branchcache: add a "pure topological head" fast path
In a narrow but actually quick common case, all topological heads are all on
the same branch and all open. In this case, computing the branch map is very
simple. We can quickly detect situation where this situation will not change.
So we update the V3 format to be able to express this situation and upgrade the
update code to detect we remains in that mode.
The branch cache is populated with the actual value when the branch map is
accessed, but the update_disk method can do the update without needing to
populate it.
Setup:
$ cat > eval.py <<EOF
> import filecmp
> from mercurial import commands, context, pycompat, registrar
> cmdtable = {}
> command = registrar.command(cmdtable)
> @command(b'eval', [], b'hg eval CMD')
> def eval_(ui, repo, *cmds, **opts):
> cmd = b" ".join(cmds)
> res = pycompat.bytestr(eval(cmd, globals(), locals()))
> ui.warn(b"%s" % res)
> EOF
$ echo "[extensions]" >> $HGRCPATH
$ echo "eval=`pwd`/eval.py" >> $HGRCPATH
Arbitraryfilectx.cmp does not follow symlinks:
$ mkdir case1
$ cd case1
$ hg init
#if symlink
$ printf "A" > real_A
$ printf "foo" > A
$ printf "foo" > B
$ ln -s A sym_A
$ hg add .
adding A
adding B
adding real_A
adding sym_A
$ hg commit -m "base"
#else
$ hg import -q --bypass - <<EOF
> # HG changeset patch
> # User test
> # Date 0 0
> base
>
> diff --git a/A b/A
> new file mode 100644
> --- /dev/null
> +++ b/A
> @@ -0,0 +1,1 @@
> +foo
> \ No newline at end of file
> diff --git a/B b/B
> new file mode 100644
> --- /dev/null
> +++ b/B
> @@ -0,0 +1,1 @@
> +foo
> \ No newline at end of file
> diff --git a/real_A b/real_A
> new file mode 100644
> --- /dev/null
> +++ b/real_A
> @@ -0,0 +1,1 @@
> +A
> \ No newline at end of file
> diff --git a/sym_A b/sym_A
> new file mode 120000
> --- /dev/null
> +++ b/sym_A
> @@ -0,0 +1,1 @@
> +A
> \ No newline at end of file
> EOF
$ hg up -q
#endif
These files are different and should return True (different):
(Note that filecmp.cmp's return semantics are inverted from ours, so we invert
for simplicity):
$ hg eval "context.arbitraryfilectx(b'A', repo).cmp(repo[None][b'real_A'])"
True (no-eol)
$ hg eval "not filecmp.cmp(b'A', b'real_A')"
True (no-eol)
These files are identical and should return False (same):
$ hg eval "context.arbitraryfilectx(b'A', repo).cmp(repo[None][b'A'])"
False (no-eol)
$ hg eval "context.arbitraryfilectx(b'A', repo).cmp(repo[None][b'B'])"
False (no-eol)
$ hg eval "not filecmp.cmp(b'A', b'B')"
False (no-eol)
This comparison should also return False, since A and sym_A are substantially
the same in the eyes of ``filectx.cmp``, which looks at data only.
$ hg eval "context.arbitraryfilectx(b'real_A', repo).cmp(repo[None][b'sym_A'])"
False (no-eol)
A naive use of filecmp on those two would wrongly return True, since it follows
the symlink to "A", which has different contents.
#if symlink
$ hg eval "not filecmp.cmp(b'real_A', b'sym_A')"
True (no-eol)
#else
$ hg eval "not filecmp.cmp(b'real_A', b'sym_A')"
False (no-eol)
#endif