From 717e821b99797845e1bef47d862f8cb0fb69cfc9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Niklas=20Hamb=C3=BCchen?= <mail@nh2.me>
Date: Tue, 2 Jul 2019 22:30:15 +0200
Subject: [PATCH] autoconf: Allow overriding CFLAGS/CXXFLAGS from outside.

As is normal for autoconf-based projects.

For example, it is a common use case to do

    ./configure CXXFLAGS=-O0

This did not work for nix until now, because the `CXXFLAGS=` declaration
would unconditionally erase what the user had specified.

The custom `OPTIMIZE` flag is removed, but the default `-O3` is retained;
autoconf would default to `-g -O2` by default otherwise as documented on:

https://www.gnu.org/software/autoconf/manual/autoconf-2.60/html_node/C-Compiler.html
https://www.gnu.org/software/autoconf/manual/autoconf-2.60/html_node/C_002b_002b-Compiler.html
---
 Makefile          | 7 -------
 configure.ac      | 6 ++++--
 perl/Makefile     | 7 -------
 perl/configure.ac | 6 ++++--
 4 files changed, 8 insertions(+), 18 deletions(-)

diff --git a/Makefile b/Makefile
index 45a3338ed..9ac82fda6 100644
--- a/Makefile
+++ b/Makefile
@@ -19,11 +19,4 @@ GLOBAL_CXXFLAGS += -g -Wall -include config.h
 
 -include Makefile.config
 
-OPTIMIZE = 1
-
-ifeq ($(OPTIMIZE), 1)
-  GLOBAL_CFLAGS += -O3
-  GLOBAL_CXXFLAGS += -O3
-endif
-
 include mk/lib.mk
diff --git a/configure.ac b/configure.ac
index 3a486fab8..571bb54d8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -50,8 +50,10 @@ AC_DEFINE_UNQUOTED(SYSTEM, ["$system"], [platform identifier ('cpu-os')])
 test "$localstatedir" = '${prefix}/var' && localstatedir=/nix/var
 
 
-CFLAGS=
-CXXFLAGS=
+# Set default flags for nix (as per AC_PROG_CC/CXX docs),
+# while still allowing the user to override them from the command line.
+: ${CFLAGS="-O3"}
+: ${CXXFLAGS="-O3"}
 AC_PROG_CC
 AC_PROG_CXX
 AC_PROG_CPP
diff --git a/perl/Makefile b/perl/Makefile
index 284c75022..f36f5d0e9 100644
--- a/perl/Makefile
+++ b/perl/Makefile
@@ -4,11 +4,4 @@ GLOBAL_CXXFLAGS += -g -Wall
 
 -include Makefile.config
 
-OPTIMIZE = 1
-
-ifeq ($(OPTIMIZE), 1)
-  GLOBAL_CFLAGS += -O3
-  GLOBAL_CXXFLAGS += -O3
-endif
-
 include mk/lib.mk
diff --git a/perl/configure.ac b/perl/configure.ac
index 966700695..e8e3610a8 100644
--- a/perl/configure.ac
+++ b/perl/configure.ac
@@ -2,8 +2,10 @@ AC_INIT(nix-perl, m4_esyscmd([bash -c "echo -n $(cat ../.version)$VERSION_SUFFIX
 AC_CONFIG_SRCDIR(MANIFEST)
 AC_CONFIG_AUX_DIR(../config)
 
-CFLAGS=
-CXXFLAGS=
+# Set default flags for nix (as per AC_PROG_CC/CXX docs),
+# while still allowing the user to override them from the command line.
+: ${CFLAGS="-O3"}
+: ${CXXFLAGS="-O3"}
 AC_PROG_CC
 AC_PROG_CXX
 AX_CXX_COMPILE_STDCXX_11