From 01dfd8b86d1248e80d868523c63c87356bca9c6f Mon Sep 17 00:00:00 2001
From: Emanuele Torre <torreemanuele6@gmail.com>
Date: Tue, 18 Jul 2023 08:49:12 +0200
Subject: [PATCH] Populate captures also for zero-width matches

Instead of just using {"captures":[]}.

sub functions are use captures for replacement expressions.
If we don't populate, captures for empty matches, the replacement
expression is run with an empty object as input instead of an object
containing the named captures with "" as value:

* before:

  $ jq -n '"123foo456bar" | gsub("[^a-z]*(?<x>[a-z]*)"; "Z\(.x)")'
  "ZfooZbarZnull"

* after:

  $ jq -n '"123foo456bar" | gsub("[^a-z]*(?<x>[a-z]*)"; "Z\(.x)")'
  "ZfooZbarZ"

---

I also removed a redundant

  result = NULL;
  if (result) {
    ...
  }
---
 src/builtin.c   | 14 +++++++++++---
 tests/onig.test |  6 +++++-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/src/builtin.c b/src/builtin.c
index d92b5482..4ba3c4ad 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -931,7 +931,17 @@ static jv f_match(jq_state *jq, jv input, jv regex, jv modifiers, jv testmode) {
         jv match = jv_object_set(jv_object(), jv_string("offset"), jv_number(idx));
         match = jv_object_set(match, jv_string("length"), jv_number(0));
         match = jv_object_set(match, jv_string("string"), jv_string(""));
-        match = jv_object_set(match, jv_string("captures"), jv_array());
+        jv captures = jv_array();
+        for (int i = 1; i < region->num_regs; ++i) {
+          jv cap = jv_object();
+          cap = jv_object_set(cap, jv_string("offset"), jv_number(idx));
+          cap = jv_object_set(cap, jv_string("string"), jv_string(""));
+          cap = jv_object_set(cap, jv_string("length"), jv_number(0));
+          cap = jv_object_set(cap, jv_string("name"), jv_null());
+          captures = jv_array_append(captures, cap);
+        }
+        onig_foreach_name(reg, f_match_name_iter, &captures);
+        match = jv_object_set(match, jv_string("captures"), captures);
         result = jv_array_append(result, match);
         // ensure '"qux" | match("(?=u)"; "g")' matches just once
         start = (const UChar*)(input_string+region->end[0]+1);
@@ -1005,8 +1015,6 @@ static jv f_match(jq_state *jq, jv input, jv regex, jv modifiers, jv testmode) {
   } while (global && start <= end);
   onig_region_free(region,1);
   region = NULL;
-  if (region)
-    onig_region_free(region,1);
   onig_free(reg);
   jv_free(input);
   jv_free(regex);
diff --git a/tests/onig.test b/tests/onig.test
index 3edb07df..5b6dab6a 100644
--- a/tests/onig.test
+++ b/tests/onig.test
@@ -1,7 +1,7 @@
 # match builtin
 [match("( )*"; "g")]
 "abc"
-[{"offset":0, "length":0, "string":"", "captures":[]}, {"offset":1, "length":0, "string":"", "captures":[]}, {"offset":2, "length":0, "string":"", "captures":[]}, {"offset":3, "length":0, "string":"", "captures":[]}]
+[{"offset":0,"length":0,"string":"","captures":[{"offset":0,"string":"","length":0,"name":null}]},{"offset":1,"length":0,"string":"","captures":[{"offset":1,"string":"","length":0,"name":null}]},{"offset":2,"length":0,"string":"","captures":[{"offset":2,"string":"","length":0,"name":null}]},{"offset":3,"length":0,"string":"","captures":[{"offset":3,"string":"","length":0,"name":null}]}]
 
 [match("( )*"; "gn")]
 "abc"
@@ -145,6 +145,10 @@ gsub("\\b(?<x>.)"; "\(.x|ascii_downcase)")
 "ABC DEF"
 "aBC dEF"
 
+gsub("[^a-z]*(?<x>[a-z]*)"; "Z\(.x)")
+"123foo456bar"
+"ZfooZbarZ"
+
 # utf-8
 sub("(?<x>.)"; "\(.x)!")
 "’"