RFC v2, 3 partsformat-patch --complete / am --exact

Documentation/config/format.txt, Documentation/git-format-patch.txt, builtin/log.c

diff --git a/Documentation/config/format.txt b/Documentation/config/format.txt
index 40cad9278f..3a38679837 100644
--- a/Documentation/config/format.txt
+++ b/Documentation/config/format.txt
@@ -87,6 +87,13 @@ format.useAutoBase::
 	A boolean value which lets you enable the `--base=auto` option of
 	format-patch by default.
 
+format.complete::
+	Provides the default value for the `--complete` option to
+	format-patch. If true, the raw commit metadata (including the
+	SHA1) is included at the bottom of the diff, before the signature.
+	This allows a recipient who has all the parent commits and/or the
+	tree to reconstruct the commit with the same SHA1.
+
 format.notes::
 	Provides the default value for the `--notes` option to
 	format-patch. Accepts a boolean value, or a ref which specifies
diff --git a/Documentation/git-format-patch.txt b/Documentation/git-format-patch.txt
index 2035d4d5d5..74fc6d8a8c 100644
--- a/Documentation/git-format-patch.txt
+++ b/Documentation/git-format-patch.txt
@@ -26,6 +26,7 @@ SYNOPSIS
 		   [--no-notes | --notes[=<ref>]]
 		   [--interdiff=<previous>]
 		   [--range-diff=<previous> [--creation-factor=<percent>]]
+		   [--[no-]complete]
 		   [--progress]
 		   [<common diff options>]
 		   [ <since> | <revision range> ]
@@ -325,6 +326,14 @@ you can use `--suffix=-patch` to get `0001-description-of-my-change-patch`.
 	range are always formatted as creation patches, independently
 	of this flag.
 
+--[no-]complete::
+	Include the raw commit metadata (including the SHA1) at the
+	bottom of the diff, before the signature. This allows a
+	recipient who has all the parent commits and/or the tree to
+	reconstruct the commit with the same SHA1. The default is
+	`--no-complete`, unless the `format.complete` configuration
+	option is set.
+
 --progress::
 	Show progress reports on stderr as patches are generated.
 
diff --git a/builtin/log.c b/builtin/log.c
index 89873d2dc2..822a0838b6 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -783,6 +783,8 @@ enum {
 	COVER_AUTO
 };
 
+static int fmt_complete;
+
 static int git_format_config(const char *var, const char *value, void *cb)
 {
 	struct rev_info *rev = cb;
@@ -888,6 +890,10 @@ static int git_format_config(const char *var, const char *value, void *cb)
 		}
 		return 0;
 	}
+	if (!strcmp(var, "format.complete")) {
+		fmt_complete = git_config_bool(var, value);
+		return 0;
+	}
 
 	return git_log_config(var, value, cb);
 }
@@ -1490,6 +1496,23 @@ static void print_bases(struct base_tree_info *bases, FILE *file)
 	oidclr(&bases->base_commit);
 }
 
+static void print_meta(struct rev_info *opt, struct commit *commit)
+{
+	const char *buffer = get_commit_buffer(commit, NULL);
+	const char *subject;
+
+	fprintf(opt->diffopt.file, "--\n");
+	fprintf(opt->diffopt.file, "commit %s\n", oid_to_hex(&commit->object.oid));
+
+	/*
+	 * TODO: hex-encode to avoid mailer mangling?
+	 */
+	if (find_commit_subject(buffer, &subject))
+		fprintf(opt->diffopt.file, "%.*s", (int) (subject - buffer), buffer);
+	else
+		fprintf(opt->diffopt.file, "%s", buffer);
+}
+
 static const char *diff_title(struct strbuf *sb, int reroll_count,
 		       const char *generic, const char *rerolled)
 {
@@ -1622,6 +1645,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			    N_("add a signature")),
 		OPT_STRING(0, "base", &base_commit, N_("base-commit"),
 			   N_("add prerequisite tree info to the patch series")),
+		OPT_BOOL(0, "complete", &fmt_complete,
+			 N_("include all the information necessary to reconstruct commit exactly")),
 		OPT_FILENAME(0, "signature-file", &signature_file,
 				N_("add a signature from a file")),
 		OPT__QUIET(&quiet, N_("don't print the patch filenames")),
@@ -1921,6 +1946,14 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 		prepare_bases(&bases, base, list, nr);
 	}
 
+	if (fmt_complete) {
+		/*
+		 * We need the commit buffer so that we can output the exact
+		 * sequence of bytes that gets hashed as part of a commit.
+		 */
+		save_commit_buffer = 1;
+	}
+
 	if (in_reply_to || thread || cover_letter)
 		rev.ref_message_ids = xcalloc(1, sizeof(struct string_list));
 	if (in_reply_to) {
@@ -2004,6 +2037,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			rev.shown_one = 0;
 		if (shown) {
 			print_bases(&bases, rev.diffopt.file);
+			if (fmt_complete)
+				print_meta(&rev, commit);
 			if (rev.mime_boundary)
 				fprintf(rev.diffopt.file, "\n--%s%s--\n\n\n",
 				       mime_boundary_leader,
--
commit 7fa59e79ef5474fb4c657fb2ff6a8341cc17c897
tree 891d334e23f950afbaaafc182384309fd8c73e48
parent d966095db01190a2196e31195ea6fa0c722aa732
author Vegard Nossum <vegard.nossum@oracle.com> 1570284959 +0200
committer Vegard Nossum <vegard.nossum@oracle.com> 1571666151 +0200

