t3508: add check_head_differs_from() helper function and use it

diff --git a/git-am.sh b/git-am.sh
index 87ffae252b3f2ff88646d142ea9c2dfb38a28953..e7f008c7baae2ff484e16882e199b6b9d75195aa 100755 (executable)
--- a/git-am.sh
+++ b/git-am.sh
@@ -52,6 +52,16 @@ else
        HAS_HEAD=
 fi
 
+cmdline="git am"
+if test '' != "$interactive"
+then
+       cmdline="$cmdline -i"
+fi
+if test '' != "$threeway"
+then
+       cmdline="$cmdline -3"
+fi
+
 sq () {
        git rev-parse --sq-quote "$@"
 }
@@ -66,15 +76,6 @@ stop_here_user_resolve () {
            printf '%s\n' "$resolvemsg"
            stop_here $1
     fi
-    cmdline="git am"
-    if test '' != "$interactive"
-    then
-        cmdline="$cmdline -i"
-    fi
-    if test '' != "$threeway"
-    then
-        cmdline="$cmdline -3"
-    fi
     echo "When you have resolved this problem run \"$cmdline --resolved\"."
     echo "If you would prefer to skip this patch, instead run \"$cmdline --skip\"."
     echo "To restore the original branch and stop patching run \"$cmdline --abort\"."
@@ -591,9 +592,11 @@ do
 
                test -s "$dotest/patch" || {
                        echo "Patch is empty.  Was it split wrong?"
+                       echo "If you would prefer to skip this patch, instead run \"$cmdline --skip\"."
+                       echo "To restore the original branch and stop patching run \"$cmdline --abort\"."
                        stop_here $this
                }
-               rm -f "$dotest/original-commit"
+               rm -f "$dotest/original-commit" "$dotest/author-script"
                if test -f "$dotest/rebasing" &&
                        commit=$(sed -e 's/^From \([0-9a-f]*\) .*/\1/' \
                                -e q "$dotest/$msgnum") &&
@@ -602,6 +605,7 @@ do
                        git cat-file commit "$commit" |
                        sed -e '1,/^$/d' >"$dotest/msg-clean"
                        echo "$commit" > "$dotest/original-commit"
+                       get_author_ident_from_commit "$commit" > "$dotest/author-script"
                else
                        {
                                sed -n '/^Subject/ s/Subject: //p' "$dotest/info"
@@ -613,9 +617,14 @@ do
                ;;
        esac
 
-       GIT_AUTHOR_NAME="$(sed -n '/^Author/ s/Author: //p' "$dotest/info")"
-       GIT_AUTHOR_EMAIL="$(sed -n '/^Email/ s/Email: //p' "$dotest/info")"
-       GIT_AUTHOR_DATE="$(sed -n '/^Date/ s/Date: //p' "$dotest/info")"
+       if test -f "$dotest/author-script"
+       then
+               eval $(cat "$dotest/author-script")
+       else
+               GIT_AUTHOR_NAME="$(sed -n '/^Author/ s/Author: //p' "$dotest/info")"
+               GIT_AUTHOR_EMAIL="$(sed -n '/^Email/ s/Email: //p' "$dotest/info")"
+               GIT_AUTHOR_DATE="$(sed -n '/^Date/ s/Date: //p' "$dotest/info")"
+       fi
 
        if test -z "$GIT_AUTHOR_EMAIL"
        then
@@ -690,7 +699,13 @@ do
        else
            action=yes
        fi
-       FIRSTLINE=$(sed 1q "$dotest/final-commit")
+
+       if test -f "$dotest/final-commit"
+       then
+               FIRSTLINE=$(sed 1q "$dotest/final-commit")
+       else
+               FIRSTLINE=""
+       fi
 
        if test $action = skip
        then
@@ -726,6 +741,8 @@ do
                resolved=
                git diff-index --quiet --cached HEAD -- && {
                        echo "No changes - did you forget to use 'git add'?"
+                       echo "If there is nothing left to stage, chances are that something else"
+                       echo "already introduced the same changes; you might want to skip this patch."
                        stop_here_user_resolve $this
                }
                unmerged=$(git ls-files -u)