Shim generation was built on a lie.
Shims are files added to the program which aren't original files authored by
the user, but files authored effectively by the compiler. These fall into
two categories: files which will be generated (like the .ngfactory shims we
generate for View Engine compatibility) as well as files used internally in
compilation (like the __ng_typecheck__.ts file).
Previously, shim generation was driven by the `rootFiles` passed to the
compiler as input. These are effectively the `files` listed in the
`tsconfig.json`. Each shim generator (e.g. the `FactoryGenerator`) would
examine the `rootFiles` and produce a list of shim file names which it would
be responsible for generating. These names would then be added to the
`rootFiles` when the program was created.
The fatal flaw here is that `rootFiles` does not always account for all of
the files in the program. In fact, it's quite rare that it does. Users don't
typically specify every file directly in `files`. Instead, they rely on
TypeScript, during program creation, starting with a few root files and
transitively discovering all of the files in the program.
This happens, however, during `ts.createProgram`, which is too late to add
new files to the `rootFiles` list.
As a result, shim generation was only including shims for files actually
listed in the `tsconfig.json` file, and not for the transitive set of files
in the user's program as it should.
This commit completely rewrites shim generation to use a different technique
for adding files to the program, inspired by View Engine's shim generator.
In this new technique, as the program is being created and `ts.SourceFile`s
are being requested from the `NgCompilerHost`, shims for those files are
generated and a reference to them is patched onto the original file's
`ts.SourceFile.referencedFiles`. This causes TS to think that the original
file references the shim, and causes the shim to be included in the program.
The original `referencedFiles` array is saved and restored after program
creation, hiding this little hack from the rest of the system.
The new shim generation engine differentiates between two kinds of shims:
top-level shims (such as the flat module entrypoint file and
__ng_typecheck__.ts) and per-file shims such as ngfactory or ngsummary
files. The former are included via `rootFiles` as before, the latter are
included via the `referencedFiles` of their corresponding original files.
As a result of this change, shims are now correctly generated for all files
in the program, not just the ones named in `tsconfig.json`.
A few mitigating factors prevented this bug from being realized until now:
* in g3, `files` does include the transitive closure of files in the program
* in CLI apps, shims are not really used
This change also makes use of a novel technique for associating information
with source files: the use of an `NgExtension` `Symbol` to patch the
information directly onto the AST object. This is used in several
circumstances:
* For shims, metadata about a `ts.SourceFile`'s status as a shim and its
origins are held in the extension data.
* For original files, the original `referencedFiles` are stashed in the
extension data for later restoration.
The main benefit of this technique is a lot less bookkeeping around `Map`s
of `ts.SourceFile`s to various kinds of data, which need to be tracked/
invalidated as part of incremental builds.
This technique is based on designs used internally in the TypeScript
compiler and is serving as a prototype of this design in ngtsc. If it works
well, it could have benefits across the rest of the compiler.
PR Close#36211
4213e8d5f0