ssr: support regex-style backreferences to previously used expressions

[nyurik]

In some cases, just like in regex, it is needed to reference an expression previously declared:

rust-analyzer ssr \
  'while $i < $end { $block; $i = $i.wrapping_add(1); } ==>> for $i in 0..$end { $block; }'

To match this type of code:

while counter < 100 {
  // ...
  counter = counter.wrapping_add(1);
}

to transform it into

for counter in 0..100 {
  // ...
}

Currently I get an error:

can't parse `rule`, Parse error: Placeholder `$i` repeats more than once

[lnicola]

You might want to try https://rust-for-linux.com/coccinelle-for-rust as an alternative.

[nyurik]

Thx, yes, i'm trying that too, not much success though :(

My code example:

while i < input_size {
    {
        histogram[input[i] as usize] += 1;
    }
    i = i.wrapping_add(1);
}

My cocci file:

@@
identifier i;
expression end;
@@

-while i < end
+for i in 0..end
 {
    {
    ...
    }
-   i = i.wrapping_add(1);
 }