This fix is for a bug in the ngtsc PartialEvaluator, which statically
evaluates expressions.
Sometimes, evaluating a reference requires resolving a function which is
declared in another module, and thus no function body is available. To
support this case, the PartialEvaluator has the concept of a foreign
function resolver.
This allows the interpretation of expressions like:
const router = RouterModule.forRoot([]);
even though the definition of the 'forRoot' function has no body. In
ngtsc today, this will be resolved to a Reference to RouterModule itself,
via the ModuleWithProviders foreign function resolver.
However, the PartialEvaluator also associates any Identifiers in the path
of this resolution with the Reference. This is done so that if the user
writes
const x = imported.y;
'x' can be generated as a local identifier instead of adding an import for
'y'.
This was at the heart of a bug. In the above case with 'router', the
PartialEvaluator added the identifier 'router' to the Reference generated
(through FFR) to RouterModule.
This is not correct. References that result from FFR expressions may not
have the same value at runtime as they do at compile time (indeed, this is
not the case for ModuleWithProviders). The Reference generated via FFR is
"synthetic" in the sense that it's constructed based on a useful
interpretation of the code, not an accurate representation of the runtime
value. Therefore, it may not be legal to refer to the Reference via the
'router' identifier.
This commit adds the ability to mark such a Reference as 'synthetic', which
allows the PartialEvaluator to not add the 'router' identifier down the
line. Tests are included for both the PartialEvaluator itself as well as the
resultant buggy behavior in ngtsc overall.
PR Close#29387
ae4a86e3b5