[PATCH] doc-diff: use single-colon rule in rendering Makefile

[PATCH] doc-diff: use single-colon rule in rendering Makefile

[Jeff King]

When rendering the troff manpages to text via "man", we create an ad-hoc
Makefile and feed it to "make". The purpose here is two-fold:

  - reuse results from a prior interrupted render of the same tree

  - use make's -j option to build in parallel

But the second part doesn't seem to work (at least with my version of
GNU make, 4.2.1). It just runs one render at a time.

We use a double-colon "all" rule for each file, like:

  all:: foo
  foo:
    ...actual render recipe...
  all:: bar
  bar:
    ...actual render recipe...
  ...and so on...

And it's this double-colon that seems to inhibit the parallelism. We can
just switch to a regular single-colon rule. Even though we do have
multiple rules for "all" here, we don't have any recipe to execute for
"all" (we only care about triggering its dependencies), so the
distinction is irrelevant.

Signed-off-by: Jeff King <peff@peff.net>
---
This has been bugging me for a while. I'm not sure if it never worked
and I didn't notice, or if it changed in some version of make.

 Documentation/doc-diff | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/doc-diff b/Documentation/doc-diff
index 88a9b20168..1694300e50 100755
--- a/Documentation/doc-diff
+++ b/Documentation/doc-diff
@@ -127,7 +127,7 @@ generate_render_makefile () {
 	while read src
 	do
 		dst=$2/${src#$1/}
-		printf 'all:: %s\n' "$dst"
+		printf 'all: %s\n' "$dst"
 		printf '%s: %s\n' "$dst" "$src"
 		printf '\t@echo >&2 "  RENDER $(notdir $@)" && \\\n'
 		printf '\tmkdir -p $(dir $@) && \\\n'
-- 
2.25.1.795.g3fd338b409