How to document a makefile?

Question

Is there a way to write "standard" comments in a Makefile to later feed them to a Doxygen-like program so as to output a nice (HTML or man for instance) documentation ? I'd like to have a clear overview of my main targets somewhere but nothing too fancy.

Answer 1

The following is a simpler solution that does not require defining user functions or aggregating help text away from the rules they document.

# This is a regular comment, that will not be displayed

## ----------------------------------------------------------------------
## This is a help comment. The purpose of this Makefile is to demonstrate
## a simple help mechanism that uses comments defined alongside the rules
## they describe without the need of additional help files or echoing of
## descriptions. Help comments are displayed in the order defined within
## the Makefile.
## ----------------------------------------------------------------------

help:     ## Show this help.
    @sed -ne '/@sed/!s/## //p' $(MAKEFILE_LIST)

build:    ## Build something.

install:  ## Install something.

deploy:   ## Deploy something.

format:   ## Help comments are display with their leading whitespace. For
          ## example, all comments in this snippet are aligned with spaces.

Running make or make help results in the following:

----------------------------------------------------------------------
This is a help comment. The purpose of this Makefile is to demonstrate
a simple help mechanism that uses comments defined alongside the rules
they describe without the need of additional help files or echoing of
descriptions. Help comments are displayed in the order defined within
the Makefile.
----------------------------------------------------------------------
help:     Show this help.
build:    Build something.
install:  Install something.
deploy:   Deploy something.
format:   Help comments are display with their leading whitespace. For
          example, all comments in this snippet are aligned with spaces.

Answer 2

In a makefile such as :

install: ## Do a
  @echo "foo"

start: ## Do b
  @echo "bar"

test: ## Do c
  @echo "baz"

help:
  @egrep -h '\s##\s' $(MAKEFILE_LIST) | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m  %-30s\033[0m %s\n", $$1, $$2}'

Will output :

Answer 3

I made my own solution using a short Perl script that formats the help as other GNU tools:

SCRIPT_VERSION=v1.0
SCRIPT_AUTHOR=John Doe

all:                ##@Build Build all the project 

clean:              ##@Cleaning Remove all intermediate objects

mrproper: clean     ##@Cleaning Remove all output and interemediate objects

HELP_FUN = \
    %help; while(<>){push@{$$help{$$2//'options'}},[$$1,$$3] \
    if/^([\w-_]+)\s*:.*\#\#(?:@(\w+))?\s(.*)$$/}; \
    print"$$_:\n", map"  $$_->[0]".(" "x(20-length($$_->[0])))."$$_->[1]\n",\
    @{$$help{$$_}},"\n" for keys %help; \

help: ##@Miscellaneous Show this help
    @echo -e "Usage: make [target] ...\n"
    @perl -e '$(HELP_FUN)' $(MAKEFILE_LIST)
    @echo -e "Written by $(SCRIPT_AUTHOR), version $(SCRIPT_VERSION)"
    @echo -e "Please report any bug or error to the author." 

Which gives this:

$ make help
Usage: make [target] ...

Miscellaneous:
  help                Show this help

Build:
  all                 Build all the project

Cleaning:
  clean               Remove all intermediate objects
  mrproper            Remove all output and interemediate objects

Written by John Doe, version v1.0
Please report any bug or error to the author.

Answer 4

One nice touch is to provide a phony help target that prints a summary of targets and options. From the Linux kernel Makefile:

help:
        @echo  'Cleaning targets:'
        @echo  '  clean           - Remove most generated files but keep the config and'
        @echo  '                    enough build support to build external modules'
        @echo  '  mrproper        - Remove all generated files + config + various backup files'
        @echo  '  distclean       - mrproper + remove editor backup and patch files'
        @echo  ''
        @echo  'Configuration targets:'
        @$(MAKE) -f $(srctree)/scripts/kconfig/Makefile help
        @echo  ''

It might be a bit of work to maintain the documentation this way, but I find it nicely separates what is intended for "users" versus what is intended for people maintaining the Makefile itself (inline comments).

Answer 5

Self-Documenting Makefiles (John Graham-Cumming, 2005) lets you write the help alongside each rule. This is a lightweight and highly nifty solution that works at least with GNU Make.

Here's my slightly modified version (def-help-section helps organize long lists of rules).

Answer 6

I wrote the MakeHelp library exactly for that purpose. It lets you write the rule docs above each rule. Very easy to use.

I find it different from the other self-documenting Makefiles here as it has no repetitiveness and allows multiline docs and private rules.

Answer 7

Here is my version that also strips away the dependencies of a target and aligns the help strings to an even column.

help:   ## Show this help.
    @sed -ne 's/^\([^[:space:]]*\):.*##/\1:\t/p' $(MAKEFILE_LIST) | column -t -s $$'\t'

image: src/*.s src/*.c src/**/*.c   ## Build the image
    riscv32-unknown-elf-gcc $^ -march=rv32i_zicsr -Wall -ggdb -O0 -o image -ffreestanding -nostdlib -lgcc

launch: ## Image Launch the image in renode
    renode --net vexriscv.resc --console

Output

help:    Show this help.
image    Build the image
launch:  Image Launch the image in renode