Implement scan/2 filter (#1961)

src/builtin.jq

@@ -90,12 +90,13 @@ def capture($val): ($val|type) as $vt | if $vt == "string" then capture($val; nu
    elif $vt == "array" and ($val | length) > 1 then capture($val[0]; $val[1])
    elif $vt == "array" and ($val | length) > 0 then capture($val[0]; null)
    else error( $vt + " not a string or array") end;
-def scan(re):
-  match(re; "g")
-  |  if (.captures|length > 0)
+def scan($re; $flags):
+  match($re; "g" + $flags)
+    | if (.captures|length > 0)
       then [ .captures | .[] | .string ]
       else .string
-      end ;
+      end;
+def scan($re): scan($re; null);
 #
 # If input is an array, then emit a stream of successive subarrays of length n (or less),
 # and similarly for strings.

tests/onig.test

@@ -126,6 +126,10 @@ gsub("^.*?a"; "b")
 ["a,b, c, d, e,f",", a,b, c, d, e,f, "]
 [[["a,b:c, d, e,f"],["a,b:c:d:e,f"],[", ",", ",", "]],[[":a,b, c, d, e,f, "],[":a,b:c:d:e,f:"],[", ",", ",", ",", ",", "]]]
 
+[.[] | scan("b+"; "i")]
+["","bBb","abcABBBCabbbc"]
+["bBb","b","BBB","bbb"]
+
 # reference to named captures
 gsub("(?<x>.)[^a]*"; "+\(.x)-")
 "Abcabc"