Set the upper limit on warnings number

This way it will be possible to prevent users from introducing new
warnings. As new fixes will be upstreamed, the maximum limit of
allowed warnings should be taken lower and lower, so this script
could be eventually replaced by -Werror.

.github/workflows/compilation.yml

@@ -20,8 +20,10 @@ jobs:
           set -x
           $CXX --version
           ./autogen.sh
-          ./configure
-          make -j "$(nproc)"
+          ./configure CXXFLAGS="-Wall -fdiagnostics-color=always"
+          make -j "$(nproc)" |& tee build.log
+      - name: Summarize warnings
+        run: python3 ./scripts/count-warnings.py build.log
 
   build_gcc8:
     name: "GCC 8 (ubuntu-18.04)"
@@ -39,8 +41,10 @@ jobs:
           set -x
           $CXX --version
           ./autogen.sh
-          ./configure
-          make -j "$(nproc)"
+          ./configure CXXFLAGS="-Wall -fdiagnostics-color=always"
+          make -j "$(nproc)" |& tee build.log
+      - name: Summarize warnings
+        run: python3 ./scripts/count-warnings.py build.log
 
   build_ubuntu:
     name: "GCC"
@@ -58,8 +62,10 @@ jobs:
           set -x
           g++ --version
           ./autogen.sh
-          ./configure
-          make -j "$(nproc)"
+          ./configure CXXFLAGS="-Wall -fdiagnostics-color=always"
+          make -j "$(nproc)" |& tee build.log
+      - name: Summarize warnings
+        run: python3 ./scripts/count-warnings.py build.log
 
   build_clang:
     name: "Clang 6 (ubuntu-18.04)"
@@ -77,8 +83,10 @@ jobs:
           set -x
           $CXX --version
           ./autogen.sh
-          ./configure
-          make -j "$(nproc)"
+          ./configure CXXFLAGS="-Wall"
+          make -j "$(nproc)" |& tee build.log
+      - name: Summarize warnings
+        run: python3 ./scripts/count-warnings.py build.log
 
   build_macos:
     name: "Clang (macOS-10.14)"
@@ -93,5 +101,7 @@ jobs:
           set -x
           clang++ --version
           ./autogen.sh
-          ./configure
-          make -j "$(sysctl -n hw.physicalcpu)"
+          ./configure CXXFLAGS="-Wall"
+          make -j "$(sysctl -n hw.physicalcpu)" 2>&1 | tee build.log
+      - name: Summarize warnings
+        run: python3 ./scripts/count-warnings.py build.log

scripts/count-warnings.py

@@ -0,0 +1,88 @@
+#!/usr/bin/python3
+
+# Copyright (c) 2019 Patryk Obara
+
+# This script counts and all warnings and prints a summary.
+#
+# Usage: ./count-warnings.py build.log
+# Usage: cat "*.log" | ./count-warnings.py -
+#
+# note: new compilers include additional flag -fdiagnostics-format=[text|json],
+# which could be used instead of parsing using regex, but we want to preserve
+# human-readable output in standard log.
+
+# pylint: disable=invalid-name
+# pylint: disable=missing-docstring
+
+import os
+import re
+import sys
+
+# Maximum allowed number of warnings; if build will include more warnings,
+# then script will return with status 1. Simply change this line if you
+# want to set a different limit.
+#
+MAX_WARNINGS = 357
+
+# For recognizing warnings in GCC format in stderr:
+#
+WARNING_PATTERN = re.compile(r'([^:]+):(\d+):\d+: warning: .* \[-W(.+)\]')
+#                               ~~~~~   ~~~  ~~~           ~~      ~~
+#                               ↑       ↑    ↑             ↑       ↑
+#                               file    line column        message type
+
+# For removing color when GCC is invoked with -fdiagnostics-color=always
+#
+ANSI_COLOR_PATTERN = re.compile(r'\x1b\[[0-9;]*[mGKH]')
+
+
+def remove_colors(line):
+    return re.sub(ANSI_COLOR_PATTERN, '', line)
+
+
+def count_warning(line, warning_types):
+    line = remove_colors(line)
+    match = WARNING_PATTERN.match(line)
+    if not match:
+        return 0
+    # file = match.group(1)
+    # line = match.group(2)
+    wtype = match.group(3)
+    count = warning_types.get(wtype) or 0
+    warning_types[wtype] = count + 1
+    return 1
+
+
+def get_input_lines(name):
+    if name == '-':
+        return sys.stdin.readlines()
+    if not os.path.isfile(name):
+        print('{}: no such file.'.format(name))
+        sys.exit(2)
+    with open(name, 'r') as logs:
+        return logs.readlines()
+
+
+def print_summary(warning_types):
+    print("Warnings grouped by type:\n")
+    summary = list(warning_types.items())
+    for warning, count in sorted(summary, key=lambda x: -x[1]):
+        print('  {:28s}: {}'.format(warning, count))
+    print()
+
+
+def main():
+    total = 0
+    warning_types = {}
+    for line in get_input_lines(sys.argv[1]):
+        total += count_warning(line, warning_types)
+    if warning_types:
+        print_summary(warning_types)
+    print('Total: {} warnings\n'.format(total))
+    if total > MAX_WARNINGS:
+        print('Error: upper limit of warnings is', MAX_WARNINGS)
+        sys.exit(1)
+
+
+if __name__ == '__main__':
+    main()