Fix "dune external-lib-deps" hint for dune exec

Previously, it was not displaying any target.

Signed-off-by: Etienne Millon <etienne@cryptosense.com>

bin/main.ml

@@ -1223,7 +1223,7 @@ let exec =
     ]
   in
   let go common context prog no_rebuild args =
-    set_common common ~targets:[];
+    set_common common ~targets:[prog];
     let log = Log.create common in
     let setup = Scheduler.go ~log ~common (Main.setup ~log common) in
     let context = Main.find_context_exn setup ~name:context in

test/blackbox-tests/dune.inc

@@ -152,6 +152,14 @@
    test-cases/exec-cmd
    (progn (run %{exe:cram.exe} -test run.t) (diff? run.t run.t.corrected)))))
 
+(alias
+ (name exec-missing)
+ (deps (package dune) (source_tree test-cases/exec-missing))
+ (action
+  (chdir
+   test-cases/exec-missing
+   (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))
@@ -729,6 +737,7 @@
   (alias env)
   (alias exclude-missing-module)
   (alias exec-cmd)
+  (alias exec-missing)
   (alias fallback-dune)
   (alias findlib)
   (alias findlib-error)
@@ -816,6 +825,7 @@
   (alias env)
   (alias exclude-missing-module)
   (alias exec-cmd)
+  (alias exec-missing)
   (alias fallback-dune)
   (alias findlib)
   (alias findlib-error)

test/blackbox-tests/test-cases/exec-missing/dune

@@ -0,0 +1,3 @@
+(executable
+ (name x)
+ (libraries does-not-exist))

test/blackbox-tests/test-cases/exec-missing/dune-project

@@ -0,0 +1 @@
+(lang dune 1.0)

test/blackbox-tests/test-cases/exec-missing/run.t

@@ -0,0 +1,7 @@
+When using dune exec, the external-lib-deps command refers to the executable:
+
+  $ dune exec ./x.exe
+  File "dune", line 3, characters 12-26:
+  Error: Library "does-not-exist" not found.
+  Hint: try: dune external-lib-deps --missing ./x.exe
+  [1]