If a target's .do file disappears, don't forget to stamp it.

If a file previously was generated but now isn't (ie. its .do file
disappears), we would never re-stamp that target, and so all its
dependencies would rebuild continually.

t/deps/.gitignore

@@ -2,3 +2,5 @@ t1a
 t2.count
 overwrite
 overwrite[123]
+genfile2
+genfile.log

t/deps/clean.do

@@ -1,3 +1,4 @@
 redo basic/clean dirtest/clean
-rm -f *~ .*~ *.count t1a overwrite overwrite[123]
+rm -f *~ .*~ *.count t1a overwrite overwrite[123] genfile2 genfile.log
+
 

t/deps/genfile1.do

@@ -0,0 +1,2 @@
+redo-ifchange genfile2
+echo $$ >>genfile.log

t/deps/gentest.do

@@ -0,0 +1,20 @@
+rm -f genfile2 genfile2.do genfile.log
+
+echo echo hello >genfile2.do
+. ../flush-cache.sh
+redo genfile1
+
+# this will cause a rebuild:
+#      genfile1 depends on genfile2 depends on genfile2.do
+rm -f genfile2.do
+. ../flush-cache.sh
+redo-ifchange genfile1
+
+# but genfile2.do was gone last time, so genfile2 no longer depends on it.
+# thus, it can be considered up-to-date.  Prior versions of redo had a bug
+# where the dependency on genfile2.do was never dropped.
+. ../flush-cache.sh
+redo-ifchange genfile1
+
+COUNT=$(wc -l <genfile.log)
+[ "$COUNT" = 2 ] || exit 77

t/deps/test.do

@@ -1,2 +1 @@
-redo test1 test2 ifchange-fail overwrite basic/test dirtest/test
-
+redo test1 test2 ifchange-fail overwrite gentest basic/test dirtest/test