Makefile for smart sam build

Makefile

INPUT_TEMPLATE_FILE := mytemplate.sam.yaml

ifndef PACKAGE_BUCKET
$(error PACKAGE_BUCKET must be defined (as environment variable))
endif

OUTPUT_TEMPLATE_FILE := __generated__.yaml


SHELL = /bin/bash

# Build dependency on the value of PACKAGE_BUCKET environment variable
# https://stackoverflow.com/a/59787919/358224
var_file := .package_bucket.txt
var_name := PACKAGE_BUCKET
is_var_updated = [[ ! -e $(var_file) ]] || [[ "$$(< $(var_file))" != "$($(var_name))" ]]
update_var_file = echo "$($(var_name))" > $(var_file)
$(shell $(is_var_updated) && $(update_var_file))


# targets that aren't really files
.PHONY: help package

help:  ## Show this help.
	@fgrep -h "##" $(MAKEFILE_LIST) | fgrep -v fgrep | sed -e 's/\\$$//' | sed -e 's/:[^#]*##/:\t/'

.aws-sam/build/template.yaml: $(INPUT_TEMPLATE_FILE) code/requirements.txt $(wildcard code/*.py)  ## sam-build target and dependencies
	sam build \
		--template-file $(INPUT_TEMPLATE_FILE) \
		--manifest ./code/requirements.txt --debug

# SAM_CLI_TELEMETRY=0 => Turn off telemetry warnings https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-telemetry.html
$(OUTPUT_TEMPLATE_FILE): $(var_file) .aws-sam/build/template.yaml ## create and upload the SAM application-bundle 
	SAM_CLI_TELEMETRY=0 \
	sam package \
		--s3-bucket "$(PACKAGE_BUCKET)" \
		--output-template-file "$(OUTPUT_TEMPLATE_FILE)" --debug

package: $(OUTPUT_TEMPLATE_FILE) ## standard target to be invoked: package the application
	# no-op

To workaround aws/aws-sam-cli#805

make noob here, how do i use this?

Create a directory structure like:

./
+-- Makefile
+-- code
|   +-- __init__.py
|   +-- lambda_function.py
|   +-- requirements.txt
+-- mytemplate.sam.yaml

In the directory run:
PACKAGE_BUCKET=my-s3-package-bucket make package