checkout: do not check out unmerged higher stages randomly

During a conflicted merge when you have unmerged stages for a
path F in the index, if you said:

    $ git checkout F

we rewrote F as many times as we have stages for it, and the
last one (typically "theirs") was left in the work tree, without
resolving the conflict.

This fixes it by noticing that a specified pathspec pattern
matches an unmerged path, and by erroring out.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-checkout.c

@@ -76,6 +76,15 @@ static int read_tree_some(struct tree *tree, const char **pathspec)
 	return 0;
 }
 
+static int skip_same_name(struct cache_entry *ce, int pos)
+{
+	while (++pos < active_nr &&
+	       !strcmp(active_cache[pos]->name, ce->name))
+		; /* skip */
+	return pos;
+}
+
+
 static int checkout_paths(struct tree *source_tree, const char **pathspec)
 {
 	int pos;
@@ -107,14 +116,32 @@ static int checkout_paths(struct tree *source_tree, const char **pathspec)
 	if (report_path_error(ps_matched, pathspec, 0))
 		return 1;
 
+	/* Any unmerged paths? */
+	for (pos = 0; pos < active_nr; pos++) {
+		struct cache_entry *ce = active_cache[pos];
+		if (pathspec_match(pathspec, NULL, ce->name, 0)) {
+			if (!ce_stage(ce))
+				continue;
+			errs = 1;
+			error("path '%s' is unmerged", ce->name);
+			pos = skip_same_name(ce, pos) - 1;
+		}
+	}
+	if (errs)
+		return 1;
+
 	/* Now we are committed to check them out */
 	memset(&state, 0, sizeof(state));
 	state.force = 1;
 	state.refresh_cache = 1;
 	for (pos = 0; pos < active_nr; pos++) {
 		struct cache_entry *ce = active_cache[pos];
 		if (pathspec_match(pathspec, NULL, ce->name, 0)) {
-			errs |= checkout_entry(ce, &state, NULL);
+			if (!ce_stage(ce)) {
+				errs |= checkout_entry(ce, &state, NULL);
+				continue;
+			}
+			pos = skip_same_name(ce, pos) - 1;
 		}
 	}
 

t/t7201-co.sh

@@ -337,4 +337,26 @@ test_expect_success \
     test refs/heads/delete-me = "$(git symbolic-ref HEAD)" &&
     test_must_fail git checkout --track -b track'
 
+test_expect_success 'checkout an unmerged path should fail' '
+	rm -f .git/index &&
+	O=$(echo original | git hash-object -w --stdin) &&
+	A=$(echo ourside | git hash-object -w --stdin) &&
+	B=$(echo theirside | git hash-object -w --stdin) &&
+	(
+		echo "100644 $A 0	fild" &&
+		echo "100644 $O 1	file" &&
+		echo "100644 $A 2	file" &&
+		echo "100644 $B 3	file" &&
+		echo "100644 $A 0	filf"
+	) | git update-index --index-info &&
+	echo "none of the above" >sample &&
+	cat sample >fild &&
+	cat sample >file &&
+	cat sample >filf &&
+	test_must_fail git checkout fild file filf &&
+	test_cmp sample fild &&
+	test_cmp sample filf &&
+	test_cmp sample file
+'
+
 test_done