repos.bzl refers to repositories before they're defined

[CodingCanuck]

Stout's repos.bzl refers to other repos' repos.bzl files by using a repository label, e.g. the use of @com_github_3rdparty_stout_atomic_backoff in:

load("@com_github_3rdparty_stout_atomic_backoff//bazel:repos.bzl", stout_atomic_backoff_repos = "repos")

This works because stout's WORKSPACE.bazel file defines these repo labels before they're used, e.g.:

local_repository(
    name = "com_github_3rdparty_stout_atomic_backoff",
    path = "stout-atomic-backoff",
)

But this does not work when using stout in another repo by following the advice on https://github.com/3rdparty/stout#bazel to call stout's repos.bzl from the other repo's repos.bzl: in order for this to work, we need to avoid referring to already-defined repo labels in our repos.bzl file.

Other repositories accomplish this by not referring to repos.bzl files in dependencies' labeled repos, but instead copying those repos.bzl files into a 3rdparty top-level folder e.g. https://github.com/3rdparty/eventuals/blob/main/bazel/repos.bzl#L15-L18 :

load("//3rdparty/bazel-rules-asio:repos.bzl", asio_repos = "repos")
load("//3rdparty/bazel-rules-curl:repos.bzl", curl_repos = "repos")
load("//3rdparty/bazel-rules-jemalloc:repos.bzl", jemalloc_repos = "repos")
load("//3rdparty/bazel-rules-libuv:repos.bzl", libuv_repos = "repos")

I suspect we should follow the same pattern here.

Concretely, I think we should remove all repo references in the style of @repo_name from our repos.bzl file (except @bazel_tools which seem both safe and commonly used across repos) and instead add new subfolders of 3rdparty/ for each repo.

[CodingCanuck]

From a chat with @benh this issue might have it backwards: we might be moving away from this pattern of repos.bzl and this new style might in fact be the way forward!