Add a test for ${<}

Signed-off-by: Jeremie Dimino <jeremie@dimino.org>

test/blackbox-tests/test-cases/dep-vars/dune

@@ -1,5 +1,11 @@
+(alias
+ (name runtest)
+ (deps (:foo a b) (:baz foo (alias x)) a b c)
+ (action (echo "foo = %{foo}\nbaz = %{baz}\n")))
 
-(rule
- (deps (:foo a b) (:baz foo (alias test)) a b c)
- (targets bar)
- (action (with-stdout-to bar (echo "foo"))))
+(rule (with-stdout-to a (echo "")))
+(rule (with-stdout-to b (echo "")))
+(rule (with-stdout-to c (echo "")))
+(rule (with-stdout-to foo (echo "")))
+
+(alias (name x))

test/blackbox-tests/test-cases/dep-vars/jbuild/jbuild

@@ -0,0 +1,8 @@
+(alias
+ ((name runtest)
+  (deps ((alias x) foo (alias x)))
+  (action (echo "< = ${<}\n"))))
+
+(alias ((name x)))
+
+(rule (with-stdout-to foo (echo "")))

test/blackbox-tests/test-cases/dep-vars/run.t

@@ -1,3 +1,6 @@
 Dependencies are allowed :patterns
 
-  $ dune build
+  $ dune runtest
+  < = foo
+  foo = a b
+  baz = foo