Report filename:line on runtime errors (fix #752)

With this patch, jq run-time errors printed to stderr will contain the
filename and line of the offending input.

But note that the JSON text parser does (yet) print the input filename
on parse error.  A jq run-time error is a jq program error, not
including syntax errors nor JSON text input format errors.

Examples:

With stdin and multiple lines:

    $ printf '{"a":43}\n{"a":{"b":66}}\n' | ./jq '.a+1'
    44
    jq: error (at stdin:2): object and number cannot be added

With multiple files:

    $ printf '{"a":43}' > 1.json
    $ printf '{"a":"hello"}\n' > 2.json
    $ printf '{"a":{"b":66}}\n' > 3.json
    $ ./jq '[.a]|@tsv' 1.json 2.json 3.json
    "43"
    "hello"
    jq: error (at 3.json:1): object is not valid in a csv row

With very long lines (spanning multiple `fgets` calls):

    $ (  printf '{"a":43}\n' ;
         printf '{"a":{"b":[' ; seq 10000 | paste -d, -s | tr -d '\n' ;
         printf ']}}\n' ;
         printf '{"a":"hello"}\n' ) | ./jq '[.a] | @tsv'
    "43"
    jq: error (at stdin:2): object is not valid in a csv row
    "hello"

With raw input:

    $ seq 1000 | ./jq --raw-input 'select(.=="700") | . + 10'
    jq: error (at stdin:700): string and number cannot be added

Caveat:
The reported line will be the last line of the (valid) parsed JSON data.
Example:

    $ printf '{\n"a":\n"hello"\n\n\n}\n' | ./jq '.a+4'
    jq: error (at stdin:6): string and number cannot be added

3 files changed, 41 insertions, 2 deletions

diff --git a/jq.h b/jq.h
index 111b1bc5..99e248ab 100644
--- a/jq.h
+++ b/jq.h
@@ -46,5 +46,6 @@ void jq_util_input_add_input(jq_util_input_state, jv);
 int jq_util_input_errors(jq_util_input_state);
 jv jq_util_input_next_input(jq_util_input_state);
 jv jq_util_input_next_input_cb(jq_state *, void *);
+jv jq_util_input_get_position(jq_state*);
 
 #endif /* !JQ_H */
diff --git a/main.c b/main.c
index 31dbc824..2433e418 100644
--- a/main.c
+++ b/main.c
@@ -132,13 +132,17 @@ static int process(jq_state *jq, jv value, int flags, int dumpopts) {
   if (jv_invalid_has_msg(jv_copy(result))) {
     // Uncaught jq exception
     jv msg = jv_invalid_get_msg(jv_copy(result));
+    jv input_pos = jq_util_input_get_position(jq);
     if (jv_get_kind(msg) == JV_KIND_STRING) {
-      fprintf(stderr, "jq: error: %s\n", jv_string_value(msg));
+      fprintf(stderr, "jq: error (at %s): %s\n",
+              jv_string_value(input_pos), jv_string_value(msg));
     } else {
       msg = jv_dump_string(msg, 0);
-      fprintf(stderr, "jq: error (not a string): %s\n", jv_string_value(msg));
+      fprintf(stderr, "jq: error (at %s) (not a string): %s\n",
+              jv_string_value(input_pos), jv_string_value(msg));
     }
     ret = 5;
+    jv_free(input_pos);
     jv_free(msg);
   }
   jv_free(result);
diff --git a/util.c b/util.c
index 1d9b0f2e..f6033b73 100644
--- a/util.c
+++ b/util.c
@@ -155,6 +155,8 @@ struct jq_util_input_state {
   jv slurped;
   char buf[4096];
   size_t buf_valid_len;
+  jv current_filename;
+  size_t current_line;
 };
 
 static void fprinter(void *data, jv fname) {
@@ -178,6 +180,8 @@ jq_util_input_state jq_util_input_init(jq_msg_cb err_cb, void *err_cb_data) {
   new_state->slurped = jv_invalid();
   new_state->buf[0] = 0;
   new_state->buf_valid_len = 0;
+  new_state->current_filename = jv_invalid();
+  new_state->current_line = 0;
 
   return new_state;
 }
@@ -204,6 +208,7 @@ void jq_util_input_free(jq_util_input_state *state) {
     jv_parser_free(old_state->parser);
   jv_free(old_state->files);
   jv_free(old_state->slurped);
+  jv_free(old_state->current_filename);
   jv_mem_free(old_state);
 }
 
@@ -237,18 +242,24 @@ static int jq_util_input_read_more(jq_util_input_state state) {
         fclose(state->current_input);
       }
       state->current_input = NULL;
+      jv_free(state->current_filename);
+      state->current_filename = jv_invalid();
+      state->current_line = 0 ;
     }
     jv f = next_file(state);
     if (jv_is_valid(f)) {
       if (!strcmp(jv_string_value(f), "-")) {
         state->current_input = stdin;
+        state->current_filename = jv_string("<stdin>");
       } else {
         state->current_input = fopen(jv_string_value(f), "r");
+        state->current_filename = jv_copy(f);
         if (!state->current_input) {
           state->err_cb(state->err_cb_data, jv_copy(f));
           state->failures++;
         }
       }
+      state->current_line = 0;
       jv_free(f);
     }
   }
@@ -268,6 +279,9 @@ static int jq_util_input_read_more(jq_util_input_state state) {
         state->failures++;
     } else {
       const char *p = memchr(state->buf, '\n', sizeof(state->buf));
+
+      if (p != NULL)
+        state->current_line++;
       
       if (p == NULL && state->parser != NULL) {
         /*
@@ -307,6 +321,26 @@ jv jq_util_input_next_input_cb(jq_state *jq, void *data) {
   return jq_util_input_next_input((jq_util_input_state)data);
 }
 
+// Return the current_filename:current_line
+jv jq_util_input_get_position(jq_state *jq) {
+  jq_input_cb cb = NULL;
+  void *cb_data = NULL;
+  jq_get_input_cb(jq, &cb, &cb_data);
+  assert(cb == jq_util_input_next_input_cb);
+  if (cb != jq_util_input_next_input_cb)
+    return jv_invalid_with_msg(jv_string("Invalid jq_util_input API usage"));
+  jq_util_input_state s = (jq_util_input_state)cb_data;
+
+  // We can't assert that current_filename is a string because if
+  // the error was a JSON parser error then we may not have set
+  // current_filename yet.
+  if (jv_get_kind(s->current_filename) != JV_KIND_STRING)
+    return jv_string("<unknown>");
+
+  jv v = jv_string_fmt("%s:%zu", jv_string_value(s->current_filename), 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) {