Split --disable-tests, fix cross builds

It might seem obnoxious to have yet more configure flags, but I found
controlling both the unit and functional tests with one flag was quite
confusing because they are so different:

- unit tests depending on building, functional tests don't (e.g. when
  we test already-built Nix)

- unit tests can be installed, functional tests cannot

- unit tests neeed extra libraries (GTest, RapidCheck), functional
  tests need extra executables (jq).

- unit tests are run by `make check`, functional tests are run by `make
  installcheck`

Really on a technical level, they seem wholly independent. Only on a
human level ("they are both are tests") do they have anything in common.

I had messed up the logic in cross builds because of this. Now I
split the flag in two (and cleaned up a few other inconsistencies), and
the logic fixed itself.

Co-Authored-By: Robert Hensing <roberth@users.noreply.github.com>

doc/internal-api/local.mk

@@ -1,19 +1,7 @@
-.PHONY: internal-api-html
-
-ifeq ($(internal_api_docs), yes)
-
 $(docdir)/internal-api/html/index.html $(docdir)/internal-api/latex: $(d)/doxygen.cfg
 	mkdir -p $(docdir)/internal-api
 	{ cat $< ; echo "OUTPUT_DIRECTORY=$(docdir)/internal-api" ; } | doxygen -
 
 # Generate the HTML API docs for Nix's unstable internal interfaces.
+.PHONY: internal-api-html
 internal-api-html: $(docdir)/internal-api/html/index.html
-
-else
-
-# Make a nicer error message
-internal-api-html:
-	@echo "Internal API docs are disabled. Configure with '--enable-internal-api-docs', or avoid calling 'make internal-api-html'."
-	@exit 1
-
-endif

doc/manual/local.mk

@@ -1,5 +1,3 @@
-ifeq ($(doc_generate),yes)
-
 # The version of Nix used to generate the doc. Can also be
 # `$(nix_INSTALL_PATH)` or just `nix` (to grap ambient from the `PATH`),
 # if one prefers.
@@ -180,6 +178,8 @@ manual-html: $(docdir)/manual/index.html
 install: $(docdir)/manual/index.html
 
 # Generate 'nix' manpages.
+.PHONY: manpages
+manpages: $(mandir)/man1/nix3-manpages
 install: $(mandir)/man1/nix3-manpages
 man: doc/manual/generated/man1/nix3-manpages
 all: doc/manual/generated/man1/nix3-manpages
@@ -225,5 +225,3 @@ $(docdir)/manual/index.html: $(MANUAL_SRCS) $(d)/book.toml $(d)/anchors.jq $(d)/
 	@rm -rf $(DESTDIR)$(docdir)/manual
 	@mv $(DESTDIR)$(docdir)/manual.tmp/html $(DESTDIR)$(docdir)/manual
 	@rm -rf $(DESTDIR)$(docdir)/manual.tmp
-
-endif

doc/manual/src/contributing/hacking.md

@@ -67,9 +67,10 @@ You can also build Nix for one of the [supported platforms](#platforms).
 ## Makefile variables
 
 - `ENABLE_BUILD=yes` to enable building the C++ code.
-- `ENABLE_TESTS=yes` to enable building the tests.
+- `ENABLE_DOC_GEN=yes` to enable building the documentation (manual, man pages, etc.).
+- `ENABLE_FUNCTIONAL_TESTS=yes` to enable building the functional tests.
+- `ENABLE_UNIT_TESTS=yes` to enable building the unit tests.
 - `OPTIMIZE=1` to enable optimizations.
-- `doc_generate=yes` to enable building the documentation (manual, man pages, etc.).
 
   The docs can take a while to build, so you may want to disable this for local development.
 

doc/manual/src/installation/prerequisites-source.md

@@ -72,7 +72,7 @@
     This is an optional dependency and can be disabled
     by providing a `--disable-cpuid` to the `configure` script.
 
-  - Unless `./configure --disable-tests` is specified, GoogleTest (GTest) and
+  - Unless `./configure --disable-unit-tests` is specified, GoogleTest (GTest) and
     RapidCheck are required, which are available at
     <https://google.github.io/googletest/> and
     <https://github.com/emil-e/rapidcheck> respectively.