Merge branch 'br/sha1-name-40-hex-no-disambiguation'

When parsing a 40-hex string into the object name, the string is
checked to see if it can be interpreted as a ref so that a warning
can be given for ambiguity. The code kicked in even when the
core.warnambiguousrefs is set to false to squelch this warning, in
which case the cycles spent to look at the ref namespace were an
expensive no-op, as the result was discarded without being used.

* br/sha1-name-40-hex-no-disambiguation:
sha1_name: don't resolve refs when core.warnambiguousrefs is false

diff --combined sha1_name.c
index b1873d8113bdeb0ff8087319c99833036aaffe1b,10bd0071628f1875c31d54ba63dd83e3445f2283..a5578f718ea092338eb16fbe7dbf867a98e82218
--- 1/sha1_name.c
--- 2/sha1_name.c
+++ b/sha1_name.c
@@@ -451,9 -451,9 +451,9 @@@ static int get_sha1_basic(const char *s
        int at, reflog_len, nth_prior = 0;
  
        if (len == 40 && !get_sha1_hex(str, sha1)) {
-               if (warn_on_object_refname_ambiguity) {
+               if (warn_ambiguous_refs && warn_on_object_refname_ambiguity) {
                        refs_found = dwim_ref(str, len, tmp_sha1, &real_ref);
-                       if (refs_found > 0 && warn_ambiguous_refs) {
+                       if (refs_found > 0) {
                                warning(warn_msg, len, str);
                                if (advice_object_name_warning)
                                        fprintf(stderr, "%s\n", _(object_name_msg));
@@@ -546,7 -546,7 +546,7 @@@
                if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
                                &co_time, &co_tz, &co_cnt)) {
                        if (!len) {
 -                              if (!prefixcmp(real_ref, "refs/heads/")) {
 +                              if (starts_with(real_ref, "refs/heads/")) {
                                        str = real_ref + 11;
                                        len = strlen(real_ref + 11);
                                } else {
@@@ -581,6 -581,8 +581,6 @@@ static int get_parent(const char *name
        if (ret)
                return ret;
        commit = lookup_commit_reference(sha1);
 -      if (!commit)
 -              return -1;
        if (parse_commit(commit))
                return -1;
        if (!idx) {
@@@ -674,15 -676,15 +674,15 @@@ static int peel_onion(const char *name
                return -1;
  
        sp++; /* beginning of type name, or closing brace for empty */
 -      if (!prefixcmp(sp, "commit}"))
 +      if (starts_with(sp, "commit}"))
                expected_type = OBJ_COMMIT;
 -      else if (!prefixcmp(sp, "tag}"))
 +      else if (starts_with(sp, "tag}"))
                expected_type = OBJ_TAG;
 -      else if (!prefixcmp(sp, "tree}"))
 +      else if (starts_with(sp, "tree}"))
                expected_type = OBJ_TREE;
 -      else if (!prefixcmp(sp, "blob}"))
 +      else if (starts_with(sp, "blob}"))
                expected_type = OBJ_BLOB;
 -      else if (!prefixcmp(sp, "object}"))
 +      else if (starts_with(sp, "object}"))
                expected_type = OBJ_ANY;
        else if (sp[0] == '}')
                expected_type = OBJ_NONE;
@@@ -909,7 -911,7 +909,7 @@@ static int grab_nth_branch_switch(unsig
        const char *match = NULL, *target = NULL;
        size_t len;
  
 -      if (!prefixcmp(message, "checkout: moving from ")) {
 +      if (starts_with(message, "checkout: moving from ")) {
                match = message + strlen("checkout: moving from ");
                target = strstr(match, " to ");
        }
@@@ -1302,7 -1304,7 +1302,7 @@@ static void diagnose_invalid_index_path
  
  static char *resolve_relative_path(const char *rel)
  {
 -      if (prefixcmp(rel, "./") && prefixcmp(rel, "../"))
 +      if (!starts_with(rel, "./") && !starts_with(rel, "../"))
                return NULL;
  
        if (!startup_info)