With this commit the compiler will "lower" expressions into exported
variables for values the compiler does not need to know statically
in order to be able to generate a factory. For example:
```
providers: [{provider: 'token', useValue: calculated()}]
```
produced an error as the expression `calculated()` is not supported
by the compiler because `calculated` is not a
[known function](https://angular.io/guide/metadata#annotationsdecorators)
With this commit this is rewritten, during emit of the .js file, into
something like:
```
export var ɵ0 = calculated();
...
provdiers: [{provider: 'token', useValue: ɵ0}]
```
The compiler then will now generate a reference to the exported `ɵ0`
instead of failing to evaluate `calculated()`.
PR Close#18905
This also allows to customize the filePaths in `.ngsummary.json` file
via the new methods `toSummaryFileName` and `fromSummaryFileName`
on the `CompilerHost`.
Refactoring the compiler to use transformers moves the code generation
after type-checking which suppresses the errors TypeScript would
generate in the user code.
`TypeChecker` currently produces the same factory code that was
generated prior the switch to transfomers, getting back the same
diagnostics as before. The refactoring will allow the code to
diverge from the factory code and allow better diagnostic error
messages than was previously possible by type-checking the factories.
Template expressions can now use a post-fix `!` operator
that asserts the target of the operator is not null. This is
similar to the TypeScript non-null assert operator. Expressions
generated in factories will be generated with the non-null assert
operator.
Closes: #10855
Chuck Jazdzewski
Tobias Bosch
Victor Berchet