Merge branch 'mh/ref-transaction'

Update "update-ref --stdin [-z]" and then introduce a transactional
support for (multi-)reference updates.

* mh/ref-transaction: (27 commits)
  ref_transaction_commit(): work with transaction->updates in place
  struct ref_update: add a type field
  struct ref_update: add a lock field
  ref_transaction_commit(): simplify code using temporary variables
  struct ref_update: store refname as a FLEX_ARRAY
  struct ref_update: rename field "ref_name" to "refname"
  refs: remove API function update_refs()
  update-ref --stdin: reimplement using reference transactions
  refs: add a concept of a reference transaction
  update-ref --stdin: harmonize error messages
  update-ref --stdin: improve the error message for unexpected EOF
  t1400: test one mistake at a time
  update-ref --stdin -z: deprecate interpreting the empty string as zeros
  update-ref.c: extract a new function, parse_next_sha1()
  t1400: test that stdin -z update treats empty <newvalue> as zeros
  update-ref --stdin: simplify error messages for missing oldvalues
  update-ref --stdin: make error messages more consistent
  update-ref --stdin: improve error messages for invalid values
  update-ref.c: extract a new function, parse_refname()
  parse_cmd_verify(): copy old_sha1 instead of evaluating <oldvalue> twice
  ...

1 files changed, 12 insertions, 6 deletions

diff --git a/Documentation/git-update-ref.txt b/Documentation/git-update-ref.txt
index 0a0a5512b3..c8f5ae5cb3 100644
--- a/Documentation/git-update-ref.txt
+++ b/Documentation/git-update-ref.txt
@@ -68,7 +68,12 @@ performs all modifications together.  Specify commands of the form:
 	option SP <opt> LF
 
 Quote fields containing whitespace as if they were strings in C source
-code.  Alternatively, use `-z` to specify commands without quoting:
+code; i.e., surrounded by double-quotes and with backslash escapes.
+Use 40 "0" characters or the empty string to specify a zero value.  To
+specify a missing value, omit the value and its preceding SP entirely.
+
+Alternatively, use `-z` to specify in NUL-terminated format, without
+quoting:
 
 	update SP <ref> NUL <newvalue> NUL [<oldvalue>] NUL
 	create SP <ref> NUL <newvalue> NUL
@@ -76,8 +81,12 @@ code.  Alternatively, use `-z` to specify commands without quoting:
 	verify SP <ref> NUL [<oldvalue>] NUL
 	option SP <opt> NUL
 
-Lines of any other format or a repeated <ref> produce an error.
-Command meanings are:
+In this format, use 40 "0" to specify a zero value, and use the empty
+string to specify a missing value.
+
+In either format, values can be specified in any form that Git
+recognizes as an object name.  Commands in any other format or a
+repeated <ref> produce an error.  Command meanings are:
 
 update::
 	Set <ref> to <newvalue> after verifying <oldvalue>, if given.
@@ -102,9 +111,6 @@ option::
 	The only valid option is `no-deref` to avoid dereferencing
 	a symbolic ref.
 
-Use 40 "0" or the empty string to specify a zero value, except that
-with `-z` an empty <oldvalue> is considered missing.
-
 If all <ref>s can be locked with matching <oldvalue>s
 simultaneously, all modifications are performed.  Otherwise, no
 modifications are performed.  Note that while each individual