Port TS PR 61505 - Cache mapper instantiations

[jakebailey]

This is an early port of microsoft/TypeScript#61505, because I like to go fast

Calculating the key increases allocs by a bit (really wish we had the yet-to-exist Go custom map implementation), but for https://github.com/AnswerOverflow/AnswerOverflow/tree/1ab687793a598789a0c86b4ca5f17ee6f3a256aa/apps/dashboard:

TypeScript 5.8 vs 5.9:

Files: 3351 Lines: 573983 Identifiers: 646173 Symbols: 652920 Types: 139674 Instantiations: 13672403 Memory used: 912429K I/O read: 0.13s I/O write: 0.00s Parse time: 1.91s Bind time: 0.60s Check time: 7.67s Emit time: 0.12s Total time: 10.30s 

Files: 3353 Lines: 575420 Identifiers: 646578 Symbols: 651905 Types: 139189 Instantiations: 797184 Memory used: 898938K I/O read: 0.10s I/O write: 0.00s Parse time: 1.84s Bind time: 0.61s Check time: 3.79s Emit time: 0.11s Total time: 6.35s 

tsgo main vs this PR;

Files: 3501 Lines: 601735 Identifiers: 661699 Symbols: 1219580 Types: 420852 Instantiations: 25441996 Memory used: 862438K Memory allocs: 63315601 Config time: 0.002s Parse time: 0.170s Bind time: 0.044s Check time: 2.034s Emit time: 0.000s Total time: 2.257s 

Files: 3501 Lines: 601735 Identifiers: 661699 Symbols: 1219580 Types: 419356 Instantiations: 2178836 Memory used: 861708K Memory allocs: 12761985 Config time: 0.003s Parse time: 0.163s Bind time: 0.048s Check time: 1.107s Emit time: 0.000s Total time: 1.327s 

(Instantiations look higher than 5.8 or 5.9 because tsgo's metrics sum up instantiations between all concurrent checkers)

Benchmark 1: ~/work/TypeScript-go/built/local-old/tsgo Time (mean ± σ): 2.270 s ± 0.078 s [User: 13.092 s, System: 1.112 s] Range (min … max): 2.164 s … 2.392 s 10 runs Benchmark 2: ~/work/TypeScript-go/built/local/tsgo Time (mean ± σ): 1.376 s ± 0.069 s [User: 7.626 s, System: 1.028 s] Range (min … max): 1.293 s … 1.531 s 10 runs Summary ~/work/TypeScript-go/built/local/tsgo ran 1.65 ± 0.10 times faster than ~/work/TypeScript-go/built/local-old/tsgo 

Benchmark 1 (3 runs): /home/jabaile/work/TypeScript-go/built/local-old/tsgo measurement mean ± σ min … max outliers delta wall_time 2.29s ± 90.2ms 2.23s … 2.39s 0 ( 0%) 0% peak_rss 1.46GB ± 92.0MB 1.36GB … 1.55GB 0 ( 0%) 0% cpu_cycles 59.7G ± 1.84G 57.7G … 61.1G 0 ( 0%) 0% instructions 85.3G ± 2.30G 82.7G … 87.2G 0 ( 0%) 0% cache_references 1.19G ± 21.0M 1.17G … 1.22G 0 ( 0%) 0% cache_misses 251M ± 6.31M 244M … 256M 0 ( 0%) 0% branch_misses 177M ± 1.79M 175M … 179M 0 ( 0%) 0% Benchmark 2 (4 runs): /home/jabaile/work/TypeScript-go/built/local/tsgo measurement mean ± σ min … max outliers delta wall_time 1.37s ± 80.5ms 1.30s … 1.47s 0 ( 0%) ⚡- 40.1% ± 7.3% peak_rss 1.13GB ± 7.47MB 1.12GB … 1.14GB 0 ( 0%) ⚡- 22.8% ± 7.9% cpu_cycles 34.1G ± 1.02G 33.3G … 35.5G 0 ( 0%) ⚡- 42.9% ± 4.6% instructions 40.8G ± 912M 39.9G … 41.7G 0 ( 0%) ⚡- 52.2% ± 3.7% cache_references 979M ± 17.1M 963M … 1.00G 0 ( 0%) ⚡- 18.0% ± 3.1% cache_misses 154M ± 8.52M 146M … 165M 0 ( 0%) ⚡- 38.5% ± 6.0% branch_misses 109M ± 2.03M 107M … 112M 0 ( 0%) ⚡- 38.8% ± 2.1% 

[Copilot]

Pull Request Overview

This PR ports TypeScript’s PR 61505 to introduce caching for type mapper instantiations, aiming to reduce repeated instantiation overhead and improve performance.

• Added a stack of active mappers with per-mapper caches backed by sync.Pool.
• Updated instantiateTypeWithAlias to check and store in those caches.
• Cleared mapper caches after each inference in getInferredType.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
internal/checker/inference.go	Inserted clearActiveMapperCaches() after each inference loop
internal/checker/checker.go	Added activeMappers, activeTypeMappersCaches, cache logic in instantiateTypeWithAlias, and push/pop/clear helper methods

Comments suppressed due to low confidence (2)

internal/checker/inference.go:1332

• [nitpick] clearActiveMapperCaches() is invoked inside the loop for each inference, leading to repeated map clears. Consider moving this call outside the loop or only once per context to avoid redundant operations.

 c.clearActiveMapperCaches() 

[Andarist]

[jakebailey]

The other "global" caches don't use two separate lists in the Go port, instead scoping them together, but I'm keeping them separate since I'm trying to reuse the maps.