fix(@angular/cli): not use buildOptimizer for JIT in prod

[trotyl]

fixes #8345

[hansl]

Is this still work in progress?

[hansl]

If you fix the lint issue, we can merge this.

[trotyl]

@hansl It was too late yesterday, just made a placeholder, will work on it soon.

[trotyl]

@hansl Do you want me to add some tests against it? Not sure if this one is urgent.
If tests not required, should be ready to merge now.

[clydin]

Is decorator removal the only problematic pass within the build optimizer? Would it be useful to add an option to the build optimizer loader to disable the pass?

[trotyl]

@clydin Without AOT there can be no tree-shaking or other kinds of dead-code elimination, all types would be referenced in metadata, the only optimization remains is tslib import.

[clydin]

The build optimizer passes facilitate dead code removal via UglifyJS for a variety of TypeScript output code structures. There is most definitely a benefit even without AOT enabled.

[trotyl]

The build optimizer passes facilitate dead code removal via UglifyJS for a variety of TypeScript output code structures.

The code-wrapping or annotation will only help when the identifier itself is removable, so it's only true for non-Angular related TypeScript libraries, but for all Angular libraries there can be little help as nothing can be removed.

[clydin]

Which would demonstrate a benefit to leaving it in place. A significantly reduced benefit currently, but a benefit nonetheless.

[clydin]

Also of note is the following result of a simple application in JIT mode with decorator removal disabled:

0.bundle.js: 814 -> 19762 bytes (2327.76%), 474 -> 5803 bytes gzipped (1124.26%)
1.bundle.js: 20367 -> 499 bytes (-97.55%), 6057 -> 314 bytes gzipped (-94.82%)
main.bundle.js: 663919 -> 614389 bytes (-7.46%), 161742 -> 150118 bytes gzipped (-7.19%)
polyfills.bundle.js: 55243 -> 55243 bytes (0%), 17953 -> 17953 bytes gzipped (0%)
Total: 740343 -> 689893 bytes (-6.81%), 186226 -> 174188 bytes gzipped (-6.46%)

And an AIO test application with the same setup:

0.bundle.js: 14879 -> 14879 bytes (0%), 6633 -> 6633 bytes gzipped (0%)
main.bundle.js: 1230957 -> 1047748 bytes (-14.88%), 278220 -> 242911 bytes gzipped (-12.69%)
polyfills.bundle.js: 55243 -> 55243 bytes (0%), 17953 -> 17953 bytes gzipped (0%)
Total: 1301079 -> 1117870 bytes (-14.08%), 302806 -> 267497 bytes gzipped (-11.66%)

[trotyl]

You're right, indeed what getPrefixClassesTransformer saves is a little higher than getScrubFileTransformer.

[filipesilva]

I think the PR at the moment is correct. While it is true that there are benefits to be had even in JIT, the intended behaviour was always that Build Optimizer can only be used with AOT (see the validateBuildOptions method). That it was possible to use it in JIT was an oversight of how defaults are processed.

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