lncfg: don't warn user about existing bbolt DB if SQLite files exist

[Dhiren-Mhatre]

Change Description

Fix issue #9708 by checking for existing SQLite database files before warning about bbolt files.

Currently, when users start LND with the SQLite backend, they see warnings about existing bbolt database files even if they've already migrated their data using lndinit migrate-db. This PR enhances the warning system to only display these messages when a SQLite file doesn't exist yet, reducing confusion for users who have already completed migration.

Steps to Test

1. Create a test environment with bbolt database files:

   mkdir -p ~/lnd-test-bolt
   lnd --lnddir=~/lnd-test-bolt --datadir=~/lnd-test-bolt
   # Create and fund a wallet
   lncli --lnddir=~/lnd-test-bolt create
   

2. Migrate to SQLite:

   lndinit --lnddir=~/lnd-test-bolt migrate-db
   

3. Run with SQLite backend before applying this fix:

   lnd --lnddir=~/lnd-test-bolt --db.backend=sqlite --db.use-native-sql
   

   Observe the warnings about existing bbolt files.

4. Run with SQLite backend after applying this fix:

   lnd --lnddir=~/lnd-test-bolt --db.backend=sqlite --db.use-native-sql
   

   No warnings should appear since SQLite files exist.

5. Delete the SQLite files and run again:

   rm ~/lnd-test-bolt/data/chain/bitcoin/regtest/chain.sqlite
   rm ~/lnd-test-bolt/data/graph/regtest/channel.sqlite
   lnd --lnddir=~/lnd-test-bolt --db.backend=sqlite --db.use-native-sql
   

   Warnings should reappear because bbolt files exist but SQLite files don't.

Pull Request Checklist

Testing

• Your PR passes all CI checks.
• Tests covering the positive and negative (error paths) are included.
• Bug fixes contain tests triggering the bug to prevent regressions.

Code Style and Documentation

• The change is not insubstantial.
• The change obeys the Code Documentation and Commenting guidelines, and lines wrap at 80.
• Commits follow the Ideal Git Commit Structure.
• Any new logging statements use an appropriate subsystem and logging level.
• Any new lncli commands have appropriate tags in the comments for the rpc in the proto file.
• There is a change description in the release notes.

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[NishantBansal2003]

Please read the contribution guidelines.
https://github.com/lightningnetwork/lnd/blob/master/docs/development_guidelines.md#ideal-git-commit-structure

[Dhiren-Mhatre]

Please read the contribution guidelines. https://github.com/lightningnetwork/lnd/blob/master/docs/development_guidelines.md#ideal-git-commit-structure

I've updated my commit messages as per the contribution guidelines.Thank you for pointing this out!

[NishantBansal2003]

Have you tested the PR locally? I tried testing it, and here are the results:

1. Running with SQLite only (no bbolt and no existing SQLite data) → warning does not show up (test passed).
2. Running with SQLite only (no bbolt but with existing SQLite data) → warning does not show up (test passed).
3. Running with SQLite (with bbolt data and no existing SQLite data) → warning does not show up (test failed).
4. Running with SQLite (with bbolt data and with existing SQLite data) → warning does not show up (test passed).

The warning does not appear in any of these cases. I believe that, if the .sqlite file does not exist, it is created automatically, so your check !lnrpc.FileExists(sqlitePath) is never executed.

Additionally, I noticed that we are only checking here:

lnd/lncfg/db.go

Lines 604 to 609 in 7e50b84

	warnExistingBoltDBs(
	logger, "sqlite", walletDBPath, WalletDBName,
	)
	warnExistingBoltDBs(
	logger, "sqlite", chanDBPath, ChannelDBName,
	)

So, currently no warnings are thrown for macaroons.db and sphinxreplay.db.

[Dhiren-Mhatre]

Have you tested the PR locally? I tried testing it, and here are the results:

1. Running with SQLite only (no bbolt and no existing SQLite data) → warning does not show up (test passed).
2. Running with SQLite only (no bbolt but with existing SQLite data) → warning does not show up (test passed).
3. Running with SQLite (with bbolt data and no existing SQLite data) → warning does not show up (test failed).
4. Running with SQLite (with bbolt data and with existing SQLite data) → warning does not show up (test passed).

The warning does not appear in any of these cases. I believe that, if the .sqlite file does not exist, it is created automatically, so your check !lnrpc.FileExists(sqlitePath) is never executed.

Additionally, I noticed that we are only checking here:

lnd/lncfg/db.go

Lines 604 to 609 in 7e50b84

	warnExistingBoltDBs(
	logger, "sqlite", walletDBPath, WalletDBName,
	)
	warnExistingBoltDBs(
	logger, "sqlite", chanDBPath, ChannelDBName,
	)

So, currently no warnings are thrown for macaroons.db and sphinxreplay.db.

You're right about those points. I was worried about the FileExists check, but I wasn't sure if the SQLite files would be auto-created. Based on your testing, it seems like my implementation isn't behaving as expected.
For the macaroons.db and sphinxreplay.db checks, I thought I was handling them in the switch statement, but you're right that they're not being checked in the main function calls.
I'll update the PR to:
Fix the logic to ensure warnings appear only when appropriate
Add explicit checks for macaroons.db and sphinxreplay.db
Thanks for the thorough review

[NishantBansal2003]

Did a quick pass: Could you explain what .migration-complete is? I couldn't find any such file.

Also, I think the code shouldn't be specific to migration but should handle general scenarios (including the migration case as well). wdyt?

[Dhiren-Mhatre]

The .migration-complete file was intended as a theoretical enhancement that doesn't actually exist yet. I added that check thinking it could be a reliable way to detect completed migrations (since SQLite files are auto-created even without migration).

I agree the code shouldn't be migration-specific. The simple approach in my second commit (just adding checks for macaroons.db and sphinxreplay.db) addresses what's actually needed:

1. It checks for all database types mentioned in the issue
2. It follows the existing pattern without introducing complex migration detection

I can update the PR to remove the migration-specific code and focus only on adding the additional file checks, which is what users need right now. Would that approach work better?

[NishantBansal2003]

I think it would be better if the approach focused on solving the original issue:

1. I think it should only look for a bbolt DB and inform the user of its existence if the user has requested a SQLite DB AND the SQLite DB does not actually exist
2. Also, if we do do these checks because the SQLite DB doesn't exist and we are trying to warn the user of what they actually have, we should also check for macaroons.db and sphinxreplay.db

I believe there are some straightforward ways to solve this issue using general logic.

Suggestion: It would be better if you push fully working and tested code that reflects the intended behavior.