[PATCH -v3 0/8] fast export/import: handle nested tags, improve incremental exports

This series improves the incremental export story for fast-export and fast-import (--export-marks and --import-marks fell a bit short), fixes a couple small export/import bugs, and enables handling nested tags. In particular, the nested tags handling makes it so that fast-export and fast-import can finally handle the git.git repo.

Changes since v2 (full range-diff below):
  - Code cleanup of patch 2 suggested by René

Elijah Newren (8):
  fast-export: fix exporting a tag and nothing else
  fast-import: fix handling of deleted tags
  fast-import: allow tags to be identified by mark labels
  fast-import: add support for new 'alias' command
  fast-export: add support for --import-marks-if-exists
  fast-export: allow user to request tags be marked with --mark-tags
  t9350: add tests for tags of things other than a commit
  fast-export: handle nested tags

 Documentation/git-fast-export.txt | 17 ++++--
 Documentation/git-fast-import.txt | 23 ++++++++
 builtin/fast-export.c             | 67 ++++++++++++++++------
 fast-import.c                     | 92 +++++++++++++++++++++++++++----
 t/t9300-fast-import.sh            | 37 +++++++++++++
 t/t9350-fast-export.sh            | 68 +++++++++++++++++++++--
 6 files changed, 266 insertions(+), 38 deletions(-)

Range-diff:
1:  a30cfbbb50 = 1:  a30cfbbb50 fast-export: fix exporting a tag and nothing else
2:  1d19498bc6 ! 2:  36fbf15134 fast-import: fix handling of deleted tags
    @@ Commit message
         So, either way nested tags imply the need to delete temporary inner tag
         references.
     
    +    Helped-by: René Scharfe <l.s.r@web.de>
         Signed-off-by: Elijah Newren <newren@gmail.com>
     
      ## fast-import.c ##
    +@@ fast-import.c: static void parse_new_tag(const char *arg)
    + static void parse_reset_branch(const char *arg)
    + {
    + 	struct branch *b;
    ++	const char *tag_name;
    + 
    + 	b = lookup_branch(arg);
    + 	if (b) {
     @@ fast-import.c: static void parse_reset_branch(const char *arg)
      		b = new_branch(arg);
      	read_next_command();
      	parse_from(b);
    -+	if (b->delete && !strncmp(b->name, "refs/tags/", 10)) {
    ++	if (b->delete && skip_prefix(b->name, "refs/tags/", &tag_name)) {
     +		/*
     +		 * Elsewhere, we call dump_branches() before dump_tags(),
     +		 * and dump_branches() will handle ref deletions first, so
    @@ fast-import.c: static void parse_reset_branch(const char *arg)
     +		 * NEEDSWORK: replace list of tags with hashmap for faster
     +		 * deletion?
     +		 */
    -+		struct strbuf tag_name = STRBUF_INIT;
     +		struct tag *t, *prev = NULL;
     +		for (t = first_tag; t; t = t->next_tag) {
    -+			strbuf_reset(&tag_name);
    -+			strbuf_addf(&tag_name, "refs/tags/%s", t->name);
    -+			if (!strcmp(b->name, tag_name.buf))
    ++			if (!strcmp(t->name, tag_name))
     +				break;
     +			prev = t;
     +		}
3:  e1fd888e4a = 3:  3b5f4270f8 fast-import: allow tags to be identified by mark labels
4:  93175f28d9 = 4:  489c7fd854 fast-import: add support for new 'alias' command
5:  8c8743395c = 5:  38fd19caee fast-export: add support for --import-marks-if-exists
6:  eebc40df33 = 6:  2017b8d9f9 fast-export: allow user to request tags be marked with --mark-tags
7:  de39f703c6 = 7:  0efdbb81b1 t9350: add tests for tags of things other than a commit
8:  ac739dbb79 = 8:  fe7c27d786 fast-export: handle nested tags