Documentation/git-mailinfo.txt, builtin/am.c, builtin/mailinfo.c, mailinfo.c, mailinfo.h, t/t5100-mailinfo.sh, t/t5100/meta-info0001, t/t5100/meta-meta0001, t/t5100/meta-msg0001, t/t5100/meta-patch0001, t/t5100/meta-samples.mbox

diff --git a/Documentation/git-mailinfo.txt b/Documentation/git-mailinfo.txt
index 3bbc731f67..14a2cca08c 100644
--- a/Documentation/git-mailinfo.txt
+++ b/Documentation/git-mailinfo.txt
@@ -9,7 +9,7 @@ git-mailinfo - Extracts patch and authorship from a single e-mail message
 SYNOPSIS
 --------
 [verse]
-'git mailinfo' [-k|-b] [-u | --encoding=<encoding> | -n] [--[no-]scissors] <msg> <patch>
+'git mailinfo' [-k|-b] [-u | --encoding=<encoding> | -n] [--[no-]scissors] <msg> <patch> [<meta>]
 
 
 DESCRIPTION
@@ -21,6 +21,10 @@ written out to the standard output to be used by 'git am'
 to create a commit.  It is usually not necessary to use this
 command directly.  See linkgit:git-am[1] instead.
 
+If specified, <meta> specifies a filename where commit metadata
+will be written. If the e-mail does not contain such information,
+this file will be empty.
+
 
 OPTIONS
 -------
diff --git a/builtin/am.c b/builtin/am.c
index 8181c2aef3..4190383bba 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1159,7 +1159,7 @@ static int parse_mail(struct am_state *state, const char *mail)
 
 	mi.input = xfopen(mail, "r");
 	mi.output = xfopen(am_path(state, "info"), "w");
-	if (mailinfo(&mi, am_path(state, "msg"), am_path(state, "patch")))
+	if (mailinfo(&mi, am_path(state, "msg"), am_path(state, "patch"), am_path(state, "meta")))
 		die("could not parse patch");
 
 	fclose(mi.input);
diff --git a/builtin/mailinfo.c b/builtin/mailinfo.c
index cfb667a594..6c0746fa8e 100644
--- a/builtin/mailinfo.c
+++ b/builtin/mailinfo.c
@@ -9,14 +9,14 @@
 #include "mailinfo.h"
 
 static const char mailinfo_usage[] =
-	"git mailinfo [-k | -b] [-m | --message-id] [-u | --encoding=<encoding> | -n] [--scissors | --no-scissors] <msg> <patch> < mail >info";
+	"git mailinfo [-k | -b] [-m | --message-id] [-u | --encoding=<encoding> | -n] [--scissors | --no-scissors] <msg> <patch> [<meta>] < mail >info";
 
 int cmd_mailinfo(int argc, const char **argv, const char *prefix)
 {
 	const char *def_charset;
 	struct mailinfo mi;
 	int status;
-	char *msgfile, *patchfile;
+	char *msgfile, *patchfile, *metafile;
 
 	setup_mailinfo(&mi);
 
@@ -47,7 +47,7 @@ int cmd_mailinfo(int argc, const char **argv, const char *prefix)
 		argc--; argv++;
 	}
 
-	if (argc != 3)
+	if (argc < 3 || argc > 4)
 		usage(mailinfo_usage);
 
 	mi.input = stdin;
@@ -56,10 +56,15 @@ int cmd_mailinfo(int argc, const char **argv, const char *prefix)
 	msgfile = prefix_filename(prefix, argv[1]);
 	patchfile = prefix_filename(prefix, argv[2]);
 
-	status = !!mailinfo(&mi, msgfile, patchfile);
+	metafile = NULL;
+	if (argc == 4)
+		metafile = prefix_filename(prefix, argv[3]);
+
+	status = !!mailinfo(&mi, msgfile, patchfile, metafile);
 	clear_mailinfo(&mi);
 
 	free(msgfile);
 	free(patchfile);
+	free(metafile);
 	return status;
 }
diff --git a/mailinfo.c b/mailinfo.c
index b395adbdf2..173cb58f6b 100644
--- a/mailinfo.c
+++ b/mailinfo.c
@@ -825,10 +825,139 @@ static int handle_commit_msg(struct mailinfo *mi, struct strbuf *line)
 	return 0;
 }
 
