[Automake-NG] [FYI] [ng] header vars: remove function $(am__mkdir)

[Stefano Lattarini]

That function expanded unconditionally to:

    test -d $1 || $(MKDIR_P) $1

This formulation was supposed to help avoiding extra forks (due to the
leading "test -d" check), but it didn't actually do so.  In fact, in the
situations '$(am__mkdir)' was most used (typically indirectly, through
other private variables like '$(am__ensure_target_dir_exists)') the
Makefile had already determined by other means (e.g., tricky uses of the
'$(wildcard)' built-in) that the relevant directory didn't exist and
thus *had* to be created, so the fork of $(MKDIR_P) has to happen anyway.

In fact, the use of '$(am__mkdir)' often ended up causing *more forks*,
because it eventually expanded to recipes like:

    target: recipe
            test -d non-existent || $(MKDIR_P) non-existent
            ... rest of the recipe ...

forcing make to spawn a shell to execute the first line of the recipe --
which, containing the shell metacharacters "||", couldn't be spawned
directly -- shell which in turn had to spawn $(MKDIR_P).
Whereas with a simpler

    target: recipe
            $(MKDIR_P) non-existent
            ... rest of the recipe ...

make would span $(MKDIR_P) directly itself, thus saving a shell execution
-- and speeding up the recipe.

* lib/am/header-vars.am (am__mkdir): Delete.
(am__ensure_dir_exists): Simply use $(MKDIR) directly.

Signed-off-by: Stefano Lattarini <address@hidden>
---
 lib/am/header-vars.mk | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/lib/am/header-vars.mk b/lib/am/header-vars.mk
index e86f5b3..0e0dab8 100644
--- a/lib/am/header-vars.mk
+++ b/lib/am/header-vars.mk
@@ -119,8 +119,6 @@ unexport CDPATH
 # FIXME: maybe normalize/sanitize $(V)?
 V ?= 0
 
-am__mkdir = test -d $1 || $(MKDIR_P) $1
-
 # In a recipe, ensure the given directory exists, creating it if
 # necessary; but tries to do so avoiding useless forks, stats, and
 # extra recipe text (the latter is useful when doing "make V=1").
@@ -130,7 +128,7 @@ am__mkdir = test -d $1 || $(MKDIR_P) $1
 # usage patterns, one of them should always be true in non-VPATH
 # builds.
 am__ensure_dir_exists = \
-  $(if $(filter .,$1),:,$(if $(wildcard $1/),:,$(call am__mkdir,$1)))
+  $(if $(filter .,$1),:,$(if $(wildcard $1/),:,$(MKDIR_P) $1))
 
 # Ensure the directory containing the target of the current recipe
 # exists, by creating it if necessary.
-- 
1.7.12.rc0