fix(@angular/cli): use safer clean-css optimization level

[iamchucky]

Target: 1.7.x

[clydin]

Please open an issue following the template guidelines and describing the problem that this would address.

[splincode]

If you are sure of this, you need to write and attach tests

[iamchucky]

@clydin please take a look at the issue #10186

Repo to reproduce

[dominikg]

i think disabling all level 2 optimizations is overkill. This sounds like an issue with shorthand merging for non-adjacent properties. clean-css level2 optimizations contain some options that read like they control exactly that.

[iamchucky]

@dominikg for my use case mentioned in the issue #10186 , yes, setting mergeIntoShorthands: false will resolve it.

Level 2 optimizations operate at rules or multiple properties level, e.g. can remove duplicate rules, remove properties redefined further down a stylesheet, or restructure rules by moving them around.

My original rationale was trying to reduce the surprises of the resulting CSS by using level 1 instead of the more aggressive level 2 as there may be other edge cases that are not just caused by mergeIntoShorthands.

I am open to suggestions and would like to know what the team thinks.

[clydin]

This appears to be a defect with the mergeIntoShorthands optimization. For cases such as this, we generally will disable the specific rule with a comment explaining why and a link to an issue within the project in question (clean-css in this case). Once the defect is corrected, the minimum version for the package should be increased to the fixed version and the disabled rule can then be removed.

@iamchucky Can you update the PR in this regard?

[iamchucky]

@clydin done, and created an issue clean-css/clean-css#1022

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