similar: compare between actual file contents for exact identity
Before this patch, similarity detection logic (for addremove and
automv) depends entirely on SHA-1 digesting. But this causes incorrect
rename detection, if:
- removing file A and adding file B occur at same committing, and
- SHA-1 hash values of file A and B are same
This may prevent security experts from managing sample files for
SHAttered issue in Mercurial repository, for example.
https://security.googleblog.com/2017/02/announcing-first-sha1-collision.html
https://shattered.it/
Hash collision itself isn't so serious for core repository
functionality of Mercurial, described by mpm as below, though.
https://www.mercurial-scm.org/wiki/mpm/SHA1
This patch compares between actual file contents after hash comparison
for exact identity.
Even after this patch, SHA-1 is still used, because it is reasonable
enough to quickly detect existence of "(almost) same" file.
- replacing SHA-1 causes decreasing performance, and
- replacement of it has ambiguity, yet
Getting content of removed file (= rfctx.data()) at each exact
comparison should be cheap enough, even though getting content of
added one costs much.
======= ============== =====================
file fctx data() reads from
======= ============== =====================
removed filectx in-memory revlog data
added workingfilectx storage
======= ============== =====================
#require execbit
$ umask 027
$ hg init test1
$ cd test1
$ touch a b
$ hg add a b
$ hg ci -m "added a b"
$ cd ..
$ hg clone test1 test3
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg init test2
$ cd test2
$ hg pull ../test1
pulling from ../test1
requesting all changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 2 changes to 2 files
(run 'hg update' to get a working copy)
$ hg co
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ chmod +x a
$ hg ci -m "chmod +x a"
the changelog should mention file a:
$ hg tip --template '{files}\n'
a
$ cd ../test1
$ echo 123 >>a
$ hg ci -m "a updated"
$ hg pull ../test2
pulling from ../test2
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg heads
changeset: 2:7f4313b42a34
tag: tip
parent: 0:22a449e20da5
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: chmod +x a
changeset: 1:c6ecefc45368
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: a updated
$ hg history
changeset: 2:7f4313b42a34
tag: tip
parent: 0:22a449e20da5
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: chmod +x a
changeset: 1:c6ecefc45368
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: a updated
changeset: 0:22a449e20da5
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: added a b
$ hg -v merge
resolving manifests
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ cat a
123
$ [ -x a ]
$ cd ../test3
$ echo 123 >>b
$ hg ci -m "b updated"
$ hg pull ../test2
pulling from ../test2
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg heads
changeset: 2:7f4313b42a34
tag: tip
parent: 0:22a449e20da5
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: chmod +x a
changeset: 1:dc57ead75f79
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: b updated
$ hg history
changeset: 2:7f4313b42a34
tag: tip
parent: 0:22a449e20da5
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: chmod +x a
changeset: 1:dc57ead75f79
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: b updated
changeset: 0:22a449e20da5
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: added a b
$ hg -v merge
resolving manifests
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ ls -l ../test[123]/a > foo
$ cut -b 1-10 < foo
-rwxr-x---
-rwxr-x---
-rwxr-x---
$ hg debugindex a
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 0 ..... 0 b80de5d13875 000000000000 000000000000 (re)
$ hg debugindex -R ../test2 a
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 0 ..... 0 b80de5d13875 000000000000 000000000000 (re)
$ hg debugindex -R ../test1 a
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 0 ..... 0 b80de5d13875 000000000000 000000000000 (re)
1 0 5 ..... 1 7fe919cc0336 b80de5d13875 000000000000 (re)
$ cd ..