docs+github+scripts: remove submodule update check

Because we want to avoid local replace directives (as they make it easy
to screw up things for external applications that use lnd as a library
without us noticing), we're going to switch over to a new process.
See section "Use of Golang submodules" in the code contribution
guideline.

.github/workflows/main.yml

@@ -104,34 +104,6 @@ jobs:
       - name: check commits
         run: scripts/check-each-commit.sh upstream/master
 
-  ########################
-  # check submodules
-  ########################
-  check-submodules:
-    name: check submodules
-    runs-on: ubuntu-latest
-    steps:
-      - name: git checkout
-        uses: actions/checkout@v2
-        with:
-          fetch-depth: 0
-
-      - name: setup go ${{ env.GO_VERSION }}
-        uses: actions/setup-go@v2
-        with:
-          go-version: '${{ env.GO_VERSION }}'
-
-      - name: fetch and rebase on master
-        run: |
-          git remote add upstream https://github.com/lightningnetwork/lnd
-          git fetch upstream
-          export GIT_COMMITTER_EMAIL="lnd-ci@example.com"
-          export GIT_COMMITTER_NAME="LND CI"
-          git rebase upstream/master
-
-      - name: check submodules
-        run: scripts/check-submodule-version.sh upstream/master
-
   ########################
   # lint code
   ########################

docs/code_contribution_guidelines.md

@@ -12,6 +12,7 @@
    1. [Code Spacing and formatting](#code-spacing-and-formatting)
    1. [Pointing to Remote Dependent Branches in Go Modules](#pointing-to-remote-dependent-branches-in-go-modules)
    1. [Use of Log Levels](#use-of-log-levels)
+   1. [Use of Golang submodules](#use-of-golang-submodules)
 5. [Code Approval Process](#code-approval-process)
    1. [Code Review](#code-review)
    1. [Rework Code (if needed)](#rework-code-if-needed)
@@ -640,6 +641,24 @@ Only use `error` for internal errors that are never expected to happen during
 normal operation. No event triggered by external sources (rpc, chain backend,
 etc) should lead to an `error` log.
 
+## Use of Golang submodules
+
+Changes to packages that are their own submodules (e.g. they contain a `go.mod`
+and `go.sum` file, for example `tor/go.mod`) require a specific process.
+We want to avoid the use of local replace directives in the root `go.mod`,
+therefore changes to a submodule are a bit involved.
+
+The main process for updating and then using code in a submodule is as follows:
+ - Create a PR for the changes to the submodule itself (e.g. edit something in
+   the `tor` package)
+ - Wait for the PR to be merged and a new tag (for example `tor/v1.0.x`) to be
+   pushed.
+ - Create a second PR that bumps the updated submodule in the root `go.mod` and
+   uses the new functionality in the main module.
+
+Of course the two PRs can be opened at the same time and be built on top of each
+other. But the merge and tag push order should always be maintained.
+
 # Code Approval Process
 
 This section describes the code approval process that is used for code

scripts/check-submodule-version.sh

@@ -1,34 +0,0 @@
-#!/bin/bash
-
-ROOT_MODULE="github.com/lightningnetwork/lnd"
-
-# The command 'go list -m all' returns all imports in the following format:
-#   github.com/lightningnetwork/lnd/cert v1.1.0 => ./cert
-# The two cut then first split by spaces and then by slashes to extract the
-# submodule names.
-SUBMODULES="$(go list -m all | grep $ROOT_MODULE/ | cut -d' ' -f1 | cut -d'/' -f4-)"
-BRANCH=$1
-
-for m in $SUBMODULES; do
-  has_changes=0
-  git diff --stat $BRANCH.. | grep -q " $m/" && has_changes=1
-  
-  if [[ $has_changes -eq 1 ]]; then
-    has_bump=0
-    git diff $BRANCH.. -- go.mod | \
-      grep -q "^\+[[:space:]]*$ROOT_MODULE/$m " && has_bump=1
-    
-    if [[ $has_bump -eq 0 ]]; then
-      echo "Submodule '$m' has changes but no version bump in go.mod was found"
-      echo "If you update code in a submodule, you must bump its version in "
-      echo "go.mod to the _next_ version so a tag for that version can be"
-      echo "pushed after merging the PR."
-      exit 1
-    else
-      echo "Submodule '$m' has changes but go.mod bumps it to: "
-      git diff $BRANCH.. -- go.mod | grep $m
-    fi
-  else
-    echo "Submodule '$m' has no changes, skipping"
-  fi
-done