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Make REG_LITERAL match the empty pattern #146

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Make REG_LITERAL match the empty pattern #146

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367e8db
parse: Make REG_LITERAL match the empty pattern
kevinushey Aug 9, 2026
0f5673d
tests: Add REG_LITERAL cases to retest
kevinushey Aug 9, 2026
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16 changes: 16 additions & 0 deletions lib/tre-parse.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1645,6 +1645,22 @@ tre_parse(tre_parse_ctx_t *ctx)
break;
}

#ifdef REG_LITERAL
/* In literal mode the branch above is skipped, so an empty
pattern would otherwise fall through without producing an
atom. Emit an empty expression, which matches the empty
string. */
if ((ctx->cflags & REG_LITERAL) && ctx->re >= ctx->re_end)
{
DPRINT(("tre_parse: literal empty: '%.*" STRF "'\n",
REST(ctx->re)));
result = tre_ast_new_literal(ctx->mem, EMPTY, -1);
if (!result)
return REG_ESPACE;
break;
}
#endif /* REG_LITERAL */

DPRINT(("tre_parse: literal: '%.*" STRF "'\n",
REST(ctx->re)));
/* Note that we can't use an tre_isalpha() test here, since there
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17 changes: 17 additions & 0 deletions tests/retest.c
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Expand Up @@ -633,6 +633,23 @@ main(int argc, char **argv)
test_exec("xxxxxx", 0, REG_NOMATCH);
#endif

/*
* Literal (REG_LITERAL) patterns.
*/

/* An empty literal pattern matches the empty string. */
test_comp("", REG_EXTENDED | REG_LITERAL, 0);
test_exec("abc", 0, REG_OK, 0, 0, END);
test_exec("", 0, REG_OK, 0, 0, END);

/* Metacharacters lose their meaning in literal mode. */
test_comp("a.c", REG_EXTENDED | REG_LITERAL, 0);
test_exec("xa.cy", 0, REG_OK, 1, 4, END);
test_exec("abc", 0, REG_NOMATCH);
test_comp("(a|b)*", REG_EXTENDED | REG_LITERAL, 0);
test_exec("x(a|b)*y", 0, REG_OK, 1, 7, END);
test_exec("ababab", 0, REG_NOMATCH);

#ifdef TRE_APPROX
/*
* Approximate matching tests.
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