utils/gn/secondary/llvm/include/llvm/Support/BUILD.gn

declare_args() {
  # If this set to false, VCSRevision.h is updated after every git commit.
  # That's technically correct, but results in rebuilds after every commit.
  # If it's true (default), VCSRevision.h will usually be somewhat
  # out-of-date, but builds will be faster.
  llvm_allow_tardy_revision = true
}

action("write_vcsrevision") {
  script = "//llvm/utils/gn/build/write_vcsrevision.py"
  header = "$target_gen_dir/VCSRevision.h"

  args = [ rebase_path(header, root_build_dir) ]
  if (!llvm_allow_tardy_revision) {
    depfile = "$header.d"
    args += [
      "-d",
      rebase_path(depfile, root_build_dir),
    ]
  }

  outputs = [
    header,
  ]
}