Remove dependency on make

[casey]

Currently, j relies on a make or gmake command being available. This causes some problems:

• Only trivial justfiles are likely to be portable across flavors of make
• Running j on windows is difficult
• Since it is a j "feature" that flags are passed to make, it can't have flags of its own
• Makefile syntax only allows leading tabs
• Make won't run a recipe if there is a file with same name as the recipe. The current workaround is to add a .PHONY directive to the justfile
• Exported variables on one line of a make recipe are not available on subsequent lines

It may be desirable to stop depending on make and move to a j-specific custom file format. This would mean that make's features would no longer be available, but a workaround to this would be to write a Makefile and call make from j.

Possible improvements this would allow:

• Add a --list flag that lists the available recipes
• Work on windows
• Relax the rule on tabs vs spaces, and just enforce that the same number of tabs and spaces precede each line of recipe
• Figure out a sane way of allowing justfiles in subdirectories

The exact syntax is up in the air, but I personally very much like the current syntax, and would like to do something similar.

[casey]

I was thinking about just starting with something like:

# single line comments are allowed
# for now, the '#' must be the first non-whitespace character on a line

# simple recipes work as before:
foo:
  cd baz
  touch bar
  echo galf

# tabs and spaces can be mixed, but there must be an equal
# number of tabs and spaces (in whatever order) before
# every line in a recipe, so that a user's tab-width setting
# doesn't matter
#
# using . for space and - for tab:

# this is okay, every line starts with one space:
a:
.echo hello
.echo hello

# this is okay, every line starts with the same whitespace:
b:
.-echo hello
.-echo hello

# this is not okay, inconsistent whitespace:
c:
.-echo hello
--echo hello

# this is okay, because it is still unambiguous:
d:
.-echo hello
-.echo hello
# (we could disallow this)

# recipes may call other recipes
bar: foo a b
  echo "I'm bar!"

# as in make, a leading @ suppresses printing the command
qux:
  @echo "Pinging the server..."
  @ping 237.1.4.5

Constructing a DAG of recipes and detecting loops doesn't seem that hard.

@aoeu, thoughts?

[casey]

Also, some kind of variable assignment is likely to be necessary. Makefiles allow setting the shell using SHELL := bash and it would be nice if justfiles still supported this.

[casey]

Would it be too crazy to use a full scripting language outside of the recipes? Imagine if everything that wasn't a recipe was parsed and run as python, with a special syntax for exporting variables as environment variables to recipes?

If there were a good python implementation in rust, I think I would seriously consider it.

[casey]

Okay, I just thought of a killer feature that we can provide if we move away from makefiles... If you add a shebang as the first line of a recipe, we run that recipe as a script instead:

stuff:
  #!/usr/bin/env python3
  def foo(a, b):
    print(a + b):
  for i in range(100):
    foo(i + i * i)

j will then extract the contents of the recipe, less the leading whitespace, and execute it as a script.

You could also use a shell shebang, if you use a lot of variables or want to continue in the case of command failure:

stuff:
  #!/bin/sh
  # variables will work as expected:
  A=hello
  echo getting $A...
  # the next line can fail and we'll still continue:
  curl http://example.com/$A > hello.html
  echo "We tried!"

[casey]

Make is gone! Support for #! recipes is also in