merge(3p/git): Merge git subtree at v2.29.2 r/1890

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

1 files changed, 132 insertions, 20 deletions

diff --git a/third_party/git/builtin/diff.c b/third_party/git/builtin/diff.c
index 42ac803091..cd4083fed9 100644
--- a/third_party/git/builtin/diff.c
+++ b/third_party/git/builtin/diff.c
@@ -6,6 +6,7 @@
 #define USE_THE_INDEX_COMPATIBILITY_MACROS
 #include "cache.h"
 #include "config.h"
+#include "ewah/ewok.h"
 #include "lockfile.h"
 #include "color.h"
 #include "commit.h"
@@ -17,13 +18,19 @@
 #include "log-tree.h"
 #include "builtin.h"
 #include "submodule.h"
-#include "sha1-array.h"
+#include "oid-array.h"
 
 #define DIFF_NO_INDEX_EXPLICIT 1
 #define DIFF_NO_INDEX_IMPLICIT 2
 
 static const char builtin_diff_usage[] =
-"git diff [<options>] [<commit> [<commit>]] [--] [<path>...]";
+"git diff [<options>] [<commit>] [--] [<path>...]\n"
+"   or: git diff [<options>] --cached [<commit>] [--] [<path>...]\n"
+"   or: git diff [<options>] <commit> [<commit>...] <commit> [--] [<path>...]\n"
+"   or: git diff [<options>] <commit>...<commit>] [--] [<path>...]\n"
+"   or: git diff [<options>] <blob> <blob>]\n"
+"   or: git diff [<options>] --no-index [--] <path> <path>]\n"
+COMMON_DIFF_OPTIONS_HELP;
 
 static const char *blob_path(struct object_array_entry *entry)
 {
@@ -196,8 +203,7 @@ static int builtin_diff_combined(struct rev_info *revs,
 		revs->dense_combined_merges = revs->combine_merges = 1;
 	for (i = 1; i < ents; i++)
 		oid_array_append(&parents, &ent[i].item->oid);
-	diff_tree_combined(&ent[0].item->oid, &parents,
-			   revs->dense_combined_merges, revs);
+	diff_tree_combined(&ent[0].item->oid, &parents, revs);
 	oid_array_clear(&parents);
 	return 0;
 }
@@ -254,6 +260,108 @@ static int builtin_diff_files(struct rev_info *revs, int argc, const char **argv
 	return run_diff_files(revs, options);
 }
 
+struct symdiff {
+	struct bitmap *skip;
+	int warn;
+	const char *base, *left, *right;
+};
+
+/*
+ * Check for symmetric-difference arguments, and if present, arrange
+ * everything we need to know to handle them correctly.  As a bonus,
+ * weed out all bogus range-based revision specifications, e.g.,
+ * "git diff A..B C..D" or "git diff A..B C" get rejected.
+ *
+ * For an actual symmetric diff, *symdiff is set this way:
+ *
+ *  - its skip is non-NULL and marks *all* rev->pending.objects[i]
+ *    indices that the caller should ignore (extra merge bases, of
+ *    which there might be many, and A in A...B).  Note that the
+ *    chosen merge base and right side are NOT marked.
+ *  - warn is set if there are multiple merge bases.
+ *  - base, left, and right point to the names to use in a
+ *    warning about multiple merge bases.
+ *
+ * If there is no symmetric diff argument, sym->skip is NULL and
+ * sym->warn is cleared.  The remaining fields are not set.
+ */
+static void symdiff_prepare(struct rev_info *rev, struct symdiff *sym)
+{
+	int i, is_symdiff = 0, basecount = 0, othercount = 0;
+	int lpos = -1, rpos = -1, basepos = -1;
+	struct bitmap *map = NULL;
+
+	/*
+	 * Use the whence fields to find merge bases and left and
+	 * right parts of symmetric difference, so that we do not
+	 * depend on the order that revisions are parsed.  If there
+	 * are any revs that aren't from these sources, we have a
+	 * "git diff C A...B" or "git diff A...B C" case.  Or we
+	 * could even get "git diff A...B C...E", for instance.
+	 *
+	 * If we don't have just one merge base, we pick one
+	 * at random.
+	 *
+	 * NB: REV_CMD_LEFT, REV_CMD_RIGHT are also used for A..B,
+	 * so we must check for SYMMETRIC_LEFT too.  The two arrays
+	 * rev->pending.objects and rev->cmdline.rev are parallel.
+	 */
+	for (i = 0; i < rev->cmdline.nr; i++) {
+		struct object *obj = rev->pending.objects[i].item;
+		switch (rev->cmdline.rev[i].whence) {
+		case REV_CMD_MERGE_BASE:
+			if (basepos < 0)
+				basepos = i;
+			basecount++;
+			break;		/* do mark all bases */
+		case REV_CMD_LEFT:
+			if (lpos >= 0)
+				usage(builtin_diff_usage);
+			lpos = i;
+			if (obj->flags & SYMMETRIC_LEFT) {
+				is_symdiff = 1;
+				break;	/* do mark A */
+			}
+			continue;
+		case REV_CMD_RIGHT:
+			if (rpos >= 0)
+				usage(builtin_diff_usage);
+			rpos = i;
+			continue;	/* don't mark B */
+		case REV_CMD_PARENTS_ONLY:
+		case REV_CMD_REF:
+		case REV_CMD_REV:
+			othercount++;
+			continue;
+		}
+		if (map == NULL)
+			map = bitmap_new();
+		bitmap_set(map, i);
+	}
+
+	/*
+	 * Forbid any additional revs for both A...B and A..B.
+	 */
+	if (lpos >= 0 && othercount > 0)
+		usage(builtin_diff_usage);
+
+	if (!is_symdiff) {
+		bitmap_free(map);
+		sym->warn = 0;
+		sym->skip = NULL;
+		return;
+	}
+
+	sym->left = rev->pending.objects[lpos].name;
+	sym->right = rev->pending.objects[rpos].name;
+	if (basecount == 0)
+		die(_("%s...%s: no merge base"), sym->left, sym->right);
+	sym->base = rev->pending.objects[basepos].name;
+	bitmap_unset(map, basepos);	/* unmark the base we want */
+	sym->warn = basecount > 1;
+	sym->skip = map;
+}
+
 int cmd_diff(int argc, const char **argv, const char *prefix)
 {
 	int i;
@@ -263,19 +371,29 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 	struct object_array_entry *blob[2];
 	int nongit = 0, no_index = 0;
 	int result = 0;
+	struct symdiff sdiff;
 
