Hello,
AFAIK, Tup runs commands through the shell, as if it used system
<http://en.cppreference.com/w/c/program/system> (I haven't found such a
call in the source code, though). However, the shell is not very reliable:
there are big differences between some of them (especially between Bash and
cmd.exe), concerning such basic aspects as string escaping (for example,
cmd.exe doesn't use single quotes) or redirection. The problem could in
fact arise that one started using features specific to his system's shell
(like pipes and redirection in Bash, which are missing or have a different
syntax in cmd.exe) without noticing, and then the build failed on other
platforms.
Plain Tupfiles need a tokenizer (either the shell's or Tup's own internal
one) because their syntax specifies commands as plain strings instead of
arrays, which is what OSes internally work with when it comes to execute a
program. It is therefore understandable that plain Tupfiles remain
dependent on the shell, because, if they were to bypass it, a shell-like
parser would need to be implemented in Tup itself and, while this would
certainly bring standardization, it wouldn't be an easy task.
However, Lua Tupfiles don't need a tokenizer. Lua supports tables, which
could be used to represent command arguments. Consider:
-- Relies on the shell (worrisome dependence)
tup.definerule{
inputs={ "main.c" },
command='gcc -o main.o main.c',
outputs={ "main.o" }
}
-- Doesn't need the shell nor any tokenizer. Yay!
tup.definerule{
inputs={ "main.c" },
command={ 'gcc' , '-o' , 'main.o' , 'main.c' },
outputs={ "main.o" }
}
Additionally, getting rid of the shell could speed up execution.
Such a change wouldn't need to break the existing interface: the
implementation of tup.definerule could just check if command is a string or
a table and act accordingly, thus preserving compatibility with existing
Lua Tupfiles.
What do you think about this?
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