git/ll-merge.c
Jeff King 06f46f237a avoid "write_in_full(fd, buf, len) != len" pattern
The return value of write_in_full() is either "-1", or the
requested number of bytes[1]. If we make a partial write
before seeing an error, we still return -1, not a partial
value. This goes back to f6aa66cb95 (write_in_full: really
write in full or return error on disk full., 2007-01-11).

So checking anything except "was the return value negative"
is pointless. And there are a couple of reasons not to do
so:

  1. It can do a funny signed/unsigned comparison. If your
     "len" is signed (e.g., a size_t) then the compiler will
     promote the "-1" to its unsigned variant.

     This works out for "!= len" (unless you really were
     trying to write the maximum size_t bytes), but is a
     bug if you check "< len" (an example of which was fixed
     recently in config.c).

     We should avoid promoting the mental model that you
     need to check the length at all, so that new sites are
     not tempted to copy us.

  2. Checking for a negative value is shorter to type,
     especially when the length is an expression.

  3. Linus says so. In d34cf19b89 (Clean up write_in_full()
     users, 2007-01-11), right after the write_in_full()
     semantics were changed, he wrote:

       I really wish every "write_in_full()" user would just
       check against "<0" now, but this fixes the nasty and
       stupid ones.

     Appeals to authority aside, this makes it clear that
     writing it this way does not have an intentional
     benefit. It's a historical curiosity that we never
     bothered to clean up (and which was undoubtedly
     cargo-culted into new sites).

So let's convert these obviously-correct cases (this
includes write_str_in_full(), which is just a wrapper for
write_in_full()).

[1] A careful reader may notice there is one way that
    write_in_full() can return a different value. If we ask
    write() to write N bytes and get a return value that is
    _larger_ than N, we could return a larger total. But
    besides the fact that this would imply a totally broken
    version of write(), it would already invoke undefined
    behavior. Our internal remaining counter is an unsigned
    size_t, which means that subtracting too many byte will
    wrap it around to a very large number. So we'll instantly
    begin reading off the end of the buffer, trying to write
    gigabytes (or petabytes) of data.

Signed-off-by: Jeff King <peff@peff.net>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-09-14 15:17:59 +09:00

