Support server restarts using pub workspaces

[sigurdm]

Currently one has to manually restart build_runner on each pub get when using workspaces.

Context being discussed in #3717

[natebosch]

I think this is the main problem

build/build_runner_core/lib/src/generate/build_definition.dart

Lines 105 to 106 in b3d3ef1

	var packageConfigId = AssetId(_targetGraph.rootPackageConfig.packageName,
	'.dart_tool/package_config.json');

This is already broken for some non-standard setups if the file isn't at exactly the hardcoded path. We could fix this for unexpected paths under the root package, but as Jake mentioned this causes a problem when the package config is outside of any package.

My first hacky idea is to add a synthetic package for this, I think we discover the package config when building the package graph so we should have the information we need. We'll also need to communicate that path through to the above lines, so we probably need to add it as another field on both PackageGraph and TargetGraph.

[jakemac53]

True, we could go the synthetic package route similar to how we handle SDK sources. Not sure what we want to call it, $workspace?

[natebosch]

Hmm, build_runner doesn't work at all for packages using pub workspaces.

build/build_runner_core/lib/src/package_graph/package_graph.dart

Lines 221 to 227 in 039aeca

	Map<String, DependencyType> _parseDependencyTypes(String rootPackagePath) {
	final pubspecLock = File(p.join(rootPackagePath, 'pubspec.lock'));
	if (!pubspecLock.existsSync()) {
	throw StateError(
	'Unable to generate package graph, no `pubspec.lock` found. '
	'This program must be ran from the root directory of your package.');
	}

I'm not sure how we wouldn't have hit this earlier though...

[natebosch]

Hmm, build_runner doesn't work at all for packages using pub workspaces.

This was a local issue, I still had some .packages files tripping things up.

[sigurdm]

I think this is done.

[sigurdm]

Sorry - I misread what this issue was about. We probably still should do this.