Quick and dirty script to turn a Makefile into a dependency graph for object file (.o) dependencies

graph.py

# Run with
#
#      python graph.py makefilename
#
#  which generates dependencies.dot which can be compiled with graphviz
#  to a png via:
#
#   dot -Tpng dependencies.dot -o dependencies.png
#
#
import re
import sys


def parse_makefile(filename):
    """Parse the Makefile and extract targets and their dependencies."""
    with open(filename, 'r') as f:
        lines = f.readlines()

    dependency_graph = {}

    # Unsplit continuation lines
    lines_new = []
    i = 0
    while (i < (len(lines)-1)):
        line = lines[i].strip()
        new_line = ""
        line_next = ""
        while len(line) > 0 and line[-1] == "\\":
          line_next = lines[i+1].strip()
          new_line = new_line + " " + line[0:-1]
          line = line_next
          i+=1

        new_line = new_line + " " + line
        lines_new.append(new_line)
        i+=1

    target_pattern = re.compile(r'^([a-zA-Z0-9\_]+)\.o(\s)*:\s*(.*)$')

    for line in lines_new:
        match = target_pattern.match(line.strip())
        if match:
            target, space, dependencies = match.groups()
            dependencies = dependencies.split()
            dependency_graph[target] = dependencies
            print(target + ": " + str(dependencies))

    return dependency_graph

def generate_dot(dependency_graph, output_filename):
    """Generate a DOT file from the dependency graph."""
    with open(output_filename, 'w') as f:
        f.write("digraph MakefileDependencies {\n")
        f.write("    rankdir=LR;\n")  # Left to right layout
        for target, dependencies in dependency_graph.items():
            for dep in dependencies:
                f.write(f'    "{dep}" -> "{target}.o";\n')
        f.write("}\n")

def main(args):
    makefile = args[1]  # Input Makefile
    dotfile = "dependencies.dot"  # Output DOT file

    dependency_graph = parse_makefile(makefile)
    generate_dot(dependency_graph, dotfile)

    print(f"DOT file generated: {dotfile}")

if __name__ == "__main__":
    main(sys.argv)