Original bug ID: 6660
Reporter: bvaugon
Assigned to: @garrigue
Status: acknowledged (set by @garrigue on 2014-12-08T08:30:03Z)
Resolution: open
Priority: normal
Severity: feature
Version: 4.02.1
Target version: undecided
Category: typing
Monitored by: @ygrek @hcarty

Bug description

Considering the following (classical) definition of fail:

# let fail fmt = Printf.ksprintf failwith fmt;;

the following call is wrongly type-checked without any warning:

# fail "error" 123;;

(***)

However, the type-checking of the code:

# (fail "error") 123;;
Warning 20: this argument will not be used by the function.

rightly raises a warning 20 on the argument 123. Thanks to this message,
the programmer understand that he simply forgot a "%d" in his format.

(***)

Remarks that the type-checker behaviour is strange on this kind
of thing, since the code:

# failwith "hahaha" 123;;
Warning 20: this argument will not be used by the function.

rightly raises a warning.

(***)

Since this kind of programming error may happen quickly, it would be
interesting that the warning 20 be raised even when all the arguments
are passed at once (in this kind of configuration).

From a more general point of view, it would be more intuitive that the
OCaml type checker verifies the property:
(f x y) is correctly typed iff ((f x) y) is correctly typed

Steps to reproduce

# let fail fmt = Printf.ksprintf failwith fmt;;
# fail "error" 123;;