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Rewrite (?:|xyz) and (?:xyz|) to (?:xyz)?. #259

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Rewrite (?:|xyz) and (?:xyz|) to (?:xyz)?. #259

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24 changes: 24 additions & 0 deletions src/libre/ast_rewrite.c
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Original file line number Diff line number Diff line change
Expand Up @@ -317,6 +317,30 @@ rewrite_alt(struct ast_expr *n, enum re_flags flags)
return 1;
}

if (n->u.alt.count == 2) {
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@hvdijk points out that this would also apply for n > 2, which I hadn't thought of.

struct ast_expr *child = NULL;

if (n->u.alt.n[0]->type == AST_EXPR_EMPTY) {
ast_expr_free(n->u.alt.n[0]);
child = n->u.alt.n[1];
} else if (n->u.alt.n[1]->type == AST_EXPR_EMPTY) {
ast_expr_free(n->u.alt.n[1]);
child = n->u.alt.n[0];
}

if (child != NULL) {
free(n->u.alt.n);

/* we repurpose the same node */
n->type = AST_EXPR_REPEAT;
n->u.repeat.e = child;
n->u.repeat.min = 0;
n->u.repeat.max = 1;

return rewrite(n, flags);
}
}

return 1;

empty:
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