Bug 5511 – std.regex optional capture with no-match cause error

version used: 2.051 An matching optional capture works: auto ms = match("ab", "(a(.*))?(b)"); assert(ms.captures.length == 4); // Ok assert(ms.captures[0] == "ab"); // Ok assert(ms.captures[1] == "a"); // Ok assert(ms.captures[2] == ""); // Ok assert(ms.captures[3] == "b"); // Ok But if optional capture doesn't match : auto ms = match("b", "(a(.*))?(b)"); // same issue with pattern "(a(.*))*(b)" assert(ms.captures.length == 4); // Failed length = 1 assert(ms.captures[0] == "b"); // Ok assert(ms.captures[1] == ""); // [email protected](1724): 1 assert(ms.captures[2] == ""); // [email protected](1724): 1 assert(ms.captures[3] == "b"); // [email protected](1724): 1 In Captures.length (line 1713 in v2.051): @property size_t length() { foreach (i; 0 .. matches.length) { if (matches[i].startIdx >= input.length) return i; } return matches.length; } for matches[1] and matches[2], startIdx == endIdx == startIdx.max but matches[3] is fine: startIdx == 0 and endIdx == 1 in RegexMatch.trymatch (line 2397 in v2.051) startIdx and endIdx are set only if matching: case engine.REparen: // ... pass if (!trymatch(pop, pop + len)) goto Lnomatch; pmatch[n + 1].startIdx = ss; pmatch[n + 1].endIdx = src; pc = pop + len; break; and in RegexMatch.test (line 1905 in v2.051) startIdx and endIdx are initialized to max for each match: foreach (i; 0 .. engine.re_nsub + 1) { pmatch[i].startIdx = -1; pmatch[i].endIdx = -1; } in RegexMatch.test (line 1905 in v2.051) initializing startIdx and endIdx to startindex instead of max seems to fix the problem: foreach (i; 0 .. engine.re_nsub + 1) { pmatch[i].startIdx = startindex; pmatch[i].endIdx = startindex; }

initializing startIdx and endIdx isn't enough if optional capture with no match contains sub-capture with match. save matches state before parse parentheses and restore state if no-match is needed. in RegexMatch.trymatch, case engine.REparen (line 2397 in v2.051) replace lines 2404-2405: if (!trymatch(pop, pop + len)) goto Lnomatch; by: if (!psave) { psave = cast(regmatch_t *)alloca( (engine.re_nsub + 1) * regmatch_t.sizeof); } memcpy(psave, pmatch.ptr, (engine.re_nsub + 1) * regmatch_t.sizeof); if (!trymatch(pop, pop + len)) { memcpy(pmatch.ptr, psave, (engine.re_nsub + 1) * regmatch_t.sizeof); goto Lnomatch; }

*** Issue 5805 has been marked as a duplicate of this issue. ***

*** Issue 5019 has been marked as a duplicate of this issue. ***

Fixed in version 2.053 https://github.com/D-Programming-Language/phobos/commit/ee612d047c8c8a840fb601180306f65ec28c7853