[v3.0] Improve asset emission performance

[lukastaegert]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

Breaking change: typed array/Buffer assets are no longer deduplicated.

• When working on Improve performance of chunk naming collision check #4643, I found that there is a similar O(n^2) issue lurking within asset emission that may slow down builds when thousands of assets are emitted.

This changes the asset emission logic in two ways:

• To deduplicate assets with string sources, we build a reverse map source -> fileName for O(1) file name lookup. This also means that typed array/Buffer assets are no longer deduplicated for performance reasons.
• To avoid a performance issue when using many unnamed assets, reference ids are now generated using a counter as id base for those assets (otherwise, they would use the same base which would lead to a very slow re-hashing process).

[github-actions]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#improve-asset-emission-performance

or load it into the REPL:
https://rollupjs.org/repl/?pr=4644

[codecov]

Codecov Report

Merging #4644 (8d6dd2f) into release-3.0.0 (52d9ca2) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@                Coverage Diff                @@
##           release-3.0.0    #4644      +/-   ##
=================================================
- Coverage          98.97%   98.97%   -0.01%     
=================================================
  Files                213      213              
  Lines               7492     7481      -11     
  Branches            2116     2112       -4     
=================================================
- Hits                7415     7404      -11     
  Misses                23       23              
  Partials              54       54              

Impacted Files	Coverage Δ
src/utils/FileEmitter.ts	100.00% <100.00%> (ø)

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[rollup-bot]

This PR has been released as part of rollup@3.0.0-7. Note that this is a pre-release, so to test it, you need to install Rollup via npm install rollup@3.0.0-7 or npm install rollup@beta. It will likely become part of a regular release later.

[rollup-bot]

This PR has been released as part of rollup@3.0.0-8. Note that this is a pre-release, so to test it, you need to install Rollup via npm install rollup@3.0.0-8 or npm install rollup@beta. It will likely become part of a regular release later.

[rollup-bot]

This PR has been released as part of rollup@3.0.0. You can test it via npm install rollup.