-static void handle_patch(struct mailinfo *mi, const struct strbuf *line)
+enum patch_parser_state {
+	SKIP_UNTIL_DIFF,
+	NEW_DIFF_OR_HUNK,
+	MATCH_HUNK_HEADER,
+	HUNK,
+};
+
+static int handle_patch(struct mailinfo *mi, const struct strbuf *line)
 {
+	int old_pos, old_size;
+	int new_pos, new_size;
+
+	switch (mi->patch_stage) {
+	case SKIP_UNTIL_DIFF:
+		if (starts_with(line->buf, "diff "))
+			mi->patch_stage = MATCH_HUNK_HEADER;
+
+		break;
+
+	case NEW_DIFF_OR_HUNK:
+		if (starts_with(line->buf, "diff ")) {
+			mi->patch_stage = MATCH_HUNK_HEADER;
+			break;
+		}
+
+		/* fallthrough */
+
+	case MATCH_HUNK_HEADER:
+		if (sscanf(line->buf, "@@ -%d,%d +%d,%d @@", &old_pos, &old_size, &new_pos, &new_size) == 4
+			|| sscanf(line->buf, "@@ -%d,%d +%d @@", &old_pos, &old_size, &new_size) == 3
+			|| sscanf(line->buf, "@@ -%d +%d,%d @@", &old_size, &old_pos, &new_size) == 3
+			|| sscanf(line->buf, "@@ -%d +%d @@", &old_size, &new_size) == 2)
+		{
+			mi->old_size = old_size;
+			mi->new_size = new_size;
+
+			if (old_size > 0 || new_size > 0)
+				mi->patch_stage = HUNK;
+
+			break;
+		}
+
+		if (mi->patch_stage == NEW_DIFF_OR_HUNK) {
+			/*
+			 * We expected a 'diff' line or a hunk header and
+			 * didn't find either; this must be the end of the
+			 * patch!
+			 */
+			return 1;
+		}
+
+		/*
+		 * We were looking for a hunk header, but found something
+		 * else, probably an 'index' line or a '---' or '+++' line.
+		 */
+		break;
+
+	case HUNK:
+		if (line->buf[0] == '-' || line->buf[0] == ' ')
+			--mi->old_size;
+		if (line->buf[0] == '+' || line->buf[0] == ' ')
+			--mi->new_size;
+
+		if (mi->format_flowed) {
+			/*
+			 * format=flowed eats blanks at line ends
+			 */
+			if (line->buf[0] == '\r' || line->buf[0] == '\n') {
+				--mi->old_size;
+				--mi->new_size;
+			}
+		}
+
+		if (mi->old_size <= 0 && mi->new_size <= 0) {
+			/* done with hunk */
+			mi->patch_stage = NEW_DIFF_OR_HUNK;
+		}
+
+		break;
+	}
+
+	fwrite(line->buf, 1, line->len, mi->patchfile);
+	mi->patch_lines++;
+	return 0;
+}
+
+/*
+ * At the end of the diff, we find a signature and (optionally) metadata.
+ *
+ * "metadata" is whatever info we need to reconstruct a commit perfectly.
+ * It does _not_ include the signature or other lines.
+ *
+ * The way we parse this is a bit strange: there may be some lines before
+ * the metadata which logically belong to the signature, even though the
+ * actual signature appears after the metadata (e.g. sometimes blank lines
+ * appear between the diff and the signature, and we don't want to count
+ * them among the metadata).
+ */
+static void handle_signature(struct mailinfo *mi, const struct strbuf *line)
+{
+	switch (mi->meta_stage) {
+	case 0:
+		/* Done with the diff */
+		if (starts_with(line->buf, "commit ")) {
+			if (mi->metafile)
+				fwrite(line->buf, 1, line->len, mi->metafile);
+
+			mi->meta_stage = 1;
+			return;
+		}
+
+		break;
+
+	case 1:
+		/* Metadata */
+		if (starts_with(line->buf, "--")) {
+			mi->meta_stage = 2;
+			return;
+		}
+
+		if (mi->metafile)
+			fwrite(line->buf, 1, line->len, mi->metafile);
+
+		return;
+
+	case 2:
+		/* Done with metadata */
+		break;
+	}
+
 	fwrite(line->buf, 1, line->len, mi->patchfile);
 	mi->patch_lines++;
+	return;
 }
 
 static void handle_filter(struct mailinfo *mi, struct strbuf *line)
@@ -840,7 +969,12 @@ static void handle_filter(struct mailinfo *mi, struct strbuf *line)
 		mi->filter_stage++;
 		/* fallthrough */
 	case 1:
-		handle_patch(mi, line);
+		if (!handle_patch(mi, line))
+			break;
+		mi->filter_stage++;
+		/* fallthrough */
+	case 2:
+		handle_signature(mi, line);
 		break;
 	}
 }
@@ -1145,7 +1279,7 @@ static void handle_info(struct mailinfo *mi)
 	fprintf(mi->output, "\n");
 }
 
-int mailinfo(struct mailinfo *mi, const char *msg, const char *patch)
+int mailinfo(struct mailinfo *mi, const char *msg, const char *patch, const char *meta)
 {
 	FILE *cmitmsg;
 	int peek;
@@ -1163,6 +1297,16 @@ int mailinfo(struct mailinfo *mi, const char *msg, const char *patch)
 		return -1;
 	}
 
+	if (meta) {
+		mi->metafile = fopen(meta, "w");
+		if (!mi->metafile) {
+			perror(meta);
+			fclose(mi->patchfile);
+			fclose(cmitmsg);
+			return -1;
+		}
+	}
+
 	mi->p_hdr_data = xcalloc(MAX_HDR_PARSED, sizeof(*(mi->p_hdr_data)));
 	mi->s_hdr_data = xcalloc(MAX_HDR_PARSED, sizeof(*(mi->s_hdr_data)));
 
@@ -1183,6 +1327,8 @@ int mailinfo(struct mailinfo *mi, const char *msg, const char *patch)
 	fwrite(mi->log_message.buf, 1, mi->log_message.len, cmitmsg);
 	fclose(cmitmsg);
 	fclose(mi->patchfile);
+	if (mi->metafile)
+		fclose(mi->metafile);
 
 	handle_info(mi);
 	strbuf_release(&line);
@@ -1212,6 +1358,8 @@ void setup_mailinfo(struct mailinfo *mi)
 	strbuf_init(&mi->log_message, 0);
 	strbuf_init(&mi->inbody_header_accum, 0);
 	mi->header_stage = 1;
+	mi->patch_stage = 0;
+	mi->meta_stage = 0;
 	mi->use_inbody_headers = 1;
 	mi->content_top = mi->content;
 	git_config(git_mailinfo_config, mi);
diff --git a/mailinfo.h b/mailinfo.h
index 79b1d6774e..fdf3ba2674 100644
--- a/mailinfo.h
+++ b/mailinfo.h
@@ -9,6 +9,7 @@ struct mailinfo {
 	FILE *input;
 	FILE *output;
 	FILE *patchfile;
+	FILE *metafile;
 
