The ppx_spice executable is a ppx file in the project root.
src/b.res is source code using ppx_spice, while src/c.res is source code without ppx_spice. src/c.res is manually written code that would be generated when using ppx_spice. Both modules have the same Spice module.
AST output of src/b.res file:
node_modules/rescript/cli/bsc -dparsetree -ppx "./ppx -uncurried" src/b.res &> b.txt
AST output of src/c.res file:
node_modules/rescript/cli/bsc -dparsetree -ppx "./ppx -uncurried" src/c.res &> c.txt
Comparing b.txt and c.txt files shows they are identical. However, when running the npm run res:build command, only b.res fails to compile.