"heritage" in Makefile

Question

I'm looking a way to overload parts of a Makefile A to another one B, hence extending A.

For instance we have the following makefile A:

TEXT="AHAHA"

default: after-default

before-default: 
    echo "BEFORE DEFAULT"

default: before-default
    echo ${TEXT}

after-default: default
    echo "AFTER DEFAULT"

I want to reuse it in a new Makefile B like this:

TEXT="HIHIHI"

before-default: 
    echo "NEW BEFORE DEFAULT"

The new makefile will print:

NEW BEFORE DEFAULT
HIHIHI
AFTER DEFAULT

This example is a bit absurd it is not possible like this way, but I want to know if it is possible to make such Makefile composition close to this idea.

Your dependency chain is inverted. The output will be printed in precisely the reverse order. Because `before-default` depends on `default`, it will first run `default` before processing `before-default`. — tripleee, May 28 '14 at 08:09
But now the first production is `before-default`, so just plain `make` will *only* run that. You want to invert the order of the rules so that `after-default` is the default target. — tripleee, May 29 '14 at 07:54

tripleee · Answer 1 · 2014-05-28T08:16:12.213

Your example will be trivially fulfilled by adding include A at the start of B. The new before-default target will override the old one.

vnix$ tail *
==> A <==
TEXT="AHAHA"

before-default: default
        echo "BEFORE DEFAULT"

default: after-default
        echo ${TEXT}

after-default:
        echo "AFTER DEFAULT"

==> B <==
include A

TEXT="HIHIHI"

before-default: default
        echo "NEW BEFORE DEFAULT"

vnix$ make -sf A
AFTER DEFAULT
AHAHA
BEFORE DEFAULT

vnix$ make -sf B
B:6: warning: overriding commands for target `before-default'
A:4: warning: ignoring old commands for target `before-default'
AFTER DEFAULT
HIHIHI
NEW BEFORE DEFAULT

This isn't a very good design, though; parametrizing things like you already do with TEXT comes with fewer surprises than having code that is being overridden elsewhere.

(See my comment above re: why the output is in the opposite order from what you were hoping.)

score 2 · Answer 2 · answered May 28 '14 at 08:12

You can do this:

File Makefile:

# Define default TEXT
TEXT := HAHAHA

# Define default target
after:
    @echo AFTER

run:
    @echo $(TEXT)

before:
    @echo BEFORE

# Define dependencies
run: before
after: run

# Include the new makefile
include inheritance.mk

File inheritance.mk:

# Redefine TEXT
TEXT := HIHIHI

# Redefine before target
before:
    @ echo NEW BEFORE

When you run make you'll have some warning but it'll work as expected:

inheritance.mk:4: warning: overriding commands for target `before'
Makefile:10: warning: ignoring old commands for target `before'
NEW BEFORE
HIHIHI
AFTER

"heritage" in Makefile

2 Answers2