 	struct strbuf name;
 	struct strbuf email;
@@ -31,16 +32,22 @@ struct mailinfo {
 	int patch_lines;
 	int filter_stage; /* still reading log or are we copying patch? */
 	int header_stage; /* still checking in-body headers? */
+	int patch_stage;
+	int meta_stage;
 	struct strbuf inbody_header_accum;
 	struct strbuf **p_hdr_data;
 	struct strbuf **s_hdr_data;
 
 	struct strbuf log_message;
 	int input_error;
+
+	/* handle_patch() */
+	int old_size;
+	int new_size;
 };
 
 void setup_mailinfo(struct mailinfo *);
-int mailinfo(struct mailinfo *, const char *msg, const char *patch);
+int mailinfo(struct mailinfo *, const char *msg, const char *patch, const char *meta);
 void clear_mailinfo(struct mailinfo *);
 
 #endif /* MAILINFO_H */
diff --git a/t/t5100-mailinfo.sh b/t/t5100-mailinfo.sh
index 9690dcad4f..76303bfaee 100755
--- a/t/t5100-mailinfo.sh
+++ b/t/t5100-mailinfo.sh
@@ -66,6 +66,28 @@ do
 	'
 done
 
+
+test_expect_success 'split box with metadata samples' \
+	'mkdir meta &&
+	git mailsplit -ometa "$DATA/meta-samples.mbox" \
+	  >meta/last &&
+	last=$(cat meta/last) &&
+	echo total is $last &&
+	test $(cat meta/last) = 1'
+
+for mail in meta/00*
+do
+	n=$(basename $mail)
+	test_expect_success "mailinfo $mail" '
+		git mailinfo -u "$mail-msg" "$mail-patch" "$mail-meta" <"$mail" >"$mail-info" &&
+		test_cmp "$DATA/meta-msg$n" "$mail-msg" &&
+		test_cmp "$DATA/meta-patch$n" "$mail-patch" &&
+		test_cmp "$DATA/meta-meta$n" "$mail-meta" &&
+		test_cmp "$DATA/meta-info$n" "$mail-info"
+	'
+done
+
+
 test_expect_success 'respect NULs' '
 
