Check exit codes of git commands in CMake

Also introduces find_command to find the path to the git executable.

CMakeLists.txt

@@ -5,38 +5,53 @@ cmake_minimum_required(VERSION 3.2)
 
 project(linuxdeployqt)
 
-# read Git revision ID
-execute_process(
-    COMMAND git rev-parse --short HEAD
-    WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
-    OUTPUT_VARIABLE GIT_COMMIT
-    OUTPUT_STRIP_TRAILING_WHITESPACE
-)
+find_program(GIT git)
 
 # make sure Git revision ID and latest tag is not stored in the CMake cache
 # otherwise, one would have to reset the CMake cache on every new commit to make sure the Git commit ID is up to date
 unset(GIT_COMMIT CACHE)
 unset(GIT_LATEST_TAG CACHE)
 
+if("${GIT}" STREQUAL "GIT-NOTFOUND")
+    message(FATAL_ERROR "Could not find git")
+endif()
+
 # read Git revision ID and latest tag number
 execute_process(
-    COMMAND git rev-parse --short HEAD
+    COMMAND "${GIT}" rev-parse --short HEAD
     WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
     OUTPUT_VARIABLE GIT_COMMIT
     OUTPUT_STRIP_TRAILING_WHITESPACE
+    RESULT_VARIABLE GIT_COMMIT_RESULT
 )
+if(NOT GIT_COMMIT_RESULT EQUAL 0)
+    message(FATAL_ERROR "Failed to determine git commit ID")
+endif()
+mark_as_advanced(GIT_COMMIT GIT_COMMIT_RESULT)
+
 execute_process(
-    COMMAND git rev-list --tags --skip=1 --max-count=1
+    COMMAND "${GIT}" rev-list --tags --skip=1 --max-count=1
     WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
     OUTPUT_VARIABLE GIT_TAG_ID
     OUTPUT_STRIP_TRAILING_WHITESPACE
+    RESULT_VARIABLE GIT_TAG_ID_RESULT
 )
+if(NOT GIT_TAG_ID_RESULT EQUAL 0)
+    message(FATAL_ERROR "Failed to determine git tag ID")
+endif()
+mark_as_advanced(GIT_TAG_ID GIT_TAG_ID_RESULT)
+
 execute_process(
-    COMMAND git describe --tags ${GIT_TAG_ID} --abbrev=0
+    COMMAND "${GIT}" describe --tags ${GIT_TAG_ID} --abbrev=0
     WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
     OUTPUT_VARIABLE GIT_TAG_NAME
     OUTPUT_STRIP_TRAILING_WHITESPACE
+    RESULT_VARIABLE GIT_TAG_NAME_RESULT
 )
+if(NOT GIT_TAG_NAME_RESULT EQUAL 0)
+    message(FATAL_ERROR "Failed to determine git tag name")
+endif()
+mark_as_advanced(GIT_TAG_NAME GIT_TAG_NAME_RESULT)
 
 # set version and build number
 set(VERSION 1-alpha)
@@ -51,6 +66,11 @@ execute_process(
     COMMAND env LC_ALL=C date -u "+%Y-%m-%d %H:%M:%S %Z"
     OUTPUT_VARIABLE DATE
     OUTPUT_STRIP_TRAILING_WHITESPACE
+    RESULT_VARIABLE DATE_RESULT
 )
+if(NOT DATE_RESULT EQUAL 0)
+    message(FATAL_ERROR "Failed to determine date string")
+endif()
+mark_as_advanced(DATE DATE_RESULT)
 
 add_subdirectory(tools/linuxdeployqt)