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[PATCH 5/5] refs.c: make @ a pseudo-ref alias to HEAD

From
Ramkumar Ramachandra <artagnon@gmail.com>
Date
May 1, 2013, 16:20 UTC
Message-ID
<1367425235-14998-6-git-send-email-artagnon@gmail.com>
In-Reply-To
<1367425235-14998-1-git-send-email-artagnon@gmail.com>

First, make sure that check_refname_format() rejects the a refname beginning with a '@'. Add a test to t1400 (update-ref) demonstrating that update-ref forbids the user from updating a ref named "@".

Now, resolve_ref_unsafe() is built to resolve any refs that have a corresponding file inside $GITDIR. Our "@" ref is a special pseudo-ref and does not have a filesystem counterpart. So, hard-interpret "@" as "HEAD" and resolve .git/HEAD as usual. This means that we can drop the 'git symbolic-ref @ HEAD' line in t1508 (at-combinations), and everything will continue working as usual.

If the user does manage to create a '.git/@' unsafely (via symbolic-ref or otherwise), it will be ignored.

In practice, this means that you will now be able to do:
    $ git show @~1
    $ git log @^2
Advertise these features in the tests and documentation.
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
---
 Documentation/git-check-ref-format.txt |  2 ++
 Documentation/revisions.txt            |  8 ++++++--
 refs.c                                 | 12 ++++++++++--
 t/t1400-update-ref.sh                  |  3 +++
 t/t1508-at-combinations.sh             |  7 ++++---
 5 files changed, 25 insertions(+), 7 deletions(-)
diff --git a/Documentation/git-check-ref-format.txt b/Documentation/git-check-ref-format.txt
index ec1739a..3de9adc 100644
--- a/Documentation/git-check-ref-format.txt
+++ b/Documentation/git-check-ref-format.txt
@@ -52,6 +52,8 @@ Git imposes the following rules on how references are named:
 
 . They cannot end with a dot `.`.
 
+. They cannot be the single character `@`.
+
 . They cannot contain a sequence `@{`.
 
 . They cannot contain a `\`.
diff --git a/Documentation/revisions.txt b/Documentation/revisions.txt
index d477b3f..9b2e653 100644
--- a/Documentation/revisions.txt
+++ b/Documentation/revisions.txt
@@ -27,6 +27,10 @@ blobs contained in a commit.
   When ambiguous, a '<refname>' is disambiguated by taking the
   first match in the following rules:
 
+  . '@' is a special pseudo-ref that refers to HEAD.  An '@' followed
+    by '\{' has no relationship to this and means something entirely
+    different (see below).
+
   . If '$GIT_DIR/<refname>' exists, that is what you mean (this is usually
     useful only for 'HEAD', 'FETCH_HEAD', 'ORIG_HEAD', 'MERGE_HEAD'
     and 'CHERRY_PICK_HEAD');
@@ -93,7 +97,7 @@ some output processing may assume ref names in UTF-8.
   refers to the branch that the branch specified by branchname is set to build on
   top of.  A missing branchname defaults to the current one.
 
-'<rev>{caret}', e.g. 'HEAD{caret}, v1.5.1{caret}0'::
+'<rev>{caret}', e.g. '@{caret}2', 'HEAD{caret}', 'v1.5.1{caret}0'::
   A suffix '{caret}' to a revision parameter means the first parent of
   that commit object.  '{caret}<n>' means the <n>th parent (i.e.
   '<rev>{caret}'
@@ -101,7 +105,7 @@ some output processing may assume ref names in UTF-8.
   '<rev>{caret}0' means the commit itself and is used when '<rev>' is the
   object name of a tag object that refers to a commit object.
 
-'<rev>{tilde}<n>', e.g. 'master{tilde}3'::
+'<rev>{tilde}<n>', e.g. '@{tilde}1', 'master{tilde}3'::
   A suffix '{tilde}<n>' to a revision parameter means the commit
   object that is the <n>th generation ancestor of the named
   commit object, following only the first parents.  I.e. '<rev>{tilde}3' is
diff --git a/refs.c b/refs.c
index de2d8eb..6a75f77 100644
--- a/refs.c
+++ b/refs.c
@@ -72,6 +72,9 @@ int check_refname_format(const char *refname, int flags)
 {
 	int component_len, component_count = 0;
 
+	if (!strcmp(refname, "@"))
+		return -1;
+
 	while (1) {
 		/* We are at the start of a path component. */
 		component_len = check_refname_component(refname, flags);
@@ -1093,8 +1096,13 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 	if (flag)
 		*flag = 0;
 
