Initial native OpenSim viewer prototype

third_party/CLI11/single-include/meson.build

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+# Because Meson does not allow outputs to be placed in subfolders, we must have
+# meson.build here when generating the single file header so that it is placed
+# in the correct location.
+
+pymod = import('python')
+prog_python = pymod.find_installation()
+
+single_main_file = files('CLI11.hpp.in')
+
+if use_single_header
+  single_header = custom_target(
+    'CLI11.hpp',
+    input: [files('../scripts/MakeSingleHeader.py'), cli11_headers, cli11_impl_headers],
+    output: 'CLI11.hpp',
+    command : [prog_python, '@INPUT@', '--main', single_main_file, '--output', '@OUTPUT@'],
+    depend_files: [single_main_file],
+  )
+else
+  # the `declare_dependency` needs to have the single_header source as a source
+  # dependency, to ensure that the generator runs before any attempts to include
+  # the header happen. Adding an empty list is an idiomatic way to ensure the
+  # variable exists but does nothing
+  single_header = []
+endif