Add monorepo_add to allow incremental build

CHANGELOG.md

@@ -85,6 +85,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### [shopsys/monorepo-tools]
 #### Added
+- [#345 - monorepo-tools: allow incremental build of monorepo](https://github.com/shopsys/shopsys/pull/345) [@lukaso]
 - [# 311 - monorepo split allows adding new package when monorepo is already tagged](https://github.com/shopsys/shopsys/pull/311)
 #### Fixed
 - [#281 - monorepo-tools: Fix scripts to work on OS X](https://github.com/shopsys/shopsys/pull/282) [@lukaso]

packages/monorepo-tools/README.md

@@ -108,6 +108,12 @@ Split monorepo built by `monorepo_build.sh` and push all `master` branches along
 
 Usage: `monorepo_split.sh <remote-name>[:<subdirectory>] <remote-name>[:<subdirectory>] ...`
 
+### [monorepo_add.sh](./monorepo_add.sh)
+
+Add repositories to an existing monorepo from specified remotes. The remotes must be already added to your repository and fetched. Only master branch will be added from each repo.
+
+Usage: `monorepo_add.sh <remote-name>[:<subdirectory>] <remote-name>[:<subdirectory>] ...`
+
 ### [rewrite_history_into.sh](./rewrite_history_into.sh)
 
 Rewrite git history (even tags) so that all filepaths are in a specific subdirectory.

packages/monorepo-tools/monorepo_add.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+
+# Add repositories to a monorepo from specified remotes
+# You must first add the remotes by "git remote add <remote-name> <repository-url>" and fetch from them by "git fetch --all"
+# It will merge master branches of the monorepo and all remotes together while keeping all current branches in monorepo intact
+# If subdirectory is not specified remote name will be used instead
+#
+# Usage: monorepo_add.sh <remote-name>[:<subdirectory>] <remote-name>[:<subdirectory>] ...
+#
+# Example: monorepo_add.sh additional-repository package-gamma:packages/gamma package-delta:packages/delta
+
+# Check provided arguments
+if [ "$#" -lt "1" ]; then
+    echo 'Please provide at least 1 remote to be added into an existing monorepo'
+    echo 'Usage: monorepo_add.sh <remote-name>[:<subdirectory>] <remote-name>[:<subdirectory>] ...'
+    echo 'Example: monorepo_add.sh additional-repository package-gamma:packages/gamma package-delta:packages/delta'
+    exit
+fi
+# Get directory of the other scripts
+MONOREPO_SCRIPT_DIR=$(dirname "$0")
+# Wipe original refs (possible left-over back-up after rewriting git history)
+$MONOREPO_SCRIPT_DIR/original_refs_wipe.sh
+for PARAM in $@; do
+    # Parse parameters in format <remote-name>[:<subdirectory>]
+    PARAM_ARR=(${PARAM//:/ })
+    REMOTE=${PARAM_ARR[0]}
+    SUBDIRECTORY=${PARAM_ARR[1]}
+    if [ "$SUBDIRECTORY" == "" ]; then
+        SUBDIRECTORY=$REMOTE
+    fi
+    echo "Building branch 'master' of the remote '$REMOTE'"
+    git checkout --detach $REMOTE/master
+    $MONOREPO_SCRIPT_DIR/rewrite_history_into.sh $SUBDIRECTORY
+    MERGE_REFS="$MERGE_REFS $(git rev-parse HEAD)"
+    # Wipe the back-up of original history
+    $MONOREPO_SCRIPT_DIR/original_refs_wipe.sh
+done
+# Merge all master branches
+COMMIT_MSG="merge multiple repositories into an existing monorepo"$'\n'$'\n'"- merged using: 'monorepo_add.sh $@'"$'\n'"- see https://github.com/shopsys/monorepo-tools"
+git checkout master
+echo "Merging refs: $MERGE_REFS"
+git merge --no-commit -q $MERGE_REFS --allow-unrelated-histories
+echo 'Resolving conflicts using trees of all parents'
+for REF in $MERGE_REFS; do
+    # Add all files from all master branches into index
+    # "git read-tree" with multiple refs cannot be used as it is limited to 8 refs
+    git ls-tree -r $REF | git update-index --index-info
+done
+git commit -m "$COMMIT_MSG"
+git reset --hard
+