syn2mas does not import user if it has warnings

[tonkku107]

Describe the bug
syn2mas will skip migrating a user if non-fatal warnings were encountered, such as a non-email 3pid type.

To Reproduce
Steps to reproduce the behavior:

1. Have a user with an msisdn 3pid
2. Run the migration
3. Observe the warning "Skipping non-email 3pid msisdn for user"
4. Notice that the specific user is entirely missing from MAS

Expected behavior
User is migrated but with the msisdn 3pid missing

Additional context
Discussion in the #matrix-auth:matrix.org room

The problematic piece of code is here:

matrix-authentication-service/tools/syn2mas/src/migrate.mts

Lines 409 to 417 in 1871b2c

	if (warningsForUser > 0) {
	if (!args.dryRun) {
	fatal(`User ${user.name} had ${warningsForUser} warnings`);
	} else {
	log.warn(`User ${user.name} had ${warningsForUser} warnings`);
	}
	} else if (!args.dryRun) {
	log.info(`Running ${executions.length} updates for user ${user.name}`);
	const tx = await mas.transaction();

[johansmitsnl]

I also have this issue, how did you solve it?

[moqmar]

Changing line 410 to if (false) { works (you can usually find the file with find "$(npm prefix -g)" -name migrate.mts). Only do this if you understood all warnings from the dry run though and are sure that you want to ignore them.

This behaviour definitely needs to be fixed, as it means that the dry run succeeds but the actual run leaves you with a corrupt MAS database that needs to be deleted and migrated to again from scratch. This is basically the opposite of how a dry run shall normally work.

[tonkku107]

This should be solved with #3878 for the rewrite of the syn2mas tool but the rewrite is still work in progress