nyc merge for large number of files throws "Invalid string length" error

[parvez]

We run 20+ parallel runs of cypress that generate 20 different coverage${ID}-final.json stored in cypress/coverage

Expected Behavior

$(npm bin)/nyc merge cypress/coverage cypress/coverage/coverage-final.json should merge them into a single coverage file without issue.

Observed Behavior

$(npm bin)/nyc merge cypress/coverage cypress/coverage/coverage-final.json throws this error:

RangeError: Invalid string length

Likely issue

Might be happening due to nodejs/node#35973 and thus lowering the number of runs to 14 works as the size of the json is lower than 500MB

[kunaljaydesai]

I ran into the same issue. I fixed it by reducing the size of the JSON files. For example, for my use case, we didn't need code coverage for files in node_modules directory. Perhaps the same or something similar can apply to your case.

[skimi]

A big reason merge can hit this error quickly is that it stringifies pretty json with a lot of white space meaning huge json
https://github.com/istanbuljs/nyc/blob/main/lib/commands/merge.js#L44

Going from JSON.stringify(map, null, 2) to simple JSON.stringify(map) adds a lot of leeway.