patch: create file even if source is not /dev/null

as long as the first hunk is -0,0 and the source and destination have the
same name. Matt found a patch like this, and /usr/bin/patch accepts it.

mercurial/patch.py

@@ -793,6 +793,17 b' def selectfile(afile_orig, bfile_orig, h'
     if reverse:
         createfunc = hunk.rmfile
     missing = not goodb and not gooda and not createfunc()
+
+    # some diff programs apparently produce create patches where the
+    # afile is not /dev/null, but rather the same name as the bfile
+    if missing and afile == bfile:
+        # this isn't very pretty
+        hunk.create = True
+        if createfunc():
+            missing = False
+        else:
+            hunk.create = False
+
     # If afile is "a/b/foo" and bfile is "a/b/foo.orig" we assume the
     # diff is between a file and its backup. In this case, the original
     # file should be patched (see original mpatch code).

tests/test-import

@@ -332,3 +332,16 b' new file mode 100644'
 EOF
 hg import --no-commit a.patch
 cd ..
+
+echo '% create file when source is not /dev/null'
+cat > create.patch <<EOF
+diff -Naur proj-orig/foo proj-new/foo
+--- proj-orig/foo       1969-12-31 16:00:00.000000000 -0800
++++ proj-new/foo        2009-07-17 16:50:45.801368000 -0700
+@@ -0,0 +1,1 @@
++a
+EOF
+hg init oddcreate
+cd oddcreate
+hg import --no-commit ../create.patch
+cat foo

tests/test-import.out

@@ -292,3 +292,6 b' R a'
 % add empty file from the end of patch (issue 1495)
 adding a
 applying a.patch
+% create file when source is not /dev/null
+applying ../create.patch
+a