treemanifest: lazily load manifests
Most operations on treemanifests already visit only relevant
submanifests. Notable examples include __getitem__, __contains__,
walk/matches with matcher, diff. By making submanifests lazily loaded,
we speed up all these operations.
The lazy loading is achieved by adding a _load() method that gets
defined where we currently eagerly parse the manifest. We make sure to
call it before any access to _dirs, _files or _flags.
Some timings on the Mozilla repo (with flat manifest timings for
reference):
hg cat -r . README.txt: 1.644s -> 0.096s (0.255s)
hg diff -r .^ -r . : 1.746s -> 0.137s (0.431s)
hg files -r . python : 1.508s -> 0.146s (0.335s)
hg files -r . : 2.125s -> 2.203s (0.712s)
$ hg init
$ touch a
$ hg add a
$ hg ci -m "a"
$ echo 123 > b
$ hg add b
$ hg diff --nodates
diff -r 3903775176ed b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123
$ hg diff --nodates -r tip
diff -r 3903775176ed b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123
$ echo foo > a
$ hg diff --nodates
diff -r 3903775176ed a
--- a/a
+++ b/a
@@ -0,0 +1,1 @@
+foo
diff -r 3903775176ed b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123
$ hg diff -r ""
hg: parse error: empty query
[255]
$ hg diff -r tip -r ""
hg: parse error: empty query
[255]