLAGS_COVERAGE)
+set(CMAKE_BUILD_TYPE "${CMAKE_BUILD_TYPE}" CACHE STRING
+  "Choose the type of build, options are: None Debug Release RelWithDebInfo MinSizeRel Coverage."
+  FORCE)
+add_cxx_compiler_flag(--coverage COVERAGE)
+
 # C++ feature checks
 cxx_feature_check(STD_REGEX)
 cxx_feature_check(GNU_POSIX_REGEX)

test/CMakeLists.txt

@@ -43,3 +43,45 @@ compile_benchmark_test(cxx03_test)
 set_target_properties(cxx03_test
     PROPERTIES COMPILE_FLAGS "${CXX03_FLAGS}")
 add_test(cxx03 cxx03_test --benchmark_min_time=0.01)
+
+# Add the coverage command(s)
+string(TOLOWER ${CMAKE_BUILD_TYPE} CMAKE_BUILD_TYPE_LOWER)
+if (${CMAKE_BUILD_TYPE_LOWER} MATCHES "coverage")
+  find_program(GCOV gcov)
+  find_program(LCOV lcov)
+  find_program(GENHTML genhtml)
+  find_program(CTEST ctest)
+  if (GCOV AND LCOV AND GENHTML AND CTEST AND HAVE_CXX_FLAG_COVERAGE)
+    add_custom_command(
+      OUTPUT ${CMAKE_BINARY_DIR}/lcov/index.html
+      COMMAND ${LCOV} -q -z -d .
+      COMMAND ${LCOV} -q --no-external -c -b "${CMAKE_SOURCE_DIR}" -d . -o before.lcov -i
+      COMMAND ${CTEST} --force-new-ctest-process
+      COMMAND ${LCOV} -q --no-external -c -b "${CMAKE_SOURCE_DIR}" -d . -o after.lcov
+      COMMAND ${LCOV} -q -a before.lcov -a after.lcov --output-file final.lcov
+      COMMAND ${LCOV} -q -r final.lcov "'${CMAKE_SOURCE_DIR}/test/*'" -o final.lcov
+      COMMAND ${GENHTML} final.lcov -o lcov --demangle-cpp --sort -p "${CMAKE_BINARY_DIR}" -t benchmark
+      DEPENDS filter_test benchmark_test options_test basic_test fixture_test cxx03_test
+      WORKING_DIRECTORY ${CMAKE_BINARY_DIR}
+      COMMENT "Running LCOV"
+    )
+    add_custom_target(coverage
+      DEPENDS ${CMAKE_BINARY_DIR}/lcov/index.html
+      COMMENT "LCOV report at lcov/index.html"
+    )
+    message(STATUS "Coverage command added")
+  else()
+    if (HAVE_CXX_FLAG_COVERAGE)
+      set(CXX_FLAG_COVERAGE_MESSAGE supported)
+    else()
+      set(CXX_FLAG_COVERAGE_MESSAGE unavailable)
+    endif()
+    message(WARNING
+      "Coverage not available:\n"
+      "  gcov: ${GCOV}\n"
+      "  lcov: ${LCOV}\n"
+      "  genhtml: ${GENHTML}\n"
+      "  ctest: ${CTEST}\n"
+      "  --coverage flag: ${CXX_FLAG_COVERAGE_MESSAGE}")
+  endif()
+endif()