revsets: let parents() return parents of working dir
This patch makes the 'set' argument to revset function parents() optional.
Like p1() and p2(), if no argument is given, returns the parent(s) of the
working directory.
Morally equivalent to 'p1()+p2()', as expected.
$ hg init repo
$ cd repo
$ cat > a <<EOF
> c
> c
> a
> a
> b
> a
> a
> c
> c
> EOF
$ hg ci -Am adda
adding a
$ cat > a <<EOF
> c
> c
> a
> a
> dd
> a
> a
> c
> c
> EOF
default context
$ hg diff --nodates
diff -r cf9f4ba66af2 a
--- a/a
+++ b/a
@@ -2,7 +2,7 @@
c
a
a
-b
+dd
a
a
c
invalid --unified
$ hg diff --nodates -U foo
abort: diff context lines count must be an integer, not 'foo'
[255]
$ hg diff --nodates -U 2
diff -r cf9f4ba66af2 a
--- a/a
+++ b/a
@@ -3,5 +3,5 @@
a
a
-b
+dd
a
a
$ hg --config diff.unified=2 diff --nodates
diff -r cf9f4ba66af2 a
--- a/a
+++ b/a
@@ -3,5 +3,5 @@
a
a
-b
+dd
a
a
$ hg diff --nodates -U 1
diff -r cf9f4ba66af2 a
--- a/a
+++ b/a
@@ -4,3 +4,3 @@
a
-b
+dd
a
invalid diff.unified
$ hg --config diff.unified=foo diff --nodates
abort: diff context lines count must be an integer, not 'foo'
[255]
test off-by-one error with diff -p
$ hg init diffp
$ cd diffp
$ echo a > a
$ hg ci -Ama
adding a
$ rm a
$ echo b > a
$ echo a >> a
$ echo c >> a
$ hg diff -U0 -p --nodates
diff -r cb9a9f314b8b a
--- a/a
+++ b/a
@@ -1,0 +1,1 @@
+b
@@ -2,0 +3,1 @@ a
+c