regex: treat \| in BRE as alternation

The standard does not define semantics for \| in BRE, but some code
depends on it meaning alternation. Empty alternative expression is
allowed to be consistent with ERE.

Based on a patch by Rob Landley.

diff --git a/src/regex/regcomp.c b/src/regex/regcomp.c
index 078f657c74b4f21bfa42a8310b6965ffca4b7740..f1f06afed5d4759e9878ab0c87a3a715473141bb 100644 (file)
--- a/src/regex/regcomp.c
+++ b/src/regex/regcomp.c
@@ -841,6 +841,14 @@ static reg_errcode_t parse_atom(tre_parse_ctx_t *ctx, const char *s)
                        /* reject repetitions after empty expression in BRE */
                        if (!ere)
                                return REG_BADRPT;
+               case '|':
+                       /* extension: treat \| as alternation in BRE */
+                       if (!ere) {
+                               node = tre_ast_new_literal(ctx->mem, EMPTY, -1, -1);
+                               s--;
+                               goto end;
+                       }
+                       /* fallthrough */
                default:
                        if (!ere && (unsigned)*s-'1' < 9) {
                                /* back reference */
@@ -918,6 +926,7 @@ parse_literal:
                s += len;
                break;
        }
+end:
        if (!node)
                return REG_ESPACE;
        ctx->n = node;
@@ -1016,13 +1025,20 @@ static reg_errcode_t tre_parse(tre_parse_ctx_t *ctx)
                if ((ere && *s == '|') ||
                    (ere && *s == ')' && depth) ||
                    (!ere && *s == '\\' && s[1] == ')') ||
+                   /* extension: treat \| as alternation in BRE */
+                   (!ere && *s == '\\' && s[1] == '|') ||
                    !*s) {
                        /* extension: empty branch is unspecified (), (|a), (a|)
                           here they are not rejected but match on empty string */
                        int c = *s;
                        nunion = tre_ast_new_union(ctx->mem, nunion, nbranch);
                        nbranch = 0;
-                       if (c != '|') {
+
+                       if (c == '\\' && s[1] == '|') {
+                               s+=2;
+                       } else if (c == '|') {
+                               s++;
+                       } else {
                                if (c == '\\') {
                                        if (!depth) return REG_EPAREN;
                                        s+=2;
@@ -1042,7 +1058,6 @@ static reg_errcode_t tre_parse(tre_parse_ctx_t *ctx)
                                nunion = tre_stack_pop_voidptr(stack);
                                goto parse_iter;
                        }
-                       s++;
                }
        }
 }