 	/*
 	 * We could get N tree-ish in the rev.pending_objects list.
-	 * Also there could be M blobs there, and P pathspecs.
+	 * Also there could be M blobs there, and P pathspecs. --cached may
+	 * also be present.
 	 *
 	 * N=0, M=0:
-	 *	cache vs files (diff-files)
+	 *      cache vs files (diff-files)
+	 *
+	 * N=0, M=0, --cached:
+	 *      HEAD vs cache (diff-index --cached)
+	 *
 	 * N=0, M=2:
 	 *      compare two random blobs.  P must be zero.
+	 *
 	 * N=0, M=1, P=1:
-	 *	compare a blob with a working tree file.
+	 *      compare a blob with a working tree file.
 	 *
 	 * N=1, M=0:
+	 *      tree vs files (diff-index)
+	 *
+	 * N=1, M=0, --cached:
 	 *      tree vs cache (diff-index --cached)
 	 *
 	 * N=2, M=0:
@@ -382,6 +500,7 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	symdiff_prepare(&rev, &sdiff);
 	for (i = 0; i < rev.pending.nr; i++) {
 		struct object_array_entry *entry = &rev.pending.objects[i];
 		struct object *obj = entry->item;
@@ -396,6 +515,8 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 			obj = &get_commit_tree(((struct commit *)obj))->object;
 
 		if (obj->type == OBJ_TREE) {
+			if (sdiff.skip && bitmap_get(sdiff.skip, i))
+				continue;
 			obj->flags |= flags;
 			add_object_array(obj, name, &ent);
 		} else if (obj->type == OBJ_BLOB) {
@@ -437,21 +558,12 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 		usage(builtin_diff_usage);
 	else if (ent.nr == 1)
 		result = builtin_diff_index(&rev, argc, argv);
-	else if (ent.nr == 2)
+	else if (ent.nr == 2) {
+		if (sdiff.warn)
+			warning(_("%s...%s: multiple merge bases, using %s"),
+				sdiff.left, sdiff.right, sdiff.base);
 		result = builtin_diff_tree(&rev, argc, argv,
 					   &ent.objects[0], &ent.objects[1]);
-	else if (ent.objects[0].item->flags & UNINTERESTING) {
-		/*
-		 * diff A...B where there is at least one merge base
-		 * between A and B.  We have ent.objects[0] ==
-		 * merge-base, ent.objects[ents-2] == A, and
-		 * ent.objects[ents-1] == B.  Show diff between the
-		 * base and B.  Note that we pick one merge base at
-		 * random if there are more than one.
-		 */
-		result = builtin_diff_tree(&rev, argc, argv,
-					   &ent.objects[0],
-					   &ent.objects[ent.nr-1]);
 	} else
 		result = builtin_diff_combined(&rev, argc, argv,
 					       ent.objects, ent.nr);