Add support for single spec repos

There are cases where we want to use the docker image that is created here in
other repositories to compile a spec. They do not follow the structure implied
here and rather contain a single bikeshed file.

This commit adds support for this in the Makefile and the spec source and its
name can be set using SRC and NAME variables.

The output folder will be a flat dist/ folder.

Note that for now we still assume that images are located in the Images folder
and this is not configurable at the moment.

build-tools/tools/Makefile

@@ -4,7 +4,7 @@
 
 # We collect all the spec names from the folders in the
 # specs directory
-SPECS = $(patsubst %.bs, %, $(shell ls specs))
+SPECS = $(patsubst %.bs, %, $(shell if [ -d "specs" ]; then ls specs; fi))
 
 # This is our target folder
 OUT = dist
@@ -79,13 +79,13 @@ $(OUT)/%-watch: $${spec-file} $${spec-sources} $(OUT)/%/Images
 
 # Run chromium to create a PDF from the already generated html page
 $(OUT)/%.pdf: $(OUT)/$${spec-name}/index.html
-	@echo "Compile $< -> $(OUT)/$*/$*.pdf"
+	@echo "Compile $< -> $@"
 	@chromium  \
 		--no-sandbox \
 		--headless=new \
 		--disable-gpu \
 		--disable-sync \
-		--print-to-pdf=$(OUT)/$*/$*.pdf \
+		--print-to-pdf=$@ \
 		--no-margine \
 		--run-all-compositor-stages-before-draw \
 		--no-pdf-header-footer \
@@ -110,6 +110,54 @@ $(OUT)/%/Images:
 # 	@[ -d $@ ] || mkdir -p $@
 # 	@mv $? $@
 
+SRC =
+NAME=
+
+.PHONY: spec
+spec: spec.html spec.pdf
+
+.PHONY: spec.html
+spec.html: ${OUT}/index.html
+
+.PHONY: spec.pdf
+spec.pdf: ${OUT}/${NAME}.pdf
+
+$(OUT)/index.html: ${SRC} $(OUT)/Images
+	@echo "Compile $< -> $(OUT)/index.html. Deps $^ to $@"
+	@[ -d $(OUT) ] || mkdir -p $(OUT)
+	bikeshed --allow-nonlocal-files spec $< $@
+
+$(OUT)/Images: Images/
+	@[ -d $(OUT) ] || mkdir -p $(OUT)
+	@if [ -d "Images" ]; then \
+		echo "Copy Images -> $(OUT)/Images"; \
+		cp -r Images $(OUT)/Images; \
+	fi
+
+$(OUT)/${NAME}.pdf: $(OUT)/index.html
+	@echo "Compile $< -> $@"
+	@chromium  \
+		--no-sandbox \
+		--headless=new \
+		--disable-gpu \
+		--disable-sync \
+		--print-to-pdf=$@ \
+		--no-margine \
+		--run-all-compositor-stages-before-draw \
+		--no-pdf-header-footer \
+		--virtual-time-budget=20000 \
+		$< 2>&1 | grep -v "bus.cc"
+
+.PHONY: spec-watch
+spec-watch: ${SRC} $(OUT)/Images
+	@[ -d $(OUT) ] || mkdir -p $(OUT)
+	bikeshed --allow-nonlocal-files watch $< $(OUT)/index.html
+
+.PHONY: spec-serve
+spec-serve: ${SRC} $(OUT)/Images
+	@[ -d $(OUT) ] || mkdir -p $(OUT)
+	bikeshed --allow-nonlocal-files serve $< $(OUT)/index.html
+
 # Helper to clean up
 .PHONY: clean
 clean:
@@ -119,6 +167,15 @@ clean:
 .PHONY: help
 help:
 	@echo "Bikeshed build script"
+	@echo ""
+	@echo "This makefile is looking for a specs folder and provides"
+	@echo "build tasks for each subfolder there."
+	@echo ""
+	@echo "In addition, you can also run this for a spec that is hosted"
+	@echo "as a single source file in the repo. For this, make sure you"
+	@echo "set the SRC and NAME variables correctly. Then use the spec"
+	@echo "targets."
+	@echo ""
 	@echo "The following make targets are available"
 	@echo
 	@echo "help				This help message"
@@ -129,3 +186,10 @@ help:
 		echo "$${s}.pdf			Build $$s as pdf"; \
 		echo "$${s}-watch			Build $$s as html and keep watching for changes"; \
 	done
+	@echo ""
+	@echo "spec				Build a single spec from SRC. Make sure you set the source file with SRC and provide a NAME that will be used for the PDF, i.e. make spec SRC=myspec.bs NAME=myspec"
+	@echo "spec.html			Build a single spec HTML from SRC. See above how to set SRC and NAME."
+	@echo "spec.pdf			Build a single spec HTML from SRC. See above how to set SRC and NAME."
+	@echo "spec-watch			Watch a single spec HTML from SRC. See above how to set SRC and NAME."
+	@echo "spec-serve			Watch and serve a single spec HTML from SRC. See above how to set SRC and NAME."
+