Prior to this change, all module metadata would be included in the
`defineNgModule` call that is set as the `ngModuleDef` field of module
types. Part of the metadata is scope information like declarations,
imports and exports that is used for computing the transitive module
scope in JIT environments, preventing those references from being
tree-shaken for production builds.
This change moves the metadata for scope computations to a pure function
call that patches the scope references onto the module type. Because the
function is marked pure, it may be tree-shaken out during production builds
such that references to declarations and exports are dropped, which in turn
allows for tree-shaken any declaration that is not otherwise referenced.
Fixes#28077, FW-1035
PR Close#29598
Previously, when the NgModule scope resolver discovered semantic errors
within a users NgModules, it would throw assertion errors. TODOs in the
codebase indicated these should become ts.Diagnostics eventually.
Besides producing better-looking errors, there is another reason to make
this change asap: these assertions were shadowing actual errors, via an
interesting mechanism:
1) a component would produce a ts.Diagnostic during its analyze() step
2) as a result, it wouldn't register component metadata with the scope
resolver
3) the NgModule for the component references it in exports, which was
detected as an invalid export (no metadata registering it as a
component).
4) the resulting assertion error would crash the compiler, hiding the
real cause of the problem (an invalid component).
This commit should mitigate this problem by converting scoping errors to
proper ts.Diagnostics. Additionally, we should consider registering some
marker indicating a class is a directive/component/pipe without actually
requiring full metadata to be produced for it, which would allow suppression
of errors like "invalid export" for such invalid types.
PR Close#29191
JoostK
Alex Rickabaugh