Detect when a .do script deletes its stdout tmp file.

This can happen if we create the .tmp file in the same directory as the
target, and the .do file first does "rm -rf" on that directory, then
re-creates it.  The result is that the stdout file is lost.

We'll make this a warning if the .do script *didn't* write to stdout
(so the loss is harmless, just weird), and an error if they *did* write
to stdout, which we can detect because we still have an open fd on the
file, so we can fstat() it.

redo/builder.py

@@ -344,8 +344,17 @@ class _BuildJob(object):
         before_t = self.before_t
         after_t = _try_stat(t)
         st1 = os.fstat(f.fileno())
+        st1b = _try_stat(self.tmpname1)
         st2 = _try_stat(self.tmpname2)
-        if (after_t and
+        if not st1.st_size and not st1b:
+            warn("%s: %s deleted %s; don't do that.\n"
+                 % (_nice(t), argv[2], self.tmpname1))
+            # not fatal, continue
+        if st1.st_size > 0 and not st1b:
+            err('%s: %s wrote to stdout but deleted %s.\n'
+                % (_nice(t), argv[2], self.tmpname1))
+            rv = 207
+        elif (after_t and
                 (not before_t or before_t.st_mtime != after_t.st_mtime) and
                 not stat.S_ISDIR(after_t.st_mode)):
             err('%s modified %s directly!\n' % (argv[2], t))
@@ -365,11 +374,15 @@ class _BuildJob(object):
                 except OSError, e:
                     dnt = os.path.dirname(t)
                     if not os.path.exists(dnt):
+                        # This could happen, so report a simple error message
+                        # that gives a hint for how to fix your .do script.
                         err('%s: target dir %r does not exist!\n' % (t, dnt))
                     else:
+                        # I don't know why this would happen, so raise the
+                        # full exception if it ever does.
                         err('%s: rename %s: %s\n' % (t, self.tmpname2, e))
                         raise
-                os.unlink(self.tmpname1)
+                unlink(self.tmpname1)
             elif st1.st_size > 0:
                 try:
                     os.rename(self.tmpname1, t)

t/202-del/.gitignore

@@ -1 +1,2 @@
 deltest2
+/destruct

t/202-del/all.do

@@ -1 +1 @@
-redo deltest deltest2
+redo deltest deltest2 deltest3

t/202-del/clean.do

@@ -1 +1,2 @@
+rm -rf destruct
 rm -f deltest2 *~ .*~

t/202-del/deltest3.do

@@ -0,0 +1,25 @@
+rm -rf destruct
+mkdir destruct
+cd destruct
+cat >destruct1.do <<-EOF
+	rm -f *.tmp
+	echo 'redir' >\$3
+EOF
+cat >destruct2.do <<-EOF
+	rm -f *.tmp
+	echo 'stdout'
+EOF
+
+# deleting unused stdout file is a warning only
+redo destruct1 2>destruct1.log || exit 11
+[ "$(cat destruct1)" = "redir" ] || exit 12
+
+# deleting *used* stdout file may be a fatal mistake,
+# but we won't enforce that, since some redo variants
+# might be more accepting or use different tmp file
+# algorithms.  So either the file should be correct,
+# or it should be missing.
+redo destruct2 2>destruct2.log || :
+if [ -e "destruct2" ]; then
+	[ "$(cat destruct2)" = "stdout" ] || exit 22
+fi