Print offending object in runtime error messages

When reporting an error to the user, add information about the offending
object/value (possibly truncated).

The goal is to give a user some context regarding which input object
caused the runtime error.

Examples:

    $ echo '"hello"' | ./jq '-.'
    jq: error: string ("hello") cannot be negated

    $ echo '"very-long-string"' | ./jq '-.'
    jq: error: string ("very-long-...) cannot be negated

    $ echo '["1",2]' | ./jq '.|join(",")'
    jq: error: string (",") and number (2) cannot be added

    $ echo '["1","2",{"a":{"b":{"c":33}}}]' | ./jq '.|join(",")'
    jq: error: string (",") and object ({"a":{"b":{...) cannot be added

    $ echo '{"a":{"b":{"c":33}}}' | ./jq '.a | @tsv'
    jq: error: object ({"b":{"c":33}}) cannot be tsv-formatted, only array

(Fix #754)

builtin.c

@@ -22,17 +22,22 @@
 
 
 static jv type_error(jv bad, const char* msg) {
-  jv err = jv_invalid_with_msg(jv_string_fmt("%s %s",
+  char errbuf[15];
+  jv err = jv_invalid_with_msg(jv_string_fmt("%s (%s) %s",
                                              jv_kind_name(jv_get_kind(bad)),
+                                             jv_dump_string_trunc(jv_copy(bad), errbuf, sizeof(errbuf)),
                                              msg));
   jv_free(bad);
   return err;
 }
 
 static jv type_error2(jv bad1, jv bad2, const char* msg) {
-  jv err = jv_invalid_with_msg(jv_string_fmt("%s and %s %s",
+  char errbuf1[15],errbuf2[15];
+  jv err = jv_invalid_with_msg(jv_string_fmt("%s (%s) and %s (%s) %s",
                                              jv_kind_name(jv_get_kind(bad1)),
+                                             jv_dump_string_trunc(jv_copy(bad1), errbuf1, sizeof(errbuf1)),
                                              jv_kind_name(jv_get_kind(bad2)),
+                                             jv_dump_string_trunc(jv_copy(bad2), errbuf2, sizeof(errbuf2)),
                                              msg));
   jv_free(bad1);
   jv_free(bad2);

execute.c

@@ -423,8 +423,10 @@ jv jq_next(jq_state *jq) {
         stack_push(jq, jv_object_set(objv, k, v));
         stack_push(jq, stktop);
       } else {
-        set_error(jq, jv_invalid_with_msg(jv_string_fmt("Cannot use %s as object key",
+        char errbuf[15];
-                                                        jv_kind_name(jv_get_kind(k)))));
+        set_error(jq, jv_invalid_with_msg(jv_string_fmt("Cannot use %s (%s) as object key",
+                                                        jv_kind_name(jv_get_kind(k)),
+                                                        jv_dump_string_trunc(jv_copy(k), errbuf, sizeof(errbuf)))));
         jv_free(stktop);
         jv_free(v);
         jv_free(k);
@@ -634,9 +636,11 @@ jv jq_next(jq_state *jq) {
       } else {
         assert(opcode == EACH || opcode == EACH_OPT);
         if (opcode == EACH) {
+          char errbuf[15];
           set_error(jq,
-                    jv_invalid_with_msg(jv_string_fmt("Cannot iterate over %s",
+                    jv_invalid_with_msg(jv_string_fmt("Cannot iterate over %s (%s)",
-                                                      jv_kind_name(jv_get_kind(container)))));
+                                                      jv_kind_name(jv_get_kind(container)),
+                                                      jv_dump_string_trunc(jv_copy(container), errbuf, sizeof(errbuf)))));
         }
         keep_going = 0;
       }

jv.h

@@ -171,6 +171,7 @@ void jv_dumpf(jv, FILE *f, int flags);
 void jv_dump(jv, int flags);
 void jv_show(jv, int flags);
 jv jv_dump_string(jv, int flags);
+char *jv_dump_string_trunc(jv x, char *outbuf, size_t bufsize);
 
 enum {
   JV_PARSE_SEQ              = 1,

jv_print.c

@@ -313,3 +313,19 @@ jv jv_dump_string(jv x, int flags) {
   jvp_dtoa_context_free(&C);
   return s;
 }
+
+char *jv_dump_string_trunc(jv x, char *outbuf, size_t bufsize) {
+  x = jv_dump_string(x,0);
+  const char* p = jv_string_value(x);
+  const size_t len = strlen(p);
+  strncpy(outbuf, p, bufsize);
+  outbuf[bufsize - 1] = 0;
+  if (len > bufsize - 1 && bufsize >= 4) {
+    // Indicate truncation with '...'
+    outbuf[bufsize - 2]='.';
+    outbuf[bufsize - 3]='.';
+    outbuf[bufsize - 4]='.';
+  }
+  jv_free(x);
+  return outbuf;
+}

tests/all.test

@@ -1173,3 +1173,15 @@ import "test_bind_order" as check; check::check
 null
 true
 
+try -. catch .
+"very-long-string"
+"string (\"very-long-...) cannot be negated"
+
+try join(",") catch .
+["1",2]
+"string (\",\") and number (2) cannot be added"
+
+try join(",") catch .
+["1","2",{"a":{"b":{"c":33}}}]
+"string (\",\") and object ({\"a\":{\"b\":{...) cannot be added"
+