408 lines
10 KiB
C

/*
* Low level 3-way in-core file merge.
*
* Copyright (c) 2007 Junio C Hamano
*/
#include "cache.h"
#include "config.h"
#include "attr.h"
#include "xdiff-interface.h"
#include "run-command.h"
#include "ll-merge.h"
#include "quote.h"
struct ll_merge_driver;
typedef int (*ll_merge_fn)(const struct ll_merge_driver *,
mmbuffer_t *result,
const char *path,
mmfile_t *orig, const char *orig_name,
mmfile_t *src1, const char *name1,
mmfile_t *src2, const char *name2,
const struct ll_merge_options *opts,
int marker_size);
struct ll_merge_driver {
const char *name;
const char *description;
ll_merge_fn fn;
const char *recursive;
struct ll_merge_driver *next;
char *cmdline;
};
/*
* Built-in low-levels
*/
static int ll_binary_merge(const struct ll_merge_driver *drv_unused,
mmbuffer_t *result,
const char *path,
mmfile_t *orig, const char *orig_name,
mmfile_t *src1, const char *name1,
mmfile_t *src2, const char *name2,
const struct ll_merge_options *opts,
int marker_size)
{
mmfile_t *stolen;
assert(opts);
/*
* The tentative merge result is the common ancestor for an
* internal merge. For the final merge, it is "ours" by
* default but -Xours/-Xtheirs can tweak the choice.
*/
if (opts->virtual_ancestor) {
stolen = orig;
} else {
switch (opts->variant) {
default:
warning("Cannot merge binary files: %s (%s vs. %s)",
path, name1, name2);
/* fallthru */
case XDL_MERGE_FAVOR_OURS:
stolen = src1;
break;
case XDL_MERGE_FAVOR_THEIRS:
stolen = src2;
break;
}
}
result->ptr = stolen->ptr;
result->size = stolen->size;
stolen->ptr = NULL;
/*
* With -Xtheirs or -Xours, we have cleanly merged;
* otherwise we got a conflict.
*/
return (opts->variant ? 0 : 1);
}
static int ll_xdl_merge(const struct ll_merge_driver *drv_unused,
mmbuffer_t *result,
const char *path,
mmfile_t *orig, const char *orig_name,
mmfile_t *src1, const char *name1,
mmfile_t *src2, const char *name2,
const struct ll_merge_options *opts,
int marker_size)
{
xmparam_t xmp;
assert(opts);
if (orig->size > MAX_XDIFF_SIZE ||
src1->size > MAX_XDIFF_SIZE ||
src2->size > MAX_XDIFF_SIZE ||
buffer_is_binary(orig->ptr, orig->size) ||
buffer_is_binary(src1->ptr, src1->size) ||
buffer_is_binary(src2->ptr, src2->size)) {
return ll_binary_merge(drv_unused, result,
path,
orig, orig_name,
src1, name1,
src2, name2,
opts, marker_size);
}
memset(&xmp, 0, sizeof(xmp));
xmp.level = XDL_MERGE_ZEALOUS;
xmp.favor = opts->variant;
xmp.xpp.flags = opts->xdl_opts;
if (git_xmerge_style >= 0)
xmp.style = git_xmerge_style;
if (marker_size > 0)
xmp.marker_size = marker_size;
xmp.ancestor = orig_name;
xmp.file1 = name1;
xmp.file2 = name2;
return xdl_merge(orig, src1, src2, &xmp, result);
}
static int ll_union_merge(const struct ll_merge_driver *drv_unused,
mmbuffer_t *result,
const char *path_unused,
mmfile_t *orig, const char *orig_name,
mmfile_t *src1, const char *name1,
mmfile_t *src2, const char *name2,
const struct ll_merge_options *opts,
int marker_size)
{
/* Use union favor */
struct ll_merge_options o;
assert(opts);
o = *opts;
o.variant = XDL_MERGE_FAVOR_UNION;
return ll_xdl_merge(drv_unused, result, path_unused,
orig, NULL, src1, NULL, src2, NULL,
&o, marker_size);
}
#define LL_BINARY_MERGE 0
#define LL_TEXT_MERGE 1
#define LL_UNION_MERGE 2
static struct ll_merge_driver ll_merge_drv[] = {
{ "binary", "built-in binary merge", ll_binary_merge },
{ "text", "built-in 3-way text merge", ll_xdl_merge },
{ "union", "built-in union merge", ll_union_merge },
};
static void create_temp(mmfile_t *src, char *path, size_t len)
{
int fd;
xsnprintf(path, len, ".merge_file_XXXXXX");
fd = xmkstemp(path);
if (write_in_full(fd, src->ptr, src->size) < 0)
die_errno("unable to write temp-file");
close(fd);
}
/*
* User defined low-level merge driver support.
*/
static int ll_ext_merge(const struct ll_merge_driver *fn,
mmbuffer_t *result,
const char *path,
mmfile_t *orig, const char *orig_name,
mmfile_t *src1, const char *name1,
mmfile_t *src2, const char *name2,
const struct ll_merge_options *opts,
int marker_size)
{
char temp[4][50];
struct strbuf cmd = STRBUF_INIT;
struct strbuf_expand_dict_entry dict[6];
struct strbuf path_sq = STRBUF_INIT;
const char *args[] = { NULL, NULL };
int status, fd, i;
struct stat st;
assert(opts);
sq_quote_buf(&path_sq, path);
dict[0].placeholder = "O"; dict[0].value = temp[0];
dict[1].placeholder = "A"; dict[1].value = temp[1];
dict[2].placeholder = "B"; dict[2].value = temp[2];
dict[3].placeholder = "L"; dict[3].value = temp[3];
dict[4].placeholder = "P"; dict[4].value = path_sq.buf;
dict[5].placeholder = NULL; dict[5].value = NULL;
if (fn->cmdline == NULL)
die("custom merge driver %s lacks command line.", fn->name);
result->ptr = NULL;
result->size = 0;
create_temp(orig, temp[0], sizeof(temp[0]));
create_temp(src1, temp[1], sizeof(temp[1]));
create_temp(src2, temp[2], sizeof(temp[2]));
xsnprintf(temp[3], sizeof(temp[3]), "%d", marker_size);
strbuf_expand(&cmd, fn->cmdline, strbuf_expand_dict_cb, &dict);
args[0] = cmd.buf;
status = run_command_v_opt(args, RUN_USING_SHELL);
