monad-one · March 1, 2018 03:11 · Feb 23, 2018 · Feb 23, 2017 · Nov 3, 2016 · Nov 3, 2016
diff --git a/Makefile b/Makefile
@@ -1,7 +1,7 @@
 # Makefile for transpiling with Babel in a Node app, or in a client- or
 # server-side shared library.
 
-.PHONY: all build clean
+.PHONY: all clean
 
 # Install `babel-cli` in a project to get the transpiler.
 babel := node_modules/.bin/babel
@@ -28,14 +28,12 @@ transpiled_files := $(patsubst src/%,lib/%,$(src_files))
 # `transpiled_files` list with a `.js.flow` extension.
 flow_files := $(patsubst %.js,%.js.flow,$(transpiled_files))
 
-all: build
-
 # Ask `make` to build all of the transpiled `.js` and `.js.flow` files that we
 # want to end up with in `lib/`.
 #
 # This target also depends on the `node_modules/` directory, so that `make`
 # automatically runs `yarn install` if `package.json` has changed.
-build: node_modules $(flow_files) $(transpiled_files)
+all: node_modules $(flow_files) $(transpiled_files)
 
 # This rule tells `make` how to transpile a source file using `babel`.
 # Transpiled files will be written to `lib/`
@@ -58,7 +56,7 @@ clean:
 	rm -rf lib
 
 # This rule informs `make` that the `node_modules/` directory is out-of-date
-# after changes to `package.json`, and instructs `make` on how to install
-# modules to get back up-to-date.
-node_modules: package.json
+# after changes to `package.json` or `yarn.lock`, and instructs `make` on how to
+# install modules to get back up-to-date.
+node_modules: package.json yarn.lock
 	yarn install
diff --git a/Makefile b/Makefile
@@ -6,48 +6,59 @@
 # Install `babel-cli` in a project to get the transpiler.
 babel := node_modules/.bin/babel
 
-# Identify modules to be transpiled by finding files ending in `.js.flow`.
-src_files := $(shell find . -name '*.js.flow' -not -path './node_modules/*')
-
-# Build list of expected output files by changing `.js.flow` to `.js` in
-# `src_files` list. Generated files are put in the same directory as the source
-# file. Because we generate the list in this way, we can selectively remove
-# generated files in the `clean` target. Modules that should be excluded from
-# transpiling (`.js` files with no corresponding `.js.flow` file) are excluded
-# from this list, so they are not overwritten when running `make`, and are not
-# removed when running `make clean`.
-out_files := $(patsubst %.js.flow,%.js,$(src_files))
+# Identify modules to be transpiled by recursively searching the `src/`
+# directory.
+src_files := $(shell find src/ -name '*.js')
+
+# Building will involve copying every `.js` file from `src/` to a corresponding
+# file in `lib/` with a `.js.flow` extension. Then we will run `babel` to
+# transpile copied files, where the transpiled file will get a `.js` extension.
+# This assignment computes the list of transpiled `.js` that we expect to end up;
+# and we will work backward from there to figure out how to build them.
+transpiled_files := $(patsubst src/%,lib/%,$(src_files))
 
 # Putting each generated file in the same directory with its corresponding
 # source file is important when working with Flow: during type-checking Flow
 # will look in npm packages for `.js.flow` files to find type definitions. So
 # putting `.js` and `.js.flow` files side-by-side is how you export type
 # definitions from a shared library.
 
