Generate MIN_VERSION_* macros with cabal

This uses `cabal configure` to determine which exact dependency versions
we are compiling against.

MIN_VERSION_* macros are the standard way to build CPP dependency switches
in Haskell packages, and they replace our custom macros (like PARALLEL3).
We can now conditionally compile against any version of our dependencies,
without first having to manually add a flag via autoconf.

All ghc and hlint invocations were adjusted to take these macros into
account.

We now require hlint >= 1.8.60, which support the --cpp-file option,
and any installed version of cabal.

In addition to providing MIN_VERSION_* macros, the `cabal configure`
step makes the build fail at configuration time if the user tries to
compile against a dependency version we don't support; before, this
case led to type errors which were not clearly user errors.

In order to obtain the sought cabal_macros.h, we have to work around
the fact that cabal does not yet provide a way to build only the macros
(see haskell/cabal#2209).
Ideally, they would be created as part of `cabal configure`, but
unfortunately they are created as the first step of `cabal build`.
Thus we `cabal build` a dummy executable (HaskellPackageVersionsDummy)
in a temporary directory to obtain cabal_macros.h.

Author: nh2

HaskellPackageVersionsDummy.hs

@@ -0,0 +1,4 @@
+module Main where
+
+main :: IO ()
+main = return ()

Makefile.am

@@ -295,6 +295,7 @@ CLEANFILES = \
 	$(addsuffix /*.o,$(HS_DIRS)) \
 	$(addsuffix /*.$(HTEST_SUFFIX)_hi,$(HS_DIRS)) \
 	$(addsuffix /*.$(HTEST_SUFFIX)_o,$(HS_DIRS)) \
+	$(HASKELL_PACKAGE_VERSIONS_FILE) \
 	$(CABAL_EXECUTABLES_APPS_STAMPS) \
 	ganeti.cabal \
 	Makefile.ghc \
@@ -1269,10 +1270,11 @@ HS_MAKEFILE_GHC_SRCS = $(HS_SRC_PROGS:%=%.hs)
 if WANT_HSTESTS
 HS_MAKEFILE_GHC_SRCS += $(HS_TEST_PROGS:%=%.hs)
 endif
-Makefile.ghc: $(HS_MAKEFILE_GHC_SRCS) Makefile \
+Makefile.ghc: $(HS_MAKEFILE_GHC_SRCS) Makefile $(HASKELL_PACKAGE_VERSIONS_FILE) \
               | $(built_base_sources) $(HS_BUILT_SRCS)
 	$(GHC) -M -dep-makefile $@ $(DEP_SUFFIXES) $(HFLAGS) $(HFLAGS_DYNAMIC) \
 		-itest/hs \
+		-optP-include -optP$(HASKELL_PACKAGE_VERSIONS_FILE) \
 		$(HS_PARALLEL3) $(HS_REGEX_PCRE) $(HEXTRA_COMBINED) $(HS_MAKEFILE_GHC_SRCS)
 # Since ghc -M does not generate dependency line for object files, dependencies
 # from a target executable seed object (e.g. src/hluxid.o) to objects which
@@ -1288,6 +1290,27 @@ Makefile.ghc: $(HS_MAKEFILE_GHC_SRCS) Makefile \
 
 @include_makefile_ghc@
 
+# Defines the MIN_VERSION_* macros for all Haskell packages used in this
+# compilation.
+# The versions are determined using cabal, which takes them from the
+# ghc-pkg database.
+# At the moment, we don't support cabal sandboxes, so we use cabal configure
+# with the --user flag.
+HASKELL_PACKAGE_VERSIONS_FILE = cabal_macros.h
+
+# Obtains MIN_VERSION_* macros from a dummy build in a temporary directory
+# since cabal cannot currently build the macros without building the project.
+# This can be removed when https://github.com/haskell/cabal/issues/2209 is
+# implemented.
+$(HASKELL_PACKAGE_VERSIONS_FILE): Makefile ganeti.cabal
+	TMP=`mktemp -d --tmpdir=.` && \
+	mkdir -p $$TMP/ && \
+	cp $(abs_top_srcdir)/ganeti.cabal.in $$TMP/tmp.cabal && \
+	cp $(abs_top_srcdir)/HaskellPackageVersionsDummy.hs $$TMP/ && \
+	(cd $$TMP && cabal configure --user && cabal build) && \
+	cp $$TMP/dist/build/autogen/cabal_macros.h $(HASKELL_PACKAGE_VERSIONS_FILE) && \
+	rm -r $$TMP/
+
 # Like the %.o rule, but allows access to the test/hs directory.
 # This uses HFLAGS instead of HTEST_FLAGS because it's only for generating
 # object files (.o for GHC <= 7.6, .o/.so for newer GHCs) that are loaded
@@ -1296,11 +1319,13 @@ Makefile.ghc: $(HS_MAKEFILE_GHC_SRCS) Makefile \
 test/hs/%.o:
 	@echo '[GHC|test]: $@ <- test/hs/$^'
 	@$(GHC) -c $(HFLAGS) -itest/hs $(HFLAGS_DYNAMIC) \
+		-optP-include -optP$(HASKELL_PACKAGE_VERSIONS_FILE) \
 		$(HS_PARALLEL3) $(HS_REGEX_PCRE) $(HEXTRA_COMBINED) $(@:%.o=%.hs)
 
-%.o:
+%.o: $(HASKELL_PACKAGE_VERSIONS_FILE)
 	@echo '[GHC]: $@ <- $^'
 	@$(GHC) -c $(HFLAGS) $(HFLAGS_DYNAMIC) \
+		-optP-include -optP$(HASKELL_PACKAGE_VERSIONS_FILE) \
 		$(HS_PARALLEL3) $(HS_REGEX_PCRE) $(HEXTRA_COMBINED) $(@:%.o=%.hs)
 
