[RFC PATCH v2 4/7] scripts: convert headerdep.pl to Python

[Breno Rodrigues Alves <breno3011alves@gmail.com>]

Faithful re-implementation of headerdep.pl in Python 3
(stdlib only). Same include graph construction, same cycle
detection, same GraphViz output mode (--graph).

Verified byte-for-byte identical to the Perl version on a
synthetic cyclic include chain.

Signed-off-by: Breno Rodrigues Alves <breno3011alves@gmail.com>
---
 scripts/headerdep.py | 137 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 137 insertions(+)
 create mode 100755 scripts/headerdep.py

diff --git a/scripts/headerdep.py b/scripts/headerdep.py
new file mode 100755
index 000000000..4b9a57ab1
--- /dev/null
+++ b/scripts/headerdep.py
@@ -0,0 +1,137 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+#
+# Detect cycles in the header file dependency graph.
+# Vegard Nossum <vegardno@ifi.uio.no>
+
+import argparse
+import os
+import re
+import sys
+
+deps = {}
+opt_include = []
+
+
+def strip(filename):
+    for inc in opt_include:
+        prefix = inc + '/'
+        if filename.startswith(prefix):
+            return filename[len(prefix):]
+    return filename
+
+
+def search(filename):
+    if os.path.isfile(filename):
+        return filename
+    for inc in opt_include:
+        path = f'{inc}/{filename}'
+        if os.path.isfile(path):
+            return path
+    return None
+
+
+def parse_all(headers):
+    queue = list(headers)
+    while queue:
+        h = queue.pop()
+        if h in deps:
+            continue
+        deps[h] = []
+        path = search(h)
+        if path is None:
+            continue
+        with open(path) as f:
+            lines = f.readlines()
+        for i, line in enumerate(lines):
+            m = re.match(r'^#\s*include\s*<(.*?)>', line)
+            if m:
+                dep = m.group(1)
+                queue.append(dep)
+                deps[h].append((i + 1, dep))
+
+
+def print_cycle(cycle):
+    # Shift line numbers to align with the "In file included" message
+    cycle = list(cycle)
+    for i in range(len(cycle) - 1):
+        cycle[i] = (cycle[i + 1][0], cycle[i][1])
+    cycle[-1] = (0, cycle[-1][1])
+
+    first = cycle.pop(0)
+    last = cycle.pop() if cycle else None
+
+    msg = 'In file included'
+    if last is not None:
+        print(f'{msg} from {last[1]},')
+    for hdr in reversed(cycle):
+        marker = ' <-- here' if last is not None and hdr[1] == last[1] else ''
+        print(f'{" " * len(msg)} from {hdr[1]}:{hdr[0]}{marker}')
+    print(f'{first[1]}:{first[0]}: warning: recursive header inclusion')
+
+
+def detect_cycles(headers, opt_all):
+    queue = [[(0, h)] for h in headers]
+    while queue:
+        top = queue.pop()
+        name = top[-1][1]
+        for dep in deps.get(name, []):
+            chain = top + [(dep[0], dep[1])]
+            if any(c[1] == dep[1] for c in top):
+                print_cycle(chain)
+                if not opt_all:
+                    return
+                continue
+            queue.append(chain)
+
+
+def mangle(name):
+    return name.replace('/', '__').replace('.', '_').replace('-', '_')
+
+
+def graph():
+    print('digraph {')
+    print()
+    print('\t/* vertices */')
+    for h in deps:
+        print(f'\t{mangle(h)} [label="{h}"];')
+    print()
+    print('\t/* edges */')
+    for h in deps:
+        for dep in deps[h]:
+            print(f'\t{mangle(h)} -> {mangle(dep[1])};')
+    print('}')
+
+
+def main(argv):
+    global opt_include
+
+    p = argparse.ArgumentParser(add_help=False)
+    p.add_argument('--all', action='store_true')
+    p.add_argument('--graph', action='store_true')
+    p.add_argument('-I', dest='includes', action='append', default=[])
+    p.add_argument('files', nargs='*')
+    p.add_argument('-h', '--help', '--version', action='store_true')
+    args = p.parse_args(argv)
+
+    if args.help:
+        print(f'Usage: {sys.argv[0]} [options] file...')
+        return 0
+
+    opt_include = list(args.includes) + ['include']
+    # Match Perl: grep { strip($_) } keeps the ORIGINAL path, using
+    # strip() only as a truthiness filter. This makes deps keys
+    # consistent with the Perl version (e.g. 'include/x.h', not 'x.h').
+    headers = [h for h in args.files if strip(h)]
+
+    parse_all(headers)
+
+    if args.graph:
+        graph()
+    else:
+        detect_cycles(headers, args.all)
+    return 0
+
+
+if __name__ == '__main__':
+    sys.exit(main(sys.argv[1:]))
\ No newline at end of file
-- 
2.43.0