dirstate-tree: Avoid BTreeMap double-lookup when inserting a dirstate entry
The child nodes of a given node in the tree-shaped dirstate are kept in a
`BTreeMap` where keys are file names as strings. Finding or inserting a value
in the map takes `O(log(n))` string comparisons, which adds up when constructing
the tree.
The `entry` API allows finding a "spot" in the map that may or may not be
occupied and then access that value or insert a new one without doing map
lookup again. However the current API is limited in that calling `entry`
requires an owned key (and so a memory allocation), even if it ends up not
being used in the case where the map already has a value with an equal key.
This is still a win, with 4% better end-to-end time for `hg status` measured
here with hyperfine:
```
Benchmark #1: ../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
Time (mean ± σ): 1.337 s ± 0.018 s [User: 892.9 ms, System: 437.5 ms]
Range (min … max): 1.316 s … 1.373 s 10 runs
Benchmark #2: ./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
Time (mean ± σ): 1.291 s ± 0.008 s [User: 853.4 ms, System: 431.1 ms]
Range (min … max): 1.283 s … 1.309 s 10 runs
Summary
'./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1' ran
1.04 ± 0.02 times faster than '../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1'
```
* ./hg is this revision
* ../hg2/hg is its parent
* $REPO is an old snapshot of mozilla-central
Differential Revision: https://phab.mercurial-scm.org/D10550
Test adding .hgeol
$ cat >> $HGRCPATH <<EOF
> [diff]
> git = 1
> EOF
$ seteol () {
> if [ $1 = "LF" ]; then
> EOL='\n'
> else
> EOL='\r\n'
> fi
> }
$ makerepo () {
> echo
> echo "# ==== setup repository ===="
> echo '% hg init'
> hg init repo
> cd repo
> printf "first\nsecond\nthird\n" > a.txt
> hg commit -d '100 0' --addremove -m 'LF commit'
> cd ..
> }
$ dotest () {
> seteol $1
> echo
> echo "% hg clone repo repo-$1"
> hg clone repo repo-$1
> cd repo-$1
> cat > .hg/hgrc <<EOF
> [extensions]
> eol =
> [eol]
> native = LF
> EOF
> cat > .hgeol <<EOF
> [patterns]
> **.txt = native
> [repository]
> native = $1
> EOF
> echo '% hg add .hgeol'
> hg add .hgeol
> echo '% hg status'
> hg status
> echo '% hg commit'
> hg commit -d '200 0' -m 'Added .hgeol file'
> echo '% hg status'
> hg status
> echo '% hg tip -p'
> hg tip -p
> cd ..
> rm -r repo-$1
> }
$ makerepo
# ==== setup repository ====
% hg init
adding a.txt
$ dotest LF
% hg clone repo repo-LF
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% hg add .hgeol
% hg status
A .hgeol
% hg commit
% hg status
% hg tip -p
changeset: 1:33503edb53b0
tag: tip
user: test
date: Thu Jan 01 00:03:20 1970 +0000
summary: Added .hgeol file
diff --git a/.hgeol b/.hgeol
new file mode 100644
--- /dev/null
+++ b/.hgeol
@@ -0,0 +1,4 @@
+[patterns]
+**.txt = native
+[repository]
+native = LF
$ dotest CRLF
% hg clone repo repo-CRLF
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
% hg add .hgeol
% hg status
M a.txt
A .hgeol
% hg commit
% hg status
% hg tip -p
changeset: 1:6e64eaa9eb23
tag: tip
user: test
date: Thu Jan 01 00:03:20 1970 +0000
summary: Added .hgeol file
diff --git a/.hgeol b/.hgeol
new file mode 100644
--- /dev/null
+++ b/.hgeol
@@ -0,0 +1,4 @@
+[patterns]
+**.txt = native
+[repository]
+native = CRLF
diff --git a/a.txt b/a.txt
--- a/a.txt
+++ b/a.txt
@@ -1,3 +1,3 @@
-first
-second
-third
+first\r (esc)
+second\r (esc)
+third\r (esc)
$ rm -r repo