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]