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Convert ViewEncapsulation to a const enum #44119

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Convert ViewEncapsulation to a const enum#44119
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P5The team acknowledges the request but does not plan to address it, it remains open for discussionarea: coreIssues related to the framework runtimearea: performanceIssues related to performancecore: CSS encapsulationrefactoringIssue that involves refactoring or code-cleanuprisk: medium
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@dario-piotrowicz

Description

@dario-piotrowicz
dario-piotrowicz
opened on Nov 8, 2021

Which @angular/* package(s) are relevant/releated to the feature request?

core

Description

The ViewEncapsulation is an enum it could be converted to a const enum as such it would be tree-shakable and produce less transpiled js code.

Proposed solution

Apply the same approach used for enum InjectFlags and const enum InternalInjectFlags:

angular/packages/core/src/di/interface/injector.ts

Lines 19 to 81 in 2d3cd2b

/**
* Injection flags for DI.
*
* @publicApi
*/
export enum InjectFlags {
// TODO(alxhub): make this 'const' (and remove `InternalInjectFlags` enum) when ngc no longer
// writes exports of it into ngfactory files.
/** Check self and check parent injector if needed */
Default = 0b0000,
/**
* Specifies that an injector should retrieve a dependency from any injector until reaching the
* host element of the current component. (Only used with Element Injector)
*/
Host = 0b0001,
/** Don't ascend to ancestors of the node requesting injection. */
Self = 0b0010,
/** Skip the node that is requesting injection. */
SkipSelf = 0b0100,
/** Inject `defaultValue` instead if token not found. */
Optional = 0b1000,
}
/**
* This enum is an exact copy of the `InjectFlags` enum above, but the difference is that this is a
* const enum, so actual enum values would be inlined in generated code. The `InjectFlags` enum can
* be turned into a const enum when ViewEngine is removed (see TODO at the `InjectFlags` enum
* above). The benefit of inlining is that we can use these flags at the top level without affecting
* tree-shaking (see "no-toplevel-property-access" tslint rule for more info).
* Keep this enum in sync with `InjectFlags` enum above.
*/
export const enum InternalInjectFlags {
/** Check self and check parent injector if needed */
Default = 0b0000,
/**
* Specifies that an injector should retrieve a dependency from any injector until reaching the
* host element of the current component. (Only used with Element Injector)
*/
Host = 0b0001,
/** Don't ascend to ancestors of the node requesting injection. */
Self = 0b0010,
/** Skip the node that is requesting injection. */
SkipSelf = 0b0100,
/** Inject `defaultValue` instead if token not found. */
Optional = 0b1000,
/**
* This token is being injected into a pipe.
*
* This flag is intentionally not in the public facing `InjectFlags` because it is only added by
* the compiler and is not a developer applicable flag.
*/
ForPipe = 0b10000,
}

Meaning: having two enums, one standard used internally and the other const which can be used by user code and tree shaken.

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    P5The team acknowledges the request but does not plan to address it, it remains open for discussionarea: coreIssues related to the framework runtimearea: performanceIssues related to performancecore: CSS encapsulationrefactoringIssue that involves refactoring or code-cleanuprisk: medium

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