 	git mailsplit -d3 -o. "$DATA/nul-plain" &&
diff --git a/t/t5100/meta-info0001 b/t/t5100/meta-info0001
new file mode 100644
index 0000000000..69889dc9ce
--- /dev/null
+++ b/t/t5100/meta-info0001
@@ -0,0 +1,5 @@
+Author: Vegard Nossum
+Email: vegard.nossum@oracle.com
+Subject: format-patch: add --complete
+Date: Sun, 20 Oct 2019 21:40:24 +0200
+
diff --git a/t/t5100/meta-meta0001 b/t/t5100/meta-meta0001
new file mode 100644
index 0000000000..1db7e9f715
--- /dev/null
+++ b/t/t5100/meta-meta0001
@@ -0,0 +1,23 @@
+commit 763f9b1cfd69ade5e22dcdcdc35d144697675a93
+tree 43a6b213a2891b5a863775771cab0c0dba3730dc
+parent 108b97dc372828f0e72e56bbb40cae8e1e83ece6
+author Vegard Nossum <vegard.nossum@oracle.com> 1570284959 +0200
+committer Vegard Nossum <vegard.nossum@oracle.com> 1571599909 +0200
+gpgsig -----BEGIN PGP SIGNATURE-----
+ Version: GnuPG v1
+ 
+ iQIcBAABAgAGBQJdrLYmAAoJEAvO9Nj+mLpY5zIQAJkdnnZMrCVme64r43M/KMm0
+ W1fmdeXiIMrI7i0McBdAsQ/KQ5yD4HBvaJWCyI0/g6IeLgVBf9//9xq4Y32iqsKn
+ XRut2Pk3H3Az0WfUlpLpDJUgzz7er8t/glaKnESb94XR/ac59tEELbePh+bXsFLH
+ 3+v8Y78zeHJd6ZLKrKmLyq/9ZaJQR+9xmGdKzZdnwM+8seE4aOhM1VtA8ik68Tn6
+ Tbaofp1jbsXcyY4nBG9GxK14wnb/8OZmQlH4J40LsZT4KDWQNWighGig8ude7SJa
+ 6FJXWJPLfOB6r2ThiJUnrf/UXeHbvYUWITiYoWOxEVb6c7RfNLqDbbGF9VQfTD0n
+ SEFO5NqOs6KofaYzALprtgpMrqksRHeLc7Ouh9xgLyLZLx/669I9lo8M1aQ7RJMy
+ V1KDG6sYbFrgy4gQ/4xqXj3NpBmMb/VcjOnCj3j040wo8q7hlpzb6ev5lcqAFEuP
+ y1owwhljMjqAdGIBw6sLVn2on+6gEQuIjbkoapBktPDw7xEpOKe9rzTGcWRRyANs
+ Z+pMWbn8c6TKonokNjERy0iPnu2t2j8x1YpqKdjY+oq8ApNZFMlU1U+UtXFfuLw5
+ ZKR5DtmXxWzvd+nKBenjzXyOt33v5eq4I/WMfATauXBgFu75mbfiKIFVD5VeMfxq
+ DoiIqvLtW+DDUkH99zXm
+ =2APb
+ -----END PGP SIGNATURE-----
+
diff --git a/t/t5100/meta-msg0001 b/t/t5100/meta-msg0001
new file mode 100644
index 0000000000..cc0690657d
--- /dev/null
+++ b/t/t5100/meta-msg0001
@@ -0,0 +1,6 @@
+Include the raw commit data between the changelog and the diffstat.
+This will allow 'git am' to reconstruct the commit exactly to the point
+where the sha1 will be the same.
+
+Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
+Previous-version: 622a0469a4970c5daac0c0323e2d6a77b3bebbdb
diff --git a/t/t5100/meta-patch0001 b/t/t5100/meta-patch0001
new file mode 100644
index 0000000000..8b926834ce
--- /dev/null
+++ b/t/t5100/meta-patch0001
@@ -0,0 +1,76 @@
+---
+ builtin/log.c | 30 ++++++++++++++++++++++++++++++
+ 1 file changed, 30 insertions(+)
+
+diff --git a/builtin/log.c b/builtin/log.c
+index c4b35fdaf9..cd96d579a7 100644
+--- a/builtin/log.c
++++ b/builtin/log.c
+@@ -1490,6 +1490,23 @@ static void print_bases(struct base_tree_info *bases, FILE *file)
+ 	oidclr(&bases->base_commit);
+ }
+ 
++static void print_meta(struct rev_info *opt, struct commit *commit)
++{
++	const char *buffer = get_commit_buffer(commit, NULL);
++	const char *subject;
++
++	fprintf(opt->diffopt.file, "--\n");
++	fprintf(opt->diffopt.file, "commit %s\n", oid_to_hex(&commit->object.oid));
++
++	/*
++	 * TODO: hex-encode to avoid mailer mangling?
++	 */
++	if (find_commit_subject(buffer, &subject))
++		fprintf(opt->diffopt.file, "%.*s", (int) (subject - buffer), buffer);
++	else
++		fprintf(opt->diffopt.file, "%s", buffer);
++}
++
+ static const char *diff_title(struct strbuf *sb, int reroll_count,
+ 		       const char *generic, const char *rerolled)
+ {
+@@ -1545,6 +1562,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
+ 	char *branch_name = NULL;
+ 	char *base_commit = NULL;
+ 	struct base_tree_info bases;
++	int complete = 0;
+ 	int show_progress = 0;
+ 	struct progress *progress = NULL;
+ 	struct oid_array idiff_prev = OID_ARRAY_INIT;
+@@ -1622,6 +1640,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
+ 			    N_("add a signature")),
+ 		OPT_STRING(0, "base", &base_commit, N_("base-commit"),
+ 			   N_("add prerequisite tree info to the patch series")),
++		OPT_BOOL(0, "complete", &complete,
++			 N_("include all the information necessary to reconstruct commit exactly")),
+ 		OPT_FILENAME(0, "signature-file", &signature_file,
+ 				N_("add a signature from a file")),
+ 		OPT__QUIET(&quiet, N_("don't print the patch filenames")),
+@@ -1905,6 +1925,14 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
+ 		prepare_bases(&bases, base, list, nr);
+ 	}
+ 
++	if (complete) {
++		/*
++		 * We need the commit buffer so that we can output the exact
++		 * sequence of bytes that gets hashed as part of a commit.
++		 */
++		save_commit_buffer = 1;
++	}
++
+ 	if (in_reply_to || thread || cover_letter)
+ 		rev.ref_message_ids = xcalloc(1, sizeof(struct string_list));
+ 	if (in_reply_to) {
+@@ -1988,6 +2016,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
+ 			rev.shown_one = 0;
+ 		if (shown) {
+ 			print_bases(&bases, rev.diffopt.file);
++			if (complete)
++				print_meta(&rev, commit);
+ 			if (rev.mime_boundary)
+ 				fprintf(rev.diffopt.file, "\n--%s%s--\n\n\n",
+ 				       mime_boundary_leader,
+--
+2.23.0.718.g5ad94255a8
+
diff --git a/t/t5100/meta-samples.mbox b/t/t5100/meta-samples.mbox
new file mode 100644
index 0000000000..ce68687b0e
--- /dev/null
+++ b/t/t5100/meta-samples.mbox
@@ -0,0 +1,133 @@
+From nobody Mon Sep 17 00:00:00 2001
+Received: from aserp3020.oracle.com (/141.146.126.70)
+	by default (Oracle Beehive Gateway v4.0)
+	with ESMTP ; Sun, 20 Oct 2019 12:42:33 -0700
+Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1])
+	by aserp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x9KJcZax145871
