[Automake-NG] [PATCH 3/3] [ng] memoize: correctly work around a bug of GNU make < 3.83

[Stefano Lattarini]

This is a follow-up to commit v1.12-218-g34a7d42 of 2012-05-15,
"[ng] memoize: expose a serious bug (affecting GNU make < 3.83)".

We implement a new workaround aimed at avoiding the subtle GNU make
bug affecting variable memoization:

  <http://lists.gnu.org/archive/html/bug-make/2012-05/msg00013.html>
  <https://savannah.gnu.org/patch/?7534>

Since that bug basically prevents dynamically reassigning to a variable
inside the expansion of the variable itself, we reimplement memoization
by having the memoized variable expanding to an $(if) branching either
to evaluate-and-store in *another* memo variable, else to the value of
that memo variable.

The new workaround works also in the situation that was causing our
previous workaround (as implemented in commit v1.12-217-gd55204f of
2012-05-12, "[ng] vars: implement memoization of make variables (new
'am__memoize' func)") to fail.

Approach suggested by Akim Demaille:
<http://lists.gnu.org/archive/html/automake-ng/2012-05/msg00074.html>
and coded by Stefano Lattarini.

* lib/am/header-vars (am__memoize): Change API and implementation.
(am__memoize_0): Delete, it's not needed anymore.
* t/memoize.tap: Update to new API, also removing checks that makes no
more sense with it.
* t/spy-override.sh: Delete, it's not needed anymore.

Co-authored-by: Akim Demaille <address@hidden>
Signed-off-by: Stefano Lattarini <address@hidden>
---
 lib/am/header-vars.am |   14 +++++----
 t/memoize.tap         |   81 +++++++++++++++++--------------------------------
 t/spy-override.sh     |   51 -------------------------------
 3 files changed, 36 insertions(+), 110 deletions(-)
 delete mode 100755 t/spy-override.sh

diff --git a/lib/am/header-vars.am b/lib/am/header-vars.am
index 95345e4..30a20dc 100644
--- a/lib/am/header-vars.am
+++ b/lib/am/header-vars.am
@@ -83,19 +83,21 @@ am__uniq = $(strip \
 ## we can't afford to re-calculate it over and over every time the
 ## variable gets expanded.  Example of usage:
 ##
-##   memo/var1 = $(shell EXPENSIVE-COMMAND-LINE)
-##   memo/var2 = $(sort VERY-LONG-LIST)
-##   $(call am__memoize, var1 var2)
+##   var1 = $(am__memoize,var1,$(shell EXPENSIVE-COMMAND-LINE))
+##   var2 = $(am__memoize,var2,$(sort VERY-LONG-LIST))
 ##
 ## This API and implementation seems to work around a bug in GNU make
 ## (present up to and including version 3.82) which caused our first
 ## implementation attempts to fail:
+##
 ##   <http://lists.gnu.org/archive/html/bug-make/2012-05/msg00013.html>
 ##   <https://savannah.gnu.org/patch/?7534>
+##
 ## So please don't change this without a very good reason.
-am__memoize_0 = $(eval $1 = $$(eval override $1 := $$$$($2))$$($1))
-am__memoize = $(foreach am__memo_var, $1, \
-                $(call $(0)_0,$(am__memo_var),memo/$(am__memo_var)))
+##
+am__memoize = \
+  $(if $(am__memoized_value/$1),$(am__memoized_value/$1),$(strip \
+    $(eval am__memoized_value/$1 := $$2))$(am__memoized_value/$1))
 
 ## Some derived variables that have been found to be useful.
 pkgdatadir = $(datadir)/@PACKAGE@
diff --git a/t/memoize.tap b/t/memoize.tap
index f379e34..ca7fede 100755
--- a/t/memoize.tap
+++ b/t/memoize.tap
@@ -19,7 +19,7 @@
 am_create_testdir=empty
 . ./defs || Exit 1
 
-plan_ 14
+plan_ 13
 
 ocwd=`pwd` || fatal_ "couldn't get current working directory"
 
@@ -52,8 +52,7 @@ tcount=0
 
 T "basic usage" <<'END'
 
-memo/foo = ok
-$(call am__memoize,foo)
+foo = $(call am__memoize,foo,ok)
 
 test:
        test '$(foo)' = ok
@@ -62,28 +61,25 @@ END
 
 #---------------------------------------------------------------------------
 
-T "call with extra spaces" <<'END'
+T "variables expanding to blanks only (1)" <<'END'
 
-memo/foo = ok
-## There are extra spaces and tabs here; do not normalize them!
-$(call am__memoize,    foo             )
+foo = $(call am__memoize,foo,$(am__empty) )
 
 test:
-       test '$(foo)' = ok
-       test '$(foo)' = ok
+       test '$(foo)' = ' '
+       test '$(foo)' = ' '
 END
 
 #---------------------------------------------------------------------------
 
-T "memoize several variables at once" <<'END'
+T "variables expanding to blanks only (2)" <<END
 
-memo/foo1 = bar
-memo/foo2 = baz
-$(call am__memoize, foo1 foo2)
+blank = \$(am__empty) $tab$tab   \$(am__empty)
+foo = \$(call am__memoize,foo,\$(blank))
 
 test:
-       test '$(foo1)' = bar
-       test '$(foo2)' = baz
+       test '\$(foo)' = ' $tab$tab   '
+       test '\$(foo)' = ' $tab$tab   '
 END
 
