[gdb/contrib] Add script to license check new files

While reading through gdb-patches backlog after a return
from PTO, I noticed that a newly added file was licensed
with "MIT", and that license was not listed in Fedora's
gdb.spec file. [Fedora no longer supports "effective"
licenses.]

That lead me to this simple script which generates a list
of all the newly added files between two given commits and
scans these files for licenses.

Example usage:
bash$ cd /path/to/binutils-gdb/gdb
bash$ ./contrib/license-check-new-files.sh -s gdb-15-branchpoint gdb-16-branchpoint
Scanning directories gdb*/...
gdb/contrib/common-misspellings.txt: no longer in repo?
gdb/contrib/spellcheck.sh: no longer in repo?
gdbsupport/unordered_dense.h: MIT

I don't think anything in here is Fedora- or RPM-specific,
so I'd like to submit this for consideration for inclusion
in contrib/.  I believe other distros may find it useful.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/contrib/license-check-new-files.sh

@@ -0,0 +1,149 @@
+#!/usr/bin/env python3
+
+# Copyright (C) 2025 Free Software Foundation, Inc.
+#
+# This file is part of GDB.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This program requires the python modules GitPython (git) and scancode-toolkit.
+# It builds a list of all the newly added files to the repository and scans
+# each file for a license, printing it to the terminal.  If "--skip" is used,
+# it will only output non-"common" licenses, e.g., omitting "GPL-3.0-or-later".
+# This makes it a little bit easier to detect any possible new licenses.
+#
+# Example:
+# bash$ cd /path/to/binutils-gdb/gdb
+# bash$ ./contrib/license-check-new-files.sh -s gdb-15-branchpoint gdb-16-branchpoint
+# Scanning directories gdb*/...
+# gdb/contrib/common-misspellings.txt: no longer in repo?
+# gdb/contrib/spellcheck.sh: no longer in repo?
+# gdbsupport/unordered_dense.h: MIT
+
+import os
+import sys
+import argparse
+from pathlib import PurePath
+from git import Repo
+from scancode import api
+
+# A list of "common" licenses. If "--skip" is used, any file
+# with a license in this list will be omitted from the output.
+COMMON_LICENSES = ["GPL-2.0-or-later", "GPL-3.0-or-later"]
+
+# Default list of directories to scan. Default scans are limited to
+# gdb-specific git directories because much of the rest of binutils-gdb
+# is actually owned by other projects/packages.
+DEFAULT_SCAN_DIRS = "gdb*"
+
+
+# Get the commit object associated with the string commit CSTR
+# from the git repository REPO.
+#
+# Returns the object or prints an error and exits.
+def get_commit(repo, cstr):
+    try:
+        return repo.commit(cstr)
+    except:
+        print(f'unknown commit "{cstr}"')
+        sys.exit(2)
+
+
+# Uses scancode-toolkit package to scan FILE's licenses.
+# Returns the full license dict from scancode on success or
+# propagates any exceptions.
+def get_licenses_for_file(file):
+    return api.get_licenses(file)
+
+
+# Helper function to print FILE to the terminal if skipping
+# common licenses.
+def skip_print_file(skip, file):
+    if skip:
+        print(f"{file}: ", end="")
+
+
+def main(argv):
+    parser = argparse.ArgumentParser()
+    parser.add_argument("from_commit")
+    parser.add_argument("to_commit")
+    parser.add_argument(
+        "-s", "--skip", help="skip common licenses in output", action="store_true"
+    )
+    parser.add_argument(
+        "-p",
+        "--paths",
+        help=f'paths to scan (default is "{DEFAULT_SCAN_DIRS}")',
+        type=str,
+        default=DEFAULT_SCAN_DIRS,
+    )
+    args = parser.parse_args()
+
+    # Commit boundaries to search for new files
+    from_commit = args.from_commit
+    to_commit = args.to_commit
+
+    # Get the list of new files from git. Try the current directory,
+    # looping up to the root attempting to find a valid git repository.
+    path = PurePath(os.getcwd())
+    paths = list(path.parents)
+    paths.insert(0, path)
+    for dir in paths:
+        try:
+            repo = Repo(dir)
+            break
+        except:
+            pass
+
+    if dir == path.parents[-1]:
+        print(f'not a git repository (or any parent up to mount point "{dir}")')
+        sys.exit(2)
+
+    # Get from/to commits
+    fc = get_commit(repo, from_commit)
+    tc = get_commit(repo, to_commit)
+
+    # Loop over new files
+    paths = [str(dir) for dir in args.paths.split(",")]
+    print(f'Scanning directories {",".join(f"{s}/" for s in paths)}...')
+    for file in fc.diff(tc, paths=paths).iter_change_type("A"):
+        filename = file.a_path
+        if not args.skip:
+            print(f"checking licenses for {filename}... ", end="", flush=True)
+        try:
+            f = dir.joinpath(dir, filename).as_posix()
+            lic = get_licenses_for_file(f)
+            if len(lic["license_clues"]) > 1:
+                print("multiple licenses detected")
+            elif (
+                not args.skip
+                or lic["detected_license_expression_spdx"] not in COMMON_LICENSES
+            ):
+                skip_print_file(args.skip, filename)
+                print(f"{lic['detected_license_expression_spdx']}")
+        except OSError:
+            # Likely hit a file that was added to the repo and subsequently removed.
+            skip_print_file(args.skip, filename)
+            print("no longer in repo?")
+        except KeyboardInterrupt:
+            print("interrupted")
+            break
+        except Exception as e:
+            # If scanning fails, there is little we can do but print an error.
+            skip_print_file(args.skip, filename)
+            print(e)
+
+
+if __name__ == "__main__":
+    main(sys.argv)