+	for <vegard.nossum@oracle.com>; Sun, 20 Oct 2019 19:42:33 GMT
+Authentication-Results: aserp3010.oracle.com;
+	spf=softfail smtp.mailfrom=vegard.nossum@oracle.com;
+	dmarc=none header.from=oracle.com
+Received: from t460.home (dhcp-10-175-57-121.vpn.oracle.com [10.175.57.121])
+	by aserp3020.oracle.com with ESMTP id 2vrbyxapj4-1
+	for <vegard.nossum@oracle.com>; Sun, 20 Oct 2019 19:42:33 +0000
+From: Vegard Nossum <vegard.nossum@oracle.com>
+To: vegard.nossum@oracle.com
+Subject: [PATCH 1/3] format-patch: add --complete
+Date: Sun, 20 Oct 2019 21:40:24 +0200
+Message-Id: <20191020194026.19245-1-vegard.nossum@oracle.com>
+X-Mailer: git-send-email 2.23.0.718.g5ad94255a8
+MIME-Version: 1.0
+Content-Transfer-Encoding: 8bit
+X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9416 signatures=668684
+X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=1 malwarescore=0
+ phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=676
+ adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1
+ engine=8.0.1-1908290000 definitions=main-1910200201
+
+Include the raw commit data between the changelog and the diffstat.
+This will allow 'git am' to reconstruct the commit exactly to the point
+where the sha1 will be the same.
+
+Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
+Previous-version: 622a0469a4970c5daac0c0323e2d6a77b3bebbdb
+---
+ builtin/log.c | 30 ++++++++++++++++++++++++++++++
+ 1 file changed, 30 insertions(+)
+
+diff --git a/builtin/log.c b/builtin/log.c
+index c4b35fdaf9..cd96d579a7 100644
+--- a/builtin/log.c
++++ b/builtin/log.c
+@@ -1490,6 +1490,23 @@ static void print_bases(struct base_tree_info *bases, FILE *file)
+ 	oidclr(&bases->base_commit);
+ }
+ 
++static void print_meta(struct rev_info *opt, struct commit *commit)
++{
++	const char *buffer = get_commit_buffer(commit, NULL);
++	const char *subject;
++
++	fprintf(opt->diffopt.file, "--\n");
++	fprintf(opt->diffopt.file, "commit %s\n", oid_to_hex(&commit->object.oid));
++
++	/*
++	 * TODO: hex-encode to avoid mailer mangling?
++	 */
++	if (find_commit_subject(buffer, &subject))
++		fprintf(opt->diffopt.file, "%.*s", (int) (subject - buffer), buffer);
++	else
++		fprintf(opt->diffopt.file, "%s", buffer);
++}
++
+ static const char *diff_title(struct strbuf *sb, int reroll_count,
+ 		       const char *generic, const char *rerolled)
+ {
+@@ -1545,6 +1562,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
+ 	char *branch_name = NULL;
+ 	char *base_commit = NULL;
+ 	struct base_tree_info bases;
++	int complete = 0;
+ 	int show_progress = 0;
+ 	struct progress *progress = NULL;
+ 	struct oid_array idiff_prev = OID_ARRAY_INIT;
+@@ -1622,6 +1640,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
+ 			    N_("add a signature")),
+ 		OPT_STRING(0, "base", &base_commit, N_("base-commit"),
+ 			   N_("add prerequisite tree info to the patch series")),
++		OPT_BOOL(0, "complete", &complete,
++			 N_("include all the information necessary to reconstruct commit exactly")),
+ 		OPT_FILENAME(0, "signature-file", &signature_file,
+ 				N_("add a signature from a file")),
+ 		OPT__QUIET(&quiet, N_("don't print the patch filenames")),
+@@ -1905,6 +1925,14 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
+ 		prepare_bases(&bases, base, list, nr);
+ 	}
+ 
++	if (complete) {
++		/*
++		 * We need the commit buffer so that we can output the exact
++		 * sequence of bytes that gets hashed as part of a commit.
++		 */
++		save_commit_buffer = 1;
++	}
++
+ 	if (in_reply_to || thread || cover_letter)
+ 		rev.ref_message_ids = xcalloc(1, sizeof(struct string_list));
+ 	if (in_reply_to) {
+@@ -1988,6 +2016,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
+ 			rev.shown_one = 0;
+ 		if (shown) {
+ 			print_bases(&bases, rev.diffopt.file);
++			if (complete)
++				print_meta(&rev, commit);
+ 			if (rev.mime_boundary)
+ 				fprintf(rev.diffopt.file, "\n--%s%s--\n\n\n",
+ 				       mime_boundary_leader,
+--
+commit 763f9b1cfd69ade5e22dcdcdc35d144697675a93
+tree 43a6b213a2891b5a863775771cab0c0dba3730dc
+parent 108b97dc372828f0e72e56bbb40cae8e1e83ece6
+author Vegard Nossum <vegard.nossum@oracle.com> 1570284959 +0200
+committer Vegard Nossum <vegard.nossum@oracle.com> 1571599909 +0200
+gpgsig -----BEGIN PGP SIGNATURE-----
+ Version: GnuPG v1
+ 
+ iQIcBAABAgAGBQJdrLYmAAoJEAvO9Nj+mLpY5zIQAJkdnnZMrCVme64r43M/KMm0
+ W1fmdeXiIMrI7i0McBdAsQ/KQ5yD4HBvaJWCyI0/g6IeLgVBf9//9xq4Y32iqsKn
+ XRut2Pk3H3Az0WfUlpLpDJUgzz7er8t/glaKnESb94XR/ac59tEELbePh+bXsFLH
+ 3+v8Y78zeHJd6ZLKrKmLyq/9ZaJQR+9xmGdKzZdnwM+8seE4aOhM1VtA8ik68Tn6
+ Tbaofp1jbsXcyY4nBG9GxK14wnb/8OZmQlH4J40LsZT4KDWQNWighGig8ude7SJa
+ 6FJXWJPLfOB6r2ThiJUnrf/UXeHbvYUWITiYoWOxEVb6c7RfNLqDbbGF9VQfTD0n
+ SEFO5NqOs6KofaYzALprtgpMrqksRHeLc7Ouh9xgLyLZLx/669I9lo8M1aQ7RJMy
+ V1KDG6sYbFrgy4gQ/4xqXj3NpBmMb/VcjOnCj3j040wo8q7hlpzb6ev5lcqAFEuP
+ y1owwhljMjqAdGIBw6sLVn2on+6gEQuIjbkoapBktPDw7xEpOKe9rzTGcWRRyANs
+ Z+pMWbn8c6TKonokNjERy0iPnu2t2j8x1YpqKdjY+oq8ApNZFMlU1U+UtXFfuLw5
+ ZKR5DtmXxWzvd+nKBenjzXyOt33v5eq4I/WMfATauXBgFu75mbfiKIFVD5VeMfxq
+ DoiIqvLtW+DDUkH99zXm
+ =2APb
+ -----END PGP SIGNATURE-----
+
+-- 
+2.23.0.718.g5ad94255a8
+
--
commit 53da20012e763a65071bfe0a42fbf4968d0e1e49
tree 46bdf2b042c66643bacf803bb9ffc28043343d5e
parent 7fa59e79ef5474fb4c657fb2ff6a8341cc17c897
author Vegard Nossum <vegard.nossum@oracle.com> 1571184248 +0200
committer Vegard Nossum <vegard.nossum@oracle.com> 1571666151 +0200

