bool upb_symtab_dfs(upb_def *def, upb_def **open_defs, int n,
upb_strtable *addtab) {
// This linear search makes the DFS O(n^2) in the length of the paths.
// Could make this O(n) with a hash table, but n is small.
for (int i = 0; i < n; i++) {
if (def == open_defs[i]) return false;
}
bool needcopy = false;
upb_msgdef *m = upb_dyncast_msgdef(def);
if (m) {
upb_msg_iter i;
open_defs[n++] = def;
for(i = upb_msg_begin(m); !upb_msg_done(i); i = upb_msg_next(m, i)) {
upb_fielddef *f = upb_msg_iter_field(i);
if (!upb_hassubdef(f)) continue;
needcopy |= upb_symtab_dfs(f->def, open_defs, n, addtab);
}
}
bool replacing = (upb_strtable_lookup(addtab, m->base.fqname) != NULL);
if (needcopy && !replacing) {
upb_symtab_ent e = {upb_def_dup(def)};
upb_strtable_insert(addtab, def->fqname, &e);
replacing = true;
}
return replacing;
}
/* Starts a depth-first traversal at "def", recursing into any subdefs
* (ie. submessage types). Adds duplicates of existing defs to addtab
* wherever necessary, so that the resulting symtab will be consistent once
* addtab is added.
*
* More specifically, if any def D is found in the DFS that:
*
* 1. can reach a def that is being replaced by something in addtab, AND
*
* 2. is not itself being replaced already (ie. this name doesn't already
* exist in addtab)
*
* ...then a duplicate (new copy) of D will be added to addtab.
*
* Returns true if this happened for any def reachable from "def."
*
* It is slightly tricky to do this correctly in the presence of cycles. If we
* detect that our DFS has hit a cycle, we might not yet know if any SCCs on
* our stack can reach a def in addtab or not. Once we figure this out, that
* answer needs to apply to *all* defs in these SCCs, even if we visited them
* already. So a straight up one-pass cycle-detecting DFS won't work.
*
* To work around this problem, we traverse each SCC (which we already
* computed, since these defs are frozen) as a single node. We first compute
* whether the SCC as a whole can reach any def in addtab, then we dup (or not)
* the entire SCC. This requires breaking the encapsulation of upb_refcounted,
* since that is where we get the data about what SCC we are in. */
static bool upb_resolve_dfs(const upb_def *def, upb_strtable *addtab,
const void *new_owner, upb_inttable *seen,
upb_status *s) {
upb_value v;
bool need_dup;
const upb_def *base;
const void* memoize_key;
/* Memoize results of this function for efficiency (since we're traversing a
* DAG this is not needed to limit the depth of the search).
*
* We memoize by SCC instead of by individual def. */
memoize_key = def->base.group;
if (upb_inttable_lookupptr(seen, memoize_key, &v))
return upb_value_getbool(v);
/* Visit submessages for all messages in the SCC. */
need_dup = false;
base = def;
do {
upb_value v;
const upb_msgdef *m;
assert(upb_def_isfrozen(def));
if (def->type == UPB_DEF_FIELD) continue;
if (upb_strtable_lookup(addtab, upb_def_fullname(def), &v)) {
need_dup = true;
}
/* For messages, continue the recursion by visiting all subdefs, but only
* ones in different SCCs. */
m = upb_dyncast_msgdef(def);
if (m) {
upb_msg_field_iter i;
for(upb_msg_field_begin(&i, m);
!upb_msg_field_done(&i);
upb_msg_field_next(&i)) {
upb_fielddef *f = upb_msg_iter_field(&i);
const upb_def *subdef;
if (!upb_fielddef_hassubdef(f)) continue;
subdef = upb_fielddef_subdef(f);
/* Skip subdefs in this SCC. */
if (def->base.group == subdef->base.group) continue;
/* |= to avoid short-circuit; we need its side-effects. */
need_dup |= upb_resolve_dfs(subdef, addtab, new_owner, seen, s);
if (!upb_ok(s)) return false;
}
}
} while ((def = (upb_def*)def->base.next) != base);
if (need_dup) {
/* Dup all defs in this SCC that don't already have entries in addtab. */
def = base;
do {
const char *name;
if (def->type == UPB_DEF_FIELD) continue;
name = upb_def_fullname(def);
if (!upb_strtable_lookup(addtab, name, NULL)) {
upb_def *newdef = upb_def_dup(def, new_owner);
if (!newdef) goto oom;
newdef->came_from_user = false;
if (!upb_strtable_insert(addtab, name, upb_value_ptr(newdef)))
goto oom;
}
} while ((def = (upb_def*)def->base.next) != base);
}
upb_inttable_insertptr(seen, memoize_key, upb_value_bool(need_dup));
return need_dup;
oom:
upb_status_seterrmsg(s, "out of memory");
return false;
}