.github: add workflow for rejecting PRs that introduce whitespace errors.

.githooks/pre-commit

@@ -0,0 +1 @@
+run-hooks

.githooks/pre-commit.d/00-stock-git-checks

@@ -0,0 +1,49 @@
+#!/usr/bin/sh
+#
+# An example hook script to verify what is about to be committed.
+# Called by "git commit" with no arguments.  The hook should
+# exit with non-zero status after issuing an appropriate message if
+# it wants to stop the commit.
+#
+# To enable this hook, rename this file to "pre-commit".
+
+if git rev-parse --verify HEAD >/dev/null 2>&1
+then
+	against=HEAD
+else
+	# Initial commit: diff against an empty tree object
+	against=$(git hash-object -t tree /dev/null)
+fi
+
+# If you want to allow non-ASCII filenames set this variable to true.
+allownonascii=$(git config --type=bool hooks.allownonascii)
+
+# Redirect output to stderr.
+exec 1>&2
+
+# Cross platform projects tend to avoid non-ASCII filenames; prevent
+# them from being added to the repository. We exploit the fact that the
+# printable range starts at the space character and ends with tilde.
+if [ "$allownonascii" != "true" ] &&
+	# Note that the use of brackets around a tr range is ok here, (it's
+	# even required, for portability to Solaris 10's /usr/bin/tr), since
+	# the square bracket bytes happen to fall in the designated range.
+	test $(git diff --cached --name-only --diff-filter=A -z $against |
+	  LC_ALL=C tr -d '[ -~]\0' | wc -c) != 0
+then
+	cat <<\EOF
+Error: Attempt to add a non-ASCII file name.
+
+This can cause problems if you want to work with people on other platforms.
+
+To be portable it is advisable to rename the file.
+
+If you know what you are doing you can disable this check using:
+
+  git config hooks.allownonascii true
+EOF
+	exit 1
+fi
+
+# If there are whitespace errors, print the offending file names and fail.
+exec git diff-index --check --cached $against --

.githooks/run-hooks

@@ -0,0 +1,34 @@
+#!/bin/bash
+
+hook="${0##*/}"
+dotd="${0}.d"
+orig="${0%/*}/../.git/hooks/$hook"
+
+exec 1>&2
+
+for h in "$dotd"/???*; do
+    case "$h" in
+        *~|*.swp)
+            continue
+            ;;
+        [0-9]*-*)
+            ;;
+        *)
+            continue
+            ;;
+    esac
+    if [ ! -x "$h" ]; then
+        continue
+    fi
+
+    echo "[running git hook ${h##*/}]"
+    $h $@
+    status=$?
+    if [ $status != 0 ]; then
+        exit $status
+    fi
+done
+
+if [ -x "$orig" ]; then
+    exec $orig
+fi

.github/workflows/project-checks.yaml

@@ -27,6 +27,14 @@ jobs:
         with:
           go-version: ${{ env.GO_VERSION }}
 
+      - name: Git-check PR for conflict markers and trailing whitespace errors.
+        if: ${{ github.event_name == 'pull_request' }}
+        run: |
+          if ! git diff-index --check origin/${{ github.base_ref }} --; then
+              echo "This PR would introduce the above errors."
+              echo "Please fix them and update the PR."
+              exit 1
+          fi
       - name: make verify
         run: |
           make verify

Makefile

@@ -433,3 +433,11 @@ site-serve: .$(DOCKER_SITE_BUILDER_IMAGE).image.stamp
 	touch $@
 
 docs: site-build
+
+#
+# rules for enabling project-specific git hooks
+#
+
+install-git-hooks:
+	$(Q)echo "Enabling in-tree git hook..."
+	git config core.hookspath .githooks