dag: add test reproducing branch overlapping

The explanation is in the script.

Signed-off-by: Efimov Vasily <[email protected]>

Author: laerreal

test/short_branch_overlapping.sh

@@ -0,0 +1,105 @@
+#!/bin/bash
+folder=tmp/a_repo
+
+nodeI=0
+
+function node() {
+    n=$nodeI
+    nodeI=$((nodeI+1))
+
+    touch $n >> /dev/null
+    git add $n >> /dev/null
+    if ! [ "$1" == "" ] ; then
+        n=$1
+    fi
+    git commit -m node-$n- >> /dev/null
+    if ! [ "$1" == "" ] ; then
+        git tag -m "" $n  >> /dev/null
+    fi
+}
+
+function get_SHA1() {
+    git log --all --grep node-$1- | grep commit | sed -e 's/commit //'
+}
+
+function goto() {
+    SHA1=$(get_SHA1 $1)
+    git checkout $SHA1 -b $2 >> /dev/null
+}
+
+function merge() {
+    n=$nodeI
+    nodeI=$((nodeI+1))
+
+    SHA1=$(get_SHA1 $1)
+    git merge --no-ff $SHA1 -m node-$n- >> /dev/null
+}
+
+function range() {
+    i=$1
+    I=$2
+    res=$i
+    while [[ i -lt I ]] ; do
+        i=$((i+1))
+        res="$res $i"
+    done
+    echo $res
+}
+
+function nodes() {
+    I=$(($1-1))
+    for i in $(range 0 $I) ; do
+        node
+    done
+}
+
+rm -rf "$folder"
+mkdir "$folder"
+cd "$folder"
+
+git init
+
+# Tags are used to get difference between row and generation values.
+# Branches master & b2 occupied 2 rows per generation because of tags.
+# Branches b0 is at the left of tags. Therefore, b0 uses 1 row per generation.
+# The same is for b1 too. The b1 is short but tag 'b1' cannot be placed
+# right at the row the branch ends, because the tags at the right were already
+# placed (they have less generation value). Hence, a gap between last two
+# commits of b1 is big. Let b0 forks at a row inside the gap. The fork commit
+# have greater generation than last commit of b1. Hence, it is placed after.
+# Because of the bug, making many enough branches starting from the fork will
+# manage to overlapping of last commit of b1 and a commit of a branch.
+
+node tag0
+node tag1
+node tag2
+node tag3
+node tag4
+nodes 1
+
+goto tag0 b0
+nodes 8
+b0_head=$n
+
+goto tag0 b1
+nodes 5
+
+goto tag0 b2
+nodes 10
+
+git checkout b0
+nodes 5
+
+goto $b0_head b5
+nodes 5
+
+goto $b0_head b6
+nodes 5
+
+goto $b0_head b7
+nodes 5
+
+git checkout b2
+
+../../../bin/git-dag --all &
+