allow repeating an option to override its value

[stefantalpalaru]

./tests/cli_example --foo:1 --bar:a --withBaz --foo:2 --bar:boo --bar:hoo --withBaz:false
foo = 2
bar = hoo
baz = false

[cheatfate]

Because this PR do not have any tests, it could break handling sequence arguments, for example when one of the arguments are declared like this https://github.com/status-im/nim-beacon-chain/blob/master/beacon_chain/conf.nim#L92-L95 you can supply multiple items only via:

./beacon_node --bootstrap-node=<node1> --botstrap-node=<node2> --botstrap-node=<node3>

And this behavior should be preserved, or new one should be introduced.

[stefantalpalaru]

it could break handling sequence arguments

As I already explained in Discord, there is no such breakage:

diff --git a/tests/cli_example.nim b/tests/cli_example.nim
index 2271320..e5773e1 100644
--- a/tests/cli_example.nim
+++ b/tests/cli_example.nim
@@ -1,9 +1,10 @@
 import
   ../confutils
 
-cli do (foo: int, bar: string, withBaz: bool, args {.argument.}: seq[string]):
+cli do (foo: int, bar: string, withBaz: bool, bootstrapNodes: seq[string], args {.argument.}: seq[string]):
   echo "foo = ", foo
   echo "bar = ", bar
   echo "baz = ", withBaz
+  echo "bootstrapNodes = ", bootstrapNodes
   for arg in args: echo "arg ", arg

./tests/cli_example --foo:1 --bar:a --withBaz --foo:2 --bar:boo --bar:hoo --withBaz:false --bootstrapNodes:node1 --bootstrapNodes:node2 test1 test2
foo = 2
bar = hoo
baz = false
bootstrapNodes = @["node1", "node2"]
arg test1
arg test2

[mratsim]

LGTM but IIRC @zah had reserves on the behavior until you cited an actual spec on CLI parsing, can you link to the spec so that we can put that in the documentation at an opportune time.

[stefantalpalaru]

"If an option that has option-arguments is repeated, the option and option-argument combinations should be interpreted in the order specified on the command line." - https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html

getopt() examples showing how it's common practice to just override old values when processing the same option multiple times in a while loop: https://linux.die.net/man/3/getopt