-# We also want to build a list of `.js.map` output files, so that we can remove
-# them in the `clean` target.
-map_files := $(patsubst %.js.flow,%.js.map,$(src_files))
+# Compute the list of type-definition source files that we want to end up with.
+# This is done by replacing the `.js` extension from every value in the
+# `transpiled_files` list with a `.js.flow` extension.
+flow_files := $(patsubst %.js,%.js.flow,$(transpiled_files))
 
 all: build
 
-# Ask `make` to build all of the output `.js` files that we want to produce.
+# Ask `make` to build all of the transpiled `.js` and `.js.flow` files that we
+# want to end up with in `lib/`.
+#
 # This target also depends on the `node_modules/` directory, so that `make`
-# automatically runs `npm install` if `package.json` has changed.
-build: node_modules $(out_files)
+# automatically runs `yarn install` if `package.json` has changed.
+build: node_modules $(flow_files) $(transpiled_files)
+
+# This rule tells `make` how to transpile a source file using `babel`.
+# Transpiled files will be written to `lib/`
+lib/%: src/%
+	mkdir -p $(dir $@)
+	$(babel) $< --out-file $@ --source-maps
 
-# This rule tells `make` how to turn a `.js.flow` file into a `.js` file.
-# Transpiling one file at a time makes incremental compilation faster:
+# Transpiling one file at a time makes incremental transpilation faster:
 # `make` will only transpile source files that have changed since the last
 # invocation.
-%.js: %.js.flow
-	$(babel) $< --out-file $@ --source-maps
 
-# When cleaning, remove files generated by the `build` target, and nothing else.
+# This rule tells `make` how to produce a `.js.flow` file. It is just a copy of
+# a source file - the rule copies a file from `src/` to `lib/` and changes the
+# extension.
+lib/%.js.flow: src/%.js
+	mkdir -p $(dir $@)
+	cp $< $@
+
 clean:
-	rm -f $(out_files) $(map_files)
+	rm -rf lib
 
 # This rule informs `make` that the `node_modules/` directory is out-of-date
 # after changes to `package.json`, and instructs `make` on how to install
 # modules to get back up-to-date.
 node_modules: package.json
-	npm install
+	yarn install
diff --git a/Makefile b/Makefile
@@ -0,0 +1,53 @@
+# Makefile for transpiling with Babel in a Node app, or in a client- or
+# server-side shared library.
+
+.PHONY: all build clean
+
+# Install `babel-cli` in a project to get the transpiler.
+babel := node_modules/.bin/babel
+
+# Identify modules to be transpiled by finding files ending in `.js.flow`.
+src_files := $(shell find . -name '*.js.flow' -not -path './node_modules/*')
+
+# Build list of expected output files by changing `.js.flow` to `.js` in
+# `src_files` list. Generated files are put in the same directory as the source
+# file. Because we generate the list in this way, we can selectively remove
+# generated files in the `clean` target. Modules that should be excluded from
+# transpiling (`.js` files with no corresponding `.js.flow` file) are excluded
+# from this list, so they are not overwritten when running `make`, and are not
+# removed when running `make clean`.
+out_files := $(patsubst %.js.flow,%.js,$(src_files))
+
+# Putting each generated file in the same directory with its corresponding
+# source file is important when working with Flow: during type-checking Flow
+# will look in npm packages for `.js.flow` files to find type definitions. So
+# putting `.js` and `.js.flow` files side-by-side is how you export type
+# definitions from a shared library.
+
+# We also want to build a list of `.js.map` output files, so that we can remove
+# them in the `clean` target.
+map_files := $(patsubst %.js.flow,%.js.map,$(src_files))
+
+all: build
+
+# Ask `make` to build all of the output `.js` files that we want to produce.
+# This target also depends on the `node_modules/` directory, so that `make`
+# automatically runs `npm install` if `package.json` has changed.
+build: node_modules $(out_files)
+
+# This rule tells `make` how to turn a `.js.flow` file into a `.js` file.
+# Transpiling one file at a time makes incremental compilation faster:
+# `make` will only transpile source files that have changed since the last
+# invocation.
+%.js: %.js.flow
+	$(babel) $< --out-file $@ --source-maps
+
+# When cleaning, remove files generated by the `build` target, and nothing else.
+clean:
+	rm -f $(out_files) $(map_files)
+
+# This rule informs `make` that the `node_modules/` directory is out-of-date
+# after changes to `package.json`, and instructs `make` on how to install
+# modules to get back up-to-date.
+node_modules: package.json
+	npm install