The code must be generated not before all other object files are compiled (and fresh).
By chance (parallel build), the rule for generating the .c files can be invoked earlier because the rule's dependencies are not completely known at the position where the rule is defined.
The code must be generated not before all other object files are compiled (and fresh). By chance (parallel build), the rule for generating the .c files can be invoked earlier because the rule's dependencies are not completely known at the position where the rule is defined.