lint: reactivate several disabled linters

[erickcestari]

This PR enables five previously-disabled linters and fixes the violations they surface. It also corrects a mislabeled section of .golangci.yml where a block of active linters was wrongly commented as "Deprecated linters".

Each linter is enabled in its own commit, with code fixes landing before the linter is switched on, so CI stays green at every commit. Code changes are also split into separate test-file and non-test-file commits.

Linters enabled:

• copyloopvar: redundant x := x loop-variable copies, unnecessary since Go 1.22 per-iteration scoping (161 files).
• wastedassign: dead stores assigned but never read (25 sites). This surfaced a real missing error check in routing/router_test.go, where err from New() was never asserted.
• bodyclose: unclosed HTTP response bodies (0 existing issues).
• rowserrcheck: unchecked sql.Rows.Err() (0 existing issues).
• sqlclosecheck: unclosed sql.Rows / sql.Stmt (0 existing issues).

Linters left disabled, now with accurate comments instead of the wrong "deprecated" label:

• contextcheck: requires threading context.Context through many existing signatures, including test harnesses.
• tparallel: requires adding t.Parallel() to many existing subtests, which can surface shared-state races.
• unparam: sizeable backlog of unused parameters to clean up first.
• nilerr: too noisy here; nearly all reports are intentional documented error-swallowing or false positives.
• noctx: only flags a couple of interface methods and a test helper with no context to thread through.

#10858 (comment)

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request modernizes the codebase by leveraging the per-iteration loop variable scoping introduced in Go 1.22. By enabling the copyloopvar linter, we ensure that redundant variable shadowing is caught automatically, and we have proactively cleaned up existing instances throughout the project to maintain cleaner, more idiomatic code.

Highlights

• Linter Configuration: Enabled the copyloopvar linter in .golangci.yml to enforce modern Go loop variable scoping practices.
• Code Cleanup: Removed redundant loop variable copies (e.g., test := test) across the entire codebase, as they are no longer necessary since Go 1.22.

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[github-actions]

🔴 PR Severity: CRITICAL

Path-based classification | 16 non-test files | 41 lines changed

🔴 Critical (10 files)

• `lnwallet/channel.go` - wallet/channel operations (lnwallet/*)
• `lnwallet/btcwallet/btcwallet.go` - wallet operations (lnwallet/*)
• `contractcourt/channel_arbitrator.go` - on-chain dispute resolution (contractcourt/*)
• `contractcourt/breach_arbitrator.go` - breach handling (contractcourt/*)
• `contractcourt/briefcase.go` - on-chain state (contractcourt/*)
• `contractcourt/chain_arbitrator.go` - chain arbitration (contractcourt/*)
• `contractcourt/taproot_briefcase.go` - taproot on-chain state (contractcourt/*)
• `channeldb/height_hint.go` - channel state persistence (channeldb/*)
• `channeldb/invoices.go` - channel state persistence (channeldb/*)
• `funding/batch.go` - channel funding workflow (funding/*)

🟠 High (5 files)

• `chainntnfs/mempool.go` - chain notifications (chainntnfs/*)
• `discovery/gossiper.go` - gossip protocol (discovery/*)
• `invoices/invoiceregistry.go` - invoice management (invoices/*)
• `lnrpc/devrpc/dev_server.go` - RPC server (lnrpc/*)
• `lnrpc/walletrpc/walletkit_server.go` - RPC server (lnrpc/*)

🟢 Low (1 file)

• `.golangci.yml` - CI/linter configuration

Analysis

This PR enables the `copyloopvar` linter and removes redundant loop variable shadow copies (e.g., `x := x`) that were needed before Go 1.22 but are now unnecessary since loop variables are scoped per-iteration. The change is purely mechanical — no logic is altered, only boilerplate removed.

Despite the low-risk nature of the change, the severity is CRITICAL because the highest-severity files touched include core packages such as `lnwallet/`, `contractcourt/`, `channeldb/`, and `funding/`. Per classification rules, the highest-severity file determines the PR severity.

No severity bump was applied: 16 non-test/non-generated files (< 20 threshold) and 41 lines changed (< 500 threshold).

---

_{To override, add a `severity-override-{critical,high,medium,low}` label.}
<!-- pr-severity-bot -->

[gemini-code-assist]

Code Review

This pull request removes obsolete loop variable rebindings across numerous test and production files, aligning with Go's modern loop semantics, and disables the copyloopvar linter. The review feedback correctly identifies several obsolete comments explaining the removed rebinding logic that should be cleaned up to maintain code clarity.

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For more details on the timeline and next steps, please review the Help Documentation.

I am having trouble creating individual review comments. Click here to see my feedback.

invoices/invoiceregistry.go (512)

Since the loop variable rebinding (addEvent := addEvent) has been removed, the comment explaining why the variable is being rebound is now obsolete and should be removed to keep the codebase clean and accurate.

References

1. Comments must explain the intention and context of the code accurately. Obsolete comments explaining removed logic should be cleaned up. ^(link)

invoices/invoiceregistry.go (526)

Since the loop variable rebinding (settleEvent := settleEvent) has been removed, the comment explaining why the variable is being rebound is now obsolete and should be removed.

References

1. Comments must explain the intention and context of the code accurately. Obsolete comments explaining removed logic should be cleaned up. ^(link)

lnrpc/walletrpc/walletkit_server_test.go (46-47)

Since the loop variable redeclarations have been removed, the comment explaining why they are being redeclared is now obsolete and should be removed.

References

1. Comments must explain the intention and context of the code accurately. Obsolete comments explaining removed logic should be cleaned up. ^(link)

[ziggie1984]

maybe check all the switched off linters maybe we can reactivate more ?

[ziggie1984]

also could you separate test files and the other files in different commits ?

[erickcestari]

maybe check all the switched off linters maybe we can reactivate more ?

True, I'll check for others linters.

[erickcestari]

Done @ziggie1984