Rework interdependencies between @apollo/client/* entry points. #6656

Before we get started refactoring how entry points are built, let's take a snapshot of the current exports of all public entry points.

This new module provides a single source of truth for all the nested entry points that we build. As a nice bonus, thanks to this unification, the @apollo/client/testing entry point no longer needs such special treatment.

This prevents collision between the actual main entry point (used by Node.js) and the dist/apollo-client.cjs.js bundle that we use for estimating the minified bundle size.

Adapted from https://github.com/apollographql/invariant-packages/tree/master/packages/rollup-plugin-invariant, this script wraps invariant(...), new InvariantError(...), and invariant.{warn,error} calls with process.env.NODE_ENV logic, so that long error messages can be stripped from production builds. I decided to abandon the Rollup plugin for this task because I'm planning to change how Rollup determines if imported modules are "external," and Rollup (understandably) stops traversing the dependency graph when it hits an external import, which means we can no longer rely on Rollup to traverse all modules that need invariants to be transformed. Also, this transformation step was never especially intertwined with the dependency traversal and rewriting logic that Rollup provides, so I think it makes things simpler to keep them separate. If Rollup provided hooks for performing arbitrary build steps, we might have been able to do this work in some initial step, but I couldn't find anything in the Rollup documentation that fit the bill (and that's fine: I wouldn't expect Rollup to attempt to be a generic build pipeline). Now, the CJS bundles for each nested entry point (e.g. @apollo/client/core or @apollo/client/react/ssr) can be computed from code that has been processed by the invariant transform, but has not yet been tampered with by Rollup, so we can trust that the exact same module identifiers from the source code are still intact.

There's not currently any risk of running the invariant transform over the ./dist directory more than once during our build process, but it doesn't hurt to make sure the transform is idempotent.

Since we aren't using Rollup to apply the invariant transform anymore, it turns out we don't need this build step at all. Instead, the CJS bundles will be generated directly from the modules generated by tsc and processed by the invariant transform.

This is a vital change (the whole point of this PR, really), because it means Rollup will no longer attempt to include code from other entry points in the CJS bundles for unrelated entry points, so there will no longer be any duplication of code between the CJS bundles.

It would be nice to make this an error that would fail the build, but there are a couple of benign violations that would be disruptive to fix at this point, like reexporting `../ApolloClient` from `./core/QueryManager`, and `./testing/index.ts` reaching into `../utilities/testing`.

Now that the CommonJS module tree uses nested entry points with their own package.json files, instead of importing everything and then filtering it (as the CJS version of @apollo/client/core used to do), we do not need to be so paranoid about the possibility that React is not installed.

This allows src/core/index.ts to avoid reaching outside the @apollo/client/core entry point to import the all-important ApolloClient module/class.

Adding new exports is safe/fine, and additions account for most of what's happening here. For example, @apollo/client/utilities needs to export a few more goodies to support other parts of the codebase, which previously reached inside the utilities entry point and imported stuff willy nilly. The only removal is RenderPromises, which can now be imported from @apollo/client/react/ssr.

This test ensures we will never forget to update these snapshot tests if/when we add a new entry point in the future.

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Rework interdependencies between @apollo/client/* entry points. #6656

Rework interdependencies between @apollo/client/* entry points. #6656

Commits on Jul 20, 2020