Documentation/git-am.txt, builtin/am.c, t/t4150-am.sh

diff --git a/Documentation/git-am.txt b/Documentation/git-am.txt
index fc3b993c33..5b75596aaf 100644
--- a/Documentation/git-am.txt
+++ b/Documentation/git-am.txt
@@ -9,7 +9,7 @@ git-am - Apply a series of patches from a mailbox
 SYNOPSIS
 --------
 [verse]
-'git am' [--signoff] [--keep] [--[no-]keep-cr] [--[no-]utf8]
+'git am' [--[no-]exact] [--signoff] [--keep] [--[no-]keep-cr] [--[no-]utf8]
 	 [--[no-]3way] [--interactive] [--committer-date-is-author-date]
 	 [--ignore-date] [--ignore-space-change | --ignore-whitespace]
 	 [--whitespace=<option>] [-C<n>] [-p<n>] [--directory=<dir>]
@@ -31,6 +31,13 @@ OPTIONS
 	supply this argument, the command reads from the standard input.
 	If you supply directories, they will be treated as Maildirs.
 
+-e::
+--[no-]exact::
+	Reconstruct the exact commit that the patch was generated from,
+	assuming the mail contains complete metadata (i.e. it was generated
+	using `git format-patch --complete`). This is only possible if all
+	the parent commits are available in the repository.
+
 -s::
 --signoff::
 	Add a `Signed-off-by:` line to the commit message, using
diff --git a/builtin/am.c b/builtin/am.c
index 4190383bba..c0fc27a2ae 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -118,6 +118,7 @@ struct am_state {
 	int allow_rerere_autoupdate;
 	const char *sign_commit;
 	int rebasing;
+	int exact;
 };
 
 /**
@@ -399,6 +400,9 @@ static void am_load(struct am_state *state)
 
 	state->rebasing = !!file_exists(am_path(state, "rebasing"));
 
+	read_state_file(&sb, state, "exact", 1);
+	state->exact = !strcmp(sb.buf, "t");
+
 	strbuf_release(&sb);
 }
 
@@ -1005,6 +1009,8 @@ static void am_setup(struct am_state *state, enum patch_format patch_format,
 	else
 		write_state_text(state, "applying", "");
 
+	write_state_bool(state, "exact", state->exact);
+
 	if (!get_oid("HEAD", &curr_head)) {
 		write_state_text(state, "abort-safety", oid_to_hex(&curr_head));
 		if (!state->rebasing)
@@ -1548,40 +1554,121 @@ static int fall_back_threeway(const struct am_state *state, const char *index_pa
  */
 static void do_commit(const struct am_state *state)
 {
+	struct object_id meta_commit = {};
+	struct object_id meta_tree = {};
+
 	struct object_id tree, parent, commit;
 	const struct object_id *old_oid;
 	struct commit_list *parents = NULL;
-	const char *reflog_msg, *author;
+	const char *reflog_msg, *author = NULL;
 	struct strbuf sb = STRBUF_INIT;
 
+	if (state->exact) {
+		/*
+		 * Scan meta file for parents + other data.
+		 *
+		 * TODO: Pass everything after the "commit ..." line
+		 * verbatim to the commit for forwards compatibility
+		 * (e.g. so we don't need to know about every type of
+		 * commit attribute that may appear in the future).
+		 */
+
+		struct strbuf line = STRBUF_INIT;
+		FILE *fp = xfopen(am_path(state, "meta"), "r");
+
+		while (!strbuf_getline_lf(&line, fp)) {
+			const char *rest;
+
+			if (skip_prefix(line.buf, "commit ", &rest)) {
+				if (get_oid_hex(rest, &meta_commit))
+					die("invalid exact metadata (commit)");
+			} else if (skip_prefix(line.buf, "tree ", &rest)) {
+				if (get_oid_hex(rest, &meta_tree))
+					die("invalid exact metadata (tree)");
+			} else if (skip_prefix(line.buf, "parent ", &rest)) {
+				if (get_oid_hex(rest, &parent))
+					die("invalid exact metadata (parent)");
+
+				commit_list_insert(lookup_commit(the_repository, &parent), &parents);
+			} else if (skip_prefix(line.buf, "author ", &rest)) {
+				author = strdup(rest);
+			} else if (skip_prefix(line.buf, "committer ", &rest)) {
+				char *name_copy;
+				char *email;
+				char *email_copy;
+				char *date;
+
+				email = strstr(rest, " <");
+				if (!email)
+					die("invalid exact metadata (committer name)");
+
+				name_copy = xstrndup(rest, email - rest);
+				email += 2;
+				setenv("GIT_COMMITTER_NAME", name_copy, 1);
+				free(name_copy);
+
+				date = strstr(email, "> ");
+				if (!date)
+					die("invalid exact metadata (committer email)");
+
+				email_copy = xstrndup(email, date - email);
+				date += 2;
+				setenv("GIT_COMMITTER_EMAIL", email_copy, 1);
+				free(email_copy);
+
+				setenv("GIT_COMMITTER_DATE", date, 1);
+			} else if (line.len == 0) {
+				break;
+			} else {
+				die("unknown exact metadata: %.*s", (int) line.len, line.buf);
+			}
+		}
+
+		fclose(fp);
+	}
+
 	if (run_hook_le(NULL, "pre-applypatch", NULL))
 		exit(1);
 
