[cmake] GetSVN.cmake takes a list of arguments

[modocache]

Summary

GetSVN.cmake currently takes one or two pairs of <source directory path,
name>, then attempts to get the remote repository URL and source control
revision of the repositories at those one or two paths.

It takes two pairs in order for Clang to get the revision of both
itself, and its dependency LLVM.

For projects that rely upon both LLVM and Clang (Apple's Swift is one
example, but there are others), GetSVN.cmake is used to fetch *three*
revisions: Swift, Clang, and LLVM.

To support this use case, change GetSVN.cmake: instead of taking one or
two pairs (specified via FIRST_SOURCE_DIR/FIRST_NAME, have it take a list
of pairs (SOURCE_DIRS/NAMES).

In order to allow Clang to migrate, have GetSVN.cmake support both sets
of arguments for now. The old arguments can be removed once Clang begins
using the new arguments, and Swift can follow when it updates its
copy of LLVM.

Test Plan:

1. Perform a clean build of Clang, verify that clang --version still prints the correct LLVM and Clang revision information.
2. Modify Clang's CMake to use the new arguments, then perform another clean build. clang --version should still print the correct revision information.

[modocache]

Here's an example of how a repository that requires three sets of source control information would use these new parameters, from Apple's Swift: https://github.com/apple/swift/pull/10824

[modocache]

Friendly ping! I'm pretty excited about this set of changes, which simplify the CMake in projects such as Swift:

1. https://reviews.llvm.org/D35132: Convert "first", "second" parameters to a parameter that takes a list of items
2. https://reviews.llvm.org/D35133: Use the new parameters in Clang's CMake
3. https://reviews.llvm.org/D35138: Delete the old "first", "second" parameters

Does anyone have any feedback on these changes?

[echristo]

From a high level it sounds fine. You'll probably want someone else that's hacked on cmake to give an ack though. :)

[jordan_rose]

It looks fine to me too. Ideally @beanz would be around to weigh in but it's not such a big change. I think it's okay to land.

[modocache]

Awesome, thanks to both of you! I went ahead and committed it, going off of @jordan_rose's comment. :)

cmake/modules/GetSVN.cmake

 # CMake project that writes Subversion revision information to a header.
 #
 # Input variables:
-#   FIRST_SOURCE_DIR  - First source directory
-#   FIRST_NAME        - The macro prefix for the first repository's info
-#   SECOND_SOURCE_DIR - Second source directory (opt)
-#   SECOND_NAME       - The macro prefix for the second repository's info (opt)
-#   HEADER_FILE       - The header file to write
+#   SOURCE_DIRS - A list of source directories.
+#   NAMES       - A list of macro prefixes for each of the source directories.
+#   HEADER_FILE - The header file to write
 #
-# The output header will contain macros FIRST_REPOSITORY and FIRST_REVISION,
-# and SECOND_REPOSITORY and SECOND_REVISION if requested, where "FIRST" and
-# "SECOND" are substituted with the names specified in the input variables.
+# The output header will contain macros <NAME>_REPOSITORY and <NAME>_REVISION,
+# where "<NAME>" and is substituted with the names specified in the input
+# variables, for each of the SOURCE_DIRS given.
 
-# Chop off cmake/modules/GetSVN.cmake 
+# Chop off cmake/modules/GetSVN.cmake
 get_filename_component(LLVM_DIR "${CMAKE_SCRIPT_MODE_FILE}" PATH)
 get_filename_component(LLVM_DIR "${LLVM_DIR}" PATH)
 get_filename_component(LLVM_DIR "${LLVM_DIR}" PATH)
 
 # Handle strange terminals
 set(ENV{TERM} "dumb")
 
 macro(get_source_info_svn path revision repository)
function(append_info name path)
   string(STRIP "${revision}" revision)
   string(STRIP "${repository}" repository)
   file(APPEND "${HEADER_FILE}.txt"
     "#define ${name}_REVISION \"${revision}\"\n")
   file(APPEND "${HEADER_FILE}.txt"
     "#define ${name}_REPOSITORY \"${repository}\"\n")
 endfunction()
 
+function(validate_inputs source_dirs names)
+  list(LENGTH source_dirs source_dirs_length)
+  list(LENGTH names names_length)
+  if (NOT source_dirs_length EQUAL names_length)
+    message(FATAL_ERROR
+            "GetSVN.cmake takes two arguments: a list of source directories, "
+            "and a list of names. Expected two lists must be of equal length, "
+            "but got ${source_dirs_length} source directories and "
+            "${names_length} names.")
+  endif()
+endfunction()
+
+if (DEFINED SOURCE_DIRS AND DEFINED NAMES)
+  validate_inputs("${SOURCE_DIRS}" "${NAMES}")
+
+  list(LENGTH SOURCE_DIRS source_dirs_length)
+  math(EXPR source_dirs_max_index ${source_dirs_length}-1)
+  foreach(index RANGE ${source_dirs_max_index})
+    list(GET SOURCE_DIRS ${index} source_dir)
+    list(GET NAMES ${index} name)
+    append_info(${name} ${source_dir})
+  endforeach()
+endif()
+
+# Allow -DFIRST_SOURCE_DIR arguments until Clang migrates to the new
+# -DSOURCE_DIRS argument.
+if(DEFINED FIRST_SOURCE_DIR)
   append_info(${FIRST_NAME} "${FIRST_SOURCE_DIR}")
   if(DEFINED SECOND_SOURCE_DIR)
     append_info(${SECOND_NAME} "${SECOND_SOURCE_DIR}")
   endif()
+endif()
 
 # Copy the file only if it has changed.
 execute_process(COMMAND ${CMAKE_COMMAND} -E copy_if_different
   "${HEADER_FILE}.txt" "${HEADER_FILE}")
 file(REMOVE "${HEADER_FILE}.txt")