Add help and debug targets, fuzzy assign WEBR_ROOT (#410)

* Set the WEBR_ROOT variable only if it's not set/doesn't have a value.

* Provide a help and debug command for top-level make

* Update Makefile

Co-authored-by: George Stagg <georgestagg@gmail.com>

---------

Co-authored-by: George Stagg <georgestagg@gmail.com>

Makefile

@@ -1,4 +1,4 @@
-WEBR_ROOT = $(abspath .)
+WEBR_ROOT ?= $(abspath .)
 WASM = $(WEBR_ROOT)/wasm
 HOST = $(WEBR_ROOT)/host
 TOOLS = $(WEBR_ROOT)/tools
@@ -8,53 +8,65 @@ default: webr
 # This is created at configure-time
 include $(TOOLS)/fortran.mk
 
-# Build webR and install the web app in `./dist`
 .PHONY: webr
-webr: $(EMFC) $(FORTRAN_WASM_LIB) libs
+webr: $(EMFC) $(FORTRAN_WASM_LIB) libs ## Build webR and install the web app in `./dist`
 	cd R && $(MAKE) && $(MAKE) install
 	cd src && $(MAKE)
 
-# Supporting libs for webr
 .PHONY: libs
-libs:
+libs: ## Compile supporting libs for webR
 	cd libs && $(MAKE)
 
-# Build webR in a temporary docker container
 .PHONY: docker-webr
-docker-webr:
+docker-webr: ## Build webR in a temporary Docker container
 	mkdir -p dist
 	docker build -t webr-build .
 	docker run --rm --mount type=bind,source=$(PWD),target=/app webr-build
 
 # Create a permanent docker container for building webR. Call `make`
 # from within the container to start the build.
 .PHONY: docker-container-%
-docker-container-%:
+docker-container-%: ## Build webR development Docker container using a supplied name
 	docker build -t webr-build .
 	docker run -dit --name $* --mount type=bind,source=$(PWD),target=/app webr-build bash
 
-docs: docs/build
-docs/build:
+docs: docs/build ## Build documentation and Quarto website
+docs/build: ## Build documentation and Quarto website
 	cd docs && $(MAKE) api && $(MAKE) html
 
 .PHONY: check
-check:
+check: ## Run unit tests and calculate coverage
 	cd src && $(MAKE) check
 
 .PHONY: check-pr
-check-pr:
+check-pr: ## Run additional pull request tests, linter, and calculate coverage
 	cd src && $(MAKE) lint && $(MAKE) check && $(MAKE) check-packages
 
 .PHONY: clean
-clean:
+clean: ## Remove Wasm R build
 	rm -rf $(HOST) $(WASM)/R-*
 	cd R && $(MAKE) clean
 
 .PHONY: clean-wasm
-clean-wasm: clean
+clean-wasm: clean ## Remove Wasm R build and supporting libs
 	rm -rf $(WASM)
 	cd libs && $(MAKE) clean
 
 .PHONY: distclean
-distclean: clean-wasm clean-tools
+distclean: clean-wasm clean-tools ## Remove Wasm R build, supporting libs, build tools, and webR distribution
 	rm -rf dist
+
+.PHONY: help
+help:  ## Show help messages for make targets
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(firstword $(MAKEFILE_LIST)) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[32m%-18s\033[0m %s\n", $$1, $$2}'
+
+.PHONY: debug
+debug: ## Print all variables for debugging
+	@printf "\033[32m%-18s\033[0m %s\n" "WEBR_ROOT" "$(WEBR_ROOT)"
+	@printf "\033[32m%-18s\033[0m %s\n" "WASM" "$(WASM)"
+	@printf "\033[32m%-18s\033[0m %s\n" "HOST" "$(HOST)"
+	@printf "\033[32m%-18s\033[0m %s\n" "TOOLS" "$(TOOLS)"
+	@printf "\033[32m%-18s\033[0m %s\n" "EMFC" "$(EMFC)"
+	@printf "\033[32m%-18s\033[0m %s\n" "FORTRAN_WASM_LIB" "$(FORTRAN_WASM_LIB)"
+	@printf "\033[32m%-18s\033[0m %s\n" "PWD" "$(PWD)"
+	@printf "\033[32m%-18s\033[0m %s\n" "MAKE" "$(MAKE)"