Sourcemap generation consuming significant resources while sourcemaps are disabled

[aem]

Description

When running tsgo --build on a project with source maps and declaration maps disabled, a significant amount of CPU and memory is spent on what seemingly should be unused source map-related functions.

tsgo setup

// <root>/tsconfig.json
//  ...
    "declaration": true,
    "emitDeclarationOnly": true,
    "sourceMap": false,
    "declarationMap": false,
    "emit": false,
//  ...

tsgo version: 7.0.0-dev.20251204.1

Details

After migrating our monorepo to tsgo with a significant local performance improvement, I went to test the new setup in CI and discovered worse performance than [email protected] on a CI machine with 4 CPU cores and 16gb memory. I ran tsgo with profiling enabled (profiles attached below) and noticed (with the help of Claude) that source map emission accounted for ~60% of cumulative CPU time during compilation despite source maps and declaration maps both being disabled during the build:

         0     0% 90.69%    126.39s 29.24%  github.com/microsoft/typescript-go/internal/printer.(*Printer).emitSourceMapsAfterNode
         0     0% 90.69%    125.28s 28.99%  github.com/microsoft/typescript-go/internal/printer.(*Printer).emitSourceMapsBeforeNode

The memory profile looks much less interesting, I suspect the ~18GiB of memory consumed by our project is just related to having ~1mm LOC and heavy use of intersection types, but I'm surprised to see the source map printer consuming the majority of CPU time while all maps are disabled.

Profiles

82514-cpuprofile.pb.gz 82514-memprofile.pb.gz