Getting GNU Make cloud-ready

The title looks cheeky, but so is the issue.

After release of GNU Make 4.2, the team went quiet for 4 years; however since the COVID times they've been releasing a new minor version about once a year. Surprisingly, upgrade to GNU Make 4.4 caused issues with Google Cloud SDK - the gcloud command.

When working on internal projects, I like to have CLOUDSDK_CORE_PROJECT environment variable populated, but I don't wan't to preset it to a fixed value, because every person on the team have their own playground project, which I want the tool to use as the deployment target. So I came with the following Makefile:

CLOUDSDK_CORE_PROJECT ?= $(shell gcloud config get-value project)
export CLOUDSDK_CORE_PROJECT

release:
	@echo Deploying to project $(CLOUDSDK_CORE_PROJECT)

This way my toolchain will pick user's default project, which usually points to their playground. And if someone wants things done differently they can set CLOUDSDK_CORE_PROJECT explicity, e.g. through .envrc - nice and simple.

This worked very well for years until I upgraded my system and started hitting the following cryptic errors when running make:

$ make
ERROR: (gcloud.config.get-value) The project property is set to the empty string, which is invalid.
To set your project, run:

  $ gcloud config set project PROJECT_ID

or to unset it, run:

  $ gcloud config unset project
ERROR: (gcloud.config.get-value) The project property is set to the empty string, which is invalid.
To set your project, run:

  $ gcloud config set project PROJECT_ID

or to unset it, run:

  $ gcloud config unset project
Deploying to project

After quite a bit of reading and bisecting upgraded packages (which is relatively easy with NixOS) I found that Make 4.4.x is the culprit. Reading through the release notes it was surprised to find a long list of backward incompatability warnings - quite astonishing for such a mature and feature-complete tool like GNU Make. Among them, the following paragraph caught my attention:

Previously makefile variables marked as export were not exported to commands started by the $(shell ...) function. Now, all exported variables are exported to $(shell ...). If this leads to recursion during expansion, then for backward-compatibility the value from the original environment is used. To detect this change search for 'shell-export' in the .FEATURES variable.

Bingo! After that I could quickly reproduce the issue:

$ CLOUDSDK_CORE_PROJECT= gcloud config get-value project
ERROR: (gcloud.config.get-value) The project property is set to the empty string, which is invalid.
To set your project, run:

  $ gcloud config set project PROJECT_ID

or to unset it, run:

  $ gcloud config unset project

So what happens is:

• CLOUDSDK_CORE_PROJECT is not set, so Make calls the default
• Since this variable is export'ed, Make makes it available to the shell assigning the empty string a value, which breaks gcloud

The fix is simple, though hacky:

CLOUDSDK_CORE_PROJECT ?= $(shell unset CLOUDSDK_CORE_PROJECT; gcloud config get-value project)
export CLOUDSDK_CORE_PROJECT

release:
	@echo Deploying to project $(CLOUDSDK_CORE_PROJECT)

I.e. if the variable is set, the default will not be called. But if it's not, we clear the empty variable from the subshell environment, thus preventing things from breaking.

Eventually trivial, such small issues can easily eat out several hours of one's time, hence I'm sharing this hopefully useful nugget of knowledge on how to make your Makefile cloud-ready :)