Add tests for fallback

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

test/blackbox-tests/dune.inc

@@ -128,6 +128,14 @@
    test-cases/exec-cmd
    (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
 
+(alias
+ (name fallback-dune)
+ (deps (package dune) (source_tree test-cases/fallback-dune))
+ (action
+  (chdir
+   test-cases/fallback-dune
+   (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
+
 (alias
  (name findlib)
  (deps (package dune) (source_tree test-cases/findlib))
@@ -606,6 +614,7 @@
   (alias env)
   (alias exclude-missing-module)
   (alias exec-cmd)
+  (alias fallback-dune)
   (alias findlib)
   (alias findlib-error)
   (alias force-test)
@@ -678,6 +687,7 @@
   (alias env)
   (alias exclude-missing-module)
   (alias exec-cmd)
+  (alias fallback-dune)
   (alias findlib)
   (alias findlib-error)
   (alias force-test)

test/blackbox-tests/test-cases/fallback-dune/dune1/dune

@@ -0,0 +1,4 @@
+(rule
+ (fallback)
+ (targets) 
+ (action (with-stdout-to foo.txt (echo "testing"))))

test/blackbox-tests/test-cases/fallback-dune/dune2/dune

@@ -0,0 +1,4 @@
+(rule
+ (fallback false)
+ (targets) 
+ (action (with-stdout-to foo.txt (echo "testing"))))

test/blackbox-tests/test-cases/fallback-dune/jbuild/jbuild

@@ -0,0 +1,5 @@
+
+(rule
+ ((fallback)
+  (targets (foo.txt))
+  (action (with-stdout-to foo.txt (echo "testing")))))

test/blackbox-tests/test-cases/fallback-dune/run.t

@@ -0,0 +1,20 @@
+fallback isn't allowed in dune
+
+  $ dune build --root dune1
+  Info: creating file dune-project with this contents: (lang dune 1.0)
+  File "dune", line 2, characters 1-11:
+  Error: 'fallback' was renamed to '(mode fallback)' in 1.0 of the dune language
+  [1]
+
+2nd fallback form isn't allowed either
+
+  $ dune build --root dune2
+  Info: creating file dune-project with this contents: (lang dune 1.0)
+  File "dune", line 2, characters 1-17:
+  Error: 'fallback' was renamed to '(mode fallback)' in 1.0 of the dune language
+  [1]
+
+But it is allowed in jbuilder
+
+  $ jbuilder build --root jbuild
+  Entering directory 'jbuild'