Add filename/line functions to jq (fix #753)

This adds `input_filename` and `input_line_number` built-in functions
for use in, for example, `error` messages.

Example:

    $ printf '{"a":1}\n{"a":2}\n' > 4.json
    $ printf '{"a":"hello"}\n' > 5.json
    $ ./jq '{ "file":input_filename, "line":input_line_number, "value":.a }' 4.json 5.json
    {
      "file": "4.json",
      "line": 1,
      "value": 1
    }
    {
      "file": "4.json",
      "line": 2,
      "value": 2
    }
    {
      "file": "5.json",
      "line": 1,
      "value": "hello"
    }

1 files changed, 23 insertions, 0 deletions

diff --git a/util.c b/util.c
index f6033b73..c8dd4f6d 100644
--- a/util.c
+++ b/util.c
@@ -341,6 +341,29 @@ jv jq_util_input_get_position(jq_state *jq) {
   return v;
 }
 
+jv jq_util_input_get_current_filename(jq_state* jq) {
+  jq_input_cb cb=NULL;
+  void *cb_data=NULL;
+  jq_get_input_cb(jq, &cb, &cb_data);
+  if (cb != jq_util_input_next_input_cb)
+    return jv_invalid_with_msg(jv_string("Unknown input filename"));
+  jq_util_input_state s = (jq_util_input_state)cb_data;
+  jv v = jv_copy(s->current_filename);
+  return v;
+}
+
+jv jq_util_input_get_current_line(jq_state* jq) {
+  jq_input_cb cb=NULL;
+  void *cb_data=NULL;
+  jq_get_input_cb(jq, &cb, &cb_data);
+  if (cb != jq_util_input_next_input_cb)
+    return jv_invalid_with_msg(jv_string("Unknown input line number"));
+  jq_util_input_state s = (jq_util_input_state)cb_data;
+  jv v = jv_number(s->current_line);
+  return v;
+}
+
+
 // Blocks to read one more input from stdin and/or given files
 // When slurping, it returns just one value
 jv jq_util_input_next_input(jq_util_input_state state) {