 # For TH+profiling we need to compile twice: Once without profiling,
@@ -1311,6 +1336,7 @@ if HPROFILE
 	@echo '[GHC|prof]: $@ <- $^'
 	@$(GHC) -c $(HFLAGS) \
 	  $(HPROFFLAGS) \
+	  -optP-include -optP$(HASKELL_PACKAGE_VERSIONS_FILE) \
 		$(HS_PARALLEL3) $(HS_REGEX_PCRE) $(HEXTRA_COMBINED) \
 		$(@:%.$(HPROF_SUFFIX)_o=%.hs)
 endif
@@ -1322,6 +1348,7 @@ endif
 %.$(HTEST_SUFFIX)_o: %.o
 	@echo '[GHC|test]: $@ <- $^'
 	@$(GHC) -c $(HTEST_FLAGS) \
+		-optP-include -optP$(HASKELL_PACKAGE_VERSIONS_FILE) \
 		$(HS_PARALLEL3) $(HS_REGEX_PCRE) $(HEXTRA_COMBINED) $(@:%.$(HTEST_SUFFIX)_o=%.hs)
 
 %.hi: %.o ;
@@ -1332,11 +1359,13 @@ if HPROFILE
 $(HS_SRC_PROGS): %: %.$(HPROF_SUFFIX)_o | stamp-directories
 	@echo '[GHC-link]: $@'
 	$(GHC) $(HFLAGS) $(HPROFFLAGS) \
+		-optP-include -optP$(HASKELL_PACKAGE_VERSIONS_FILE) \
 		$(HS_PARALLEL3) $(HS_REGEX_PCRE) $(HEXTRA_COMBINED) --make $(@:%=%.hs)
 else
 $(HS_SRC_PROGS): %: %.o | stamp-directories
 	@echo '[GHC-link]: $@'
 	$(GHC) $(HFLAGS) $(HFLAGS_DYNAMIC) \
+		-optP-include -optP$(HASKELL_PACKAGE_VERSIONS_FILE) \
 		$(HS_PARALLEL3) $(HS_REGEX_PCRE) $(HEXTRA_COMBINED) --make $(@:%=%.hs)
 endif
 	@rm -f $(notdir $@).tix
@@ -1351,6 +1380,7 @@ $(HS_TEST_PROGS): %: %.$(HTEST_SUFFIX)_o \
 	fi
 	@echo '[GHC-link|test]: $@'
 	$(GHC) $(HTEST_FLAGS) \
+		-optP-include -optP$(HASKELL_PACKAGE_VERSIONS_FILE) \
 		$(HS_PARALLEL3) $(HS_REGEX_PCRE) $(HEXTRA_COMBINED) --make $(@:%=%.hs)
 	@rm -f $(notdir $@).tix
 	@touch "$@"
@@ -1516,6 +1546,7 @@ EXTRA_DIST += \
 	doc/users/users.in \
 	ganeti.cabal \
 	ganeti.cabal.in \
+	HaskellPackageVersionsDummy.hs \
 	$(dist_TESTS) \
 	$(TEST_FILES) \
 	$(python_test_support) \
@@ -2600,6 +2631,7 @@ hlint: $(HS_BUILT_SRCS) src/lint-hints.hs
 	  --ignore "Use void" \
 	  --ignore "Reduce duplication" \
 	  --hint src/lint-hints \
+	  --cpp-file=$(HASKELL_PACKAGE_VERSIONS_FILE) \
 	  $(filter-out $(HLINT_EXCLUDES),$(HS_LIBTEST_SRCS) $(HS_PROG_SRCS))
 	@if [ ! -f doc/hs-lint.html ]; then \
 	  echo "All good" > doc/hs-lint.html; \
@@ -2735,6 +2767,7 @@ $(APIDOC_HS_DIR)/index.html: $(HS_LIBTESTBUILT_SRCS) Makefile
 	set -e ; \
 	export LC_ALL=en_US.UTF-8; \
 	OPTGHC="--optghc=-isrc --optghc=-itest/hs"; \
+	OPTGHC="$$OPTGHC --optghc=-optP-include --optghc=-optP$(HASKELL_PACKAGE_VERSIONS_FILE)"; \
 	if [ "$(HS_PARALLEL3)" ]; \
 	then OPTGHC="$$OPTGHC --optghc=$(HS_PARALLEL3)"; \
 	fi; \

configure.ac

@@ -659,6 +659,13 @@ if test -z "$GHC_PKG"; then
   AC_MSG_FAILURE([ghc-pkg not found, compilation will not be possible])
 fi
 
+# Check for cabal
+AC_ARG_VAR(CABAL, [cabal path])
+AC_PATH_PROG(CABAL, [cabal], [])
+if test -z "$CABAL"; then
+  AC_MSG_FAILURE([cabal not found, compilation will not be possible])
+fi
+
 # check for modules, first custom/special checks
 AC_MSG_NOTICE([checking for required haskell modules])
 HS_PARALLEL3=

ganeti.cabal.in

@@ -81,3 +81,11 @@ library
     Haskell2010
   ghc-options:
     -Wall
+
+-- Only there so that we can call `cabal build HaskellPackageVersionsDummy`
+-- to generate cabal_macros.h. Cabal does not yet provide a feature that
+-- builds just cabal_macros.h.
+executable HaskellPackageVersionsDummy
+  main-is: HaskellPackageVersionsDummy.hs
+  default-language: Haskell2010
+  build-depends: base