Merge ~cjwatson/launchpad:the-wheels-on-the-bus into launchpad:master

[Colin Watson]

Build a wheelhouse with relocation-safe paths

The paths to the wheels in pip's download cache (download-cache/wheels/) depend on the hashes of the paths to the sdists from which they're built. As a result, a build on one machine that's pushed out to a different file system path on another machine won't use the cached wheels and will build them all again from scratch, which is very slow.

Instead, extend "make build_wheels" to use "pip wheel" to build a wheelhouse of all our dependencies that forms part of the deployment artifact and survives this kind of relocation. This allows us to have more reasonable deployment times again without having to commit lots of wheels to lp-source-dependencies that might be architecture- or series-dependent.

[William Grant (wgrant)]

review: Approve (code)

diff --git a/.gitignore b/.gitignore
index 25bc29d..b61b548 100644
--- a/.gitignore
+++ b/.gitignore
@@ -73,3 +73,4 @@ callgrind.out.*
 !logs/README.txt
 /logs
 yarn/node_modules
+/wheelhouse
diff --git a/Makefile b/Makefile
index b416d3d..14a6f31 100644
--- a/Makefile
+++ b/Makefile
@@ -20,7 +20,7 @@ PIP_ENV += PIP_NO_INDEX=$(PIP_NO_INDEX)
 # system-installed Python packages.  If we ever manage to remove the need
 # for virtualenv --system-site-packages, then we can remove this too.
 PIP_ENV += PIP_IGNORE_INSTALLED=1
-PIP_ENV += PIP_FIND_LINKS=file://$(WD)/download-cache/dist/
+PIP_ENV += PIP_FIND_LINKS="file://$(WD)/wheelhouse/ file://$(WD)/download-cache/dist/"
 
 VIRTUALENV := $(PIP_ENV) virtualenv
 PIP := PYTHONPATH= $(PIP_ENV) env/bin/pip --cache-dir=$(WD)/download-cache/
@@ -221,10 +221,20 @@ jsbuild: $(LP_JS_BUILD) $(YUI_SYMLINK)
 
 # This target is used by LOSAs to prepare a build to be pushed out to
 # destination machines.  We only want wheels: they are the expensive bits,
-# and the other bits might run into problems like bug 575037.  This
-# target runs pip, and then removes everything created except for the
-# wheels.
-build_wheels: $(PIP_BIN) clean_pip
+# and the other bits might run into problems like bug 575037.  This target
+# runs pip, builds a wheelhouse with predictable paths that can be used even
+# if the build is pushed to a different path on the destination machines,
+# and then removes everything created except for the wheels.
+#
+# It doesn't seem to be straightforward to build a wheelhouse of all our
+# dependencies without also building a useless wheel of Launchpad itself;
+# fortunately that doesn't take too long, and we just remove it afterwards.
+build_wheels: $(PIP_BIN)
+	$(RM) -r wheelhouse
+	$(SHHH) $(PIP) wheel \
+		-c setup-requirements.txt -c constraints.txt -w wheelhouse .
+	$(RM) wheelhouse/lp-[0-9]*.whl
+	$(MAKE) clean_pip
 
 # Compatibility.
 build_eggs: build_wheels
@@ -242,6 +252,7 @@ $(PY): download-cache constraints.txt setup.py
 	$(VIRTUALENV) \
 		--python=$(PYTHON) --system-site-packages --never-download \
 		--extra-search-dir=$(WD)/download-cache/dist/ \
+		--extra-search-dir=$(WD)/wheelhouse/ \
 		env
 	ln -sfn env/bin bin
 	$(SHHH) $(PIP) install -r setup-requirements.txt
@@ -388,7 +399,7 @@ lxc-clean: clean_js clean_pip clean_logs
 	if test -f sourcecode/pygettextpo/Makefile; then \
 		$(MAKE) -C sourcecode/pygettextpo clean; \
 	fi
-	$(RM) -r env
+	$(RM) -r env wheelhouse
 	$(RM) -r $(LP_BUILT_JS_ROOT)/*
 	$(RM) -r $(CODEHOSTING_ROOT)/*
 	$(RM) -r $(APIDOC_DIR)