[PATCH] hgweb: compute changeset parents and children for log pages lazily

[Anton Shestakov]

# HG changeset patch
# User Anton Shestakov <av6 at dwimlabs.net>
# Date 1447167779 -28800
#      Tue Nov 10 23:02:59 2015 +0800
# Node ID 6501f73ee550ccb6b73be8b0c611706ceaf666bd
# Parent  8b2fbe3f59b1b969878691cb472369ad0067f165
hgweb: compute changeset parents and children for log pages lazily

Log pages, i.e. changelog, filelog and search results page computed children
and parents for each changeset shown, because spartan hgweb style shows this
info. Turns out, computing all this is heavy and also unnecessary for log pages
in all other hgweb styles.

Luckily, templates allow an easy way to do computations on demand: just pass
the heavy part of code as a callable and it will be only called when needed.

Here are some benchmarks on the mercurial repository (best of 3):

time wget http://127.0.0.1:8021/

before: 0m0.050s
after:  0m0.040s

time wget http://127.0.0.1:8021/?revcount=960

before: 0m1.164s
after:  0m0.389s

time wget http://127.0.0.1:8021/log/tip/mercurial/commands.py

before: 0m0.047s
after:  0m0.042s

time wget http://127.0.0.1:8021/log/tip/mercurial/commands.py?revcount=960

before: 0m0.830s
after:  0m0.434s

diff --git a/mercurial/hgweb/webcommands.py b/mercurial/hgweb/webcommands.py
--- a/mercurial/hgweb/webcommands.py
+++ b/mercurial/hgweb/webcommands.py
@@ -264,8 +264,8 @@ def _search(web, req, tmpl):
             yield tmpl('searchentry',
                        parity=parity.next(),
                        author=ctx.user(),
-                       parent=webutil.parents(ctx),
-                       child=webutil.children(ctx),
+                       parent=lambda **x: webutil.parents(ctx),
+                       child=lambda **x: webutil.children(ctx),
                        changelogtag=showtags,
                        desc=ctx.description(),
                        extra=ctx.extra(),
@@ -1000,8 +1000,8 @@ def filelog(web, req, tmpl):
                       "author": iterfctx.user(),
                       "date": iterfctx.date(),
                       "rename": webutil.renamelink(iterfctx),
-                      "parent": webutil.parents(iterfctx),
-                      "child": webutil.children(iterfctx),
+                      "parent": lambda **x: webutil.parents(iterfctx),
+                      "child": lambda **x: webutil.children(iterfctx),
                       "desc": iterfctx.description(),
                       "extra": iterfctx.extra(),
                       "tags": webutil.nodetagsdict(repo, iterfctx.node()),
diff --git a/mercurial/hgweb/webutil.py b/mercurial/hgweb/webutil.py
--- a/mercurial/hgweb/webutil.py
+++ b/mercurial/hgweb/webutil.py
@@ -297,8 +297,8 @@ def changelistentry(web, ctx, tmpl):
 
     return {
         "author": ctx.user(),
-        "parent": parents(ctx, rev - 1),
-        "child": children(ctx, rev + 1),
+        "parent": lambda **x: parents(ctx, rev - 1),
+        "child": lambda **x: children(ctx, rev + 1),
         "changelogtag": showtags,
         "desc": ctx.description(),
         "extra": ctx.extra(),