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git/builtin/patch-id.c
Michael S. Tsirkin 30e12b924b patch-id: make it stable against hunk reordering
Patch id changes if users reorder file diffs that make up a patch.

As the result is functionally equivalent, a different patch id is
surprising to many users.
In particular, reordering files using diff -O is helpful to make patches
more readable (e.g. API header diff before implementation diff).

Add an option to change patch-id behaviour making it stable against
these kinds of patch change:
calculate SHA1 hash for each hunk separately and sum all hashes
(using a symmetrical sum) to get patch id

We use a 20byte sum and not xor - since xor would give 0 output
for patches that have two identical diffs, which isn't all that
unlikely (e.g. append the same line in two places).

The new behaviour is enabled
- when patchid.stable is true
- when --stable flag is present

Using a new flag --unstable or setting patchid.stable to false force
the historical behaviour.

In the documentation, clarify that patch ID can now be a sum of hashes,
not a hash.
Document how command line and config options affect the
behaviour.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2014-06-10 13:09:24 -07:00

201 lines
4 KiB
C

#include "builtin.h"
static void flush_current_id(int patchlen, unsigned char *id, unsigned char *result)
{
char name[50];
if (!patchlen)
return;
memcpy(name, sha1_to_hex(id), 41);
printf("%s %s\n", sha1_to_hex(result), name);
}
static int remove_space(char *line)
{
char *src = line;
char *dst = line;
unsigned char c;
while ((c = *src++) != '\0') {
if (!isspace(c))
*dst++ = c;
}
return dst - line;
}
static int scan_hunk_header(const char *p, int *p_before, int *p_after)
{
static const char digits[] = "0123456789";
const char *q, *r;
int n;
q = p + 4;
n = strspn(q, digits);
if (q[n] == ',') {
q += n + 1;
n = strspn(q, digits);
}
if (n == 0 || q[n] != ' ' || q[n+1] != '+')
return 0;
r = q + n + 2;
n = strspn(r, digits);
if (r[n] == ',') {
r += n + 1;
n = strspn(r, digits);
}
if (n == 0)
return 0;
*p_before = atoi(q);
*p_after = atoi(r);
return 1;
}
static void flush_one_hunk(unsigned char *result, git_SHA_CTX *ctx)
{
unsigned char hash[20];
unsigned short carry = 0;
int i;
git_SHA1_Final(hash, ctx);
git_SHA1_Init(ctx);
/* 20-byte sum, with carry */
for (i = 0; i < 20; ++i) {
carry += result[i] + hash[i];
result[i] = carry;
carry >>= 8;
}
}
static int get_one_patchid(unsigned char *next_sha1, unsigned char *result,
struct strbuf *line_buf, int stable)
{
int patchlen = 0, found_next = 0;
int before = -1, after = -1;
git_SHA_CTX ctx;
git_SHA1_Init(&ctx);
hashclr(result);
while (strbuf_getwholeline(line_buf, stdin, '\n') != EOF) {
char *line = line_buf->buf;
char *p = line;
int len;
if (!memcmp(line, "diff-tree ", 10))
p += 10;
else if (!memcmp(line, "commit ", 7))
p += 7;
else if (!memcmp(line, "From ", 5))
p += 5;
else if (!memcmp(line, "\\ ", 2) && 12 < strlen(line))
continue;
if (!get_sha1_hex(p, next_sha1)) {
found_next = 1;
break;
}
/* Ignore commit comments */
if (!patchlen && memcmp(line, "diff ", 5))
continue;
/* Parsing diff header? */
if (before == -1) {
if (!memcmp(line, "index ", 6))
continue;
else if (!memcmp(line, "--- ", 4))
before = after = 1;
else if (!isalpha(line[0]))
break;
}
/* Looking for a valid hunk header? */
if (before == 0 && after == 0) {
if (!memcmp(line, "@@ -", 4)) {
/* Parse next hunk, but ignore line numbers. */
scan_hunk_header(line, &before, &after);
continue;
}
/* Split at the end of the patch. */
if (memcmp(line, "diff ", 5))
break;
/* Else we're parsing another header. */
if (stable)
flush_one_hunk(result, &ctx);
before = after = -1;
}
/* If we get here, we're inside a hunk. */
if (line[0] == '-' || line[0] == ' ')
before--;
if (line[0] == '+' || line[0] == ' ')
after--;
/* Compute the sha without whitespace */
len = remove_space(line);
patchlen += len;
git_SHA1_Update(&ctx, line, len);
}
if (!found_next)
hashclr(next_sha1);
flush_one_hunk(result, &ctx);
return patchlen;
}
static void generate_id_list(int stable)
{
unsigned char sha1[20], n[20], result[20];
int patchlen;
struct strbuf line_buf = STRBUF_INIT;
hashclr(sha1);
while (!feof(stdin)) {
patchlen = get_one_patchid(n, result, &line_buf, stable);
flush_current_id(patchlen, sha1, result);
hashcpy(sha1, n);
}
strbuf_release(&line_buf);
}
static const char patch_id_usage[] = "git patch-id [--stable | --unstable] < patch";
static int git_patch_id_config(const char *var, const char *value, void *cb)
{
int *stable = cb;
if (!strcmp(var, "patchid.stable")) {
*stable = git_config_bool(var, value);
return 0;
}
return git_default_config(var, value, cb);
}
int cmd_patch_id(int argc, const char **argv, const char *prefix)
{
int stable = -1;
git_config(git_patch_id_config, &stable);
/* If nothing is set, default to unstable. */
if (stable < 0)
stable = 0;
if (argc == 2 && !strcmp(argv[1], "--stable"))
stable = 1;
else if (argc == 2 && !strcmp(argv[1], "--unstable"))
stable = 0;
else if (argc != 1)
usage(patch_id_usage);
generate_id_list(stable);
return 0;
}