depends: Fix id_string invocations

We now use a script named gen_id to generate the base build_id/host_id.
This solves 2 problems:

1. GNU Make special-casing exit code 127 (command not found) meant that
   warnings about missing tools would propagate to the user's terminal
   and broke our opportunistic build_id construction.
2. This change ensures that we don't have arbitrary characters in our
   make variables that would be misinterpreted by Make.

See comments in depends/Makefile and depends/gen_id for more
information.

1 files changed, 24 insertions, 30 deletions

diff --git a/depends/Makefile b/depends/Makefile
index dadb21515a..c3d66cf8ec 100644
--- a/depends/Makefile
+++ b/depends/Makefile
@@ -112,37 +112,31 @@ include builders/$(build_os).mk
 include builders/default.mk
 include packages/packages.mk
 
-full_env=$(shell printenv)
-
-build_id_string:=$(BUILD_ID_SALT)
-
-# GCC only prints COLLECT_LTO_WRAPPER when invoked with just "-v", but we want
-# the information from "-v -E -" as well, so just include both.
+# Previously, we directly invoked the well-known programs using $(shell ...)
+# to contruct build_id_string. However, that was problematic because:
 #
-# '3>&1 1>&2 2>&3 > /dev/null' is supposed to swap stdin and stdout and silence
-# stdin, since we only want the stderr output
-build_id_string+=$(shell $(build_CC) -v < /dev/null 3>&1 1>&2 2>&3 > /dev/null) $(shell $(build_CC) -v -E - < /dev/null 3>&1 1>&2 2>&3 > /dev/null)
-build_id_string+=$(shell $(build_AR) --version 2>/dev/null) $(filter AR_%,$(full_env)) ZERO_AR_DATE=$(ZERO_AR_DATE)
-build_id_string+=$(shell $(build_CXX) -v < /dev/null 3>&1 1>&2 2>&3 > /dev/null) $(shell $(build_CXX) -v -E - < /dev/null 3>&1 1>&2 2>&3 > /dev/null)
-build_id_string+=$(shell $(build_RANLIB) --version 2>/dev/null) $(filter RANLIB_%,$(full_env))
-build_id_string+=$(shell $(build_STRIP) --version 2>/dev/null) $(filter STRIP_%,$(full_env))
-
-$(host_arch)_$(host_os)_id_string:=$(HOST_ID_SALT)
-$(host_arch)_$(host_os)_id_string+=$(shell $(host_CC) -v < /dev/null 3>&1 1>&2 2>&3 > /dev/null) $(shell $(host_CC) -v -E - < /dev/null 3>&1 1>&2 2>&3 > /dev/null)
-$(host_arch)_$(host_os)_id_string+=$(shell $(host_AR) --version 2>/dev/null) $(filter AR_%,$(full_env)) ZERO_AR_DATE=$(ZERO_AR_DATE)
-$(host_arch)_$(host_os)_id_string+=$(shell $(host_CXX) -v < /dev/null 3>&1 1>&2 2>&3 > /dev/null) $(shell $(host_CXX) -v -E - < /dev/null 3>&1 1>&2 2>&3 > /dev/null)
-$(host_arch)_$(host_os)_id_string+=$(shell $(host_RANLIB) --version 2>/dev/null) $(filter RANLIB_%,$(full_env))
-$(host_arch)_$(host_os)_id_string+=$(shell $(host_STRIP) --version 2>/dev/null) $(filter STRIP_%,$(full_env))
-
-ifneq ($(strip $(FORCE_USE_SYSTEM_CLANG)),)
-# Make sure that cache is invalidated when switching between system and
-# depends-managed, pinned clang
-build_id_string+=system_clang
-$(host_arch)_$(host_os)_id_string+=system_clang
-endif
-
-build_id_string+=GUIX_ENVIRONMENT=$(realpath $(GUIX_ENVIRONMENT))
-$(host_arch)_$(host_os)_id_string+=GUIX_ENVIRONMENT=$(realpath $(GUIX_ENVIRONMENT))
+# 1. When invoking a shell, GNU Make special-cases exit code 127 (command not
+#    found) by not capturing the output but instead passing it through. This is
+#    not done for any other exit code.
+#
+# 2. Characters like '#' (from these programs' output) would end up in make
+#    variables like build_id_string, which would be wrongly interpreted by make
+#    when these variables were used.
+#
+# Therefore, we should avoid having arbitrary strings in make variables where
+# possible. The gen_id script used here hashes the output to construct a
+# "make-safe" id.
+#
+# Also note that these lines need to be:
+#
+#     1. After including {hosts,builders}/*.mk, since they rely on the tool
+#        variables (e.g. build_CC, host_STRIP, etc.) to be set.
+#
+#     2. Before including packages/*.mk (excluding packages/packages.mk), since
+#        they rely on the build_id variables
+#
+build_id:=$(shell env CC='$(build_CC)' CXX='$(build_CXX)' AR='$(build_AR)' RANLIB='$(build_RANLIB)' STRIP='$(build_STRIP)' SHA256SUM='$(build_SHA256SUM)' DEBUG='$(DEBUG)' ./gen_id '$(BUILD_ID_SALT)' 'GUIX_ENVIRONMENT=$(realpath $(GUIX_ENVIRONMENT))')
+$(host_arch)_$(host_os)_id:=$(shell env CC='$(host_CC)' CXX='$(host_CXX)' AR='$(host_AR)' RANLIB='$(host_RANLIB)' STRIP='$(host_STRIP)' SHA256SUM='$(build_SHA256SUM)' DEBUG='$(DEBUG)' ./gen_id '$(HOST_ID_SALT)' 'GUIX_ENVIRONMENT=$(realpath $(GUIX_ENVIRONMENT))')
 
 qrencode_packages_$(NO_QR) = $(qrencode_packages)