fd = open(temp[1], O_RDONLY);
if (fd < 0)
goto bad;
if (fstat(fd, &st))
goto close_bad;
result->size = st.st_size;
result->ptr = xmallocz(result->size);
if (read_in_full(fd, result->ptr, result->size) != result->size) {
FREE_AND_NULL(result->ptr);
result->size = 0;
}
close_bad:
close(fd);
bad:
for (i = 0; i < 3; i++)
unlink_or_warn(temp[i]);
strbuf_release(&cmd);
strbuf_release(&path_sq);
return status;
}
/*
* merge.default and merge.driver configuration items
*/
static struct ll_merge_driver *ll_user_merge, **ll_user_merge_tail;
static const char *default_ll_merge;
static int read_merge_config(const char *var, const char *value, void *cb)
{
struct ll_merge_driver *fn;
const char *key, *name;
int namelen;
if (!strcmp(var, "merge.default"))
return git_config_string(&default_ll_merge, var, value);
/*
* We are not interested in anything but "merge.<name>.variable";
* especially, we do not want to look at variables such as
* "merge.summary", "merge.tool", and "merge.verbosity".
*/
if (parse_config_key(var, "merge", &name, &namelen, &key) < 0 || !name)
return 0;
/*
* Find existing one as we might be processing merge.<name>.var2
* after seeing merge.<name>.var1.
*/
for (fn = ll_user_merge; fn; fn = fn->next)
if (!strncmp(fn->name, name, namelen) && !fn->name[namelen])
break;
if (!fn) {
fn = xcalloc(1, sizeof(struct ll_merge_driver));
fn->name = xmemdupz(name, namelen);
fn->fn = ll_ext_merge;
*ll_user_merge_tail = fn;
ll_user_merge_tail = &(fn->next);
}
if (!strcmp("name", key))
return git_config_string(&fn->description, var, value);
if (!strcmp("driver", key)) {
if (!value)
return error("%s: lacks value", var);
/*
* merge.<name>.driver specifies the command line:
*
* command-line
*
* The command-line will be interpolated with the following
* tokens and is given to the shell:
*
* %O - temporary file name for the merge base.
* %A - temporary file name for our version.
* %B - temporary file name for the other branches' version.
* %L - conflict marker length
* %P - the original path (safely quoted for the shell)
*
* The external merge driver should write the results in the
* file named by %A, and signal that it has done with zero exit
* status.
*/
fn->cmdline = xstrdup(value);
return 0;
}
if (!strcmp("recursive", key))
return git_config_string(&fn->recursive, var, value);
return 0;
}
static void initialize_ll_merge(void)
{
if (ll_user_merge_tail)
return;
ll_user_merge_tail = &ll_user_merge;
git_config(read_merge_config, NULL);
}
static const struct ll_merge_driver *find_ll_merge_driver(const char *merge_attr)
{
struct ll_merge_driver *fn;
const char *name;
int i;
initialize_ll_merge();
if (ATTR_TRUE(merge_attr))
return &ll_merge_drv[LL_TEXT_MERGE];
else if (ATTR_FALSE(merge_attr))
return &ll_merge_drv[LL_BINARY_MERGE];
else if (ATTR_UNSET(merge_attr)) {
if (!default_ll_merge)
return &ll_merge_drv[LL_TEXT_MERGE];
else
name = default_ll_merge;
}
else
name = merge_attr;
for (fn = ll_user_merge; fn; fn = fn->next)
if (!strcmp(fn->name, name))
return fn;
for (i = 0; i < ARRAY_SIZE(ll_merge_drv); i++)
if (!strcmp(ll_merge_drv[i].name, name))
return &ll_merge_drv[i];
/* default to the 3-way */
return &ll_merge_drv[LL_TEXT_MERGE];
}
static void normalize_file(mmfile_t *mm, const char *path)
{
struct strbuf strbuf = STRBUF_INIT;
if (renormalize_buffer(&the_index, path, mm->ptr, mm->size, &strbuf)) {
free(mm->ptr);
mm->size = strbuf.len;
mm->ptr = strbuf_detach(&strbuf, NULL);
}
}
int ll_merge(mmbuffer_t *result_buf,
const char *path,
mmfile_t *ancestor, const char *ancestor_label,
mmfile_t *ours, const char *our_label,
mmfile_t *theirs, const char *their_label,
const struct ll_merge_options *opts)
{
static struct attr_check *check;
static const struct ll_merge_options default_opts;
const char *ll_driver_name = NULL;
int marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
const struct ll_merge_driver *driver;
if (!opts)
opts = &default_opts;
if (opts->renormalize) {
normalize_file(ancestor, path);
normalize_file(ours, path);
normalize_file(theirs, path);
}
if (!check)
check = attr_check_initl("merge", "conflict-marker-size", NULL);
if (!git_check_attr(path, check)) {
ll_driver_name = check->items[0].value;
if (check->items[1].value) {
marker_size = atoi(check->items[1].value);
if (marker_size <= 0)
marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
}
}
driver = find_ll_merge_driver(ll_driver_name);
if (opts->virtual_ancestor) {
if (driver->recursive)
driver = find_ll_merge_driver(driver->recursive);
marker_size += 2;
}
return driver->fn(driver, result_buf, path, ancestor, ancestor_label,
ours, our_label, theirs, their_label,
opts, marker_size);
}
int ll_merge_marker_size(const char *path)
{
static struct attr_check *check;
int marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
if (!check)
check = attr_check_initl("conflict-marker-size", NULL);
if (!git_check_attr(path, check) && check->items[0].value) {
marker_size = atoi(check->items[0].value);
if (marker_size <= 0)
marker_size = DEFAULT_CONFLICT_MARKER_SIZE;
}
return marker_size;
}