 	if (write_cache_as_tree(&tree, 0, NULL))
 		die(_("git write-tree failed to write a tree"));
 
+	if (state->exact && !oideq(&tree, &meta_tree))
+		die("tree mismatch");
+
 	if (!get_oid_commit("HEAD", &parent)) {
 		old_oid = &parent;
-		commit_list_insert(lookup_commit(the_repository, &parent),
-				   &parents);
+		if (!state->exact) {
+			commit_list_insert(lookup_commit(the_repository, &parent),
+					   &parents);
+		}
 	} else {
 		old_oid = NULL;
 		say(state, stderr, _("applying to an empty history"));
 	}
 
-	author = fmt_ident(state->author_name, state->author_email,
-		WANT_AUTHOR_IDENT,
-			state->ignore_date ? NULL : state->author_date,
-			IDENT_STRICT);
-
-	if (state->committer_date_is_author_date)
-		setenv("GIT_COMMITTER_DATE",
-			state->ignore_date ? "" : state->author_date, 1);
+	if (state->exact) {
+		/*
+		 * Already got author above.
+		 */
+	} else {
+		author = fmt_ident(state->author_name, state->author_email,
+			WANT_AUTHOR_IDENT,
+				state->ignore_date ? NULL : state->author_date,
+				IDENT_STRICT);
+
+		if (state->committer_date_is_author_date)
+			setenv("GIT_COMMITTER_DATE",
+				state->ignore_date ? "" : state->author_date, 1);
+	}
 
 	if (commit_tree(state->msg, state->msg_len, &tree, parents, &commit,
 			author, state->sign_commit))
 		die(_("failed to write commit object"));
 
+	if (state->exact && !oideq(&commit, &meta_commit))
+		die("sha1 mismatch");
+
 	reflog_msg = getenv("GIT_REFLOG_ACTION");
 	if (!reflog_msg)
 		reflog_msg = "am";
@@ -2182,6 +2269,8 @@ int cmd_am(int argc, const char **argv, const char *prefix)
 			0, PARSE_OPT_NONEG),
 		OPT_BOOL('c', "scissors", &state.scissors,
 			N_("strip everything before a scissors line")),
+		OPT_BOOL('e', "exact", &state.exact,
+			N_("preserve exact metadata, including sha1")),
 		OPT_PASSTHRU_ARGV(0, "whitespace", &state.git_apply_opts, N_("action"),
 			N_("pass it through git-apply"),
 			0),
diff --git a/t/t4150-am.sh b/t/t4150-am.sh
index 4f1e24ecbe..56a0804dcb 100755
--- a/t/t4150-am.sh
+++ b/t/t4150-am.sh
@@ -147,6 +147,7 @@ test_expect_success setup '
 		git diff-tree --no-commit-id -p second
 	} >patch1-hg.eml &&
 
+	git format-patch --stdout --complete first >patch1-complete &&
 
 	echo file >file &&
 	git add file &&
@@ -1061,6 +1062,35 @@ test_expect_success 'am --quit keeps HEAD where it is' '
 	test_cmp expected actual
 '
 
+test_expect_success 'am --no-exact with metadata succeeds' '
+	rm -fr .git/rebase-apply &&
+	git reset --hard &&
+	git checkout first &&
+	git am --no-exact patch1-complete
+'
+
+test_expect_success 'am --exact without metadata fails' '
+	rm -fr .git/rebase-apply &&
+	git reset --hard &&
+	git checkout first &&
+	test_must_fail git am --exact patch1
+'
+
+test_expect_success 'am --exact with metadata preserves sha1' '
+	rm -fr .git/rebase-apply &&
+	git reset --hard &&
+	git checkout first &&
+	git am --exact patch1-complete &&
+	test_cmp_rev second HEAD
+'
+
+test_expect_success 'am --exact with metadata applied to the wrong tree fails' '
+	rm -fr .git/rebase-apply &&
+	git reset --hard &&
+	git checkout second &&
+	test_must_fail git am --exact patch1-complete
+'
+
 test_expect_success 'am and .gitattibutes' '
 	test_create_repo attributes &&
 	(
--
commit 429e6ce36ee1fb8e020c76756894bf7e196e7c4e
tree 69ec15522af90642ea38dc761510fd1fa82bdfb2
parent 53da20012e763a65071bfe0a42fbf4968d0e1e49
author Vegard Nossum <vegard.nossum@oracle.com> 1571186178 +0200
committer Vegard Nossum <vegard.nossum@oracle.com> 1571740256 +0200