utils.md
In pkgbuild: Find Tools Needed to Build R Packages

should_add_compiler_flags errors

Code
  should_add_compiler_flags()
Condition
  Error in `should_add_compiler_flags()`:
  ! Invalid `pkg.build_extra_flags` option.
  i It must be `TRUE`, `FALSE` or "missing", not an integer vector.

Code
  should_add_compiler_flags()
Condition
  Error in `should_add_compiler_flags()`:
  ! Invalid `pkg_build_extra_flags` option.
  i It must be `TRUE`, `FALSE` or "missing", not "foobar".

Code
  should_add_compiler_flags()
Condition
  Error in `should_add_compiler_flags()`:
  ! Invalid `PKG_BUILD_EXTRA_FLAGS` environment variable.
  i Must be one of `true`, `false` or `missing`.