Re: [PATCH] add a script to diff rendered documentation

[Jeff King <peff@peff.net>]

On Fri, Aug 03, 2018 at 04:52:05PM -0400, Jeff King wrote:

> I wrote this up for my own use after our discussion in [1]. I'm not sure
> if it's too ugly for inclusion, or if it might be helpful to others.
> I've only just written it, but my plan is to try to run it on anything I
> submit to check the formatting. So it _seems_ useful and appears to
> work, but only after a few minutes of playing with it. :)
> 
> [1] https://public-inbox.org/git/20180720223608.GE18502@genre.crustytoothpaste.net/

OK, people seem to think this is possibly useful, so here it is with a
little bit of polish based on earlier reviews:

 - we now default to $(getconf _NPROCESSORS_ONLN) parallelism, or 1 if
   that doesn't work (thanks for the getconf suggestion, Jonathan)

 - fixed formatting of usage message, per Eric's suggestion

 - put "make" as a noun in quotes ;)

I suspect the rendering step could be done a little more efficiently. In
addition to `man`, we run a shell, a `mkdir`, and a `mv` for each file.
Probably the whole thing could be done via a single perl script,
exec-ing man as appropriate. But we'd lose the parallelism, unless we do
something clever with threads. So I've left it for now, but if anybody
is interested in poking at it, go for it.

-- >8 --
Subject: [PATCH] add a script to diff rendered documentation

After making a change to the documentation, it's easy to
forget to check the rendered version to make sure it was
formatted as you intended. And simply doing a diff between
the two built versions is less trivial than you might hope:

  - diffing the roff or html output isn't particularly
    readable; what we really care about is what the end user
    will see

  - you have to tweak a few build variables to avoid
    spurious differences (e.g., version numbers, build
    times)

Let's provide a script that builds and installs the manpages
for two commits, renders the results using "man", and diffs
the result. Since this is time-consuming, we'll also do our
best to avoid repeated work, keeping intermediate results
between runs.

Some of this could probably be made a little less ugly if we
built support into Documentation/Makefile. But by relying
only on "make install-man" working, this script should work
for generating a diff between any two versions, whether they
include this script or not.

Signed-off-by: Jeff King <peff@peff.net>
---
 Documentation/.gitignore |   1 +
 Documentation/doc-diff   | 109 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 110 insertions(+)
 create mode 100755 Documentation/doc-diff

diff --git a/Documentation/.gitignore b/Documentation/.gitignore
index c7096f11f1..3ef54e0adb 100644
--- a/Documentation/.gitignore
+++ b/Documentation/.gitignore
@@ -12,3 +12,4 @@ cmds-*.txt
 mergetools-*.txt
 manpage-base-url.xsl
 SubmittingPatches.txt
+tmp-doc-diff/
diff --git a/Documentation/doc-diff b/Documentation/doc-diff
new file mode 100755
index 0000000000..5d5b243384
--- /dev/null
+++ b/Documentation/doc-diff
@@ -0,0 +1,109 @@
+#!/bin/sh
+
+OPTIONS_SPEC="\
+doc-diff [options] <from> <to> [-- <diff-options>]
+--
+j	parallel argument to pass to make
+f	force rebuild; do not rely on cached results
+"
+SUBDIRECTORY_OK=1
+. "$(git --exec-path)/git-sh-setup"
+
+parallel=
+force=
+while test $# -gt 0
+do
+	case "$1" in
+	-j)
+		parallel=${1#-j} ;;
+	-f)
+		force=t ;;
+	--)
+		shift; break ;;
+	*)
+		usage ;;
+	esac
+	shift
+done
+
+if test -z "$parallel"
+then
+	parallel=$(getconf _NPROCESSORS_ONLN 2>/dev/null)
+	if test $? != 0 || test -z "$parallel"
+	then
+		parallel=1
+	fi
+fi
+
+test $# -gt 1 || usage
+from=$1; shift
+to=$1; shift
+
+from_oid=$(git rev-parse --verify "$from") || exit 1
+to_oid=$(git rev-parse --verify "$to") || exit 1
+
+cd_to_toplevel
+tmp=Documentation/tmp-doc-diff
+
+if test -n "$force"
+then
+	rm -rf "$tmp"
+fi
+
+# We'll do both builds in a single worktree, which lets "make" reuse
+# results that don't differ between the two trees.
+if ! test -d "$tmp/worktree"
+then
+	git worktree add --detach "$tmp/worktree" "$from" &&
+	dots=$(echo "$tmp/worktree" | sed 's#[^/]*#..#g') &&
+	ln -s "$dots/config.mak" "$tmp/worktree/config.mak"
+fi
+
+# generate_render_makefile <srcdir> <dstdir>
+generate_render_makefile () {
+	find "$1" -type f |
+	while read src
+	do
+		dst=$2/${src#$1/}
+		printf 'all:: %s\n' "$dst"
+		printf '%s: %s\n' "$dst" "$src"
+		printf '\t@echo >&2 "  RENDER $(notdir $@)" && \\\n'
+		printf '\tmkdir -p $(dir $@) && \\\n'
+		printf '\tMANWIDTH=80 man -l $< >$@+ && \\\n'
+		printf '\tmv $@+ $@\n'
+	done
+}
+
+# render_tree <dirname> <committish>
+render_tree () {
+	# Skip install-man entirely if we already have an installed directory.
+	# We can't rely on make here, since "install-man" unconditionally
+	# copies the files (spending effort, but also updating timestamps that
+	# we then can't rely on during the render step). We use "mv" to make
+	# sure we don't get confused by a previous run that failed partway
+	# through.
+	if ! test -d "$tmp/installed/$1"
+	then
+		git -C "$tmp/worktree" checkout "$2" &&
+		make -j$parallel -C "$tmp/worktree" \
+			GIT_VERSION=omitted \
+			SOURCE_DATE_EPOCH=0 \
+			DESTDIR="$PWD/$tmp/installed/$1+" \
+			install-man &&
+		mv "$tmp/installed/$1+" "$tmp/installed/$1"
+	fi &&
+
+	# As with "installed" above, we skip the render if it's already been
+	# done.  So using make here is primarily just about running in
+	# parallel.
+	if ! test -d "$tmp/rendered/$1"
+	then
+		generate_render_makefile "$tmp/installed/$1" "$tmp/rendered/$1+" |
+		make -j$parallel -f - &&
+		mv "$tmp/rendered/$1+" "$tmp/rendered/$1"
+	fi
+}
+
+render_tree $from_oid "$from" &&
+render_tree $to_oid "$to" &&
+git -C $tmp/rendered diff --no-index "$@" $from_oid $to_oid
-- 
2.18.0.912.g3ccaa4d859