[throwaway894345]

> I agree that monorepos are great if you're using version control systems in their current state. But I can't help but wonder if it's a question of monorepos being good, or version control/tooling inhibiting other options.

Ultimately the problem is that we need tooling which is aware of dependencies, and the repo abstraction isn't. Whether that code lives in a single repo or in many repos is fairly irrelevant, but keeping the code in a single repo is usually a fair bit easier for many things (especially when you're working in a single language since the language's build tools are usually well-suited for this basic case) and you don't need to manually update dependency manifest files, test how a given upstream change affects every downstream package, or coordinate half a dozen PRs for every change.

[WorldMaker]

If you are using a dependency manager the repo abstraction, with multiple repos, does start to align as a useful node abstraction at the dependency graph level. For instance, if you are working in JS/TS, every repo has a top-level package.json file that is very easily consumed by tooling to discover dependencies. Github has a dependency graph that's pretty comprehensive for public packages as dependended on by public repos. For instance, the repos that depend on Typescript: https://github.com/microsoft/TypeScript/network/dependents?p...

There's often less tooling available for private repository hosts and private package feeds, but dependency management from a per-repo standpoint is if not a solved problem in practice, an easily solvable problem. (Github has some tools for private repos if you pay for them. Other systems can borrow from the same playbooks.)

(Other languages have similar dependency manifest files, most of which are similarly slurpable by easily automated tooling given the need/chance. Dependency discovery doesn't have to be a problem in multi-repository environments.)

> test how a given upstream change affects every downstream package, or coordinate half a dozen PRs for every change

Some of this is push versus pull questions. One developer needing to push a lot of changes is a lot of work for that one developer. Downstream "owners" needing to pull changes at a frequency is in some cases much tinier slices of work spread out/delegated over a larger team of people, many of whom may be closer to downstream projects to better fix and/or troubleshoot secondary impacts.

Monorepos make push easier, definitely. Sometimes pull is a better workflow. (Especially if you are using the same dependency tooling for third-party components. These days given CVEs and such you want a regular update cadence on third-party components anyway, using the same tools for first-party updates keeps more reason to keep that cadence regular. Lots of small changes over time rather than big upgrade processes all at once.)