Migrate unique_ptr and shared_ptr uses to py::smart_holder

[linusheck]

Fixes #303. I ran this script on the source code:

#!/usr/bin/env python3
import re
from pathlib import Path


def split_args(s):
    parts, start, depth = [], 0, 0
    for i, c in enumerate(s):
        depth += c in "<([{"
        depth -= c in ">)]}"
        if c == "," and depth == 0:
            parts.append(s[start:i])
            start = i + 1
    return parts + [s[start:]]


for path in Path("src").rglob("*"):
    if path.suffix not in {".cpp", ".h"}:
        continue
    text, pos = path.read_text(), 0
    while (start := text.find("py::class_<", pos)) >= 0:
        if text[text.rfind("\n", 0, start) + 1 : start].lstrip().startswith("//"):
            pos = start + 1
            continue
        end, depth = start + len("py::class_"), 0
        while end < len(text):
            depth += text[end] == "<"
            depth -= text[end] == ">"
            if depth == 0:
                break
            end += 1
        args = split_args(text[start + len("py::class_<") : end])
        args = [a for a in args if not re.fullmatch(r"\s*std::(?:shared|unique)_ptr<.*>\s*", a, re.S)]
        replacement = "py::classh<" + ",".join(args) + ">"
        text = text[:start] + replacement + text[end + 1 :]
        pos = start + len(replacement)
    text = re.sub(r"(?m)^PYBIND11_DECLARE_HOLDER_TYPE\(T, std::shared_ptr<T(?: const)?>\)\n\n?", "", text)
    path.write_text(text)

[volkm]

Documentation

[volkm]

LGTM.

[volkm]

@sjunges Any comments or things to consider before merging?

[volkm]

This seems to be the only case where we used a unique_ptrinstead of a shared_ptr. I would argue that using the smart pointer holder here is still a good idea.

[linusheck]

With the smart pointer, you mean the unique_ptr or the smart_holder? :)

[volkm]

Smart holder :)

[sjunges]

Why not use the smart holder everywhere? I think the main problem could be on places where we have problems with the ownership?

[volkm]

We are now actually using the smart holder everywhere. I just wanted to point out that we originally used a unique_ptr here, in case this was relevant. But I believe it was not important.

[sjunges]

LGTM