make checkdiff does CI documentation checks (#900)

Fixes #744

contrib/checkdiff.bash

@@ -0,0 +1,77 @@
+#!/bin/bash
+
+# SPDX-License-Identifier: MIT
+#
+# Copyright (c) 2021 Rangi
+#
+# 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.
+
+declare -A FILES
+while read -r -d '' file; do
+	FILES["$file"]="true"
+done < <(git diff --name-only -z $1 HEAD)
+
+edited () {
+	${FILES["$1"]:-"false"}
+}
+
+dependency () {
+	if edited "$1" && ! edited "$2"; then
+		echo "'$1' was modified, but not '$2'! $3" | xargs
+	fi
+}
+
+# Pull requests that edit the first file without the second may be correct,
+# but are suspicious enough to require review.
+
+dependency include/linkdefs.h    src/rgbds.5 \
+           "Was the object file format changed?"
+
+dependency src/asm/parser.y      src/asm/rgbasm.5 \
+           "Was the rgbasm grammar changed?"
+
+dependency include/asm/warning.h src/asm/rgbasm.1 \
+           "Were the rgbasm warnings changed?"
+
+dependency src/asm/object.c      include/linkdefs.h \
+           "Should the object file revision be bumped?"
+dependency src/link/object.c     include/linkdefs.h \
+           "Should the object file revision be bumped?"
+
+dependency Makefile              CMakeLists.txt \
+           "Did the build process change?"
+dependency Makefile              src/CMakeLists.txt \
+           "Did the build process change?"
+
+dependency src/asm/main.c        src/asm/rgbasm.1 \
+           "Did the rgbasm CLI change?"
+dependency src/asm/main.c        contrib/zsh_compl/_rgbasm \
+           "Did the rgbasm CLI change?"
+dependency src/link/main.c       src/link/rgblink.1 \
+           "Did the rgblink CLI change?"
+dependency src/link/main.c       contrib/zsh_compl/_rgblink \
+           "Did the rgblink CLI change?"
+dependency src/fix/main.c        src/fix/rgbfix.1 \
+           "Did the rgbfix CLI change?"
+dependency src/fix/main.c        contrib/zsh_compl/_rgbfix \
+           "Did the rgbfix CLI change?"
+dependency src/gfx/main.c        src/gfx/rgbgfx.1 \
+           "Did the rgbgfx CLI change?"
+dependency src/gfx/main.c        contrib/zsh_compl/_rgbgfx \
+           "Did the rgbgfx CLI change?"