Merge topic 'ExternalProject_GitUpdate'

f2128d4c ExternalProject: Improve handling of git remote branches
ff2451dc ExternalProject: Strip trailing space from git hash

Modules/ExternalProject.cmake

@@ -454,6 +454,7 @@ execute_process(
   WORKING_DIRECTORY \"${work_dir}\"
   RESULT_VARIABLE error_code
   OUTPUT_VARIABLE head_sha
+  OUTPUT_STRIP_TRAILING_WHITESPACE
   )
 if(error_code)
   message(FATAL_ERROR \"Failed to get the hash for HEAD\")
@@ -472,6 +473,17 @@ else()
   set(is_remote_ref 0)
 endif()
 
+# Tag is in the form <remote>/<tag> (i.e. origin/master) we must strip
+# the remote from the tag.
+if(\"\${show_ref_output}\" MATCHES \"refs/remotes/${git_tag}\")
+  string(REGEX MATCH \"^([^/]+)/(.+)$\" _unused \"${git_tag}\")
+  set(git_remote \"\${CMAKE_MATCH_1}\")
+  set(git_tag \"\${CMAKE_MATCH_2}\")
+else()
+  set(git_remote \"origin\")
+  set(git_tag \"${git_tag}\")
+endif()
+
 # This will fail if the tag does not exist (it probably has not been fetched
 # yet).
 execute_process(
@@ -479,6 +491,7 @@ execute_process(
   WORKING_DIRECTORY \"${work_dir}\"
   RESULT_VARIABLE error_code
   OUTPUT_VARIABLE tag_sha
+  OUTPUT_STRIP_TRAILING_WHITESPACE
   )
 
 # Is the hash checkout out that we want?
@@ -492,13 +505,94 @@ if(error_code OR is_remote_ref OR NOT (\"\${tag_sha}\" STREQUAL \"\${head_sha}\"
     message(FATAL_ERROR \"Failed to fetch repository '${git_repository}'\")
   endif()
 
-  execute_process(
-    COMMAND \"${git_EXECUTABLE}\" checkout ${git_tag}
-    WORKING_DIRECTORY \"${work_dir}\"
-    RESULT_VARIABLE error_code
-    )
-  if(error_code)
-    message(FATAL_ERROR \"Failed to checkout tag: '${git_tag}'\")
+  if(is_remote_ref)
+    # Check if stash is needed
+    execute_process(
+      COMMAND \"${git_EXECUTABLE}\" status --porcelain
+      WORKING_DIRECTORY \"${work_dir}\"
+      RESULT_VARIABLE error_code
+      OUTPUT_VARIABLE repo_status
+      )
+    if(error_code)
+      message(FATAL_ERROR \"Failed to get the status\")
+    endif()
+    string(LENGTH \"\${repo_status}\" need_stash)
+
+    # If not in clean state, stash changes in order to be able to be able to
+    # perform git pull --rebase
+    if(need_stash)
+      execute_process(
+        COMMAND \"${git_EXECUTABLE}\" stash save --all --quiet
+        WORKING_DIRECTORY \"${work_dir}\"
+        RESULT_VARIABLE error_code
+        )
+      if(error_code)
+        message(FATAL_ERROR \"Failed to stash changes\")
+      endif()
+    endif()
+
+    # Pull changes from the remote branch
+    execute_process(
+      COMMAND \"${git_EXECUTABLE}\" rebase \${git_remote}/\${git_tag}
+      WORKING_DIRECTORY \"${work_dir}\"
+      RESULT_VARIABLE error_code
+      )
+    if(error_code)
+      # Rebase failed: Restore previous state.
+      execute_process(
+        COMMAND \"${git_EXECUTABLE}\" rebase --abort
+        WORKING_DIRECTORY \"${work_dir}\"
+      )
+      if(need_stash)
+        execute_process(
+          COMMAND \"${git_EXECUTABLE}\" stash pop --index --quiet
+          WORKING_DIRECTORY \"${work_dir}\"
+          )
+      endif()
+      message(FATAL_ERROR \"\\nFailed to rebase in: '${work_dir}/${src_name}'.\\nYou will have to resolve the conflicts manually\")
+    endif()
+
+    if(need_stash)
+      execute_process(
+        COMMAND \"${git_EXECUTABLE}\" stash pop --index --quiet
+        WORKING_DIRECTORY \"${work_dir}\"
+        RESULT_VARIABLE error_code
+        )
+      if(error_code)
+        # Stash pop --index failed: Try again dropping the index
+        execute_process(
+          COMMAND \"${git_EXECUTABLE}\" reset --hard --quiet
+          WORKING_DIRECTORY \"${work_dir}\"
+          RESULT_VARIABLE error_code
+          )
+        execute_process(
+          COMMAND \"${git_EXECUTABLE}\" stash pop --quiet
+          WORKING_DIRECTORY \"${work_dir}\"
+          RESULT_VARIABLE error_code
+          )
+        if(error_code)
+          # Stash pop failed: Restore previous state.
+          execute_process(
+            COMMAND \"${git_EXECUTABLE}\" reset --hard --quiet \${head_sha}
+            WORKING_DIRECTORY \"${work_dir}\"
+          )
+          execute_process(
+            COMMAND \"${git_EXECUTABLE}\" stash pop --index --quiet
+            WORKING_DIRECTORY \"${work_dir}\"
+          )
+          message(FATAL_ERROR \"\\nFailed to unstash changes in: '${work_dir}/${src_name}'.\\nYou will have to resolve the conflicts manually\")
+        endif()
+      endif()
+    endif()
+  else()
+    execute_process(
+      COMMAND \"${git_EXECUTABLE}\" checkout ${git_tag}
+      WORKING_DIRECTORY \"${work_dir}\"
+      RESULT_VARIABLE error_code
+      )
+    if(error_code)
+      message(FATAL_ERROR \"Failed to checkout tag: '${git_tag}'\")
+    endif()
   endif()
 
   execute_process(