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makefile_standards.md

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Makefile Standards

Every releasable repo—including libraries, services and tools—must have a makefile for building, testing, versioning and packaging the repo. Since we have a range of technologies and build tools, our CI tools need a standard interface to build and test our code. The makefile was selected to be a common abstraction over the underlying build tools.

All makefiles in the repo should be named Makefile and be in the root of the repo.

Structure

The makefile should be structured in three sections separated by an empty line:

  1. Environment variables
  2. Internal variables
  3. Targets

Environment variables

Environment variables are options that can be overridden from the command line. These should be in UPPER_SNAKE_CASE and should be declared at the top of the file using the conditional assignment (?=) to specify the default value to use if the variable is not set.

For example:

OVERRIDABLE_VARIABLE ?= default

If an environment variable is required the makefile should output an error message:

ifndef ORACLE_HOME
$(error ORACLE_HOME environment variable is not defined)
endif

NB: Note that the error line is not tab indented.

Internal variables

Internal variables are any variables that are used internally and can not be overridden from the command line. These should be in lower_snake_case and should be declared at the top of the file below the environment variables using the immediate assignment (:=).

For example:

internal_variable  := foo
internal_evaluated := $(shell if [[ -n $(foo) ]]; then echo bar; else har; fi)

Targets

In keeping with makefile functionality targets that generate a particular file should be named after the file, otherwise they should be lower_snake_case.

PHONY targets

Targets that do not create a file of the same name as the target are known as phony targets. These targets should be specified as .PHONY in order save make having to check if the file exists, and also to ensure that if a file or directory of that name is ever created the target will still run.

Phony targets should be marked as .PHONY on the line above the target declaration:

.PHONY: dist
dist: clean build package