-	if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
-		return NULL;
+	if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL) < 0) {
+		/* Handle the pseudo-ref @ */
+		if (!strcmp(refname, "@"))
+			refname = "HEAD";
+		else
+			return NULL;
+	}
 
 	for (;;) {
 		char path[PATH_MAX];
diff --git a/t/t1400-update-ref.sh b/t/t1400-update-ref.sh
index e415ee0..ee93979 100755
--- a/t/t1400-update-ref.sh
+++ b/t/t1400-update-ref.sh
@@ -127,6 +127,9 @@ test_expect_success '(not) change HEAD with wrong SHA1' "
 test_expect_success "(not) changed .git/$m" "
 	! test $B"' = $(cat .git/'"$m"')
 '
+test_expect_success 'disallow creating a ref with name @' '
+	test_must_fail git update-ref @ HEAD
+'
 rm -f .git/$m
 
 : a repository with working tree always has reflog these days...
diff --git a/t/t1508-at-combinations.sh b/t/t1508-at-combinations.sh
index 73c457d..8f8e32d 100755
--- a/t/t1508-at-combinations.sh
+++ b/t/t1508-at-combinations.sh
@@ -54,12 +54,13 @@ nonsense "@{0}@{0}"
 nonsense "@{1}@{u}"
 nonsense "HEAD@{-1}"
 
-# Make sure that the @-parser isn't buggy; check things with
-# symbolic-ref @ pointing to HEAD.
-git symbolic-ref @ HEAD
+# Check everything with the pseudo-ref @
 check "@@{1}" new-one
 check "@@{now}" new-two
 check "@@{u}" upstream-two
 nonsense "@@{-1}"
 
+check "@~1" new-one
+check "@^0" new-two
+
 test_done

-- 
1.8.3.rc0.24.g6456091
Previous: Felipe ContrerasNext: Felipe Contreras
Message 44 of 49 in “A natural solution to the @ -> HEAD problem”
  1. 0/5 A natural solution to the @ -> HEAD problemRamkumar Ramachandra, May 1, 2013
  2. 1/5 t1508 (at-combinations): more tests; document failuresRamkumar Ramachandra, May 1, 2013
  3. Junio C HamanoMay 1, 2013
  4. Ramkumar RamachandraMay 1, 2013
  5. Jeff KingMay 1, 2013
  6. Ramkumar RamachandraMay 1, 2013
  7. Junio C HamanoMay 1, 2013
  8. Felipe ContrerasMay 2, 2013
  9. Ramkumar RamachandraMay 2, 2013
  10. Felipe ContrerasMay 2, 2013
  11. Ramkumar RamachandraMay 2, 2013
  12. Ramkumar RamachandraMay 2, 2013
  13. Felipe ContrerasMay 2, 2013
  14. Ramkumar RamachandraMay 2, 2013
  15. Felipe ContrerasMay 2, 2013
  16. Ramkumar RamachandraMay 2, 2013
  17. Felipe ContrerasMay 2, 2013
  18. Ramkumar RamachandraMay 2, 2013
  19. David AguilarMay 4, 2013
  20. David AguilarMay 4, 2013
  21. 2/5 sha1_name.c: don't waste cycles in the @-parsing loopRamkumar Ramachandra, May 1, 2013
  22. Felipe ContrerasMay 1, 2013
  23. Ramkumar RamachandraMay 1, 2013
  24. Junio C HamanoMay 2, 2013
  25. 3/5 sha1_name.c: simplify @-parsing in get_sha1_basic()Ramkumar Ramachandra, May 1, 2013
  26. Felipe ContrerasMay 1, 2013
  27. Ramkumar RamachandraMay 1, 2013
  28. Jonathan NiederMay 1, 2013
  29. Ramkumar RamachandraMay 1, 2013
  30. Felipe ContrerasMay 1, 2013
  31. Ramkumar RamachandraMay 1, 2013
  32. Felipe ContrerasMay 1, 2013
  33. Ramkumar RamachandraMay 1, 2013
  34. Felipe ContrerasMay 1, 2013
  35. Ramkumar RamachandraMay 1, 2013
  36. 4/5 remote.c: teach branch_get() to treat symrefs other than HEADRamkumar Ramachandra, May 1, 2013
  37. Felipe ContrerasMay 1, 2013
  38. Ramkumar RamachandraMay 1, 2013
  39. Felipe ContrerasMay 1, 2013
  40. Ramkumar RamachandraMay 1, 2013
  41. Felipe ContrerasMay 1, 2013
  42. Ramkumar RamachandraMay 1, 2013
  43. Felipe ContrerasMay 1, 2013
  44. 5/5 refs.c: make @ a pseudo-ref alias to HEADRamkumar Ramachandra, May 1, 2013
  45. Felipe ContrerasMay 1, 2013
  46. Ramkumar RamachandraMay 1, 2013
  47. Felipe ContrerasMay 1, 2013
  48. Ramkumar RamachandraMay 1, 2013
  49. Ramkumar RamachandraMay 1, 2013

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