Handle .do files that start with "#!/" to specify an explicit interpreter.

Now you can have your .do files interpreted by whatever interpreter you
want.

README.md

@@ -437,15 +437,28 @@ changed, you can run `redo-ifchange target` instead.
 
 # Can my .do files be written in a language other than sh?
 
-FIXME: Not presently.  In theory, we could support starting your .do files
-with the magic "#!/" sequence (eg. #!/usr/bin/python) and then using that
-shell to run your .do script.  But that opens new problems, like figuring
-out what is the equivalent of the `redo-ifchange` command in python.  Do you
-just run it in a subprocess?  That might be unnecessarily slow.  And so on.
+Yes.  If the first line of your .do file starts with the
+magic "#!/" sequence (eg. `#!/usr/bin/python`), then redo
+will execute your script using that particular interpreter.
 
-Right now, `redo` explicitly runs `sh filename.do`.  The main reasons for
-this are to make the #!/ line optional, and so you don't have to remember to
-`chmod +x` your .do files.
+Note that this is slightly different from normal Unix
+execution semantics: redo never execs your script directly;
+it only looks for the "#!/" line.  The main reason for this
+is so that your .do scripts don't have to be marked
+executable (chmod +x).  Executable .do scripts would
+suggest to users that they should run them directly, and
+they shouldn't; .do scripts should always be executed
+inside an instance of redo, so that dependencies can be
+tracked correctly.
+
+WARNING: If your .do script *is* written in Unix sh, we
+recommend *not* including the `#!/bin/sh` line.  That's
+because there are many variations of /bin/sh, and not all
+of them are POSIX compliant.  redo tries pretty hard to
+find a good default shell that will be "as POSIXy as
+possible," and if you override it using #!/bin/sh, you lose
+this benefit and you'll have to worry more about
+portability.
 
 
 # Can a single .do script generate multiple outputs?

builder.py

@@ -128,6 +128,9 @@ class BuildJob:
         if vars.VERBOSE: argv[1] += 'v'
         if vars.XTRACE: argv[1] += 'x'
         if vars.VERBOSE or vars.XTRACE: log_('\n')
+        firstline = open(dofile).readline().strip()
+        if firstline.startswith('#!/'):
+            argv[0:2] = firstline[2:].split(' ')
         log('%s\n' % _nice(t))
         self.argv = argv
         sf.is_generated = True

minimal/do

@@ -57,7 +57,13 @@ _run_dofile()
 	export DO_DEPTH="$DO_DEPTH  "
 	export REDO_TARGET=$PWD/$TARGET
 	set -e
+	read line1 <"$PWD/$DOFILE"
+	cmd=${line1#"#!/"}
+	if [ "$cmd" != "$line1" ]; then
+		/$cmd "$PWD/$DOFILE" "$@" >"$TARGET.tmp2"
+	else
 		. "$PWD/$DOFILE" >"$TARGET.tmp2"
+	fi
 }
 
 

t/.gitignore

@@ -23,3 +23,4 @@ test2.args
 /ifcreate[12]
 /broken
 /shellfile
+/nonshelltest

t/clean.do

@@ -1,6 +1,6 @@
 redo example/clean curse/clean deps/clean "space dir/clean" stamp/clean \
 	defaults-flat/clean
-rm -f broken shellfile mode1 makedir.log chdir1 deltest2 \
+rm -f broken nonshelltest shellfile mode1 makedir.log chdir1 deltest2 \
 	hello [by]ellow *.o *~ .*~ *.log CC LD passfail silence silence.do \
 	touch1 touch1.do always1 ifcreate[12].dep ifcreate[12]
 rm -rf makedir

t/nonshelltest.do

@@ -0,0 +1,3 @@
+#!/usr/bin/env perl
+$a="perly";
+print "hello $a world\n";

t/test.do

@@ -1,5 +1,6 @@
 redo-ifchange all
 ./hello >&2
-redo shelltest deltest deltest2 test.args test2.args passfailtest chdirtest \
+redo nonshelltest shelltest \
+	deltest deltest2 test.args test2.args passfailtest chdirtest \
 	curse/test deps/test "space dir/test" modetest makedir2 \
 	silencetest touchtest stamp/test alwaystest ifcreate-test