 #---------------------------------------------------------------------------
@@ -96,8 +92,7 @@ done
 
 T "very long variable name" <<END
 
-memo/$var = foo
-\$(call am__memoize,$var)
+$var = \$(call am__memoize,$var,foo)
 
 test:
        test '\$($var)' = foo
@@ -116,8 +111,7 @@ done
 
 T "very long variable name with long content" <<END
 
-memo/$var = $val
-\$(call am__memoize,$var)
+$var = \$(call am__memoize,$var,$val)
 
 test:
        test '\$($var)' = '$val'
@@ -128,8 +122,7 @@ END
 
 T "on indirect recursive variable expansion" <<'END'
 
-memo/foo = $(indir)
-$(call am__memoize,foo)
+foo = $(call am__memoize,foo,$(indir))
 
 ## This is delibrately placed after the memoize call.
 indir = zardoz
@@ -143,8 +136,7 @@ END
 
 T "on indirect immediate variable expansion" <<'END'
 
-memo/foo = $(indir)
-$(call am__memoize,foo)
+foo = $(call am__memoize,foo,$(indir))
 
 ## This is delibrately placed after the memoize call.
 indir := blob
@@ -159,9 +151,7 @@ END
 T "on function call" <<'END'
 
 my_func = $(firstword $(sort $(1)))
-
-memo/foo = $(call my_func, 6 3 1 7)
-$(call am__memoize,foo)
+foo = $(call am__memoize,foo,$(call my_func, 6 3 1 7))
 
 test:
        test '$(foo)' = 1
@@ -170,22 +160,10 @@ END
 
 #---------------------------------------------------------------------------
 
-T "out-of-order memoization should work" <<'END'
-
-$(call am__memoize,foo)
-test:
-       test '$(foo)' = ok
-       test '$(foo)' = ok
-memo/foo = ok
-END
-
-#---------------------------------------------------------------------------
-
 T "memoization actually takes place (1)" <<'END'
 
 indir := ok
-memo/foo = $(indir)
-$(call am__memoize,foo)
+foo = $(call am__memoize,foo,$(indir))
 expand-it := $(foo)
 override indir := ko
 
@@ -198,10 +176,8 @@ END
 
 T "memoization actually takes place (2)" <<'END'
 
-memo/foo1 = $(shell test -f x && echo "+")
-memo/foo2 = $(shell test -f y || echo "-")
-$(call am__memoize,foo1)
-$(call am__memoize,foo2)
+foo1 = $(call am__memoize,foo1,$(shell test -f x && echo "+"))
+foo2 = $(call am__memoize,foo2,$(shell test -f y || echo "-"))
 
 test: one two
 two: one
@@ -229,12 +205,11 @@ END
 
 T "definition on multiple lines" <<'END'
 
-memo/foo = a \
-b \
-c \
-\
-d
-$(call am__memoize,foo)
+foo = $(call am__memoize,foo,a \
+  b \
+  c \
+  \
+  d)
 
 test:
        test '$(foo)' = 'a b c d'
@@ -253,8 +228,7 @@ T "known GNU make issue 
(https://savannah.gnu.org/patch/?7534)" <<'END'
 setup := $(shell mkdir -p t/pm && : > t/pm/Cond2.pl)
 
 TESTS = $(wildcard t/pm/Cond2.pl)
-memo/am__test_bases = $(TESTS)
-$(call am__memoize,am__test_bases)
+am__test_bases = $(call am__memoize,am__test_bases,$(TESTS))
 
 test:
        test '$(am__test_bases)' = 't/pm/Cond2.pl'
@@ -276,10 +250,11 @@ for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 
20; do
   mv -f t1 t
 done
 
-(echo 'memo/list = \' && cat t && echo "  $line") > big.mk
+echo "list = \$(call am__memoize,list,$line \\" >> big.mk
+cat t >> big.mk
+echo "  $line)" >> big.mk
 
 cat >> big.mk << 'END'
-$(call am__memoize,list)
 test:
        test x'$(word  1, $(list))' = x'dummy'
        test x'$(word  3, $(list))' = x'='
diff --git a/t/spy-override.sh b/t/spy-override.sh
deleted file mode 100755
index de552e4..0000000
--- a/t/spy-override.sh
+++ /dev/null
@@ -1,51 +0,0 @@
-#! /bin/sh
-# Copyright (C) 2012 Free Software Foundation, Inc.
-#
-# This program is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation; either version 2, or (at your option)
-# any later version.
-#
-# This program is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
-
-# Verify that use of 'override' directive to re-set a variable does
-# not cause any warning or extra output.
-
-am_create_testdir=empty
-. ./defs || Exit 1
-
-cat > Makefile <<'END'
-foo = 1
-override foo = 2
-
-bar = 3
-override bar := 4
-
-override baz = 6
-override zap := 8
-
-override zardoz += doz
-
-nihil:
-       @:
-sanity-check:
-       test '$(foo)' = 2
-       test '$(bar)' = 4
-       test '$(baz)' = 6
-       test '$(zap)' = 8
-       test '$(zardoz)' = 'zar doz'
-.PHONY: nihil sanity-check
-END
-
-$MAKE sanity-check baz=5 zap=7 zardoz=zar
-$MAKE --no-print-directory nihil >output 2>&1 \
-  && test ! -s output \
-  || { cat output; Exit 1; }
-
-:
-- 
1.7.9.5