3 files changed, 60 insertions, 1 deletions

diff --git a/src/backend/regex/regc_color.c b/src/backend/regex/regc_color.c
index 30bda0e5ad0..8ae788f5195 100644
--- a/src/backend/regex/regc_color.c
+++ b/src/backend/regex/regc_color.c
@@ -1075,9 +1075,19 @@ colorcomplement(struct nfa *nfa,
 
 	assert(of != from);
 
-	/* A RAINBOW arc matches all colors, making the complement empty */
+	/*
+	 * A RAINBOW arc matches all colors, making the complement empty.  But we
+	 * can't just return without making any arcs, because that would leave the
+	 * NFA disconnected which would break any future delsub().  Instead, make
+	 * a CANTMATCH arc.  Also set the HASCANTMATCH flag so we know we need to
+	 * clean that up at the start of NFA optimization.
+	 */
 	if (findarc(of, PLAIN, RAINBOW) != NULL)
+	{
+		newarc(nfa, CANTMATCH, 0, from, to);
+		nfa->flags |= HASCANTMATCH;
 		return;
+	}
 
 	/* Otherwise, transiently mark the colors that appear in of's out-arcs */
 	for (a = of->outs; a != NULL; a = a->outchain)
@@ -1089,6 +1099,12 @@ colorcomplement(struct nfa *nfa,
 			assert(!UNUSEDCOLOR(cd));
 			cd->flags |= COLMARK;
 		}
+
+		/*
+		 * There's no syntax for re-complementing a color set, so we cannot
+		 * see CANTMATCH arcs here.
+		 */
+		assert(a->type != CANTMATCH);
 	}
 
 	/* Scan colors, clear transient marks, add arcs for unmarked colors */
diff --git a/src/backend/regex/regc_nfa.c b/src/backend/regex/regc_nfa.c
index 0e93c74287e..82409b46327 100644
--- a/src/backend/regex/regc_nfa.c
+++ b/src/backend/regex/regc_nfa.c
@@ -1435,6 +1435,7 @@ removetraverse(struct nfa *nfa,
 		{
 			case PLAIN:
 			case EMPTY:
+			case CANTMATCH:
 				/* nothing to do */
 				break;
 			case AHEAD:
@@ -1572,6 +1573,12 @@ optimize(struct nfa *nfa,
 	if (verbose)
 		fprintf(f, "\ninitial cleanup:\n");
 #endif
+	/* If we have any CANTMATCH arcs, drop them; but this is uncommon */
+	if (nfa->flags & HASCANTMATCH)
+	{
+		removecantmatch(nfa);
+		nfa->flags &= ~HASCANTMATCH;
+	}
 	cleanup(nfa);				/* may simplify situation */
 #ifdef REG_DEBUG
 	if (verbose)
@@ -2894,6 +2901,34 @@ clonesuccessorstates(struct nfa *nfa,
 }
 
 /*
+ * removecantmatch - remove CANTMATCH arcs, which are no longer useful
+ * once we are done with the parsing phase.  (We need them only to
+ * preserve connectedness of NFA subgraphs during parsing.)
+ */
+static void
+removecantmatch(struct nfa *nfa)
+{
+	struct state *s;
+
+	for (s = nfa->states; s != NULL; s = s->next)
+	{
+		struct arc *a;
+		struct arc *nexta;
+
+		for (a = s->outs; a != NULL; a = nexta)
+		{
+			nexta = a->outchain;
+			if (a->type == CANTMATCH)
+			{
+				freearc(nfa, a);
+				if (NISERR())
+					return;
+			}
+		}
+	}
+}
+
+/*
  * cleanup - clean up NFA after optimizations
  */
 static void
@@ -3601,6 +3636,8 @@ dumpnfa(struct nfa *nfa,
 		fprintf(f, ", eol [%ld]", (long) nfa->eos[1]);
 	if (nfa->flags & HASLACONS)
 		fprintf(f, ", haslacons");
+	if (nfa->flags & HASCANTMATCH)
+		fprintf(f, ", hascantmatch");
 	if (nfa->flags & MATCHALL)
 	{
 		fprintf(f, ", minmatchall %d", nfa->minmatchall);
@@ -3723,6 +3760,9 @@ dumparc(struct arc *a,
 			break;
 		case EMPTY:
 			break;
+		case CANTMATCH:
+			fprintf(f, "X");
+			break;
 		default:
 			fprintf(f, "0x%x/0%lo", a->type, (long) a->co);
 			break;
diff --git a/src/backend/regex/regcomp.c b/src/backend/regex/regcomp.c
index b735fa6eaff..4dfff46cc08 100644
--- a/src/backend/regex/regcomp.c
+++ b/src/backend/regex/regcomp.c
@@ -177,6 +177,7 @@ static void breakconstraintloop(struct nfa *, struct state *);
 static void clonesuccessorstates(struct nfa *, struct state *, struct state *,
 								 struct state *, struct arc *,
 								 char *, char *, int);
+static void removecantmatch(struct nfa *);
 static void cleanup(struct nfa *);
 static void markreachable(struct nfa *, struct state *, struct state *, struct state *);
 static void markcanreach(struct nfa *, struct state *, struct state *, struct state *);
@@ -299,6 +300,7 @@ struct vars
 #define BEHIND	'r'				/* color-lookbehind arc */
 #define WBDRY	'w'				/* word boundary constraint */
 #define NWBDRY	'W'				/* non-word-boundary constraint */
+#define CANTMATCH 'x'			/* arc that cannot match anything */
 #define SBEGIN	'A'				/* beginning of string (even if not BOL) */
 #define SEND	'Z'				/* end of string (even if not EOL) */
 
@@ -2288,6 +2290,7 @@ nfanode(struct vars *v,
 	nfa = newnfa(v, v->cm, v->nfa);
 	NOERRZ();
 	dupnfa(nfa, t->begin, t->end, nfa->init, nfa->final);
+	nfa->flags = v->nfa->flags;
 	if (!ISERR())
 		specialcolors(nfa);
 	if (!ISERR())