License Header Processor

Purpose

Checks that source files carry a license header. Native (in-process; no external tools required).

How It Works

Each file must start with the header: the lines of header_lines, every one of them, in order, each matching a whole line exactly and ending with a newline. Line endings are compared after reading \r\n and \r as \n. Two things may come before the header:

• A shebang line (#!...), skipped when skip_shebang is on (the default), so scripts can keep it first.
• optional_prefix_lines, all of them or none, matched exactly. This is how kernel sources carry the SPDX line the kernel requires first, followed by the project’s license block. One stanza then covers ordinary sources (header at the top) and kernel sources (SPDX line, then header).

The SPDX line can also be the header itself: with header_lines = ["// SPDX-License-Identifier: GPL-2.0"], every file must open with exactly that line.

The first line that differs is reported, with its line number in the file and its number in the header. When a file starts with the prefix, the mismatch is reported in the header after it:

src/user.c:1: license header line 1 differs: expected "// SPDX-License-Identifier: GPL-2.0", found "/*"
src/broken.c:3: license header line 2 differs: expected " * This file is part of the demo package.", found " * Some other package."
src/short.c:17: file ends without a newline after license header line 17

A file that is not valid UTF-8 fails with a read error. header_lines is required and must not be empty.

Source Files

• Input: files under src_dirs with one of the default extensions: .py .rs .js .ts .c .cc .h .hh .java .rb .go .sh .bash
• Output: none (checker)

The default src_dirs is empty, so a stanza with no src_dirs or src_files checks nothing: name the directories ([""] for the whole project) or files to check.

Configuration

# Kernel sources must open with the SPDX line
[processor.checker.license_header.kernel]
src_dirs = ["src/kernel_standalone"]
src_extensions = [".c", ".h"]
header_lines = ["// SPDX-License-Identifier: GPL-2.0"]

# Every source must start with the project's license block, kernel
# sources with their SPDX line before it. Shortened here: list every line
# of the real header, since all of them must match.
[processor.checker.license_header.block]
src_dirs = ["src"]
src_extensions = [".c", ".cc", ".h", ".hh"]
skip_shebang = false
optional_prefix_lines = ["// SPDX-License-Identifier: GPL-2.0"]
header_lines = [
    "/*",
    " * This file is part of the demos-os-linux package.",
    " * Copyright (C) 2011-2026 Mark Veltzer <mark.veltzer@gmail.com>",
    " */",
]

Changing header_lines, optional_prefix_lines or skip_shebang re-checks every file.

Batch support

Files are checked individually within a batch, so one bad file fails only its own product.

Clean behavior

This processor is a Checker — rsconstruct clean outputs is a no-op for it (checkers produce no outputs). See Clean behavior and rsconstruct clean.