Support for peerDependencies and peerDependenciesMeta.optional seems consistent for Yarn 1/2/3, PNPM 6 and NPM 8.
Exception: NPM v7 always install the peerDependencies, which has the consequence to download deps that might not be needed (the --legacy-peer-deps can help).
NPM v8 reverted the behaviour to align with other package managers
Remark: There's still few blind spots for frameworks that comes with precompiled
version of libraries (ie: nextjs has webpack 'inlined'). Not sure how package managers will
know they are present (the meta.optional: true might be used)
Without peerDeps and peerMeta it's very difficult to achieve
- Multi-ranges support (^4 || ^5)
- Conditional install of certain deps (ie: database driver, webpack...)
(PS: as the node resolution algo is very lax, an alternative is to not declare the dependency when there's enough probablity it will exists in the consuming app/package. This is not recommended and create other issues. Better to be strict.)
Without peerDependency.optional, most pm will emit a warning but don't download the dep.
Exception: npm 7 will download (except with --legacy-peer-deps), yarn pnp/pnpm linkers will fail.
| PM | peer-deps (no meta) | if not present in the current app | Solution |
| -------------------------- | ------------------------- | ---------------------------------- | -------------------- |
| NPM 6 | | warn | |
| NPM 7 --legacy-peer-deps | Ok | warn | |
| NPM 7 | NOK Ok:auto-install | **can't control install** | ? |
| NPM 8 | Ok | warn | |
| NPM 8 --strict-peer-deps | Ok (error) | **error** | Must install |
| YARN 1 | Ok | warn | Install if needed |
| YARN 3.0+ (node-modules) | Ok | warn | Install if needed |
| YARN 3.0+ (pnp linker) | TBD | **error** | Must install |
| YARN 3.1+ (pnpm linker) | TBD | **error** | Must install |
| PNPM 6 | TBD | ? | ? |
### Test 2: With peer-deps+meta.optional
With peerDependency.optional=true, most pm will work as expected
Exception: npm 7 will download the dep (except with --legacy-peer-deps)
| PM | peer-deps+meta.optional | if not present in the current app | Solution |
| -------------------------- | ------------------------- | ---------------------------------- | -------------------- |
| NPM 6 | | silent | |
| NPM 7 --legacy-peer-deps | Ok | silent | |
| NPM 7 | NOK: auto-install | **can't control install** | ? |
| NPM 8 | Ok | silent | |
| NPM 8 --strict-peer-deps | TBD | ? | |
| YARN 1 | Ok | silent | Install if needed |
| YARN 3.0+ (node-modules) | Ok | silent | Install if needed |
| YARN 3.0+ (pnp linker) | TBD | ?error? | May have to install |
| YARN 3.1+ (pnpm linker) | TBD | ?error? | May have to install |
| PNPM 6 | TBD | ? | ? |