Now region parsing fails on ambiguous cases.

Also improved return values so NULL is primary way of detecting
failure rather than tid.  This is more in line with the old
hts_parse_reg code.

See samtools/hts-specs#124 (comment)
for heuristic suggestions.

hts.c

@@ -2631,8 +2631,13 @@ long long hts_parse_decimal(const char *str, char **strend, int flags)
  * This is necessary due to GRCh38 HLA additions which have reference names
  * like "HLA-DRB1*12:17".
  *
- * On success the end of the reference is returned (colon or end of string).
- * On failure NULL is returned, and if tid/getid are supplied *tid will be -1.
+ * getid is optional and may be passed in as NULL. If given it is used to
+ * validate the reference name exists and is unambiguously parseable. If not
+ * given the best guess will be made but no has guarantees in validity.
+ *
+ * On success the end of the reference is returned (colon or end of string)
+ * beg/end will be set, plus tid if getid has been supplied.
+ * On failure NULL is returned.
  */
 const char *hts_parse_reg2(const char *s, int *tid, int *beg, int *end,
  hts_name2id_f getid, void *hdr)
@@ -2642,18 +2647,37 @@ const char *hts_parse_reg2(const char *s, int *tid, int *beg, int *end,
  int tid_, s_len = strlen(s); // int is sufficient given beg/end types
  if (!tid) tid = &tid_; // simplifies code below
 
+ // No colon implies entirety of the reference
  const char *colon = strrchr(s, ':');
  if (colon == NULL) {
  *beg = 0; *end = INT_MAX;
  *tid = getid ? getid(hdr, s) : 0;
  return *tid >= 0 ? s + s_len : NULL;
  }
 
- // Has a colon, but check whole name first
+ // Has a colon, but check whole name first.
  if (getid) {
  *beg = 0; *end = INT_MAX;
- if ((*tid = getid(hdr, s)) >= 0)
+ if ((*tid = getid(hdr, s)) >= 0) {
+ // Entire name matches, but also check this isn't
+ // ambiguous. eg we have ref chr1 and ref chr1:100-200
+ // both present.
+ kstring_t ks = { 0, 0, NULL };
+ kputsn(s, colon-s, &ks); // convert to nul terminated string
+ if (!ks.s) {
+ *tid = -1;
+ return NULL;
+ }
+ if (getid(hdr, ks.s) >= 0) {
+ free(ks.s);
+ *tid = -1;
+ hts_log_error("Range %s is ambiguous", s);
+ return NULL;
+ }
+ free(ks.s);
+
  return s + s_len;
+ }
  }
 
  char *hyphen;
@@ -2674,6 +2698,8 @@ const char *hts_parse_reg2(const char *s, int *tid, int *beg, int *end,
  }
  *tid = getid(hdr, ks.s);
  free(ks.s);
+ if (*tid < 0)
+ return NULL;
  } else {
  *tid = 0;
  }
@@ -2694,14 +2720,9 @@ hts_itr_t *hts_itr_querys(const hts_idx_t *idx, const char *reg, hts_name2id_f g
  else if (strcmp(reg, "*") == 0)
  return itr_query(idx, HTS_IDX_NOCOOR, 0, 0, readrec);
 
- if ((tid = getid(hdr, reg)) >= 0) {
- beg = 0; end = INT_MAX;
- return itr_query(idx, tid, beg, end, readrec);
- }
-
- hts_parse_reg2(reg, &tid, &beg, &end, getid, hdr);
+ if (!hts_parse_reg2(reg, &tid, &beg, &end, getid, hdr))
+ return NULL;
 
- if (tid < 0) return NULL;
  return itr_query(idx, tid, beg, end, readrec);
 }