node v18.0.0-nightly20220222c071bd581a's fetch() breaks current sourcemap support

[trentm]

The node v18.0.0-nightly20220222c071bd581a release from a few days ago started breaking nightly tests (https://apm-ci.elastic.co/job/apm-agent-nodejs/job/apm-agent-nodejs-mbp/job/main/53/):

...
[2022-02-23T08:05:13.285Z] node_tests_1     | running test: cd . && node --unhandled-rejections=strict test/sourcemaps/index.test.js > test_output/test-sourcemaps-index.test.js.tap 2&>1
[2022-02-23T08:05:14.225Z] node_tests_1     | 
[2022-02-23T08:05:14.225Z] node_tests_1     | TAP version 13
[2022-02-23T08:05:14.225Z] node_tests_1     | # source map inlined
[2022-02-23T08:05:14.225Z] node_tests_1     | ok 1 should be strictly equal
[2022-02-23T08:05:14.225Z] node_tests_1     | ok 2 should be strictly equal
[2022-02-23T08:05:14.225Z] node_tests_1     | not ok 3 should be strictly equal
[2022-02-23T08:05:14.225Z] node_tests_1     |   ---
[2022-02-23T08:05:14.225Z] node_tests_1     |     operator: equal
[2022-02-23T08:05:14.225Z] node_tests_1     |     expected: |-
[2022-02-23T08:05:14.225Z] node_tests_1     |       'generateError (test/sourcemaps/fixtures/src/error.js)'
[2022-02-23T08:05:14.226Z] node_tests_1     |     actual: |-
[2022-02-23T08:05:14.226Z] node_tests_1     |       'generateError (test/sourcemaps/fixtures/lib/error-inline.js)'
[2022-02-23T08:05:14.226Z] node_tests_1     |     at: assertSourceFound (/app/test/sourcemaps/index.test.js:105:5)
[2022-02-23T08:05:14.226Z] node_tests_1     |     stack: |-
[2022-02-23T08:05:14.226Z] node_tests_1     |       Error: should be strictly equal
[2022-02-23T08:05:14.226Z] node_tests_1     |           at Test.assert [as _assert] (/app/node_modules/tape/lib/test.js:314:54)
[2022-02-23T08:05:14.226Z] node_tests_1     |           at Test.bound [as _assert] (/app/node_modules/tape/lib/test.js:99:32)
[2022-02-23T08:05:14.226Z] node_tests_1     |           at Test.strictEqual (/app/node_modules/tape/lib/test.js:478:10)
[2022-02-23T08:05:14.226Z] node_tests_1     |           at Test.bound [as strictEqual] (/app/node_modules/tape/lib/test.js:99:32)
[2022-02-23T08:05:14.226Z] node_tests_1     |           at assertSourceFound (/app/test/sourcemaps/index.test.js:105:5)
[2022-02-23T08:05:14.226Z] node_tests_1     |           at Object.sendError (/app/test/sourcemaps/index.test.js:96:7)
[2022-02-23T08:05:14.226Z] node_tests_1     |           at filterAndSendError (/app/lib/agent.js:108:639)
[2022-02-23T08:05:14.226Z] node_tests_1     |           at finish (/app/lib/errors.js:72:617)
[2022-02-23T08:05:14.226Z] node_tests_1     |           at /app/lib/errors.js:66:158
[2022-02-23T08:05:14.226Z] node_tests_1     |           at finish (/app/lib/stacktraces.js:89:191)
[2022-02-23T08:05:14.226Z] node_tests_1     |           at /app/node_modules/after-all-results/index.js:20:25
[2022-02-23T08:05:14.226Z] node_tests_1     |           at processTicksAndRejections (node:internal/process/task_queues:77:11)
[2022-02-23T08:05:14.226Z] node_tests_1     |   ...
...

With verbose logging, the issue in the APM agent's usage of the source-map package is this:

[2022-02-28T18:48:02.800Z] DEBUG (elastic-apm-node): could not process file source map
    filename: "/Users/trentm/el/apm-agent-nodejs12/test/sourcemaps/fixtures/lib/error-inline.js"
    error: {
        "type": "Error",
        "message":
            Error parsing sourcemap for file "/Users/trentm/el/apm-agent-nodejs12/test/sourcemaps/fixtures/lib/error-inline.js":
            You must provide the URL of lib/mappings.wasm by calling SourceMapConsumer.initialize({ 'lib/mappings.wasm': ... }) before using SourceMapConsumer,
        "stack_trace":
            Error: Error parsing sourcemap for file "/Users/trentm/el/apm-agent-nodejs12/test/sourcemaps/fixtures/lib/error-inline.js":
            You must provide the URL of lib/mappings.wasm by calling SourceMapConsumer.initialize({ 'lib/mappings.wasm': ... }) before using SourceMapConsumer
                at readWasm (/Users/trentm/el/apm-agent-nodejs12/node_modules/source-map/lib/read-wasm.js:8:13)
                at wasm (/Users/trentm/el/apm-agent-nodejs12/node_modules/source-map/lib/wasm.js:25:16)
                at /Users/trentm/el/apm-agent-nodejs12/node_modules/source-map/lib/source-map-consumer.js:264:14
    }

This is due to:

1. The current release version of source-map v0.7.3 uses if (typeof fetch === "function") to differentiate between browser and node.js environments: if (typeof fetch === "function") misidentifies node environment mozilla/source-map#349
2. And because node#master recently enabled an implementation of fetch by default: lib: enable fetch by default nodejs/node#41811

The same issue (broken source-map support) happened with early builds of node v18 when using the --experimental-fetch CLI option. The issue can be worked around in recent node v18 nightly builds by using the --no-experimental-fetch CLI option.
The same issue happens if fetch() is polyfilled, e.g. as Next.js does (according to discussion at GoogleChrome/workbox#2712).

source-map hasn't had a release since May 2018, before mozilla/source-map#349 was fixed. There is a beta release that could be considered:

    "0.7.3": "2018-05-16T17:29:49.200Z",
    "0.8.0-beta.0": "2018-11-16T00:03:32.324Z"

[trentm]

There is a beta release that could be considered:

changes: mozilla/source-map@0.7.3...0.8.0-beta.0
changelog: https://github.com/mozilla/source-map/blob/master/CHANGELOG.md#080-beta0

[trentm]

I've opened rexxars/load-source-map#6 on the load-source-map repo that would fix this for us.

Options:

1. Wait for a release with that PR and update. Meanwhile ignore "nightly" test failures until then, or skip the sourcemap tests with node v18 until then.
2. Inline the load-source-map functionality and drop that dep. Then we can control the version of 'source-map' it uses.

[trentm]

Note to self to repro:

export PATH=$HOME/tmp/node-v18.0.0-nightly20220222c071bd581a-darwin-x64/bin:$PATH
node test/sourcemaps/index.test.js

[trentm]

Option 3: This spectacularly awful hack:

diff --git a/lib/stacktraces.js b/lib/stacktraces.js
index 3ea1b962..9f1540e9 100644
--- a/lib/stacktraces.js
+++ b/lib/stacktraces.js
@@ -14,7 +14,10 @@ const asyncCache = require('async-cache')
 const afterAllResults = require('after-all-results')
 const errorCallsites = require('error-callsites')
 const errorStackParser = require('error-stack-parser')
+const _fetchCache = global.fetch
+if (_fetchCache !== undefined) delete global.fetch
 const loadSourceMap = require('load-source-map')
+if (_fetchCache !== undefined) global.fetch = _fetchCache
 const LRU = require('lru-cache')

 const fileCache = asyncCache({