Add pre-commit hook to check for copyright header

Change-Id: I1d3b9d51305d257c9c322caf4cf4d97667fb687b
Signed-off-by: Ben Davis <ben.davis@arm.com>

3 files changed, 198 insertions, 0 deletions

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index db9a019..49f0ccd 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -8,3 +8,12 @@ repos:
       rev: v10.0.1
       hooks:
           - id: clang-format
+
+    - repo: local
+      hooks:
+          - id: copyright-check
+            name: copyright-check
+            description: Checks for a valid copyright header
+            entry: check_copyright.py
+            language: script
+            types_or: [c, c++]
diff --git a/README.md b/README.md
index ea55a2d..f829d95 100644
--- a/README.md
+++ b/README.md
@@ -138,6 +138,13 @@ We are open for contributions.
  * Code should be formatted with clang-format using the project's .clang-format
    configuration.
 
+We use [pre-commit](https://pre-commit.com/) for local git hooks to help ensure
+code quality and standardization. To install the hooks run the following
+commands in the root of the repository:
+
+    $ pip install pre-commit
+    $ pre-commit install
+
 Contributors are expected to abide by the
 [freedesktop.org code of conduct](https://www.freedesktop.org/wiki/CodeOfConduct/).
 
diff --git a/check_copyright.py b/check_copyright.py
new file mode 100755
index 0000000..855fe82
--- /dev/null
+++ b/check_copyright.py
@@ -0,0 +1,182 @@
+#!/usr/bin/env python3
+
+# Copyright (c) 2022 Arm Limited.
+#
+# SPDX-License-Identifier: MIT
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to
+# deal in the Software without restriction, including without limitation the
+# rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+# sell copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+'''
+This script will check the files passed as arguments for a valid copyright
+header. It will run against all changed files as part of the pre-commit hook
+after running `pre-commit install` in the root of the repository. It can also
+be run manually e.g. `./check_copyright.py file1 dir1/file2`
+
+A valid copyright header includes the word 'Copyright' followed by the
+relevant copyright years. It also requires an SPDX licence id string identifying
+the license as MIT, as follows: 'SPDX-License-Identifier: MIT'
+'''
+
+import datetime
+import re
+import sys
+from typing import List
+
+# Set the limit on number of lines at top of file to search
+MAX_SEARCH_LINES = 20
+CURRENT_YEAR = datetime.datetime.now().year
+
+# Regex for positive copyright string
+COPYRIGHT_YEAR_REGEX = re.compile(
+    r".*\bCOPYRIGHT.*%s.*" % str(CURRENT_YEAR), re.IGNORECASE
+)
+
+# Regex for positive SPDX id string
+SPDX_REGEX = re.compile(r".*SPDX-License-Identifier: MIT.*", re.IGNORECASE)
+
+# To match eg: "Copyright (C) 2014-2021"
+PATTERN_STRING = r"\bCopyright\b.*[0-9,)]"
+PATTERN_COPYRIGHT = re.compile(PATTERN_STRING, re.IGNORECASE)
+
+
+def generate_years_string(years: List[int]) -> str:
+    """
+    Create a compacted string representation of a list of years.
+
+    E.g. [1991, 2001, 2002, 2003, 2006, 2007] becomes "1991, 2001-2003,
+    2006-2007"
+    """
+
+    generated_years_string = ""
+    if len(years) > 0:
+        y_mod_strings = ["%d" % years[0]]
+
+        last_element_was_incremental = False
+        for i in range(1, len(years)):
+            # Are we in an incremental sequence?
+            if years[i] == years[i - 1] + 1:
+
+                last_element_was_incremental = True
+
+                # Are we at the last element?
+                if i == len(years) - 1:
+                    y_mod_strings.append("-%d" % years[i])
+                else:
+                    continue
+
+            else:
+                # End of a sequence?
+                if last_element_was_incremental:
+                    y_mod_strings.append("-%d, " % years[i - 1])
+                else:
+                    y_mod_strings.append(", ")
+
+                y_mod_strings.append("%d" % years[i])
+                last_element_was_incremental = False
+
+        generated_years_string = "".join(y_mod_strings)
+
+    return generated_years_string
+
+
+def parse_years_string(s: str) -> List[int]:
+    """
+    Given the string "1999, 2001-2005" this function returns the list:
+    [1999, 2001, 2002, 2003, 2004, 2005]
+    """
+    singles = re.findall(r"(?<![-\d])\d+(?![-\d])", s)
+    years = [int(x) for x in singles]
+
+    ranges = re.findall(r"\d+-\d+", s)
+    for r in ranges:
+        limits = re.findall(r"\d+", r)
+        years.extend(range(int(limits[0]), int(limits[1]) + 1))
+
+    years = list(set(y for y in years if 1900 < y <= CURRENT_YEAR))
+    years.sort()
+
+    return years
+
+
+def update_header(filename: str) -> None:
+    """
+    Updates the Copyright header in 'filename' to hold the correct years.
+    """
+
+    with open(filename, "r+", encoding="utf-8") as file_handle:
+        file_data = file_handle.read()
+
+        copyright_match = re.search(PATTERN_COPYRIGHT, file_data)
+        if copyright_match:
+
+            notice_years = parse_years_string(copyright_match.group(0))
+
+            if not notice_years or notice_years[-1] != CURRENT_YEAR:
+                notice_years.append(CURRENT_YEAR)
+
+            years_string = generate_years_string(notice_years)
+
+            file_data = re.sub(
+                PATTERN_COPYRIGHT, "Copyright (c) %s" % years_string, file_data, 1
+            )
+            file_handle.seek(0)
+            file_handle.write(file_data)
+            file_handle.truncate()
+
+
+bad_copyright_files = []
+bad_spdx_files = []
+
+for changed_file in sys.argv[1:]:
+    copyright_found = False
+    spdx_found = False
+
+    with open(changed_file, encoding="utf-8") as f:
+        for line_num, line in enumerate(f):
+            if line_num > MAX_SEARCH_LINES:
+                break
+            if COPYRIGHT_YEAR_REGEX.match(line):
+                copyright_found = True
+            if SPDX_REGEX.match(line):
+                spdx_found = True
+
+    if not copyright_found:
+        bad_copyright_files.append(changed_file)
+        update_header(changed_file)
+    if not spdx_found:
+        bad_spdx_files.append(changed_file)
+
+if bad_copyright_files:
+    print(
+        "The following files did not have a valid copyright header: "
+        + str(bad_copyright_files)
+        + "\nAn attempted fix may have been made please check the files and re-commit",
+        file=sys.stderr,
+    )
+
+if bad_spdx_files:
+    print(
+        "The following files do not have a valid SPDX licence identifier: "
+        + str(bad_spdx_files)
+        + "\nPlease add the identifier as follows 'SPDX-License-Identifier: MIT'",
+        file=sys.stderr,
+    )
+
+if bad_copyright_files or bad_spdx_files:
+    sys.exit(1)