Add ${path-no-dep:...}

To be able to resolve path names that are not dependencies.

doc/jbuild.rst

@@ -593,8 +593,13 @@ In addition, ``(action ...)`` fields support the following special variables:
 - ``@`` expands to the list of target
 - ``<`` expands to the first dependency, or the empty string if there are no
   dependencies
--  ``^`` expands to the list of dependencies, separated by spaces
--  ``path:<path>`` expands to ``<path>``
+- ``^`` expands to the list of dependencies, separated by spaces
+- ``path:<path>`` expands to ``<path>``
+- ``path-no-dep:<path>`` is the same as ``path:<path>``, except that
+  ``<path>`` is not considered as a dependency of the action. For instance
+  ``(chdir ${ROOT} (run foo --base ${path-no-dep:bar}))`` in ``src/blah/jbuild``
+  will expand to ``(chdir ../.. (run foo --base src/blah/bar))`` where
+  ``src/blah/bar`` doesn't have to be an existing or buildable file
 - ``exe:<path>`` is the same as ``<path>``, except when cross-compiling, in
   which case it will expand to ``<path>`` from the host build context
 - ``bin:<program>`` expands to a path to ``program``. If ``program``

src/super_context.ml

@@ -514,6 +514,7 @@ module Action = struct
         let open Action.Var_expansion in
         let cos, var = parse_bang key in
         match String.lsplit2 var ~on:':' with
+        | Some ("path-no-dep", s) -> Some (path_exp (Path.relative dir s))
         | Some ("exe"     , s) -> static_dep_exp acc (Path.relative dir s)
         | Some ("path"    , s) -> static_dep_exp acc (Path.relative dir s)
         | Some ("bin"     , s) -> begin

test/blackbox-tests/test-cases/misc/jbuild

@@ -38,3 +38,22 @@
 ;; For some tests in subdirs
 
 (rule (with-stdout-to 023e1a58-4d08-11e7-a041-aa000008c8a6 (echo "plop")))
+
+;; Test for ${path-no-dep}
+
+(rule
+ (progn
+  (with-stdout-to pnd-result
+   (chdir sub-tree/dir
+    (progn
+     (echo "${path-no-dep:file-that-doesn't-exist}\n")
+     (echo "${path-no-dep:.}\n"))))
+  (with-stdout-to pnd-expected
+   (progn
+    (echo "../../file-that-doesn't-exist\n")
+    (echo "../..\n")))))
+
+(alias
+ ((name   runtest)
+  (deps   (pnd-result pnd-expected))
+  (action (run diff -u ${!^}))))

test/blackbox-tests/test-cases/misc/run.t

@@ -2,3 +2,4 @@
           diff alias runtest
           diff alias runtest
           diff alias runtest
+          diff alias runtest