regex_replace.c

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/*
 * This file is part of the Fun programming language.
 * https://fun-lang.xyz/
 *
 * Copyright 2025 Johannes Findeisen <you@hanez.org>
 * Licensed under the terms of the Apache-2.0 license.
 * https://opensource.org/license/apache-2-0
 */

/* Regex global replace opcode using POSIX regex */
#ifdef __unix__
#include <regex.h>
#include <stdlib.h>
#include <string.h>
#endif

case OP_REGEX_REPLACE: {
 Value repl = pop_value(vm);
 Value pattern = pop_value(vm);
 Value str = pop_value(vm);
 if (str.type != VAL_STRING || pattern.type != VAL_STRING || repl.type != VAL_STRING) {
 fprintf(stderr, "Runtime type error: REGEX_REPLACE expects (string, string, string)\n");
 exit(1);
 }
#ifndef __unix__
 /* Not supported: return original string */
 Value out = make_string(str.s ? str.s : "");
 free_value(repl);
 free_value(pattern);
 free_value(str);
 push_value(vm, out);
 break;
#else
 regex_t rx;
 int rc = regcomp(&rx, pattern.s ? pattern.s : "", REG_EXTENDED);
 if (rc != 0) {
 /* invalid regex -> return original */
 Value out = make_string(str.s ? str.s : "");
 free_value(repl);
 free_value(pattern);
 free_value(str);
 push_value(vm, out);
 break;
 }

 const char *s = str.s ? str.s : "";
 const char *r = repl.s ? repl.s : "";

 size_t out_cap = strlen(s) + 1;
 char *outbuf = (char *)malloc(out_cap);
 size_t out_len = 0;
 size_t pos = 0;

 enum { MAX_CAP = 16 };
 regmatch_t caps[MAX_CAP];

 while (1) {
 if (regexec(&rx, s + pos, MAX_CAP, caps, 0) != 0) {
 /* no more matches: append the rest */
 size_t rest = strlen(s + pos);
 if (out_len + rest + 1 > out_cap) {
 out_cap = out_len + rest + 1;
 outbuf = (char *)realloc(outbuf, out_cap);
 }
 memcpy(outbuf + out_len, s + pos, rest + 1);
 out_len += rest;
 break;
 }
 int mstart = (int)caps[0].rm_so;
 int mend = (int)caps[0].rm_eo;
 if (mstart < 0 || mend < mstart) {
 /* Shouldn't happen, avoid infinite loop */
 break;
 }
 /* append prefix */
 size_t pre_len = (size_t)mstart;
 if (out_len + pre_len + 1 > out_cap) {
 out_cap = (out_len + pre_len + 1) * 2;
 outbuf = (char *)realloc(outbuf, out_cap);
 }
 memcpy(outbuf + out_len, s + pos, pre_len);
 out_len += pre_len;

 /* append replacement (no backref expansion for simplicity) */
 size_t rlen = strlen(r);
 if (out_len + rlen + 1 > out_cap) {
 out_cap = (out_len + rlen + 1) * 2;
 outbuf = (char *)realloc(outbuf, out_cap);
 }
 memcpy(outbuf + out_len, r, rlen);
 out_len += rlen;

 /* advance */
 pos += (size_t)mend;
 if (mend == 0) { /* prevent zero-length match infinite loop */
 if (pos < strlen(s)) {
 if (out_len + 1 > out_cap) {
 out_cap = out_len + 2;
 outbuf = (char *)realloc(outbuf, out_cap);
 }
 outbuf[out_len++] = s[pos++];
 } else {
 break;
 }
 }
 }

 Value out = make_string(outbuf ? outbuf : "");
 if (outbuf) free(outbuf);
 regfree(&rx);
 free_value(repl);
 free_value(pattern);
 free_value(str);
 push_value(vm, out);
 break;
#endif
}