Merge multiple profiles in Speedscope's JSON format into one file

merge-speedscope-json.js

#!/usr/bin/env node
"use strict";

const fs = require("fs");

const SPEEDSCOPE_JSON_SCHEMA = "https://www.speedscope.app/file-format-schema.json";

const [node, prog, ...options] = process.argv;

if (options[options.length - 2] !== "-o") {
    console.error(`Usage: ${node} ${prog} <INPUT-FILES> -o <OUTPUT-FILE>`);
    process.exit(1);
}

const outputFile = options.pop();
options.pop();
const inputFiles = options;

const output = {
    frameIndices: {},
    frames: [],
    profiles: [],
};

for (const inputFile of inputFiles) {
    console.log(`Processing input from ${inputFile}...`);
    const json = JSON.parse(fs.readFileSync(inputFile));
    const input = {
        frames: json.shared.frames,
        profiles: json.profiles,
    };

    for (const profile of input.profiles) {
        for (const event of profile.events) {
            const frame = input.frames[event.frame].name;
            let frameIndex = output.frameIndices[frame];
            if (frameIndex === undefined) {
                frameIndex = output.frames.length;
                output.frames.push({ name: frame });
                output.frameIndices[frame] = frameIndex;
            }
            event.frame = frameIndex;
        }
        output.profiles.push(profile);
    }
}

console.log(`Writing output to ${outputFile}...`);
fs.writeFileSync(outputFile, JSON.stringify({
    "$schema": SPEEDSCOPE_JSON_SCHEMA,
    "activeProfileIndex": 0,
    "exporter": "merge-speedscope-json",
    "profiles": output.profiles,
    "shared": { "frames": output.frames },
}));

Here is how to reproduce this crash.
You'd need to pull from master in solution-spider repo to get the latest version of the makefiles.

make run-ft daml_profile_dir=/tmp/prof ftags=@SPD-8658 (/tmp/prof must exist)

It should emit around 3.2Gb json.

Then try to combine all the files.