Back in the 1980s I found a book at the public library where somebody had a BASIC program that would read a BASIC program without line numbers and with structured programming loops and rewrite it an ordinary BASIC. It was oriented towards CP/M so I typed the program in and modified it to run on my TRS-80 Coco. It was kinda like

https://en.wikipedia.org/wiki/Ratfor

Similarly I've written awk programs that write shell scripts (guilty pleasure), Python programs that write AVR-8 assembly, toolkits to write Java ASTs with static imports like

    @Test
    public void buildAList() {
        var stream = callBuild(callAdd(callAdd(callAdd(callBuilder(), Literal.of(7)),
                Literal.of(11)),Literal.of(15)));
        var expr = callToList(stream);
        var l = expr.evaluateRT();
        assertEquals(3,l.size());
        assertEquals(7, l.get(0));
        assertEquals(11, l.get(1));
        assertEquals(15, l.get(2));
    }

and evaluate with a tree-walking interpreter or use as a code generator in maven, do transformations on the ASTs, etc.

There are many paths to metaprogramming but the Lisp family leads in putting it on your fingertips. Once you learn those methods you can apply them in the trashiest programming languages, but I think often people miss the point.