Merge branch 'jc/am-3-nonstandard-popt' into maint

The code to synthesize the fake ancestor tree used by 3-way merge
fallback in "git am" was not prepared to read a patch created with
a non-standard -p<num> value.

* jc/am-3-nonstandard-popt:
  test: "am -3" can accept non-standard -p<num>
  am -3: allow nonstandard -p<num> option

git-am.sh

@@ -127,15 +127,18 @@ fall_back_3way () {
     mkdir "$dotest/patch-merge-tmp-dir"
 
     # First see if the patch records the index info that we can use.
-    git apply --build-fake-ancestor "$dotest/patch-merge-tmp-index" \
-	"$dotest/patch" &&
+    cmd="git apply $git_apply_opt --build-fake-ancestor" &&
+    cmd="$cmd "'"$dotest/patch-merge-tmp-index" "$dotest/patch"' &&
+    eval "$cmd" &&
     GIT_INDEX_FILE="$dotest/patch-merge-tmp-index" \
     git write-tree >"$dotest/patch-merge-base+" ||
     cannot_fallback "$(gettext "Repository lacks necessary blobs to fall back on 3-way merge.")"
 
     say Using index info to reconstruct a base tree...
-    if GIT_INDEX_FILE="$dotest/patch-merge-tmp-index" \
-	git apply --cached <"$dotest/patch"
+
+    cmd='GIT_INDEX_FILE="$dotest/patch-merge-tmp-index"'
+    cmd="$cmd git apply --cached $git_apply_opt"' <"$dotest/patch"'
+    if eval "$cmd"
     then
 	mv "$dotest/patch-merge-base+" "$dotest/patch-merge-base"
 	mv "$dotest/patch-merge-tmp-index" "$dotest/patch-merge-index"

t/t4150-am.sh

@@ -123,6 +123,7 @@ test_expect_success setup '
 	git commit -m "added another file" &&
 
 	git format-patch --stdout master >lorem-move.patch &&
+	git format-patch --no-prefix --stdout master >lorem-zero.patch &&
 
 	git checkout -b rename &&
 	git mv file renamed &&
@@ -276,6 +277,20 @@ test_expect_success 'am -3 falls back to 3-way merge' '
 	git diff --exit-code lorem
 '
 
+test_expect_success 'am -3 -p0 can read --no-prefix patch' '
+	rm -fr .git/rebase-apply &&
+	git reset --hard &&
+	git checkout -b lorem3 master2 &&
+	sed -n -e "3,\$p" msg >file &&
+	head -n 9 msg >>file &&
+	git add file &&
+	test_tick &&
+	git commit -m "copied stuff" &&
+	git am -3 -p0 lorem-zero.patch &&
+	! test -d .git/rebase-apply &&
+	git diff --exit-code lorem
+'
+
 test_expect_success 'am can rename a file' '
 	grep "^rename from" rename.patch &&
 	rm -fr .git/rebase-apply &&