The compiler performs cycle analysis for the used directives and pipes
of a component's template to avoid introducing a cyclic import into the
generated output. The used directives and pipes are represented by their
output expression which would typically be an `ExternalExpr`; those are
responsible for the generation of an `import` statement. Cycle analysis
needs to determine the `ts.SourceFile` that would end up being imported
by these `ExternalExpr`s, as the `ts.SourceFile` is then checked against
the program's `ImportGraph` to determine if the import is allowed, i.e.
does not introduce a cycle. To accomplish this, the `ExternalExpr` was
dissected and ran through module resolution to obtain the imported
`ts.SourceFile`.
This module resolution step is relatively expensive, as it typically
needs to hit the filesystem. Even in the presence of a module resolution
cache would these module resolution requests generally see cache misses,
as the generated import originates from a file for which the cache has
not previously seen the imported module specifier.
This commit removes the need for the module resolution by wrapping the
generated `Expression` in an `EmittedReference` struct. This allows the
reference emitter mechanism that is responsible for generating the
`Expression` to also communicate from which `ts.SourceFile` the
generated `Expression` would be imported, precluding the need for module
resolution down the road.
PR Close#40948
87bca2a5c6