Makefiles operate at a low level of abstraction. The Makefile abstraction is "run this command when the output files don't exist or are older than the input files." You manually specify every tool to be run and all of its arguments.
These tools operate at a higher level of abstraction. The BUILD file abstraction is something like "I am declaring a C library with these sources and headers." The build system then turns that into a set of commands to run. This higher-level abstraction provides a bunch of compelling features:
- Reliability: it's easy to write Makefiles that are fragile, for example one that works when run on a single CPU but fails when run with -j, because of undeclared dependencies. When the tool is in charge, it has more control and can sandbox each build step so that undeclared dependencies simply won't be available in the sandbox.
- Reproducibility: similar to the previous point, it's easy to write a Makefile that produces incorrect results with an incremental rebuild. For example, unless you implement your own header scanning (or manually list your header dependencies) "make" won't know to rebuild a source file when a header changes. These tools can ensure that builds are reproducible and incremental rebuilds are always correct.
Besides that, working at a higher level generally means writing less code to accomplish the same task, and the code you do write is closer to expressing your actual intent compared with a Makefile.
These tools operate at a higher level of abstraction. The BUILD file abstraction is something like "I am declaring a C library with these sources and headers." The build system then turns that into a set of commands to run. This higher-level abstraction provides a bunch of compelling features:
- Reliability: it's easy to write Makefiles that are fragile, for example one that works when run on a single CPU but fails when run with -j, because of undeclared dependencies. When the tool is in charge, it has more control and can sandbox each build step so that undeclared dependencies simply won't be available in the sandbox.
- Reproducibility: similar to the previous point, it's easy to write a Makefile that produces incorrect results with an incremental rebuild. For example, unless you implement your own header scanning (or manually list your header dependencies) "make" won't know to rebuild a source file when a header changes. These tools can ensure that builds are reproducible and incremental rebuilds are always correct.
Besides that, working at a higher level generally means writing less code to accomplish the same task, and the code you do write is closer to expressing your actual intent compared with a Makefile.